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Group Title: Patterns of geographic variation in Florida snakes (FLMNH Bulletin v.25, no.3)
Title: Patterns of geographic variation in Florida snakes
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Permanent Link: http://ufdc.ufl.edu/UF00095813/00001
 Material Information
Title: Patterns of geographic variation in Florida snakes
Physical Description: p. 158-256 : maps ; 23 cm.
Language: English
Creator: Christman, Steven P
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1980
Copyright Date: 1980
 Subjects
Subject: Snakes -- Variation -- Florida   ( lcsh )
Snakes -- Geographical distribution -- Florida   ( lcsh )
Reptiles -- Variation   ( lcsh )
Reptiles -- Geographical distribution   ( lcsh )
Reptiles -- Florida   ( lcsh )
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government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 246-249.
General Note: Bulletin of the Florida State Museum, Volume 25, Number 3
General Note: Based on the author's thesis (Ph. D.)--University of Florida.
Statement of Responsibility: Steven P. Christman.
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Holding Location: University of Florida
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Resource Identifier: oclc - 07597259
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of the
FLORIDA STATE MUSEUM
Biological Sciences


Volume 25


1980


Number 3


PATTERNS OF GEOGRAPHIC VARIATION IN FLORIDA SNAKES


STEVEN P. CHRISTMAN


UNIVERSITY OF FLORIDA


GAINESVILLE







Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES,
are published at irregular intervals. Volumes contain about 300 pages and are not neces-
sarily completed in any one calendar year.













OLIVER L. AUSTIN, JR., Editor

RHODA J. RYBAK, Managing Editor


Consultants for this issue:

WALTER AUFFENBERG

ROBERT P. REYNOLDS

NORMAN J. SCOTT, JR.













Communications concerning purchase or exchange of the publications and all manuscripts
should be addressed to: Managing Editor, Bulletin; Florida State Museum; University of
Florida; Gainesville, Florida 32611.
Copyright 1980 by the Florida State Museum of the University of Florida


Publication date: October 15, 1980


Price: $5.00











PATTERNS OF GEOGRAPHIC VARIATION
IN FLORIDA SNAKES


STEVEN P. CHRISTMAN1


SYNOPSIS: I analyzed geographic variation within Florida for 15 species of snakes. Contour
maps were machine-produced for each of over 200 morphologic and 17 environmental
variables. Factor analysis of the maps showed that seven major patterns of geographic varia-
tion account for over 60% of the total variation. Each of the patterns of geographic variation
can be explained in terms of natural selection and gene-flow characteristics in past or present
environments. Disjunct populations showing phenetic similarities are the result of an earlier
widespread phenotype followed by differentiation in geographically intermediate regions.
Recourse to land bridge hypotheses and retrogressive evolution are not necessary to explain
polytopic phenotypes. The geographic localities of primitive species or primitive
characteristics within a species are not the centers of origin, but are merely regions in which
evolution has proceeded relatively more slowly. A north-south dine on the Florida peninsula
is the most obvious pattern of geographic variation, common to all species examined for at
least some characters. Most species examined showed aspects of a Suwannee Straits pattern
with dramatic character-state shifts occurring in the region of the present Suwannee River.



TABLE OF CONTENTS

INTRODUCTION .. .. . ..................................... 158
ACKNOWLEDGMENTS ........... ..... ...... ....... 160
M ETHODS ......... ............. .................. ... . ...... 160
The D ata ................. ....... ................................. 160
The Problem of Samples and Populations .................................. 162
The Mapping Procedure. ........... ........................... ..... 163
Comparison of Mapped Data ....................... ........ .. ..... 163
RESULTS ................... .... ..... .. . .. ..... .. .... ..... 164
The Species .. ........ ....... ................ ...... . 165
Environmental Data. ........ ............................... 202
The Patterns ......... ............. ........................... 202
The Correlations ................ ..................................... 219
D IscussIoN ............. ........ .. ................................ 220
Patterns of Geographic Variation .... .......... .......... ......... 220
Phylogenetic Considerations ....................................... 227
SUMM ARY ........... .. ...... . ............................ ....... 243
LITERATURE CITED ........... ... ... .. ................. 246
APPENDIX A, CHARACTERS EXAMINED .. .... .. ......... ...... .... .. ... 249
APPENDIX B, ENVIRONMENTAL VARIABLES EXAMINED ................ ............ 256




' The author is research wildlife biologist with the National Fish and Wildlife Laboratory, U.S. Fish and Wildlife Service,
412 N. E. 16th Avenue, Gainesville, Florida 32601. This paper is based on a dissertation submitted to the University of
Florida in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

CHRISTMAN, STEVEN P. 1980. Patterns of Geographic Variation in Florida Snakes. Bull.
Florida State Mus., Biol. Sci. 25(3): 157:256.







BULLETIN FLORIDA STATE MUSEUM


INTRODUCTION
Darwin's theory of natural selection has as its keystone one basic re-
quirement: variation. Implicit in any interpretation of natural selection
as the guiding force behind organic evolution is the assumption that
organisms are not all alike. The members of a population of sexually-
reproducing plants or animals are in fact (except for identical twins) all
different, both genetically and phenotypically. Mutations and recom-
binations of existing genes insure the continuance of this variability.
Selection acts on the differences between organisms by eliminating unfit
phenotypes (and hence their associated genotypes) from the reproductive
effort of a population. Phenotypes that are unfit in one part of a species'
geographic distribution may be suitable in another region. Thus
geographic variation in selective pressures, brought about by geographic
variation in environment, predisposes organisms to vary geographically in
morphological, physiological, and behavioral traits, even within a single
biological species.
The process of speciation begins when differential selective pressures
act on populations of a species in different parts of its geographic range.
Natural selection creates different phenotypes in response to different
selective regimes. When the degree of phenotypic divergence also includes
reproductive incompatibility, the populations involved are said to have
reached the species level.
Populations of organisms change phenotypically and genetically
through time as they become better adapted to their environment and as
their environment changes. This process is called evolution. Populations
of organisms also change phenotypically and genetically through space as
they adapt to different environments. This phenomenon has been called
geographic variation, but is really just another form of evolution. Albert
Einstein has shown the equivalence of space and time in the physical
world, and Preston (1960, 1962) has demonstrated analogies between
space and time in ecology and species diversity. In the present study, it is
assumed that character variation through space is a form of organic evo-
lution just as character variation through time is unquestionably so.
It is presently impossible to study the environmental factors responsi-
ble for character variation through time. We do not have accurate data
on temperature or rainfall variations throughout the evolutionary history
of any species. We are not able to assess the relative importance of various
selective pressures that have brought about the species of today. However,
we can study evolution through space. We do have accurate environmen-
tal measurements taken at many geographic points, and should be able to
correlate these with character variation as we see it throughout a species'
distribution. Assuming an analogy between space and time, I believe the
patterns of character variation in space are brought about and main-


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 159

trained in the same ways as patterns of character variation through time
(evolution, in the Darwinian sense).
Thus the key to an understanding of organic evolution lies in an
understanding of geographic variation and the environmental factors
responsible for its maintenance.
Although the study of geographic variation in living systems is not a
new one, the use of modern multivariate methods to describe and com-
pare patterns of variation has hardly begun. Most previous studies have
simply described or illustrated, one at a time, the geographic variation of
each of a set of characters pertaining to a single plant or animal species. A
few very recent studies have utilized multivariate techniques to analyze
the degree and type of covariation among characters of a single species.
Still fewer investigators have attempted to demonstrate correlations be-
tween environmental characteristics and intraspecific geographic varia-
tion. Previous to this study, to my knowledge, no one has attempted to in-
vestigate quantitatively patterns of geographic variation common to
several species, and to compare these patterns with environmental varia-
tion.
Florida is basically a peninsula with a warm temperate climate
grading into that of a subtropical region. It has such diverse habitats as
wooded swamps, prairies (marshes), flat pine lands, and scrubby
chaparral-like deserts (Florida scrub). It thus seems surprising that most
studies concerned with the biogeography of Florida have concentrated on
historical causation and left little credit to the power of natural selection
as a factor in establishing patterns of geographic variation. Changing sea
levels, "Ocala Islands," Suwannee Straits, and the like have all been cited
as influencing the patterns of distribution and variation in Florida plants
and animals. No doubt many of the distributional patterns and much of
the variation seen in Florida organisms have been influenced by these
historical phenomena. Recent work by several authors, however, has
shown that demes or micro-geographic populations can and do differen-
tiate as they become adapted to their own unique environment. Species,
in the conventional sense, are not panmictic. Rather, they are groups of
populations, each adapted to its own particular portion of the total
species' distribution. Therefore any analysis of geographic variation
should include tests for correlation with components of the environment.
Only after all possible correlations with environmental factors have been
eliminated, should historical phenomena be suggested as causation in
biogeography.
Leon Croizat, in a series of works spanning the last 30 years (especially
1958, 1962), has advocated a method of biogeographical analysis that
begins without a priori assumptions, and lets the data speak for itself. His
method is to plot the distribution of the species of a larger group (genus,








BULLETIN FLORIDA STATE MUSEUM


family etc.) on a map, and to connect the disjunct ranges with straight
lines. When many groups are treated in this way, the lines of connection
(tracks) do not form a random network over the map, but rather tend to
follow the same routes. These routes, an aspect of the data, and in no way
influenced by preconceived ideas of past geography or climate, can and
must be interpreted as representing remnants of former widespread
distributions.
By plotting the geographic pattern of morphologic variation of a
single character of a single species on a map, and then considering many
such maps together, one is, in effect, using a modification of Croizat's
panbiogeographic analysis on a smaller scale. One begins with no assump-
tions of past dispersal routes, climate, or geography. Instead, the data are
mapped and the patterns emerging interpreted in the most parsimonious
manner.
The method is simple: Computerized contour maps are produced
depicting the geographic variation of each character to be investigated,
one character per map. Next the maps are compared, and a smaller
number of underlying patterns extracted and mapped. In this manner,
patterns of organic geographic variation can be identified and compared
with geographic variation in environmental factors. Patterns of morpho-
logic variation that do not correlate with existing environmental variables
may be correlated with untested environmental variables, or they may
have received their present shape by past paleoclimatic or geographic
factors.
ACKNOWLEDGMENTS
During the course of my graduate studies at the University of Florida I received financial
support from the Society of The Sigma Xi, and I held a National Defense Education Act
Fellowship for one year. Funds for computer analysis were made available by the Northeast
Regional Data Center.
I thank the curators and staff of 24 major museums for the loans of hundreds of specimens.
I thank Walter Auffenberg, Richard Blaney, Douglas Rossman, Sam Telford, Kenneth
Williams, and Larry D. Wilson for allowing me to use some of their data on snake mor-
phology. I thank William Ingram III and Howard I. Kochman for assistance with the com-
puter programming. And I thank especially my wife, Sheila, for supporting me while I
counted scales.
METHODS
THE DATA
I analyzed character variation data on 3567 specimens of 15 species of Florida snakes
(Table 1). I chose the species on the basis of availability of specimens or data and, more im-
portantly, because all are wide-ranging, rather ubiquitous species with representatives (tax-
onomically distinct or not) in Texas and eastern Mexico. It was assumed that species with
wide distributions across the southern United States would be phenetically (and genetically)
plastic throughout their ranges as they adapt to different environments, and I hoped that
some light could be shed on the postulated "Gulf Coast Corridor" phenomenon of Auffenberg
and Milstead (1965) by studying character variation in species associated with the Gulf
Coastal Plain.


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 161

Table 1.-Species examined, numbers and origin of data.


Species Males Females Unknown Data Source

Storeria dekayi 69 82 this study
Thamnophis sirtalis 74 118 this study
Thamnophis sauritus 101 118 60 Douglas Rossman
Coluber constrictor 238 200 2 this study
Masticophis flagellum 40 42 3 Larry D. Wilson
Opheodrys aestivus 79 97 this study
Elaphe guttata 267 188 this study
Elaphe obsoleta 370 Walter Auffenberg
Lampropeltis getulus 117 54 36 Richard Blaney
Lampropeltis triangulum 59 61 Kenneth Williams
Diadophis punctatus 132 162 1 this study
Cemophora coccinea 42 39 9 Kenneth Williams
and Larry D. Wilson
Tantilla relicta, this study and
oolitica, coronata 97 97 4 Sam Telford
Sistrurus miliarius 188 132 this study
Crotalus adamanteus 98 96 this study


The characters examined were primarily standard taxonomic variables with a history of
application for the species studied. Although color is probably the single most important
aspect of a snake's phenotype at the infraspecific level, this character was largely ignored
because of the unpredictable color changes specimens undergo in preservative. Aspects of
pattern, carination, and scutellation constitute the bulk of the characters employed in the
present analysis. See Appendix A for a description of the characters examined. Figure 1 shows
places referred to.
I calculated Pearson Product-Moment correlation coefficients (Nie et al. 1970) between
every character and sex and snout-vent length. Unless otherwise noted, all characters mapped
and used in subsequent analyses showed no correlation with sex or body size.
Once the data were accumulated, they were coded, qualitative characters were ranked,
and everything was punched on computer Holerith cards. Various combinations of characters
were utilized to produce new characters, such as ventrals plus caudals or percent tail.
In addition to the data on snake morphology, I also recorded and analyzed summary data
on Florida climate from the Climatic Summary of the United States, U.S. Department of
Commerce. Appendix B lists the environmental variables investigated. Mean data from 196
weather stations in Florida, southern Georgia, and southern Alabama were used. The
average period of record on which means were based was 29 years.
To associate data from an individual snake or weather station with the appropriate
geographic locality, I developed a row and column coordinate system. Using the 1972 edition
of the American Automobile Association (AAA) road map for Florida as a base map, I
assigned each specimen and weather station a down and across value representing its locality
on the base map. These coordinates were punched on the cards together with the data.
Although the use of the AAA road map for a base may seem limiting, it is not, because the
coordinates can easily be changed to any other system with the appropriate conversion factor.
Actual latitude and longitude values could not be used because longitude varies in inter-line
distance with the curvature of the earth, and the computational algorithms employed require
that the grid system be uniform.








BULLETIN FLORIDA STATE MUSEUM


RIVER


SUWANNEE


TAMPA tQU
BAY











0 50
KM


FIGURE 1.-Place names referred to in text.

THE PROBLEM OF SAMPLES AND POPULATIONS

Every previous study of geographic variation that I know of has pooled and averaged data
on organisms from neighboring localities and applied the resultant average value to an ar-
bitrary point or area representing all the individuals that live there. This seems to me an
unrealistic approach to the problem. Whether the method lumps specimens by state, county,
circular or square grids, or the irregular "splotch" system of Rossman (1963) and his students
(Blaney 1971a, Williams 1970), it implies that the values associated with the geographic units
represent values for populations. There is no reason to believe that population distributions
assume regular shapes or are determined by political boundaries. Nor does there seem to be
any valid reason to lump specimens with similar character states from adjacent localities-
how does one define "similar" and "adjacent"?
The method used in the present study is, I believe, less arbitrary, and does not assume a
knowledge of either population structure or geography. For every character to be studied the
character state for each specimen is plotted on a map at the exact point where the specimen
was collected. If several specimens are available from the same point, they are averaged and
the mean weighted accordingly; otherwise each specimen is plotted independently. The next


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 163

step involves calculating estimated data values for intermediate localities based only on the
actual data values available. In this way values for all points on the map (or any fraction
thereof) are calculated based on the points for which there are actual values. Contour lines
are then constructed, and the areas of character change readily identified. Instead of the a
priori assumptions of geographic structure that are implicit in any scheme involving the
means of putative populations, this method allows the patterns of geographic variation to
emerge from the consideration of individual specimens.
THE MAPPING PROCEDURE

I used the SYMAP mapping procedure, developed by the Harvard University Laboratory
for Computer Graphics, to construct contour maps of character variation. This program has
been used previously in studies of geographic variation by Jackson (1970) and Johnston and
Sealander (1971) and is described in some detail in Peucker (1972).
Briefly the mapping procedure involves the calculation of estimated data values (EDV's)
for a regular grid of points across the map surface. Each EDV is estimated by considering
actual data values (ADV's) lying in its vicinity. Actual data values are weighted inversely
according to the square of their distance from the EDV. Between 6 and 11 ADV's are con-
sidered in estimating each EDV. When all EDV's are calculated, there will be a value for
the character at each of a regularly spaced grid of points on the map surface. Differential
shading distinguishes the levels of character state variation, and contour lines are represented
by the absence of shading.
This method of character mapping still suffers from the one drawback common to all car-
tographic procedures: The map is only as good as the data. Obviously the more points on the
map with actual data values, the less interpolation will be required to form the regular grid of
estimated data values. Ideally one would like to have specimens from localities spaced evenly
over the study area, which is usually impossible.
Throughout the following discussion one must remember that the mapping procedure
employed does nothing more than map the data as they appear, and interpolate between data
points, just as a cartographer does mentally when constructing a contour map by hand. There
is nothing mysterious or even very sophisticated in the method. It is faster than mapping
manually, and it removes any possible investigator bias from contour line placement.
I produced over 230 contour maps of geographic variation in Florida snakes. Some of
these were linear combinations of original characters, and were not used in the multivariate
analyses to follow. Others were correlated with body size, indicating a growth-related pat-
tern, or with sex, and these were also omitted from further analyses. Publishing costs permit-
ted printing fewer than half the contour maps produced.

COMPARISON OF MAPPED DATA

The problem of comparing mapped data is complex. If the different variables were
located geographically at the same points, simple product-moment correlation analysis could
be performed and any correlative tendencies readily identified. But when the maps to be com-
pared have different data points, a preliminary step to standardize the points is required.
That is, given two maps of Florida, one with X data points and the other with Y data points
located at different geographic places, it is necessary to interpolate one data set so that its new
data points correspond with the other's, or to interpolate both to a standard set of points. If
the data are treated in this manner it should be possible to compare (for instance) climatic
variables from National Weather Stations with morphological variables of snakes from
wherever they were collected (usually not at weather stations).
The SYMAP mapping routine, discussed above, calculates estimated data values for a
finite set of points on a map based on the points for which actual data values exist. By storing
the EDV's for each map on magnetic tape, multiple sets of geographic data can be standard-
ized to a common set of geographic points on one base map. Each of the standardized points








BULLETIN FLORIDA STATE MUSEUM


on the base map then will have a set of variables, one from each of the original contour maps.
The standardized EDV's can then be treated as elements in a matrix for multivariate analysis.
I used the Statistical Package for the Social Sciences (SPSS) Factor Analysis procedure (Nie
et al. 1970) to search for underlying patterns in the geographic variation represented by the
entire set of snake morphology maps. If morphological characteristics of several species vary
geographically in a similar manner, this suggests the presence of some underlying components
or "factors" that determine how the set of contour maps are covarying. Thus factor analysis
can be used to search for patterns of geographic variation that several species may share. First
a matrix of product-moment correlation coefficients between the values at all points on all
maps was calculated. R-type factor analysis with "varimax rotation" was employed to extract
a smaller number of summarizing axes that explain the covariation in the characters (i.e. the
maps). A more detailed discussion of factor analysis may be found in Harmon (1967).
I also used factor analysis to describe the covariation in environmental variables, in-
cluding elevation, temperature, and precipitation in Florida. Thirteen environmental
variables were contour-mapped and factor-analyzed by the same techniques used in the snake
morphology analysis. The first three factors, mean annual temperature, maximum summer
temperature, and average precipitation respectively, accounted for over 74% of the total
variation.
At the time of this study the SPSS Factor Analysis routine was limited to 100 characters
(maps, in this instance). I therefore selected 100 contour maps of snake and environmental
variation for the overall factor analysis of contour maps. I was able to select 97 maps of snake
variation by eliminating linear combinations, male and female redundancies, and characters
that were highly correlated, such as, for example, ring width and ring position in Diadophis
punctatus. The original contour maps of the three climatic variables (average temperature,
maximum summer temperature, the average precipitation) were included in the overall fac-
tor analysis.
Factor analysis with varimax rotation of the 100 contour maps yielded two dozen factors
that I call "patterns of geographic variation." By selecting those maps that contributed the
most to each factor and visually comparing these to each other, I sketched in diagrammatic
fashion the major patterns of geographic variation common to these 15 species of Florida
snakes.
In addition to describing the important patterns of geographic variation, I have sum-
marized all the variation of the entire set of snake morphology maps in a single contour map.
This particular summary analysis was based on 166 contour maps of 14 species (Cemophora
coccinea was inadvertently omitted). I used the principle components analysis routine of the
Statistical Analysis System (Barr et al. 1976) without rotation to provide a summary of the
variation contained in the 166 maps. That summary is, by definition, the first component
(factor) extracted. Factor scores were assigned to each of 688 regularly-spaced points on the
map surface (approximately 16 km between points) and these mapped with the SYMAP
routine. The result was a single contour map summarizing the geographic variation observed
in 166 characters of 14 species of snakes in Florida.

RESULTS
Note that the mapping procedure employed does nothing more than
assign a character state value to the appropriate locality and then inter-
polate between the localities to predict the location of a change in
character state. Each specimen is weighted equally, so geographically
isolated specimens may contribute more heavily in the analysis than in-
dividual specimens from better-collected regions. When interpreting the
maps in this section, it is important to bear this in mind, and to refer to
the specimen locality maps provided for each species.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 165

Some of the contour maps showed no discernible geographic pattern.
That is, the various levels of shading seemed to be interspersed at random,
creating a surface that I could not describe as anything but random. I
have omitted any discussion of these characters in the section to follow.
Results are presented first by species and compared with previous
studies. Patterns of geographic variation are discussed in the second sec-
tion, and finally, a third section deals with correlations between observed
patterns and environmental factors.

THE SPECIES
Storeria dekayi (Holbrook), Brown Snake
I examined 151 S. dekayi from Florida and southern Georgia (Fig. 2)
for possible geographic variation in 21 characters (Appendix A). The
numbers of supralabials and infralabials are essentially unvarying over
the study area. More than 93% of the specimens examined had 14
supralabials combining both sides, and 87.4% had 14 infralabials. The
number of postocular scales was usually 4 (88.3%). None of the
characters examined was found to be size-correlated The following
characters showed apparent geographic variation.
NUMBER OF VENTRALS.-The number of ventral scales was only
slightly correlated with sex, with the males usually having lower counts
(r = 0.3559). In general the number increases southward on the penin-
sula and drops again on the Lower Keys. Snakes from the Everglades
region have highest ventral counts, and those on the Lower Keys and in
the Panhandle the lowest. A reasonable degree of concordant variation
exists between the sexes.








. E







FIGURE 2.-Localities of 151 Storeria dekayi specimens examined.
FIGURE 3.-Storeria dekayi, both sexes. Sum of ventrals plus caudals. Levels hv increasing
shading: 169-186, 187-200, 201-215, 215-227. n = 138.







BULLETIN FLORIDA STATE MUSEUM


NUMBER OF SUBCAUDALS.--Males tend to have more subcaudals than
females (r = 0.5167). Variation is similar to that described above for
ventrals. Brown snakes from the Panhandle and from the Lower Keys
have the lowest subcaudal counts. Otherwise the variation is clinal, in-
creasing southward on the Florida peninsula. Snakes from the
Apalachicola Valley may be more similar to snakes from Central Florida
in this character. Again concordance in the variation between the sexes is
very good.
NUMBER OF VENTRALS PLUS CAUDALS.--Although both the number of
ventrals and the number of subcaudals are correlated with sex (see above)
their sum is not (r = 0.1522), so the sexes are lumped to increase sample
size in Figure 3. Geographic variation in this character consists of increas-
ing counts southward on the peninsula and a major drop on the Lower
Keys. Snakes from west of the Suwannee River in the Panhandle also have
low values for this character. (The area west of the Yellow River is repre-
sented by only a single specimen, an inadequate sample.)
PERCENT TAIL.--Males tend to have proportionately longer tails than
females (r = 0.7214). Brown snakes from the southern mainland have
the longest tails relative to body length. Snakes from the Lower Keys have
somewhat shorter tails, more like specimens from northern Florida.
DORSAL SCALE Rows.-Dorsal scales were counted at the standard
three places along the body, but all three varied the same way, so only
midbody scale rows are mapped (Fig. 4). Brown snakes from the Pan-
handle east to the vicinity of the Suwannee River have 17 scale rows
around the body, whereas those from the remainder of the state have 15.
PREOCULAR SCALES.-Generally S. dekayi has a single preocular scale
on each side of the head, but many individuals from the Lower Keys and

: r "". "':: i '






.-.:





FIGURE 4.-Storeria dekayi, both sexes. Number of dorsal scale rows at mid-body. Lighter
shading = 15 scale rows, darker shading, 17. n = 151.
FIGURE 5.-Storeria dekayi, both sexes. Number of preoculars (both sides). Lighter shading
= 2, darker shading, 3 or 4. n = 149.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 167

a high proportion of specimens from near Jacksonville and Gainesville
have two preoculars on each side (Fig. 5).
VENTRAL DARK PIGMENTATION.-Generally speaking, brown snakes
from the southwest coast of the peninsula have the darkest bellies and
those from the Lower Keys the lightest.
TEMPORAL PIGMENT SHAPE.-Dark pigment on the temporal scale in S.
dekayi is usually in a tear-shaped blotch with one end wider and continu-
ing onto adjacent scales (see Appendix A). The wider end may be directed
posteriorly, as in most snakes from the Panhandle, or it may be directed to
the front, as in peninsula specimens. Brown snakes from the Lower Keys
often have the temporal pigment so reduced as to have no obvious orienta-
tion, but when present, the wider end is directed to the front (Fig. 6).
SUBOCULAR PIGMENTATION.-The number of supralabial scales con-
tained within the subocular dark blotch in Florida S. dekayi varies
geographically as shown in Figure 7. Generally, snakes from the penin-
sula tend to have larger subocular spots than specimens from the Pan-
handle. Many individuals from the Everglades region have very small
subocular spots, or none at all. Subocular spots on specimens from the
Lower Keys are diffuse and faint, but cover three to five supralabials.














FIGURE 6.-Storeria dekayi, both sexes. Orientation of the dark temporal spot. Lighter
shading = a spot with the wider end directed posteriorly, darker shading, anteriorly.
n = 99.
FIGURE 7.-Storeria dekayi, both sexes. Number of supralabials included in the subocular
dark spot. Levels by increasing shading: 0, 1-2, 3-5. n = 148.

Thamnophis sirtalis (Linnaeus), Garter Snake
Data on 192 T. sirtalis from Florida (Fig. 8) were analyzed for varia-
tion in 13 characters (Appendix A). Dorsal scale rows varied little
throughout the study area; most specimens had 19-19-17 rows (94.7%,
95.7%, and 96.8%, respectively); 91.0% of those examined had 14
supralabials and 92.4% had 20 infralabials. None of the characters ex-







BULLETIN FLORIDA STATE MUSEUM


FIGURE 8.-Localities of 192 Thamnophis sirtalis specimens examined.
amined was size- or sex-correlated. The following characters appear to
show trends of geographic variation within Florida.
NUMBER OF VENTRALS.-Although differentiation within Florida for
this character is minimal, some trends are apparent. Generally, snakes
from Lake Okeechobee southward have the highest ventral counts and
those from the Panhandle tend to have low counts, but no well-developed
dine is discernible within the state.
NUMBER OF SUBCAUDALS.--Trends in the geography of subcaudal
count variation are not clear. Figures 9 and 10 show the general lack of
concordance between the sexes for this character. Patterns like these may
imply that the sexes are responding differently in subcaudal count expres-
sion, or they may be the result of sampling bias from inadequate sample
sizes (51 males, 62 females). Alternatively, the number of subcaudal scales














FIGURE 9.- Thamnophis sirtalis, males only. Number of subcaudal scales. Lighter
shading = 58-73, darker shading, 74-98. n = 51.
FIGURE 10.-Thamnophis sirtalis, females only. Number of subcaudal scales. Lighter
shading = 58-71, darker shading, 72-86. n = 62.


Vol. 25, No. 3


r







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 169

in Florida T. sirtalis may not correlate with anything that varies
geographically.
NUMBER OF VENTRALS PLUS CAUDALS.-Garter snakes tend to have the
highest counts in the northern peninsula and extreme southern peninsula,
with lower counts found in the intervening region and in the Panhandle.
PERCENT TAIL.-Tail length divided by total length varies as shown in
Figures 11 and 12. In general, specimens from the Apalachicola Valley,
the northern peninsula, and the southern peninsula have proportionately
longer tails than snakes from elsewhere. Although the pattern appears
complex, the concordance between the sexes is quite good, supporting the
reality of the trends, based, as they are, on different sets of specimens.





:.-- : ;-. -






FIGUE 11.- Thamnophis sirtalis, males only. Tail length divided by total length. Lighter
shading = 0.22-0.24, darker shading 0.25-0.33. n = 53.
FIGURE 12.-Thamnophis sirtalis, females only. Tail length divided by total length. Lighter
shading = 0.16-0.22, dark shading, 0.23-0.33. n = 65.
DORSAL SPOTTING.-That some individual garter snakes are marked
with black spots dorsally is well known. Linnaeus (1766) described the
phase as Coluber ordinatus; Cope (1900) considered it a subspecies of T.
sirtalis, and more recent authors have considered it little more than an oc-
casional pattern variant without geographic correlation (Rossman 1965).
Figure 13 shows the geographic variation in this character in Florida.
Snakes from the western Panhandle usually have a well-developed pat-
tern of dorsal checks, sometimes to the complete exclusion of longitudinal
stripes, and the west coast of the peninsula and parts of the Central
Highlands support populations with dorsal checking. Specimens from the
southern Everglades are almost invariably heavily spotted.
PARIETAL SPoTs.-Rossman (1963) considered the nature of the paired
parietal light spots important in Thamnophis taxonomy. The geographic
variation in this character is remarkably similar to that seen in the
previous character, dorsal spotting. Figure 14 shows the geographic pat-
tern as found in the present study. Again, the Panhandle, the southwest
coast of the peninsula, and the southern Everglades stand out as areas







BULLETIN FLORIDA STATE MUSEUM


FIGURE 13.-Thamnophis sirtalis, both sexes. Development of dorsal checks. Increasing
shading = increasing development of the dorsal checking pattern, n = 192.
FIGURE 14.- Thamnophis sirtalis, both sexes. Development of the parietal light spot. Lighter
shading = poorly developed or absent spot, darker shading, a well-developed spot. n = 187.

with higher states for this character. Concordance between the sexes is
good.
Thamnophis sauritus (Linnaeus), Ribbon Snake
I analyzed data on 279 T. sauritus from Florida and southern Georgia
(Fig. 15) for variation in 13 characters (Appendix A). Another 12 speci-
mens from the Lower Florida Keys were examined and included in the
discussion, but were not available at the time of mapping. The number
of infralabials was essentially unvarying throughout the study area;
92.6% had 10 on each side. None of the characters investigated was cor-
related with snout-vent length. Those characters that showed trends of
geographic variation follow.
NUMBER OF VENTRALs.-Males and females do not differ significantly
in ventral counts (r = 0.2910). The maps show a fairly well-defined in-
crease in ventral counts for both sexes southward on the Florida penin-
sula. High counts tend to extend farther northward along the coasts, and
specimens from the Gulf Hammock region on the west coast have ventral
counts comparable to those from the most southerly localities. Data from
Paulson (1968) and from the present study indicate that T. sauritus from
the Lower Keys have ventral counts like those in specimens from the
southern mainland. Seven males from the Lower Keys averaged 163.4
ventrals and five females averaged 160.2.
NUMBER OF SUBCAUDALS.-Males usually have more subcaudal scales
than females (r = 0.5801). Ribbon snakes from the Panhandle west of the
Choctawhatchee River tend to have more subcaudals than specimens
from the rest of the Panhandle and northern peninsula. Peninsula snakes
usually have higher counts than those from the Panhandle, and there
seems to be a weakly differentiated dine of increasing counts southward


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 171

on the peninsula. Specimens from the Lower Keys have higher subcaudal
counts than ribbon snakes from anywhere else in Florida; seven males
averaged 137.9 subcaudals and three females averaged 126.0.
NUMBER OF VENTRALS PLUS CAUDALS.-The summation of the two
previous counts correlated with sex (r = 0.5201); males had more total
ventral and subcaudal scales than females. Figures 16 and 17 show this
character varies clinally, with values increasing southward. Higher values
extend farther north along the coasts of the peninsula. The highest values
are in Lower Key specimens. Seven males from the Lower Keys had an
average ventral plus caudal value of 301.3, and three females averaged
286.2 ventrals plus caudals.







--7 .:----








FIGURE 15.-Localities of 279 Thamnophis sauritus specimens examined.
FIGURE 16.--Thamnophis sauritus, males only (Keys specimens excluded). Number of ven-
trals plus caudals. Levels by increasing shading: 268-281, 282-290, 291-300. n = 58.














FIGURE 17.- Thamnophis sauritus, females only (Keys specimens excluded). Number of ven-
trals plus caudals. Levels by increasing shading: 256-271, 272-279, 280-293. n = 91.
FIGURE 18.-Thamnophis sauritus, both sexes (Keys specimens excluded). Number of
supralabial scales. Lighter shading = 14 darker shading, 16. n = 271.







BULLETIN FLORIDA STATE MUSEUM


PERCENT TAIL -Ribbon snakes with the longest tails relative to snout-
vent length tend to occur in the central part of the peninsula, with
specimens having lower values occurring both north and south. The few
specimens available from the extreme western Panhandle and the Lower
Keys suggest that snakes from these areas also have longer relative tail
lengths.
SUPRALABIALS.-Ribbon snakes from the Panhandle generally have
seven upper labials on each side, whereas those from the peninsula have
eight. Although not mapped, the ribbon snakes from the Lower Keys oc-
casionally have seven supralabials. Figure 18 shows the geographic varia-
tion in supralabial number for both sexes.
DORSAL STRIPE EDGE.-Figures 19 and 20 show geographic variation
in the width and development of the black border of the dorsal stripe.
Although the pattern is complex, congruence between the sexes is good.
Snakes from the Panhandle west of the Apalachicola River and from parts
of the central peninsula tend to have well-developed dorsal stripe edges.
Those from the Lower Keys have extremely well-developed black dorsal
stripe borders. Many specimens from the northern half of the peninsula
lack a stripe border altogether, and some lack even the mid-dorsal yellow
stripe (Rossman 1963)
PARIETAL SPOTs.-Although Rossman (1963) stated that the nature of
the paired parietal light spots of T. sauritus does not vary geographically,
my analysis of his data indicates that it does (Fig. 21).
Most Florida T. sauritus lack a distinct parietal spot, but specimens
from the extreme northern peninsula, the region east of Tampa Bay, and
the southern tip of the peninsula have distinct parietal spots. The few


: ..-_










FIGUHE 19.- Thamrnophis sauritus, males only (Keys specimens excluded). Development of
the black edge of the mid-dorsal stripe. Darker shading = a well-developed edge, lighter
shading no black edge, or a very thin one. n = 62.
FIGURE 20.-Thamnophis sauritus, females only (Keys specimens excluded). Development of
the black edge of the mid-dorsal stripe. Darker shading = a well-developed edge, lighter
shading no such edge, or a very thin one. n = 117.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 173














FIGUBE 21.- Thamnophis sauritus, both sexes (Keys specimens excluded). Size of the parietal
light spot. Lightest shading = no spot, darkest, a well-developed spot, and intermediate, the
intermediate condition. n = 256.
FIGUREa 22.-Thamnophis sauritus, both sexes (Keys specimens excluded). Darkness of the
ground color. Lighter shading = light brown or gray ground color, and darker shading, dark
brown. n = 146.
specimens available from the Lower Keys have weakly developed parietal
spots.
GROUND COLoR.-The ground color of most Florida ribbon snakes is
tan or light brown, but in specimens from the Gulf Hammock region it is
usually a very dark brown or black. Some Everglades and southern
mainland specimens also have a darker ground color, but specimens from
the Lower Keys are light brown or tan (Fig. 22).
Coluber constrictor Linnaeus, Racer
I examined 440 C. constrictor from Florida (Fig. 23) for variation in
18 characters (Appendix A). The numbers of supralabials and infralabials
were practically nonvariant with seven and eight respectively on each
side. Aspects of the color and pattern were scored only on adult snakes
(over 70 cm in snout-vent length). With ontogenetic change in color and
pattern thus removed from consideration, none of the characters in-
vestigated correlated with snout-vent length. Those variables that showed
trends of geographic variation within the study area are discussed below.
NUMBER OF VENTRALS.-Males and females show no significant dif-
ference in ventral counts (r = 0.2253), and the sexes were lumped to pro-
duce Figure 24. The degree of concordance between variation patterns in
the two sexes is very good, and the number of ventrals increases in a well-
developed dine as one proceeds southward down the peninsula.
Specimens from the Lower Keys do not follow this trend; they have much
lower ventral counts than specimens from the southern tip of the
mainland. It is also noteworthy that occasional specimens from the
Apalachicola River Valley have higher than expected ventral counts, be-
ing more like specimens from farther south on the peninsula.







174 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 3
















FIGURE 23. -Localities of 440 Coluber constrictor specimens examined.
FIGURE 24.-Coluber constrictor, both sexes. Number of ventral scales. Levels by increasing
shading: 164-176, 177-180, 181-191. n = 440.

NUMBER OF SUBCAUDAL. -Males tend to have more subcaudal scales
than females (r = 0.3898), although the correlation is not strong.
Panhandle specimens usually have lower counts than those from the
peninsula, where a weakly defined clinal increase in subcaudal numbers
for each sex is observed.
NUMBER OF VENTRALS PLUS CAUDALs.-Figure 25 shows the line on
the peninsula of increasing ventral plus subcaudal counts southward, ex-
cept for a dip on the Lower Keys. The sexes are lumped in this map, for
the counts are independent of sex (r = 0.1618).
SUPRALABIAL-LOREAL CONTACT.-Auffenberg (1955) first noted the
variability of this character. In some specimens, especially in the
southeastern United States, the first supralabial is in contact with the
loreal. Although Auffenberg did not believe this character varied with
any degree of geographic regularity, my analysis shows that it does.
Figure 26 shows that specimens from extreme northern Florida, the area
east of Tampa Bay and extreme southern Florida, including the Middle
Keys, tend to have the first supralabial in contact with the loreal more fre-
quently than specimens from the remainder of the state.
VENTRAL WHITE.-Variation in the amount of white on the ventral
surface is shown in Figure 27. Racers under 70 cm were excluded from
this analysis. Snakes from South Florida and the Everglades region have
almost totally white undersides. Snakes with the darkest bellies (i.e. the
least white) are found on the Lower Keys and extreme northern Florida.
Lighter ventrums seem to be associated with the coastal and treeless parts
of the state. Upper Keys snakes are intermediate between Lower Keys
and south Florida mainland specimens. The correspondence between the
sexes is excellent.








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 175
















FIGURE 25.-Coluber constrictor, both sexes. Number of ventrals plus caudals. Levels by in-
creasing shading: 258-280, 281-288, 289-307. n = 193.
FIGURE 26.-Coluber constrictor, both sexes. Contact between the first supralabial and the
loreal. Lighter shading = no such contact, darker shading, contact on one or both sides of
the head. n = 437.
GULAR BROWN PIGMENTATION.--The variation in the presence or
absence of brown pigment on the gular scales is essentially as Auffenberg
(1955) described it for the race C. c. helvigularis. Most racers from the
Lower Apalachicola River Valley have brown pigment on the gulars.
Snakes from the rest of the state seldom have such pigment. When the
sexes were mapped separately, the patterns were virtually identical.
SUPRALABIAL BROWN PIGMENTATION.-See Figure 28 for the
geographic variation in this character. Racers from the Apalachicola
Valley have the most brown pigment on the supralabial scales. Snakes




'--_ _










FIGURE 27.-Coluber constrictor, both sexes (juveniles excluded). Amount of ventral white.
Increasing shading = decreasing ventral white. n = 393.
FIGURE 28.--Coluber constrictor, both sexes. Amount of brown pigment on the supralabials.
Lightest shading = none, darkest shading, much, and intermediate shading, the in-
termediate condition. n = 403.







BULLETIN FLORIDA STATE MUSEUM


FIGURE 29.-Coluber constrictor, both sexes. Black pigment on the gular scales. Darker
shading = snakes with black pigment on the gulars, n = 434.
FIGURE 30.-Coluber constrictor, both sexes. Black pigment on the supralabials. Darkest
shading = essentially all black supralabials, lightest shading, no black, and intermediate
shading, the intermediate condition. n = 403.
from the southern part of the Florida peninsula and the Everglades tend
to have less, and those from the extreme southern tip of the peninsula and
from the Lower Keys generally have none.
GULAR BLACK PIGMENTATION.-The presence or absence of black on
the gular scales varies as shown in Figure 29. The extreme northern base
of the peninsula just south of the Okefenokee Swamp, the area east of
Tampa Bay, and the Lower Keys support populations of C. constrictor
with black on the gular scales.
SUPRALABIAL BLACK PIGMENTATION.-The amount of black pigmenta-
tion on the supralabial scales varies much like the previous character (Fig.
30). Snakes from extreme northern Florida, the area east of Tampa Bay,
and the Lower Florida Keys have more black on the supralabial scales
than specimens from anywhere else in Florida.
Masticophis flagellum (Shaw), Coachwhip
I analyzed data on 85 M. flagellum from Florida, southern Alabama,
and southern Georgia (Fig. 31) for variation in 9 characters (Appendix A).
Over 96% of them had 16 supralabials. None of the characters was size-
correlated. Those that appear to vary geographically follow.
NUMBER OF VENTRALS.-Male coachwhips usually have more ventrals
than females (r = 0.4010). The highest ventral counts are generally
found in snakes from the peninsula, and especially its western half. Cor-
respondence between the sexes is weak.
NUMBER OF SUBCAUDALS.--Males and females are not significantly dif-
ferent in subcaudal counts (r = 0.2425). Specimens from the Panhandle
and western parts of the peninsula usually have more subcaudal scales
than snakes from the eastern peninsula.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION


FIGURE 31.-Localities of 85 Masticophis flagellum specimens examined.
VENTRALS PLUS CAUDALS.-The summation of the preceding two
characters is not correlated with sex (r = 0.3219). Again the Panhandle
and western part of the peninsula are characterized by coachwhips with
higher ventral plus subcaudal counts.
PERCENT TAIL.-Tail length divided by total length is not correlated
with sex (r = 0.2422). Longer tails seem to be associated with specimens
from the Panhandle and western parts of the peninsula.
COLOR PHASE.-Most Masticophis from the Panhandle of Florida are
of the light color phase and most from the peninsula are dark, but as
Figures 32 and 33 show, some individual variation occurs in this charac-
ter, and snakes of the light phase are more common in two peninsular
areas. This same pattern appears in both sexes, lending credence to its
reality, but unfortunately the sample sizes are very small.













FIGuRE 32.-Masticophis flagellum, males only. Color phase. Light shading = light phase,
dark shading, the dark phase. n = 40.
FIGURE 33. -Masticophis flagellum, females only. Color phase. Light shading = light phase,
dark shading, the dark phase. n = 42.







BULLETIN FLORIDA STATE MUSEUM


Opheodrys aestivus (Linnaeus), Rough Green Snake
I examined 176 Florida 0. aestivus (Fig. 34) for variation in 16
characters (Appendix A). Supralabial and infralabial counts remained
essentially constant; 87.4% had 14 supralabials and 75.6% had 16 in-
fralabials. Dorsal scale rows were 17-17-15 for over 95% of the
specimens. Three measurements of the frontal scale were found to cor-
relate with snout-vent length after dividing by snout-vent length. The
characters that appear to show geographic variation are discussed below.














FIGURE 34.-Localities of 176 Opheodrys aestivus specimens examined.
NUMBER OF VENTRALS.-Females typically have more ventral scales
than males (r = 0.3991). Although specimens from the southern parts of
the state, and especially the southwest, usually have the highest ventral
scale counts, no well-developed dine is manifest.
NUMBER OF SUBCAUDALS.-Males tend to have higher subcaudal counts
than females (r = 0.5513). Specimens from the western Panhandle east
to the Apalachicola River tend to have the most subcaudal scales, whereas
specimens from the Everglades and southern peninsula have the fewest.
VENTRALS PLUS CAUDALS.-Although both ventrals and caudals were
correlated with sex, their summation was not (r = 0.2807). Figure 35
shows the geographic variation in this character for the combined sexes.
Highest values are associated with snakes from the western Panhandle
and parts of South Florida. Snakes from the Everglades region have the
lowest ventrals plus caudals value. The variation is complex, and no sim-
ple north-south dine is discernible.
PERCENT TAIL.-Relative tail length varies with sex. Males usually
have proportionately longer tails (r = 0.5211). Concordance between
the sexes is poor, but generally both sexes tend to have slightly longer tails
in the Panhandle and shorter tails south of Lake Okeechobee. Males show
a pattern of longer tails on the Lower Keys, while the females do not.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 179

KEELING OF THE SECOND DORSAL SCALE Row.-Figures 36 and 37 show
the variation in the development of the keel on the scales of the second
dorsal row at midbody. The maps for the two sexes indicate that the
variation is very similar. North of central Florida and in the Panhandle
green snakes tend to have reduced or no keeling on these scales. In central
Florida south throughout the peninsula states for this character tend to be
higher, with the highest states frequently associated with snakes from
coastal regions. On the Lower Keys the males have keeled scales on the
second row, but the females apparently do not.















FIGURE 35.-Opheodrys aestivus, both sexes. Sum of ventrals plus caudals. Levels by increas-
ing shading: 282-295, 296-303, 304-322. n = 138.
FIGURE 36.-Opheodrys aestivus, male only. Keel on the scales of the second dorsal row at
mid-body. Lightest shading = no keel, darkest shading, a well-developed keel, and in-
termediate shading, the intermediate condition. n = 79.


FIGURE 37.-Opheodrys aestivus, females only. Keel on the scales of the second dorsal row at
mid-body. Lightest shading = no keel, darkest shading, a well-developed keel, and in-
termediate shading, the intermediate condition. n = 97.
FIGURE 38.-Opheodrys aestivus, both sexes. Extent of supralabial dark pigmentation. In-
creased shading = increased labial pigmentation. n = 175.







180 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 3

SUPRALABIAL PIGMENTATION.-Figure 38 shows the variation in the
amount of dark pigmentation on the upper labial scales. A very strong
degree of concordance between the sexes may be taken as evidence for the
reality of the pattern. In general snakes with more dark pigment on the
supralabials occur in the Panhandle, the northern peninsula, and
southward along the west coast. Green snakes from the Keys have very
light-colored upper labials.
Elaphe guttata (Linnaeus), Corn Snake
I examined 455 E. guttata from Florida, southern Georgia, and
southern Alabama (Fig. 39) for variation in 16 characters (Appendix A).
Some of the characters varied little throughout the study area. Dorsal
scale rows counted at three points along the body were almost always
25-27-19. Measurements of the frontal scale were divided by snout-vent
length and still found to correlate with snout-vent length. These
characters were excluded from the analysis that follows.


.- .




: ~ .~=- 8.






FIGURE 39.-Localities of 455 Elaphe guttata specimens examined.
NUMBER OF VENTRALS.-Females usually have more ventral scales
than males (r = 0.5933). In both sexes ventral counts increase southward
on the peninsula, with the highest values associated with snakes from the
Lower Keys. Coastal areas also seem to support E. guttata with higher
ventral counts.
NUMBER OF SUBCAUDALS.-Males tend to have more subcaudal scales
than females (r = 0.5015). The number of subcaudals appears to increase
southward on the peninsula, but the trend is not as clear-cut as in the
preceding character.
VENTRALS PLUS CAUDALS.-AS the summation of ventrals and caudals
is not correlated with sex (r = 0.1118), the sexes were combined to in-
crease sample size (Fig. 40). The highest counts occur on snakes from the
Keys and adjacent mainland. Higher counts are frequently associated









1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 181


with coastal areas as well; the lowest counts are on snakes from the north-
ern peninsula and Panhandle.
NUMBER OF BODY BLOTCHES.-E. guttata from the Lower Keys have
the highest dorsal blotch counts, specimens from the Panhandle and
northern peninsula the lowest. Higher counts reach farther northward on
the peninsula along both coasts. Figures 41 and 42 show the variation in
number of body blotches. The rather high degree of individual variation
in this character partially obscures its clinal nature.
NUMBER OF TAIL BLOTCHES.-Corn snakes from the Lower Keys and




**: -. --


FIGURE 40.-Elaphe guttata, both sexes. Sum of ventrals plus caudals. Levels by increased
shading: 273-292, 293-299, 300-319. n = 367.
FIGURE 41.-Elaphe guttata, males only. Number of body blotches. Lighter
shading = 26-34, darker shading, 35-46. r = 266.













-. .





FIGURE 42.-Elaphe guttata, females only. Number of body blotches. Lighter
shading = 26-34, darker shading, 35-50. n = 186.
FIGURE 43.-Elaphe guttata, both sexes. Width of the black dorsal blotch border. Lighter
shading = narrow or absent, darker shading, blotch borders more than one scale in width.
n = 453 specimens.


i
ii


.I
1~
il- i
-i- _-~-~
--
--







BULLETIN FLORIDA STATE MUSEUM


southern peninsula have the highest tail blotch counts, those from the
Panhandle the lowest. The increase southward is probably clinal,
although complicated by individual variation.
BLOTCH BORDER.-The red blotches on the dorsum are usually sur-
rounded by a narrow black border, the width of which varies
geographically as shown in Figure 43. Snakes from the extreme South
Florida mainland and parts of the western Panhandle have much wider
blotch borders.
LATERAL BLOTCH SHAPE.-Snakes from the Panhandle east to the
Aucilla River frequently have the border of the lateral blotch open ven-
trally, suggesting an inverted U rather than a complete circle. The
character occurs sporadically throughout Florida, but is almost universal
in Panhandle specimens (Fig. 44).
VENTRAL PIGMENTATION.-Specimens from the Lower Keys have the
least dark pigment ventrally. Snakes in coastal areas and offshore islands
have reduced pigment, whereas most specimens from the rest of the
peninsula and Panhandle tend to have much black pigment on their ven-
tral surfaces (Fig. 45).
VENTRAL CHECK SHAPE.-The ventral dark pigmentation is generally
confined to discrete rectangles. Snakes from the Lower Keys and coastal
regions (especially the southwest coast) have small, often square pigment
spots ventrally. Specimens from the interior, especially in the northern
parts of the state, have their ventral pigment in elongated rectangles.
Many specimens from the Panhandle and extreme northern Florida have
wide rectangular spots covering entire ventral scutes.





.......... .









n = 423.
FIGURE 45.-Elaphe guttata, both sexes. Amount of ventral dark pigmentation. Darker
shading = increased dark pigment ventrally. n = 455.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 183

Elaphe obsoleta (Say), Rat Snake
I analyzed data on 370 Florida E. obsoleta (Fig. 46) for variation in six
characters (Appendix A), none of which was correlated with size. The sex
of the specimens was not determined, and no specimens less than 100 cm
snout-vent length were examined.
NUMBER OF DORSAL BLOTCHES.-This character increases clinally
southward (Fig. 47).
GROUND COLOR.-This character reflects the amount of melanin or
dark pigmentation on the dorsum. Specimens from coastal areas have the
lightest ground colors, those from the interior of the peninsula, the
Panhandle, and the Upper Keys have darker dorsums (Fig. 48). (The spe-
cies does not occur on the Lower Keys.)


I: -= --











FIGURE 46.-Localities of 370 Elaphe obsoleta specimens examined.
FIGURE 47.-Elaphe obsoleta, both sexes (excluding juveniles). Number of dorsal body
blotches. Levels by increasing shading: 28-35, 36-38, 39-49. n = 222.
STRIPE DEVELOPMENT.-E. obsoleta from the Panhandle east to the
vicinity of the Suwannee River generally lack dorsal stripes. Specimens
from the northern peninsula have the most well-defined stripes; those
from southern Florida usually have the stripes moderately developed
(Fig. 49).
BLOTCH DEVELOPMENT.-Rat snakes from the Panhandle eastward to
the Suwannee and southward along the west coast to the Withlacoochee
have dorsal blotches. Specimens south of the Suwannee have dorsal stripes
as well, and are recognized as the subspecies E. o. williamsi. Specimens
from extreme southern Florida and the Upper Keys have fairly well-
developed dorsal blotches and have been called E. o. deckerti (Fig. 50).
VENTRAL PIGMENTATION.-Figure 51 shows the variation in the
amount of dark pigment in the ventral pattern of Florida rat snakes.







BULLETIN FLORIDA STATE MUSEUM


:....- s^.-'e .---



*-- . .- "

FIGURE 48.-Elaphe obsoleta, both sexes (excluding juveniles). Ground color. Darker
shading = darker ground color, n = 370.
FIGURE 49.-Elaphe obsoleta, both sexes (excluding juveniles). Development of the dorsal
stripes. Increasing shading = increasingly defined dorsal stripes. n = 322.




N--









FIGURE 50.-Elaphe obsoleta, both sexes (excluding juveniles). Development of the dorsal
blotches. Increasing shading = increasingly defined dorsal blotches. n = 323.
FIGURE 51.-Elaphe obsoleta, both sexes (excluding juveniles). Amount of dark ventral
pigmentation. Darker shading = darker ventrums. n = 323.
Specimens from the Panhandle east to the Suwannee River have the
darkest bellies.
SUPRALABIAL PIGMENTATION.-The variation in the amount of dark
pigment on the upper labial scales varies identically to that in ventral
pigmentation, except that snakes with dark supralabials occur also on the
Upper Keys.

Lampropeltis getulus (Linnaeus), Kingsnake

I analyzed data on 207 L. getulus from Florida, southern Georgia and
southern Alabama (Fig. 52) and investigated 11 characters for geographic
variation (Appendix A). As head length divided by snout-vent length cor-
related with snout-vent length, further consideration of this character


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 185

















FIGURE 52.-Localities of 207 Lampropeltis getulus specimens examined.
was omitted. The characters that seem to vary geographically are dis-
cussed below.
NUMBER OF VENTRALS.-As the number of ventral scales does not cor-
relate with sex (r = 0.1392), the sexes were lumped to increase the sam-
ple size. Kingsnakes from the Panhandle tend to have fewer ventrals than
those from the peninsula. The tendency is not pronounced, however, and
if any dine exists within the peninsula, it does not emerge from examina-
tion of the map.
NUMBER OF SUBCAUDALS.-Males usually have more subcaudals than
females (r = 0.6306), but the sexes show little geographic concordance in
the patterns. Subcaudal counts show a very generalized tendency to be
higher in the southern peninsula.
PERCENT TAIL. -Tail length divided by total length varies as shown in



_:.-. '- '::. ':*:-










FIGURE 53.-Lampropeltis getulus, males only. Tail length divided by total length. Darker
shading = proportionately longer tails. n = 63.
FIGURE 54.-Lampropeltis getulus, females only. Tail length divided by total length. Darker
shading = proportionately longer tails. n = 33.








BULLETIN FLORIDA STATE MUSEUM


Figures 53 and 54. Males have proportionately longer tails than females
(r = 0.4837), thus the sexes have been treated separately in the
geographical analysis. Snakes with proportionately longer tails occur in
extreme southern Florida and apparently the Apalachicola River Valley.
DORSAL SCALE Rows.--Kingsnakes from the Panhandle east to the
vicinity of the Aucilla River and some specimens from extreme southern
Florida have 21 midbody scale rows, whereas peninsula specimens usually
have 23 (Fig. 55).
NUMBER OF INFRALABIALS.-Most Florida kingsnakes have 18 lower
labial scales, counting both sides, but many from the extreme north have
19 or 20; those from the east coast frequently have 20.
NUMBER OF CROSS BANDs.-Figures 56 and 57 show the variation in













FIGURE 55.-Lampropeltis getulus, both sexes. Number of dorsal scale rows at mid-body.
Lighter shading = 21, darker shading, 23. n = 71.
FIGURE 56.-Lampropeltis getulus, males only. Number of body bands. Levels by increasing
shading: 15-26, 27-38, 39-50, 51-62. n = 90.














FIGURE 57.-Lampropeltis getulus, females only. Number of body bands. Levels by increas-
ing shading: 17-28, 29-39, 40-51, 52-63. n = 42.
FIGURE 58.-Lampropeltis getulus, both sexes. Amount of light pigment in the dorsal pattern.
Increased shading = increased amounts of light pigment. n = 172.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 187

the number of dorsal precaudal cross bands in Florida L. getulus. The
concordance between the sexes is excellent, and suggests that the sexes res-
pond similarly to whatever environmental factor selects for cross band
counts. A weak (r = 0.4038) correlation between snout-vent length and
number of cross bands implies that larger snakes tend to have fewer cross
bands, but no correlation is evident between snout-vent length and lati-
tude (r = 0.1678). The number of cross bands increases in a regular dine
southward on the peninsula.
DORSAL PATTERN.-The amount of light pigment in the dorsal pattern
varies geographically (Fig. 58). Congruence between the sexes is good.
Areas where kingsnakes tend to have more light pigment dorsally include
the Everglades and southern peninsula, the Lower Apalachicola Valley,
and extreme northern Florida. Frequently snakes from east of Tampa Bay
are light colored as well.
Lampropeltis triangulum (Lacepede), Scarlet Kingsnake
I analyzed data on 120 L. triangulum from Florida, southern
Georgia, and southern Alabama (Fig. 59) for variation trends in each of
15 characters (Appendix A). None of the characters investigated showed
correlations with snout-vent length. Those characters that seem to vary
geographically are discussed below.














FIGURE 59.-Localities of 120 Lampropeltis triangulum specimens examined.
NUMBER OF VENTRALS.-Males and females do not differ appreciably
in number of ventral scales (r = 0.2330), but they do seem to differ in
their patterns of geographic variation. Sample sizes are admittedly small,
and trends uncovered by the mapping technique may be a result of sam-
pling bias. The data available (Figs. 60 and 61) suggest that male scarlet
kingsnakes have higher ventral counts in northern Florida, but females
have lower counts there.
NUMBER OF SUBCAUDALS.-Males generally have more subcaudal







BULLETIN FLORIDA STATE MUSEUM


scales than females (r = 0.6352). Concordance between the sexes is fair.
If any geographic tendency exists, it is for snakes from the Panhandle and
parts of southern Florida around Lake Okeechobee to have higher sub-
caudal counts.
VENTRALS PLUS CAUDALS.-The summation of the preceding two
characters does not correlate with sex (r = 0.1106), and samples are com-
bined for Figure 62. Snakes from the Panhandle have higher ventral plus
caudal counts than specimens from most of the peninsula, but snakes from
the east coast and around Lake Okeechobee also seem to have high ventral
plus caudal counts.









_---N-- ~*-.-.-. _


FIGURE 60.-Lampropeltis triangulum, males only. Number of ventral scales. Levels by in-
creasing shading: 159-169, 170-185. n = 56.
FIGURE 61.-Lampropeltis triangulum, females only. Number of ventral scales. Levels by in-
creasing shading: 162-174, 175-185. n = 61.
PERCENT TAIL.-Males have proportionately longer tails
(r = 0.6537). The variation is not clear-cut, but seems to show a slight
tendency for relative tail length to increase clinally from north to south on
the peninsula.
DORSAL SCALE Rows.-Females usually have 19 midbody scale rows,
males either 19 or 17. Figures 63 and 64 show the variation. Males from
the Panhandle usually have 19 scale rows at midbody, and males from the
peninsula may have either 19 or 17.
RED BODY BANDS.-High cross band counts are associated with
specimens from northern Florida, including the Panhandle, the Central
Highlands, and apparently the region around Miami in southern Florida.
RED TAIL BANDs.-Specimens from the Panhandle and northern
peninsula generally have higher tail band counts than those from the rest
of the state.
TOTAL RED BANDs.-The sum of precaudal and caudal red bands
varies as shown in Figure 65. Highest counts occur in northern Florida,
the area east of Tampa Bay, and the southeastern peninsula region.
Scarlet kingsnakes from the southern half of the peninsula (not counting


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 189




..:.- .=.
-- "--..











FIGURE 62.-Lampropeltis triangulum, both sexes. Sum of ventrals plus caudals. Levels by in-
creasing shading: 197-211, 212-214, 215-227. n = 107.
FIGURE 63.-Lampropeltis triangulum, males only. Number of dorsal scale rows at mid-body.
Lighter shading = 17, darker shading, 19. n = 59.
X--' .. ----.= ---- .. .=












FIGURE 64.-Lampropeltis triangulum, females only. Number of dorsal scale rows at mid-
body. Lighter shading = 17, darker shading, 19. n = 59.
FIcuRE 65.-Lampropeltis triangulum, both sexes. Number of red bands, body and tail.
Levels by increasing shading: 15-18, 19-20, 21-25. n = 80.

the Miami Rim area) have lower band counts than specimens from the
Panhandle and northern half of the peninsula.

Diadophis punctatus (Linnaeus), Ringneck Snake

I examined 295 D. punctatus from Florida, southern Georgia, and
southern Alabama (Fig. 66) for variation in 23 characters (see Appendix
A). None of the characters examined was correlated with body size. Those
that show apparent geographic variation are discussed below.
NUMBER OF VENTRALS.-Figures 67 and 68 show the variation in ven-
tral numbers for male and female Florida ringneck snakes. The correla-
tion coefficient between ventral counts and sex was 0.6314. Snakes from
the Panhandle and northern peninsula have the highest ventral counts.
Concordance between the sexes is very good.








190 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 3

NUMBER OF SUBCAUDALS.-Males have more subcaudal scales than
females (r = 0.7425), and the variation is more complex than that in ven-
tral counts. Basically, ringnecks from the peninsula have lower subcaudal
counts than those from the Panhandle, but many individuals from ex-
treme southern Florida have counts like those in Panhandle specimens.
VENTRALS PLUS CAUDALS.-The summation of ventrals and sub-
caudals is not correlated with sex (r = 0.0624), and the samples were
combined in Figure 69. Snakes from the Panhandle and northern penin-
sula have the highest counts. Snakes with intermediate values occupy the
southern tip of the peninsula, and specimens with low counts occur on the
Lower Keys and most of the central Florida peninsula.

















FIGURE 67.-Diadophis punctatus, males only. Number of ventral scales. Levels by increasing
shading: 124-135, 136-138, 139-148. n = 132.
: i ." ' -- :













FIGURE 68.-Diadophis punctatus, females only. Number of ventral scales. Levels by increas-
ing shading: 133-142, 143-144, 145-154. n = 162.
FIGURE 69.-Diadophis punctatus, both sexes. Sum of ventrals plus caudals. Levels by increas-
ing shading: 171-181, 182-185, 186-198. n = 280.








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 191

PERCENT TAIL.-Relative tail length was correlated with sex
(r = 0.8058), so males and females were mapped separately. Snakes from
the southern half of the peninsula and the Keys have proportionately
longer tails than those from the rest of the state.
NUMBER OF SUPRALABIALS.-Most southeastern ringneck snakes have
16 total supralabial scales. Occasional specimens with only 14 occur more
frequently in the Panhandle and northern peninsula.
SUBCAUDAL SPOTS.-The number of small black spots on the underside
of the tail varies as in Figure 70. Snakes from the Panhandle, the Gulf
Hammock region, and the Lower Keys often have such spots, which are
usually lacking in specimens from elsewhere.
LABIAL PIGMENTATION.-Pigment on the labials may be in discrete
spots, diffuse smudges, or absent. Figure 71 shows the variation of this
character for both sexes. Specimens from the Lower Keys have no such
pigment or it is very diffuse, those from the southern Everglades and parts
of the Gulf Hammock region usually have diffuse labial pigment. Most
Florida ringneck snakes have labial pigment confined to discrete spots.











termediate shading, the intermediate condition. n 291.......


FIGURE 70.-Diadophis punctatus, both sexes. Number of subcaudal black spots. Lightest
shading = none, intermediate shading, 1-5, and darkest shading, 6-59. n = 293.
FIGURE 71.-Diadophis punctatus, both sexes. Nature of the labial pigmentation. Darkest
shading = labial pigment in discrete spots, lightest shading, either none or very diffuse, in-
termediate shading, the intermediate condition, n = 291.
PIGMENTED SUPRALABIALS.-The number of upper labial scales with
black pigment varies as in Figure 72. Specimens from South Florida and
the Keys as well as many from the Gulf Hammock region score high for
this character, Panhandle snakes the lowest, and specimens from the rest
of the state receive intermediate scores.
PIGMENTED LABIALS.-This character is the summation of labials,
supra- and infra-, with black pigment. Its geography is almost identical to
Figure 72. Snakes from the Gulf Hammock region and the southern tip of







BULLETIN FLORIDA STATE MUSEUM


the peninsula including the Keys have the most pigment, those from the
Panhandle the least, and most peninsular specimens are intermediate.
RING SEPARATION.-Most ringneck snakes from Florida have a mid-
dorsal break in the neck ring, but Figure 73 shows the variation in this
character is complex. Lower Keys and Gulf Hammock specimens may
lack a nuchal ring altogether, and many from coastal areas and the
Panhandle have no middorsal ring interruption.
RING WIDTH.-The width of the nuchal ring varies as shown in Figure
74. The widest rings are in the Panhandle and northern peninsula.

... -.












FIGURE 72.-Diadophis punctatus, both sexes. Number of supralabial with black spots,
right side. Levels by increasing shading: 0-1, 2-4, 5-7. n = 295.
FIGURE 73.-Diadophis punctatus, both sexes. Width (in scale lengths) of the mid-dorsal in-
terruption in the nuchal ring. Lightest shading = 0, intermediate shading, 1-5, and darkest
shading, > 5 or neck ring absent. n = 293.
i---







i,., '.----


7V MT-
""-----














FIGURE 74.-Diadophis punctatus, both sexes. Width (in scale lengths) of the nuchal ring.
Lighter shading = 0.5-1.5, and darker shading, 1.5-3.0. n = 291.
FIGURE 75.-Diadophis punctatus, both sexes. Displacement (in scale lengths) of the nuchal
ring behind the parietal scales. Levels by increasing shading: 0.75-1.75, 1.75-2.5, 2.75-3.5.
n = 291.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 193

RING POSITION.-The position of the nuchal ring relative to the
parietal scales varies as shown in Figure 75. In the Panhandle and north-
ern peninsula neck rings tend to originate nearer the parietals than in
southern specimens.
Cemophora coccinea (Blumenbach), Scarlet Snake
I analyzed data on 90 C. coccinea from Florida and southern Georgia
(Fig. 76) for variation in 17 characters (Appendix A). The sample size is
unfortunately small. The characters examined that show geographic
variation are discussed below.
NUMBER OF VENTRALS.-As the number of ventral scales correlates
with sex (r = 0.4144), the sexes are mapped separately (Figs. 77 and 78).
Snakes from the Panhandle and the southern end of the peninsula tend to
have fewer ventral scales than those from the central peninsula.















FIGURE 76.-Localities of 90 Cemophora coccinea specimens examined.

NUMBER OF SUBCAUDALS.-This character correlates only weakly with
sex (r = 0.3385) with males having the higher counts. In both sexes Pan-
handle snakes tend to have fewer subcaudals than peninsula specimens.
Specimens from the southern tip of the state also have low subcaudal
counts.
VENTRALS PLUS CAUDALS.-This character summarizes the variation
apparent in the two preceding counts and is not correlated with sex
(r = 0.2240). Figure 79 shows the pattern for both sexes. Lowest counts
occur in the Panhandle east to the Suwannee and in the southern penin-
sula south of Lake Okeechobee. Snakes from between the Suwannee and
Lake Okeechobee have higher ventral scute counts.
PERCENT TAIL.-The sexes show no significant difference in relative
tail lengths. Snakes from more southern sites tend to have proportionately
longer tails, but the tendency is not sharply defined. In the Panhandle








BULLETIN FLORIDA STATE MUSEUM


females have relatively longer and males shorter tails. Thus sexual dimor-
phism is pronounced in the few Panhandle specimens examined, but lack-
ing in the peninsular specimens. The two Panhandle females have longer
tail length/snout vent ratios (mean = 0.158) than the three males
available (mean = 0.140).
INFRALABIALS.-Florida snakes may have 14, 16, or 18 lower labial
scales. Specimens from the Everglades Region frequently have 14 in-
fralabials, and many specimens from the central and northcentral penin-
sula have 18.
SUPRALABIALs.-Snakes from the Panhandle west of the Aucilla River,
northeast Florida, and the Everglades usually have 11 to 13 upper labials.
Snakes from the central peninsula tend to have 14 or 15 (Fig. 80).


FIGURE 77.-Cemophora coccinea, males only. Number
shading = 158-170, darker shading, 171-182. n = 41.
FIGURE 78.-Cemophora coccinea, females only. Number
shading = 165-174, darker shading, 175-185. n = 37.




... ... -


imi




-":7




of ventral scales. Lighter

of ventral scales. Lighter







S_ --.



-----
--= s- I^


FIGURE 79.-Cemophora coccinea, both sexes. Sum of ventrals plus caudals. Levels by in-
creasing shading: 197-212, 213-218, 219-228. n = 84.
FIGURE 80.-Cemophora coccinea, both sexes. Number of supralabial scales (both sides).
Levels by increasing shading: 11-12, 13, 14-15. n = 85.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 195

NUMBER OF RED BODY BANDs.-Snakes from northern Florida and the
Osceola National Forest region, from just south of Tampa Bay, and from
the Everglades, have fewer cross bands than snakes from the rest of the
state.
NUMBER OF RED TAIL BANDs.-The number of cross bands on the tail
correlates with sex (r = 0.5179). Although concordance between the
sexes is poorly developed, a general tendency for scarlet snakes in the
north to have more tail bands is apparent.
DORSAL SCALE Rows.-Of the specimens examined 90.4% had 19 dor-
sal scale rows at mid body. Everglades snakes had 17 anterior scale rows,
and those from extreme northern Florida usually had 21, whereas those
from the rest of Florida usually had 19. All Cemophora examined from
the Panhandle had 19 posterior scale rows, but peninsula specimens had
fewer than 19.
LENGTH OF THE WHITE BANDs.-Snakes from the western Panhandle,
northcentral peninsula, and the west coast of the peninsula tend to have
longer white bands.
LENGTH OF RED BANDs.-Longer red bands are the rule in northern
Florida, around Lake Okeechobee, and in the extreme southern
Everglades.
Tantilla coronata (Baird and Girard), Tantilla relicta Telford,
and Tantilla oolitica Telford, Crowned Snakes
I analyzed data on 198 Tantilla specimens from Florida (Fig. 81) for
variation in 11 characters (Appendix A). Those characters that seem to
vary geographically are discussed below.
NUMBER OF VENTRALS.-Females generally have more ventrals than



h.-











FIGURE 81.-Localities of 198 Tantilla sp. specimens examined.
FIGURE 82.- Tantilla, males only. Number of subcaudal scales. Levels by increasing shading:
45-52, 53-58, 59-67. n = 81.







BULLETIN FLORIDA STATE MUSEUM


FIGURE 83.-Tantilla, females only. Number of subcaudal scales. Levels by increasing
shading: 40-48, 49-52, 53-61. n = 68.
FIGURE 84.- Tantilla, both sexes. Sum of ventrals plus caudals. Levels by increasing shading:
156-180, 181-187, 188-209. n = 149.

males (r = 0.4150) and the sexes were mapped separately. In both sexes
the ventral scale number decreases southward on the peninsula until
southernmost Florida; Miami and Key Largo specimens have high ventral
counts, reminiscent of northern populations.
NUMBER OF SUBCAUDALS.-The highest subcaudal counts occur on
snakes from the Big Bend region of northern Florida and decrease quickly
to the west and more gradually to the south. Figures 82 and 83 show the
variation for males and females, which differ in mean subcaudal counts
(r = 0.4194).
VENTRALS PLUS CAUDALS.-The sum of the preceding two counts pro-
duces a variable that does not correlate with sex (r = 0.0783). Figure 84
shows this character's pattern. Panhandle and northern peninsula snakes
have the highest counts, which decrease clinally southward until in the
Miami area they increase to approximate the northern counts.
PERCENT TAIL.-Males usually have proportionately longer tails than
females (r = 0.6339). Both sexes vary geographically with relatively
longer tails occurring in the Big Bend region and the peninsula west coast.
SUPRALABIALS.-Snakes from Highlands County often have six upper
labials on each side; specimens from the rest of the state usually have
seven.
PARIETAL PIGMENTATION.-Snakes from the Miami area and parts of
the Big Bend region of northern Florida lack light spots on the parietal
scales (Fig. 85). Specimens from the Panhandle east to the Ochlockonee
River, from Highlands County, and from the lower east coast of the
peninsula have extensive light parietal markings, often forming a partial
nuchal ring. Snakes from the rest of the peninsula have intermediate
amounts of light pigment in the parietal region.
SNOUT PIGMENTATION.--Most specimens from the lower east coast


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 197

have a large white spot on the rostral and internasal scales (Fig. 86).
Highlands County snakes also have some light pigment on the snout, but
most populations lack this characteristic.














FIGURE 85.-Tantilla, both sexes. Light pigment on the parietal scales. Lightest
shading = none, intermediate shading, some light pigment, and darkest shading, much light
pigment forming a nuchal band. n = 197.
FIGURE 86.-Tantilla, both sexes. Size of the light spot on the snout. Lightest shading =
none, darkest shading, a large spot, and intermediate shading, a small light spot. n = 197.

Sistrurus miliarius (Linnaeus), Pygmy Rattlesnake

I examined 320 S. miliarius from Florida, southern Georgia, and
southern Alabama (Fig. 87) for variation in 22 characters (see Appendix
A). Much of the variation was irregular owing to a large degree of indi-
vidual variation among snakes from nearby localities. Smoothing algo-
rithms might help clarify the picture by plotting averages of adjacent
specimens, but the mapping procedure employed here does not smooth,
but plots the data exactly as they appear. Three ratios concerned with the
frontal scale and snout-vent length were correlated with snout-vent




.. !


::


FIGURE 87.-Localities of 320 Sistrurus miliarius specimens examined.







BULLETIN FLORIDA STATE MUSEUM


length and excluded from further consideration. Those characters for
which geographic trends were noted are discussed below.
NUMBER OF VENTRALS.-Females tend to have more ventral scales
than males (r = 0.4672), and the sexes were treated separately. The
lowest ventral counts are associated with snakes from the Panhandle, the
highest with those from the central peninsula.
NUMBER OF SUBCAUDALs.-Males usually have more subcaudal scales
than females (r = 0.6267). The pattern is similar to that in ventral
counts. Specimens from the Panhandle have the lowest counts, those from
the central peninsula the highest. As with the preceding character,
pygmies from the lowlands south of Lake Okeechobee tend to have lower
counts than those just north and south of this region.
VENTRALS PLUS CAUDALS.--Although ventrals and caudals are both
correlated with sex, their summation is not (r = 0.0570). For the varia-
tion in the combined sexes see Figure 88. Snakes from the Panhandle east
to the Aucilla River and in the Everglades region south of Lake
Okeechobee tend to have the lowest values; those from the peninsula
north of the Everglades show a clinal increase from north to south.
DORSAL SCALE Rows.-Figures 89 and 90 show the variation in the
number of dorsal scale rows at two points along the body. The lowest
counts are in Panhandle specimens and the highest in specimens from
both coasts. Snakes with intermediate counts occur in most of the interior
peninsula. Nearly all Sistrurus from coastal locations in Florida have 25
scale rows at mid-body. The map doesn't show this pattern clearly
because EDV's along the coast were often calculated from inland ADV's
when these were nearer than coastal ADV's.
NUMBER OF DORSAL BLOTCHES.-Pygmy rattlers from the Panhandle
west of the Ochlockonee and from many coastal areas on the peninsula





'-z-" -=" -----. a -"- --"






FIGURE 88.-Sistrurus miliarius, both sexes. Number of ventrals plus caudals. Levels by in-
creasing shading: 156-169, 170-173, 174-186. n = 312.
FIGURE 89.-Sistrurus miliarius, both sexes. Number of dorsal scale rows one head length
posterior to the head. Levels by increasing shading: 23, 25, and 27-29. n = 303.


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 199





..- ---- -. -- - "..--.
-- -_"- -.-. ,r. :.-,






---S


FIGURE 90.-Sistrurus miliarius, both sexes. Number of dorsal scale rows at mid-body. Levels
by increasing shading: 21, 23, and 25. n = 316.
FIGURE 91.-Sistrurus miliarius, both sexes. Blotch length divided by inter-blotch space
length. Levels by increasing shading: 0.33-1.00, 1.01-1.33, and 1.34-2.50. n = 318.

often have more dorsal body blotches than those from the rest of the state.
DORSAL BLOTCH/SPACE RATIO. -This character varies as shown in
Figure 91. Pygmies west of the Ochlockonee River in the Panhandle and
in the Everglades usually have crossband-like body blotches that are nar-
rower than the interblotch spaces. Snakes from peninsula coastal areas
tend to have larger blotches with very narrow spaces between. Many
specimens from the peninsula interior have spot/space ratios intermediate
between these.
DORSAL BLOTCH SHAPE.-When the length (in scales) of a typical mid-
body dorsal blotch is divided by its width, the resulting ratio varies
geographically as depicted in Figure 92. Panhandle and Everglades
snakes have blotches more like crossbands, those from most of the penin-
sula more roundish blotches.


+r- --".-----

_--=








FIGURE 92.-Sistrurus miliarius, both sexes. Blotch shape. The darker the shading, the longer
the dorsal blotches in relation to their width, n = 319.
FIGURE 93.-Sistrurus miliarius, both sexes. Contrast between dorsal blotches and ground col-
or. Darker shading = greater contrast, n = 317.







BULLETIN FLORIDA STATE MUSEUM


DORSAL BLOTCH-GROUND COLOR CONTRAST.-Snakes from the Pan-
handle and parts of southern Florida, including the Everglades, have
more contrast between their dorsal blotches and their ground color, re-
sulting in a more distinctive dorsal pattern. Coastal area snakes also tend
to have higher values for this character (Fig. 93).
VENTRAL PIGMENTATION.--Pygmy rattlers from much of the Pan-
handle west of the Ochlockonee and from South Florida tend to be
whiter ventrally than specimens from the rest of the state.
Crotalus adamanteus Beauvois, Eastern Diamondback Rattlesnake
I examined 194 C. adamanteus (Fig. 94) for variation in 18 characters
(Appendix A). Most characters showed considerable individual variation
that obscured geographic variation; consequently many of the maps ap-
pear noisy. Several characters did not vary geographically within the
study area.








ii : i l: : :- "1 ''F L





FIGURE 94.-Localities of 194 Crotalus adamanteus specimens examined.
FIGURE 95.-Crotalus adamanteus, both sexes. Number of mid-body scale rows. Lighter
shading = 25 and 27 scale rows, darker shading, 29 and 31. n = 191.

NUMBER OF VENTRALS.-Female rattlesnakes usually have more ven-
tral scales than males (r = 0.6808). The only geographic trend apparent
in the variation of ventral counts is that snakes from the Florida Keys and
adjacent mainland consistently have more ventrals than specimens from
elsewhere in Florida, but no dine is manifest.
NUMBER OF SUBCAUDALS.-Males have more subcaudals than females
(r = 0.7971). The variation in subcaudal counts within Florida is com-
plex and seems to have no geographic component.
DORSAL SCALE Rows.-I can discern no geographic trend in the varia-
tion of dorsal scale row counts in Florida C. adamanteus. Figure 95 shows
the spotty occurrence of specimens with higher scale row counts.


Vol. 25, No. 3









1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 201


NUMBER OF INFRALABIALS.-The variation in this character is also
complex, but some geographic trends are apparent. Snakes from northern
Florida and from the Lower Keys typically have more lower labials than
specimens from the central peninsula (Fig. 96).

DORSAL BLOTCHES.-The number of diamonds on Florida C. adaman-
teus varies geographically as shown in Figure 97. Specimens from the
Panhandle, the Keys, and the west coast of the peninsula tend to have
fewer blotches than those from the peninsula interior.
LABIAL PIGMENTATION.-The number of immaculate supralabials
varies geographically as shown in Figure 98. Specimens from the western

'= :_--=j3 --


FIGURE 96.-Crotalus adamanteus, both sexes. Number of infralabials. Levels by increasing
shading: 30-33, 34, 35-40. n = 187.

FIGURE 97.-Crotalus adamanteus, both sexes. Number of blotches. Lighter
shading = 22-27, darker shading, 28-34. n = 190.























FIGURE 99.-Crotalus adamanteus, both sexes. Amount of dark pigmentation on the ventrum.
Darker shading darker centers. n = 192.
FIGURE 98.-Crotalus adamanteus, both sexes. Number of immaculate supralabials. Levels
by increasing shading: 0-1, 2-4, 5-8. n = 192.

FIGURE 99.- Crotalus adamanteus, both sexes. Amount of dark pigmentation on the ventrum.
Darker shading = darker venters, n = 192.


-~-~-s~
--
-

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L=~-- ~-
" E~-
; :
.--.-
r







BULLETIN FLORIDA STATE MUSEUM


Panhandle, the Upper Keys, and the Everglades region tend to have dark
pigmentation on all upper labial scales. Snakes from the Central Ridge
east of Tampa Bay and from the Lower Keys frequently have the most im-
maculate labials.
VENTRAL PIGMENTATION.-Snakes from the Panhandle, the
Everglades region, and the west coast of the peninsula tend to have lighter
ventral patterns than those from the interior of the peninsula. Snakes
from the Lower Keys usually have darker ventral patterns, more like
specimens from north-central Florida (Fig. 99).

ENVIRONMENTAL DATA
I mapped environmental data from 196 weather stations in Florida,
Georgia, and Alabama (Fig. 100). Figures 101-105 show the geographic
variation of selected variables.





i









FIGURE 100.-Locations of 196 weather stations supplying data from Florida, Georgia and
Alabama.
FIGURE 101.-Elevation (in meters) above mean sea level. Levels by increasing shading: 1-8,
9-26, 27-45, 46-142. n = 195.

THE PATTERNS
When an entire set of 166 contour maps of snake morphological varia-
tion was subjected to principal components analysis, the first component
accounted for 17.0% of the total variation. If the original contour maps
had nothing in common, we would expect each component to explain
only 1/166 or 0.6% of the total variation. Thus the first component ac-
tually accounts for a very large portion of the information in the original
166 contour maps. Component 1 may be thought of as the best possible
summary of the geographic variation exhibited by these 14 snake species
(C. coccinea was omitted) in Florida. Figure 106 is a SYMAP-produced
contour map of component 1. Table 2 lists the 166 characters examined,


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION


FIGURE 102.-Mean annual temperature (in C). Levels by increasing shading: 18.9-20.1,
20.2-21.5, 21.6-22.9, 23.0-24.5, 24.6-25.7. n = 130.
FIGURE 103.-Mean annual total precipitation (in cm). Levels by increasing shading: 93-119,
120-140, 141-179. n = 196.
b



IEEHE












shading: 18-56, 57-95, 96-135. n = 130.
FIGURE 105.-Mean daily maximum August temperature (in C). Levels by increasing
shading: 29.0-30.9, 31.0-32.5, 32.6-34.2. n = 130.

their loadings on the first component, and their communalities. The com-
ponent loading shows the percentage of variation explained by the first
component for each character. The communality represents the propor-
tion of variation in the character accounted for by the entire principal
components solution, which actually extracted 38 components.
Figure 106 dipicts what the naturalist actually sees in the geographic
variation of these fourteen species in Florida. Principal components
analysis without rotation maximizes the amount of variation included in
the first component. Thus Figure 106 is an artificial picture of the totality
of geographic variation in fourteen species of snakes in Florida. Its basic,










204 BULLETIN FLORIDA STATE MUSEUM Vol. 25, No. 3



underlying component is a well-developed north-south dine running the

length of the Florida peninsula.






::::::: ::::::::::::::: .. ....... .




..... ...........1. 1 1 nu.. ni..3



IIII***********I***********l***
.. ... ......****


































FIGURE 106.-Geographic variation in the first principal component extracted from a matrix
of 166 contour maps of morphological variation in 14 species of Florida snakes. The map ac-
counts for 17.0% of the total variation in 166 characters and summarizes the major pattern
of geographic variation in these species, the North-South Cline. n = 688.


The purpose of this study, however, was to search for patterns of

geographic variation that the species studied hold in common, not a single
summary of all the geographic variation. To extract mutually exclusive

patterns from the set of contour maps it was necessary to rotate the initial

factor axes (varimax rotation) while still retaining their orthogonality.

For this I used the SPSS factor analysis procedure and 100 contour maps

(including characters from all 15 species and three environmental maps)
as explained in the Methods section.

The factor analysis procedure extracted 24 factors (patterns of

geographic variation), which accounted for 76.9% of the total informa-

tion in the 100 maps. The maps (characters) analyzed and their com-

munalities (percentage of variation accounted for) are presented in Table
II1 III1lllIII 1111 11111111111 ill
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munalities (percentage of variation accounted for) are presented in Table








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 205

Table 2.-Results of the Principal Components Analysis without rotation of 166 contour
maps of morphologic variation in 14 species of Florida snakes. Provided are the variables in-
cluded, their loadings on the first summarizing component, and their communalities for the
entire solution.


Loading on
Variable Component 1 Communality



S. dekayi
temporal pigment shape 0.75178 0.857320
mid-body scale rows -0.87844 0.959967
ventral dark pigmentation 0.59895 0.804973
temporal pigment amount 0.02760 0.779860
subocular pigmentation 0.59535 0.861935
preocular scales -0.03356 0.796338
postocular scales -0.04229 0.813917
black labial scales 0.22597 0.834405
supralabial scales 0.11204 0.829155
infralabial scales 0.06424 0.832628
ventral scales (male) 0.69085 0.917066
subcaudal scales (male) 0.73955 0.946921
percent tail (male) 0.47772 0.867071
ventral scales (female) 0.62153 0.908910
subcaudal scales (female) 0.75891 0.927840
percent tail (female) 0.56426 0.844254

T. sirtalis
parietal spots -0.20325 0.821911
dorsal spotting -0.09702 0.811677
supralabial scales 0.28191 0.807484
ventral scales (male) 0.41559 0.878690
subcaudal scales (male) -0.06502 0.895418
percent tail (male) 0.27741 0.851664
ventral scales (female) 0.61143 0.759186
subcaudal scales (female) 0.59289 0.861226
percent tail (female) -0.09788 0.841539

T. sauritus
parietal spot size 0.17049 0.814010
parietal spot 0.16398 0.875267
ground color -0.12291 0.842355
dorsal stripe edge -0.09702 0.805224
supralabial scales 0.83640 0.913688
ventral scales (male) 0.77527 0.884419
subcaudal scales (male) 0.47862 0.874414
percent tail (male) -0.27616 0.844263
ventral scales (female) 0.69939 0.809959
subcaudal scales (female) 0.33650 0.813132
percent tail (female) -0.02428 0.850746








BULLETIN FLORIDA STATE MUSEUM


Table 2 Continued

Loading on
Variable Component 1 Communality


C. constrictor
blackness -0.33009 0.736223
ventral white 0.39338 0.870350
gular brown pigmentation -0.36636 0.783164
gular black pigmentation 0.01367 0.844681
supralabial brown pigmentation 0.32943 0.804774
supralabial black pigmentation -0.08446 0.860120
loreal-supralabial contact 0.12820 0.649116
ventral scales (male) 0.72032 0.806584
subcaudal scales (male) 0.56194 0.786852
ventral scales (female) 0.82968 0.842804
subcaudal scales (female) 0.75308 0.860562

M. flagellum
color phase 0.52892 0.838177
infralabial scales 0.02678 0.872822
ventral scales (male) 0.11576 0.821633
subcaudal scales (male) -0.11563 0.821633
percent tail (male) -0.11879 0.874451
ventral scales (female) 0.13353 0.890004
subcaudal scales (female) -0.24867 0.892576
percent tail (female) -0.23883 0.865887

O. aestivus
supralabial pigmentation -0.44361 0.800417
second scale row keeling 0.57483 0.829060
infralabial scales 0.13914 0.755147
ventral scales (male) -0.04336 0.860999
subcaudal scales (male) 0.58992 0.917308
percent tail (male) -0.35519 0.801422
ventral scales (female) 0.37148 0.812593
subcaudal scales (female) -0.36932 0.852755
percent tail (female) 0.63580 0.832181

E. guttata
body blotches 0.57096 0.770194
tail blotches 0.40638 0.772105
mid-body scale rows 0.09533 0.714691
lateral blotch shape -0.33356 0.643102
ventral pigmentation -0.37264 0.736798
blotch border -0.05851 0.733278
ventral check shape -0.02959 0.706474
ventral scales (male) 0.49797 0.778119
subcaudal scales (male) 0.44114 0.830048
percent tail (male) 0.25626 0.758150
ventral scales (female) 0.63752 0.831445


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 207

Table 2 continued

Loading on
Variable Component 1 Communality


subcaudal scales (female) 0.30011 0.864125
percent tail (female) -0.13015 0.744075

E. obsoleta
dorsal blotches 0.63544 0.837826
ground color (darkness) -0.10859 0.778195
stripe development 0.53941 0.823807
blotch development -0.72341 0.847160
ventral pigmentation 0.76161 0.901291
supralabial pigmentation -0.75117 0.877764

L. getulus
dorsal cross bands 0.88325 0.935943
mid-body scale row 0.77041 0.906259
dorsal pattern 0.50862 0.813884
infralabial scales -0.03700 0.784680
ventral scales (male) 0.36681 0.794619
subcaudal scales (male) -0.06543 0.738864
percent tail (male) 0.03785 0.730315
ventral scales (female) 0.22155 0.888972
subcaudal scales (female) 0.28291 0.866032
percent tail (female) -0.22312 0.829679

L. triangulum
mid-body scale rows -0.38625 0.837915
red body bands -0.46686 0.838038
red tail bands -0.43715 0.857626
infralabial scales 0.23095 0.857427
loreal scales -0.11961 0.814579
ventral scales (male) -0.51637 0.869459
subcaudal scales (male) -0.02223 0.876373
percent tail (male) 0.14400 0.812309
mid-body scale rows (male) -0.65058 0.862233
ventral scales (female) -0.04569 0.832411
subcaudal scales (female) -0.77806 0.879400
percent tail (female) -0.33692 0.810978
mid-body scale rows (female) 0.01500 0.833400

D. punctatus
paired gular scales -0.28419 0.764453
ventral pigmentation -0.02896 0.800611
ventral spot shape -0.28664 0.804063
ring separation 0.33222 0.790843
ring position 0.44038 0.812375
ring width -0.55495 0.723710
labial pigmentation -0.26576 0.792337








BULLETIN FLORIDA STATE MUSEUM


Table 2 continued

Loading on
Variable Component 1 Communality


subcaudal spots -0.26160 0.764708
immaculate ventral scales 0.02396 0.738373
supralabial scales 0.38404 0.717300
pigmented labials 0.51803 0.806656
ventral scales (male) -0.49355 0.822025
subcaudal scales (male) 0.06949 0.835554
percent tail (male) 0.40379 0.879478
ventral scales (female) -0.64135 0.818082
subcaudal scales (female) -0.29922 0.816859
percent tail (female) 0.03604 0.806662
T. relicta, oolitica, coronata
infralabial-chin shield 0.24407 0.716007
parietal pigmentation -0.40639 0.901413
snout pigmentation 0.50772 0.783422
nuchal collar width -0.26084 0.800727
mental-chin shield contact 0.08308 0.805688
supralabial scales -0.03638 0.809969
ventral scales (male) -0.70326 0.936221
subcaudal scales (male) 0.14401 0.933545
percent tail (male) 0.45205 0.907943
ventral scales (female) -0.73648 0.965518
subcaudal scales (female) -0.01988 0.917414
percent tail (female) 0.24749 0.870040
S. miliarius
dorsal blotches -0.09613 0.783995
tail bands -0.19109 0.731414
divided subcaudal scales 0.05648 0.692906
anterior scale rows 0.61645 0.831487
mid-body scale rows 0.41786 0.786220
posterior scale rows 0.35181 0.657073
dorsal blotch-ground color contrast -0.26618 0.695940
ventral pigmentation 0.00091 0.666744
supralabial scales 0.22321 0.699299
infralabial scales 0.18836 0.665685
dorsal blotch shape 0.44574 0.801361
inter-blotch distance 0.50330 0.726141
ventral scales (male) 0.63696 0.812932
subcaudal scales (male) 0.57465 0.820075
percent tail (male) 0.19769 0.762859
ventral scales (female) 0.59573 0.870476
subcaudal scales (female) 0.52361 0.828918
percent tail (female) 0.21109 0.806835
C. adamanteus


Vol. 25, No. 3


divided subcaudal scales


0.01062


0.757572







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 209

Table 2 continued

Loading on
Variable Component 1 Communality

dorsal blotches 0.15805 0.768355
mid-body scale rows -0.03543 0.714004
black subcaudal scales 0.21744 0.651669
ventral pigmentation -0.10999 0.771955
labial pigmentation 0.03727 0.809250
immaculate supralabials 0.12439 0.777874
supralabial scales 0.11801 0.756410
infralabial scales -0.25936 0.795670
ventral scales (male) 0.30361 0.848964
subcaudal scales (male) -0.00287 0.799858
ventral scales (female) 0.24668 0.801790
subcaudal scales (female) -0.05363 0.742912


3. Table 3 also gives the principal pattern of geographic variation with
which each character is most closely associated, and the factor loading on
the first factor extracted.
Much of the geographic variation observed in Florida snakes is
oriented along a north-south axis. Factor 1 accounted for 26.7% of the
variation explained by the factor analysis procedure and most of the
variation in those characters that showed distinct north-south changes. Of
the 100 maps analyzed, 38 had Factor 1 as their principal factor and 10
had over 50 % of their variation explained by Factor 1 (Table 3). For all of
the maps Factor 1 accounts for that part of the variation that is north-
south oriented.
Factor 1 actually identifies two important patterns of geographic
variation. Unfortunately, the statistics available (factor analysis) do not
have the power to separate a dine from a simple one step character state
shift. It was therefore necessary to examine the original contour maps
loading highest on Factor 1 and visually select those that had a single one-
step character state shift. The North-South Cline Pattern describes the
geographic variation for those characters that vary in a dine southward
on the peninsula. The Suwannee Straits Pattern is shared by those species
that demonstrate abrupt character state changes in the region of the pre-
sent Suwannee River.
Table 3 presents the characters (maps) and their factor loadings on
Factor 1. The factor loadings may be interpreted as the relative impor-
tance of the various characters (i.e., maps) to the definition of the factor;
their square is the percentage of the character's variation accounted for by
the factor. The important observation to be made here is that nearly all of
the characters analyzed have a major portion of their variation that can








BULLETIN FLORIDA STATE MUSEUM


Table 3.-Results of the Factor Analysis with Varimax Rotation of 100 Contour Maps of
Snake Morphologic and Environmental Variation. Note that many variables exhibit aspects
of more than one pattern, but only the principal pattern is included here, except where two
patterns were relatively equal in importance.


Principal Pattern
Loading on of Geographic
Variable Communality Factor 1 Variation


S. dekayi
mid-body scale rows
ventral dark pigmentation
temporal pigment shape
temporal pigment amount
subocular pigmentation
ventrals plus caudals
preocular scales
postocular scales
black labial scales

T. sirtalis
parietal spots
dorsal spotting
ventrals plus caudals
supralabial scales
T. sauritus
parietal spot size
dorsal stripe edge
ventrals plus caudals
supralabial scales
C. constrictor
ventral white

gular brown pigmentation
gular black pigmentation
supralabial brown pig-
mentation
supralabial black pigmen-
tation
loreal-supralabial contact
ventrals plus caudals

M. flagellum
color phase
ventrals plus caudals
infralabial scales
0. aestivus
supralabial pigmentation


.95369
.68403
.80744
.58571
.83800
.82341
.54303
.71416
.73975


.62678
.73091
.54009
.95685


.57189
.66962
.63856
.91204


.76578

.46922
.80162

.79836
.84235

.42071
.78969


.75184
.77890
.69603


.51104


-0.88912
.58711
.73400
.03903
.59878
.68715
-.09941
-.02662
.15218


-.17929
-.02442
.50298
.23957


.02563
.03231
.30364
.77160


Suwannee Straits
Suwannee Straits
Suwannee Straits
Factor 20
Suwannee Straits
North-South Cline
Lower Keys-N. Florida
Factor 13
Factor 18


Factor 9
Factor 9
North-South Cline
Factor 13


Factor 22
Factor 19
Factor 22
Suwannee Straits


.29000 Everglades, Lower
Keys-N. Florida
- .36889 none
.01574 Lower Keys-N. Florida

- .34031 none
-.03129 Lower Keys-N. Florida

.13485 Factor 19
.73851 North-South Cline


.39039
-.31311
.01632


Suwannee Straits
Factor 15
Panhandle-Everglades


-.26689 Factor 7


Vol. 25, No. 3








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 211

Table 3 continued

Principal Pattern
Loading on of Geographic
Variable Communality Factor 1 Variation


second scale row keeling

ventrals plus caudals
infralabials scales
E. guttata
body blotches
tail blotches
mid-body scale rows
ventral pigmentation
blotch border
ventral check shape
ventrals plus caudals

E. obsoleta
dorsal blotches
stripe development
blotch development
ventral pigmentation
supralabial pigmentation
L. getulus
dorsal cross bands
mid-body scale rows
dorsal pattern

ventrals plus caudals
infralabial scales

L. triangulum
mid-body scale rows
red body bands
red tail bands
ventrals plus caudals
infralabial scales
loreal scales
C. coccinea
anterior scale rows
posterior scale rows

red body bands
red tail bands
width fifth red band
width fifth white band
supralabial scales


.76185

.75063
.54415


.62129
.58125
.40211
.54088
.62571
.39840
.59094


.73191
.70248
.81187
.87962
.84859


.92423
.86965
.70095

.66946
.68396


.58845
.74186
.74450
.77099
.76916
.65063


.65221
.86221

.88621
.77072
.77706
.86478
.92083


.48867 North-South Cline,
Factor 7
- .31820 none
.08321 Factor 24


.51736 North-South Cline
.38104 North-South Cline
.06079 Factor 16
-.35622 Coastal
- .03501 Everglades
- .01880 Coastal
.45058 North-South Cline


.70040 North-South Cline
.68599 Suwannee Straits
-.81544 Suwannee Straits
- .84751 Suwannee Straits
- .84396 Suwannee Straits


.77272 North-South Cline
.78203 Suwannee Straits
.38190 North-South Cline,
Everglades
.47711 North-South Cline
-.00146 Factor 10


-.30452 Central Highlands
- .23409 Factor 7
- .28188 Factor 7
-.43181 North-South Cline
.29109 Panhandle-Everglades
-.14573 Factor 11


-.16574 Factor 20
- .45041 Suwannee Straits,
Everglades
- .08845 Everglades
-.31636 Factor 11
- .25570 Everglades
.49117 Suwannee Straits
.72762 Suwannee Straits








BULLETIN FLORIDA STATE MUSEUM


Table 3 continued


Principal Pattern
Loading on of Geographic
Variable Communality Factor 1 Variation


infralabial scales
ventrals plus caudals


D. punctatus
ventral pigmentation
ventral spot shape
ring separation

ring width
labial pigmentation
immaculate ventral scales
ventrals plus caudals
supralabial scales
pigmented labials


T. relicta, oolitica, coronata
infralabial-chin shield
parietal pigmentation
snout pigmentation
nuchal collar width
ventrals plus caudals
supralabial scales

S. miliarius
body blotches
tail bands
anterior scale rows

mid-body scale rows
blotch-ground color
contrast
ventral pigmentation
ventrals plus caudals
supralabial scales
infralabial scales
dorsal blotch shape

inter-blotch space
C. adamanteus
dorsal blotches
black subcaudal scales
ventral pigmentation


.86708
.85531



.68257
.58628
.51227

.52656
.59992
.55130
.57328
.30275
.64861



.65249
.77002
.65309
.71403
.80101
.77949


.53895
.44302
.71182

.46439
.40396

.46360
.75488
.50758
.49931
.56716

.52296


.55132
.41927
.51970


.05655 Everglades
.53298 North-South Cline,
Everglades


.00094 Factor 8
- .20558 Factor 8
.30422 Suwannee Straits,
Panhandle-Everglades
- .53219 Suwannee Straits
-.15822 Coastal
- .05158 Factor 8
-.58642 North-South Cline
.31443 Suwannee Straits
.41560 North-South Cline,
Suwannee Straits


-.17786 Factor 23
-.40090 North-South Cline
.35250 Factor 7
- .20308 Central Highlands
- .55866 North-South Cline
-.03635 Central Highlands


- .07901 Factor 19
-.15767 Factor 19
-.48877 North-South Cline,
Coastal
.28273 Factor 18, Coastal
-.30038 Factor 21

- .01047 Panhandle-Everglades
.58551 North-South Cline
.16292 Factor 17
.15802 Factor 17
.42178 North-South Cline,
Panhandle-Everglades
.41702 North-South Cline


.14065 Factor 14
-.18888 none
-.05206 Factor 22


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 213

Table 3 continued

Principal Pattern
Loading on of Geographic
Variable Communality Factor 1 Variation


immaculate supralabials .44236 .17053 Everglades, Panhandle-
Everglades
ventrals plus caudals .48915 .14411 Factor 23
supralabial scales .70976 .10392 Factor 12
infralabial scales .61233 .20077 Factor 12
Florida environment
mean annual temperature .76211 .82022 North-South Cline
mean annual precipitation .59495 -.35357 Panhandle-Everglades
mean annual number of .67363 .23942 Coastal
days temperature
exceeds 32.2C

be described as either a north-south gradient or a character shift along
north-south lines, or both.
The North-South Cline Pattern (Factor 1, in part) is the most impor-
tant pattern of geographic variation observed in Florida snakes. Even
characters that vary primarily in some other pattern usually have some
component of their variation that can be described as a north-south dine.
Many characters (e.g. ventrals plus caudals in Storeria dekayi, Tham-
nophis sirtalis, Coluber constrictor, Elaphe guttata, Lampropeltis
getulus, Lampropeltis triangulum, Cemophora coccinea, Diadophis
punctatus, and Sistrurus miliarius, and blotches or crossbands in Elaphe
guttata, Elaphe obsoleta, and Lampropeltis getulus) vary primarily in the
North-South Cline Pattern.
The Suwannee Straits Pattern (Factor 1, in part) is presented in Figure
107, and is best exemplified by the variation in such characters as mid-
body scale rows in Storeria dekayi, number of supralabials in Tham-
nophis sauritus, midbody scale rows in Lampropeltis getulus, and dorsal
blotch development in adult Elaphe obsoleta. Like the North-South Cline
Pattern, this pattern is frequently superimposed on other patterns of
geographic variation (see, for example, number of labial spots in
Diadophis punctatus).
The second factor extracted from the matrix of 100 maps accounted
for another large proportion of the information. Table 4 presents factor
loadings on Factor 2 for the variables that were important in its construc-
tion. This pattern may be called the Everglades Pattern (Fig. 108) and is
the principal pattern of variation for such characters as the number of im-
maculate labials in Crotalus adamanteus, development of the dorsal








BULLETIN FLORIDA STATE MUSEUM


FIGURE 107.-Suwannee Straits Pattern of Geographic Variation (Factor 1, in part).
FIGURE 108.-Everglades Pattern of Geographic Variation (Factor 2).

Table 4.-Everglades pattern of geographic variation (Factor 2). Variables followed by an
asterisk have Factor 2 as their principal pattern.


Variable Factor Loading


C. constrictor
ventral white -0.42099
E. guttata
blotch border* -0.45133
ventrals plus caudals 0.29934
L. getulus
dorsal pattern 0.28488
C. coccinea
posterior scale rows 0.37496
red body bands* 0.74285
width fifth red band* -0.56371
infralabial scales* 0.84919
ventrals plus caudals 0.45206
C. adamanteus
immaculate supralabials* 0.36125



blotch border in Elaphe guttata, and number of crossbands, number of
infralabials, and length of the red bands in Cemophora coccinea.
Factor 3 describes a Lower Keys-North Florida Pattern (Table 5, Fig.
109) and is best illustrated by the variation seen in supralabial and gular
black pigmentation in Coluber constrictor and number of preocular scales


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1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 215

Table 5.-Lower Keys-North Florida pattern (Factor 3). Variables followed by an asterisk
have Factor 3 as their principal pattern.


Variable Factor Loading


S. dekayi
ventrals plus caudals .0.23989
preocular scales* 0.40677
black labial scales 0.23295
C. constrictor
ventral white 0.45636
gular black pigmentation* 0.85700
supralabial black pigmentation* 0.88389
supralabial brown pigmentation -0.32688
loreal-supralabial contact 0.28467
0. aestivus
ventrals plus caudals 0.27052


in Storeria dekayi. This pattern summarizes the geography of a phenetic
resemblance between populations in northern Florida, the region east of
Tampa Bay and the Lower Keys. Ventral white in Coluber constrictor,
ventral plus caudals in Storeria dekayi, and supralabial-loreal contact in
Coluber constrictor also have elements of this pattern.
The fourth factor is the Panhandle-Everglades Pattern, (Table 6, Fig.
110) in which infraspecific populations in the Florida Panhandle and the
Everglades region are more similar to each other than either is to
geographically intermediate populations. The number of infralabials in
Masticophis flagellum and Lampropeltis triangulum, and the amount of















FIGURE 109.-Lower Keys-North Florida Pattern of Geographic Variation (Factor 3).
FIGURE 110.-Panhandle-Everglades Pattern of Geographic Variation (Factor 4).








BULLETIN FLORIDA STATE MUSEUM


Table 6.-Panhandle-Everglades pattern (Factor 4). Variables followed by an asterisk have
Factor 4 as their principal pattern.


Variable Factor Leading


M. flagellum
color phase -0.31427
infralabial scales* 0.72896
O. aestivus
ventrals plus caudals 0.28898
second scale row keeling -0.24849
E. guttata
body blotches 0.27224
L. triangulum
infralabial scales* -0.46470
ventrals plus caudals 0.27908
D. punctatus
ring separation 0.30168
T. relicta
supralabial scales 0.28222
S. miliarius
ventral pigmentation* -0.44881
dorsal blotch shape 0.31826
C. adamanteus
black subcaudal scales 0.26556
immaculate supralabials 0.30508
Florida environment
mean annual precipitation -0.37981


white in the ventral pattern of Sistrurus miliarius illustrate this pattern.
Spot shape in Sistrurus miliarius, supralabial brown pigment in Coluber
constrictor, and ring separation in Diadophis punctatus also have
elements of the Panhandle-Everglades Pattern.
The Coastal Pattern is defined by Factor 5 (Table 7, Fig. 111). Such
characters as ventral pigmentation and dorsal blotch border in Elaphe
guttata, labial pigmentation in Diadophis punctatus, and dorsal scale
rows and body blotches in Sistrurus miliarius load highly on Factor 5. In
this pattern populations from coastal regions and the Florida Keys (when
the species occurs there) tend to form a phenetic entity distinct from
populations farther inland.
Factor 6 represents the Central Highlands Pattern (Table 8, Fig. 112)


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1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION


FIGURE 111.-Coastal Pattern of Geographic Variation (Factor 5).
FIGURE 112.-Central Highlands Pattern of Geographic Variation (Factor 6).

Table 7.-Coastal pattern (Factor 5). Variables followed by an asterisk have Factor 6 as their
principal pattern.

Variable Factor Loading


M. flagellum
color phase 0.28903
E. guttata
ventral pigmentation* 0.46907
blotch border -0.34480
ventral check shape 0.61322
L. triangulum
mid-body scale rows 0.23046
S. miliarius
body blotches 0.25744
anterior scale rows 0.34333
mid-body scale rows 0.22124
C. adamanteus
immaculate supralabials 0.24009
Florida environment
mean annual number of days -0.40011
temperature exceeds 32.2C


seen in the number of midbody scale rows in Lampropeltis triangulum,
number of supralabial scales in Tantilla, and nuchal collar width in Tan-
tilla. The Central Highlands Pattern is characterized by geographic varia-
tion in which the region around Lake Okeechobee, and especially the








BULLETIN FLORIDA STATE MUSEUM


Table 8.-Central Highlands pattern (Factor 6). Variables followed by asterisk have Factor 6
as their principal pattern.

Variable Factor Loading


S. dekayi
temporal pigment amount 0.28584
T. sauritus
dorsal stripe edge 0.25478
0. aestivus
infralabial scales 0.23024
E. guttata
ventral pigmentation -0.23154
L. getulus
ventrals plus caudals 0.25687
L. triangulum
mid-body scale rows* 0.41243
T. relicta
nuchal collar width* 0.71364
ventral plus caudals 0.41977
supralabial scales* 0.65938
infralabial-chin shield 0.23273



high ridge immediately to the west, is inhabited by snakes phenetically
different from conspecifics to the north and to the south.
The remaining factors produced by the statistical procedure account
for smaller amounts of the information in the maps, and their interpreta-
tion is omitted.
The multivariate analysis of the contour maps has shown that the
variation can be reduced to seven major patterns (North-South Cline Pat-
tern, Suwannee Straits Pattern, Everglades Pattern, Lower Keys-North
Florida Pattern, Panhandle-Everglades Pattern, Coastal Pattern, and
Central Highlands Pattern). There are other patterns, but these are of
lesser importance, and are shared by fewer species. For example, Tham-
nophis sauritus ground color is distinctive in the Gulf Hammock region of
central Florida. This character fell out of the analysis in Factor 22, which
also received small loadings from Crotalus adamanteus ventral pigmenta-
tion and T. sauritus parietal spot size. However, Factor 22 accounted for
only 1.2% of the variation explained in the analysis.
The seven major patterns of geographic variation in Florida snakes ac-
count for 60.4% of the information contained in the original 100 contour


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 219

maps. The remaining information is partitioned into lesser patterns, some
of them unique to a particular species or character.
THE CORRELATIONS

To search for correlations between the patterns of geographic varia-
tion and environmental factors, I analyzed 13 parameters of environ-
mental variation. When these variables were factor-analyzed, three fac-
tors were extracted that accounted for 74.4 % of the variation: (1) average
annual temperature, (2) maximum summer temperatures, and (3)
average annual rainfall. These factors were included in the factor analysis
of the snake morphological data.
Average annual temperature loads very highly on Factor 1 (Table 3).
Inspection of Figure 102 reveals that average annual temperature belongs
in the North-South Cline Pattern. Thus the North-South Cline Pattern of
geographic variation is correlated with mean annual temperature.
Similarly, the Panhandle-Everglades Pattern is correlated with mean an-
nual rainfall (Fig. 103), and the Coastal Pattern is correlated negatively
with maximum summer temperatures (Figs. 104 and 105).
Although correlation does not prove cause and effect, its existence sug-
gests the possibility of such a relationship. Until experimental disproof is
at hand, I would hypothesize that mean annual temperature has an im-
portant influence on morphological variation in Florida snakes. Using the
same line of reasoning, moderate temperature extremes may be responsi-
ble for the Coastal Pattern, and mean annual rainfall may influence snake
morphology to vary in the Panhandle-Everglades Pattern.
The remaining patterns of variation are not highly correlated with
any environmental variables tested. These patterns may be maintained by
some other environmental variables (biotic or physical) that were not ex-
amined, or they may be remnants of previous environmental conditions.
If the latter be true, we must acknowledge that present selective regimes
have been insufficient to change phenotypes to adapt to present condi-
tions. For example, the Suwannee Straits Pattern does not seem to cor-
relate with any known environmental variable, and may reflect past
adaptations to an insular environment during former periods of high sea
level. The Florida peninsula is no longer an island, but selection has not
been strong enough to eliminate (or spread out) the abrupt character
changes in the region of the former Suwannee Straits. Furthermore,
adaptations acquired during periods of former isolation may have been
accompanied by reduced reproductive compatibility with mainland
populations. This process speciationn) would tend to preserve character
states in both populations after they became geographically rejoined.
Such a pattern would not necessarily be expected to correlate with any
present environmental measurement, and would have to be interpreted as







BULLETIN FLORIDA STATE MUSEUM


a remnant of some past selective influence, the exact nature of which re-
mains unknown.
DISCUSSION
PATTERNS OF GEOGRAPHIC VARIATION
Analysis of geographic variation in 15 species of Florida snakes makes
obvious a small number of underlying patterns of variation. That is, most
of the geographic variation examined can be described with recourse to no
more than seven main patterns of spatial evolution. Some of these pat-
terns are related to present environmental conditions, whereas others
seem not to be.
The most important pattern of variation observed in Florida snakes is
a north-south dine with increasing or decreasing character states
southward on the peninsula. As all snake species examined have some
(and frequently many) characters that vary in the North-South Cline Pat-
tern, this probably represents an adaptive response to present environ-
mental conditions. Measurements of mean annual temperature load vary
highly on Factor 1, with increasing temperatures southward on the penin-
sula. Thus average temperature may be an important contributor to the
maintenance of the North-South Cline Pattern in Florida snakes.
Previous workers (e.g. Edgren 1961, Smith 1956, Duellman and
Schwartz 1958, and others) have pointed out the existence of north-south
dines in snake variation, and Fox et al. (1961) showed a correlation be-
tween developmental temperature and snake meristic counts. Thus the
developmental temperature of embryonic snakes may be the mechanism
maintaining north-south dines in snake meristics, but the adaptive
significance of such a pattern remains to be discovered.
Most of the characters that vary according to the North-South Cline
Pattern of geographic variation are meristic (Table 2). Ventral and sub-
caudal counts usually increase southward, as do cross-band and blotch
counts, but some species reverse this trend and show decreasing counts to
the south (e.g. Diadophis punctatus scale counts). In most species studied,
relative tail length also increases southward. The end result of this varia-
tion is that most snake species tend to have relatively longer tails and more
ventral and subcaudal scales in warmer parts of their Florida ranges.
Many species also have more crossbands or body blotches in warmer
regions.
Ventral and subcaudal counts reflect the number of vertebrae
(Ruthven and Thompson 1913). If a correlation exists between vertebral
number and body shape (this has not been tested), perhaps the lower
heating and cooling rates of more heavily-bodied snakes in cooler regions
might be adaptive. Thus snakes from cooler regions have fewer vertebrae
and probably have relatively less surface area per unit of volume. These


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 221

snakes would be expected to retain body heat longer after initial warming
than more slender snakes from warmer regions. I hypothesize that snakes
with more vertebrae and relatively longer tails tend to have more slender
bodies resulting in more surface area per unit of body volume. This body
shape would tend to lose heat more rapidly than a stockier shape. In
cooler regions, a slower cooling rate might allow snakes more foraging
time after achieving optimal body temperature.
North-south dines in crossband and blotch counts may also be related
to mean annual temperature. The increasing crossband counts in Lam-
propeltis getulus southward on the Florida peninsula results in a lighter-
colored phenotype in the southernmost parts of its range. A lighter dorsal
color presumably reflects more solar energy in low latitudes. Similarly
ventral and dorsal color in Coluber constrictor generally lighten
southward in Florida.
The discussion thus far has assumed that the well-developed dines
seen in the geographic variation of Florida snakes are ecoclines (sensu
Auffenberg 1955), maintained by adaptation to environmental conditions
that also vary clinally. Although the North-South Cline Pattern correlates
well with various measures of average temperature, possibly the pattern is
really a geocline, maintained by reduced gene flow from the central por-
tions of the various species' distributions. Brown (1957) defined centrifu-
gal speciation as the process by which peripheral populations of a species
may come to be divergent from more centrally-located populations. This
happens when the central populations diverge from some ancestral condi-
tion while the peripheral populations remain unchanged. He argued ef-
fectively on theoretical grounds that the central part of a species' range
should be the principal area of evolutionary change, with adaptive
changes then spreading to the periphery at a rate determined by gene
flow. The more distant or isolated a peripheral population, the longer it
will take for an evolutionary change to reach it. Populations completely
isolated (such as on islands) may never acquire the new adaptation, and
thus remain "primitive" with respect to that adaptation.
It follows that populations of a species occurring near the end of a
peninsula (which is directed away from the central parts of the total
range) may retain primitive characteristics long since lost by populations
near the center of the range. Even peninsulas that are oriented east-west
should show clinal variation for those species whose main distribution is
on the mainland. Probably both types of dines are operating in Florida. It
is interesting to compare Figures 102 (mean annual temperature) and 106
(North-South Cline Pattern for Florida snakes). The isophenes of the
temperature dine are roughly parallel to latitude, whereas the isophenes
of the snake morphology dine seem to be perpendicular to the axis of the
peninsula, favoring a geoclinal interpretation.







BULLETIN FLORIDA STATE MUSEUM


The Suwannee Straits Pattern (Fig. 107) appears in many of the snake
species studied. I could find no component of present climate correlating
with this pattern. Brooks (1968, 1973) and others before him have shown
that Plio-Pleistocene fluctuations in world wide sea level have period-
ically inundated much of peninsular Florida. When the sea stood at 46 m
above present mean sea level (Okeefenokee Terrace), Florida was reduced
to an archipelago of small islands separated from the mainland in the
region of the present Suwannee River. More recently, during the Aftonian
Interglacial, sea levels standing some 27 to 30 m above the present
separated Florida from the mainland by a low-lying, presumably
brackish water barrier, the Suwannee Straits (Neill 1957). Snake popula-
tions thus isolated may well have acquired divergent characteristics, or
remained relatively unchanged while populations to the north were
changing.
On the other hand Remington (1968) suggested that this pattern (his
"Northern Florida Suture Zone") owes its shape to a habitat barrier as op-
posed to a physical one, and is younger in age than eustatic sea level rises
would dictate. He cites evidence that northern Florida went through a
period of moist, dense forestation about 3000 to 4000 years ago (see also
Watts 1971). This band of forest may have acted as a barrier for non-
forest species, resulting in partial isolation for peninsular populations.
For one reason or another, populations of snakes in peninsular Florida
demonstrate different phenotypes than conspecific populations on the
mainland. Whatever isolating barrier effected this divergence is no longer
visible, but the remnants of its reality are retained in a series of dramatic
character-state shifts occurring today in populations in the Suwannee
River region. Such seemingly unrelated characters as number of supra-
labials in Thamnophis sauritus, number of dorsal scale rows in Storeria
dekayi, and stripe development in Elaphe obsoleta show major changes
as one crosses the region of the former Suwannee Straits.
More often than not, the phenotypes associated with peninsular
populations are considered the more primitive. Does this mean that these
species originated on the Florida peninsula and thence spread northward
as Ross (1974) or Brundin (1975) might have us believe? Croizat (1958,
1962), and Croizat et al. (1974) have shown that the "center of origin"
concept is an unrealistic approach in evolutionary studies. New species
are spawned when former species are split by physical or biotic barriers.
Species do nor originate at a point in space and then spread to their pre-
sent distribution as Darwin (1859:353) stated: "Hence it seems to me, as it
has to many other naturalists, that the view of each species having been
produced in one area alone, and having subsequently migrated from that
area as far as its powers of migration and subsistence under past and pre-
sent conditions permitted, is the most probable." Udvardy (1969:7) put it


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 223

even more bluntly: "Every animal species originated from a few ancestors
in a limited area; if a particular species is now found to be widespread, it
must of necessity have reached parts of its present range at an earlier
period."
Speciation is a process of vicariance.* New species form within the
ranges of preexisting species. This process proceeds with the impetus pro-
vided by natural selection and the mechanism provided by a reduced gene
flow between populations. All species pairs (cognates) were originally
parapatric. If they are now sympatric, then dispersal is indicated, and we
may rightfully ask where the original vicariating barrier was positioned.
The center of origin for a species is its present distribution unless dispersal
has occurred. The center of origin for a group (e.g. a genus) is a meaning-
less concept, because we must look back in time to when the group was
but one of a pair of vicariating populations. When we do this, we again
find that the center of origin is the original range of that population.
In their efforts to locate "centers of origin," biogeographers have for-
mulated rules, a summary of which may be found in Cain (1944). One of
the most often used rules states that the area occupied by the most
primitive members of a group must be the area of origin for the group
(Ross 1974). When a systematist determines the distribution of the most
primitive character states for a wide-ranging species, or the location of
the most primitive species of a genus, he is not locating the center of origin
of that group. Rather, he is defining the area where differentiation
(= evolution) has proceeded relatively more slowly. Indeed, this area
may actually be one of the latest regions colonized by the group in ques-
tion. If for some reason differentiation proceeds more slowly in one area
relative to another, primitive species or character states will be preserved
in that area. Thus islands often harbor the most primitive members of a
taxonomic group. This does not suggest that the group originated there,
but that once it got there, it changed less than populations elsewhere. The
biogeographer should ask why evolution proceeds slowly in some places
and faster in others.
Peninsular Florida has been cited as the center of origin for a number
of plant and animal groups, chiefly because representatives there retain
more primitive characters than representatives to the north. In other
groups the Mexican Plateau region has been called the center of origin
because primitive members occur there. In many vertebrate species
studied, and several of the snake species reported on here, peninsular
Florida and the Mexican Plateau region harbor primitive populations of
wide-ranging groups. Biogeographers have explained this by suggesting
an origin on the Mexican Plateau, dispersal into eastern North America
accompanied with differentiation, and subsequent dispersal onto the
* Vicariance may be defined as the historical process giving rise to geminate (- vicariant) taxa. Speciation is typically a
process of vicariance, whereas sympatry and distribution are functions of dispersal (See Croizat et al. 1974).







BULLETIN FLORIDA STATE MUSEUM


Florida peninsula accompanied, this time with regressive differentiation
back to the original phenotype (e.g. Trapido 1944). More recently Auf-
fenberg and Milstead (1965), and Blaney (1971b) explained this situation
by postulating a now submerged land bridge connecting the Florida
peninsula with the west including, supposedly, the Mexican Plateau area
when lower Pleistocene sea levels exposed a portion of the Gulf Coast con-
tinental shelf. Organisms supposedly migrated eastward along this cor-
ridor to occupy the Florida peninsula, thus giving rise to the situation seen
today with phenotypic resemblances between Floridian and Mexican
populations while geographically intermediate populations remain diver-
gent.
This model assumes that the newly exposed Gulf Coast Corridor was
colonized by populations from the west that subsequently migrated
eastward, while adjacent populations to the north of the corridor failed to
take advantage of the new habitat. It is difficult, at best, to see why
Florida would not have been colonized by populations to the north, or
why the newly exposed continental shelf was not colonized by populations
immediately adjacent to it. No evidence suggests that the Gulf Coast Cor-
ridor appeared overnight; on the contrary, the sea levels are thought to
have dropped gradually as water became tied up in northern glaciers
(Flint 1971). Furthermore the Gulf Coast Corridor Land Bridge theory
requires that the species in question were not already present in Florida,
or if they were, their phenotypes were swamped by the immigrating
populations from the west. The phenetic similarity between species occur-
ring on the Florida peninsula and the Mexican Plateau, while populations
occurring in between remain divergent, can be explained without
recourse to a land bridge or to retrogressive evolution. An evolutionary
(sensu Croizat 1962) explanation requires fewer assumptions and does not
rely on dispersal as a major force in the differentiation process.
When disjunct populations of a species are more similar to each other
than either is to intermediate populations, the simplest explanation sug-
gests that the disjunct populations probably represent the primitive
(= ancestral) condition. To believe otherwise requires that the popula-
tions in the disjunct regions have developed independently to achieve
similar phenotypes. It requires fewer assumptions to believe that the
geographically intermediate populations have diverged while the disjunct
populations have remained relatively unchanged. Thus something in the
environment of both the Florida peninsula and the Mexican Plateau has
allowed species there to remain unchanged relative to conspecific popula-
tions in the south-central United States. In other words, evolution ( = dif-
ferentiation) proceeded relatively more rapidly in the continental region
between the Suwannee Straits and the Mississippi Embayment. The ques-
tion for biogeographers is not "why are Floridian and Mexican popula-


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 225

tions similar?," but rather "why are geographically intermediate popula-
tions different from Floridian and Mexican populations?"
Two explanations are possible for lower evolutionary rates in Florida
and Mexico, and both probably are responsible for the patterns seen to-
day. The first involves gene flow. Florida is a peninsula (and has from
time to time been an island) and as such is partially isolated from con-
tinental populations. Populations west of the Mississippi Embayment, in-
cluding the Mexican and Guatemalan Plateaus are also relatively
isolated from populations on the main continent. When a new adaptive
character state occurs in a population of sexually reproducing organisms,
it will spread throughout the population everywhere that it remains adap-
tive, but if gene communication with outlying populations is reduced,
the new adaptation may simply not reach these peripheral populations.
Brown (1957) showed on theoretical grounds that new phenotypes are
most likely to occur near the center of a species' geographic distribution.
Thus it is not surprising that peripheral populations tend to retain more
primitive character states than populations in the main body of the spe-
cies' range. This is why islands frequently harbor the most primitive
members of many groups. Thus snake species occurring across the south-
ern North American continent changed more in the central region than
they did in the peripheries.
The second explanation contributing to this pattern of geographic
variation is concerned with the selective pressures responsible for evolu-
tionary change. Analysis of Pleistocene pollen deposits (Watts 1969)
showed that climatic changes occurred during the glacial ages in Florida.
However, these fluctuations were apparently of a lesser magnitude than
simultaneous fluctuations occurring to the north on the North American
continent (Whitehead 1965). Climatic fluctuations, including wind and
rain patterns as well as temperature, were felt more strongly on the main
North American continent than on the Florida peninsula and,
presumably, the Mexican Plateau (and southward). Plant communities in
North Carolina and Virginia underwent radical changes during the
Pleistocene, whereas those in Florida changed less dramatically (Watts
1970). Under the influence of dramatically changing climates and vegeta-
tion, phenotypes would change as well. Populations of these same species
on the Florida peninsula and southwestern United States and Mexico
where climates remained more stable, would be expected to change less.
The Everglades Pattern of geographic variation (Fig. 108) is shared by
several snake species. The selective pressures responsible for maintaining
distinctive phenotypes in snake species occurring in the Everglades are
probably related to the unique habitat there. A lighter dorsal and ventral
color in both Lampropeltis getulus and Coluber constrictor may be adap-
tive in the open treeless environment of the marshlands. It is noteworthy







BULLETIN FLORIDA STATE MUSEUM


that these species also have reduced dark pigment in the treeless Great
Plains region.
Most interesting is the Lower Keys-North Florida Pattern (Fig. 109) in
which several species have similar phenotypes in extreme northern
Florida, the Lower Keys, and the high ridge east of Tampa Bay. This pat-
tern has been recognized by previous authors (e.g. Neill 1957; Duellman
and Schwartz 1958), though they failed to note the apparent inclusion of
the area east of Tampa Bay. Several species have been reported to vary in
the Lower Keys-North Florida Pattern. McConkey (1957) noted the
similarity between Lower Keys and North Florida populations of the
lizard Eumeces egregius, and Duellman and Schwartz (1958) discuss this
situation with regard to five species (Scincella laterale, Eumeces egregious,
Coluber constrictor, Diadophis punctatus, and Storeria dekayi). The in-
clusion of Diadophis in this list is apparently not warranted. Duellman
and Schwartz (1958), using a very small sample size, stated that ventral
counts for Lower Keys ringneck snakes were similar to northern Florida
counts, and distinct from southern mainland counts. Maps 67 and 68,
based on larger samples, fail to show this pattern..
Nevertheless enough species show aspects of the Lower Keys-North
Florida Pattern in their geographic variation to suggest that the
phenomenon must be real. The simplest explanation suggests that the
distinctive phenotypes, distributed as they are in three disjunct regions,
have arisen only once. This implies that snake populations in the re-
mainder of Florida have diverged since the establishment of the species in
extreme northern Florida, the area east of Tampa Bay, and the Lower
Florida Keys. The problem is to discover what these regions have in com-
mon that has permitted slower divergence from the ancestral condition.
Geological and biological evidence summarized by Duellman and
Schwartz (1958) support the contention that the Lower Keys were con-
nected to the central Florida mainland when the Upper Keys were still
submerged. The eastern rim of the southern Florida mainland and the
Lower Keys are composed of Miami oolite, a formation apparently older
than either the sediment-filled Everglades or the coral reef formation that
is now the Upper Keys. Snake species established on the Lower Keys
before the Upper Keys emerged were probably phenotypically similar to
peninsular populations. As southern Florida and the Upper Keys
emerged, these areas were colonized by populations from the north that
adapted to conditions there. The isolation of the Lower Keys has allowed
populations there to remain more like the original stock. Further evidence
is provided by the fact that extreme northern Florida and the area east of
Tampa Bay have the highest elevations in the peninsula (Fig. 101). Con-
ceivably the Lower Keys and eastern rim of the southern mainland have
also been much higher with respect to present sea levels. The limestone


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1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 227

formation on the Lower Keys shows all the signs of extensive erosion and
solution (Duellman and Schwartz 1958) and may have had a history of
emergence much longer than its present elevation suggests. That is,
although the maximum elevation of the Lower Keys is today only about 6
m above present mean sea level, the islands may have been emergent even
when sea level stood 27-30 m above present.
I believe that the snake species under scrutiny were already present on
the Lower Keys, the area east of Tampa Bay and extreme northern
Florida before the Everglades and Upper Keys were available for col-
onization. When these latter regions were finally inhabited, selection ef-
fected evolutionary divergence without altering phenotypes on the Lower
Keys.
Mean annual precipitation (Fig. 103) is highest in the Florida Pan-
handle and Everglades regions. Snake species showing the Panhandle-
Everglades Pattern of geographic variation (Fig. 110) may be responding
to similar selective regimes created by rainfall patterns.
Populations of snakes along the coast and on offshore islands of
Florida are frequently distinct from populations farther inland. The
Coastal Pattern (Fig. 111) is probably maintained by something in the
ecology of the coastal environment. Elevations are lower and
temperatures are less extreme, either or both of which may help maintain
the Coastal Pattern.
Several of the species examined show major character state shifts in
the region west and northwest of Lake Okeechobee. The Central
Highlands Pattern (Fig. 112) is probably maintained by conditions unique
to the high elevation scrub and sandhill habitats of the area.
PHYLOGENETIC CONSIDERATIONS
Storeria dekayi.-Ventrals and subcaudals increase clinally to the
south on the peninsula. S. dekayi from the southern parts of the state have
proportionately longer tails. Duellman and Schwartz (1958) noted the
phenotypic resemblance in ventral and subcaudal counts between Lower
Keys and northern Florida brown snakes, separated by divergent penin-
sular snakes. This study shows that the phenomenon is also well-
developed in preocular counts and ventral dark pigmentation. Another
major geographic pattern of character variation in this snake is the ex-
istence of two well-differentiated morphotypes, exemplified by mid-body
scale rows and the shape of the temporal spot (Figs. 4 and 6).
Current taxonomy (Neill 1950a, Conant 1975) recognizes these as the
subspecies S. d. wrightorum in the north and west and S. d. victa on the
peninsula. Apparently no specimens are available from the region be-
tween the two morphotypes, where snakes with intermediate
characteristics might be sought. Thus, no evidence exists for intergrada-







BULLETIN FLORIDA STATE MUSEUM


tion between S. d. victa and S. d. wrightorum in Florida and the two may
be entirely allopatric. Neill (1950a) made a weak case for the apparent
conspecificity of the two forms by suggesting intergradation in the
Coastal Plain of eastern Georgia, but he failed to list any specimens.
Whether or not the two forms are reproductively isolated (i.e. distinct
species) is of little consequence to a discussion of their origin.
Storeria occurs on the Lower Keys but apparently not on the Upper
Keys (Duellman and Schwartz 1958). The Lower Keys population is
phenetically more closely related to populations from northern Florida
than to populations from the southern mainland. This common pattern
was discussed in the last section.
Besides having characteristics reminiscent of more northern popula-
tions, the snakes on the Lower Keys are noteworthy also for their reduced
pigmentation dorsally, ventrally, and on the head. In addition, brown
snakes from the Lower Keys usually have two preoculars on each side, a
character shared in the genus only with S. storerioides and S. oc-
cipitomaculatum. Trapido (1944) postulated that S. storerioides was
closest to the ancestor of S. dekayi, which in turn gave rise to victa. He
wrestled with the difficulty of assuming an increase in dorsal scale rows
from storerioides to dekayi and a subsequent decrease again in victa, but
finally concluded that dekayi must have given rise to victa (op. cit.:44). I
believe his conclusions were largely correct, but the assumption of a
reversal in scale row evolution is unnecessary. Fifteen scale rows in S.
dekayi victa on the Florida peninsula is primitive, not derived. Storeria
dekayi with 17 scale rows represents the derived condition. My scheme
takes this into account, as well as the similarity in preocular counts be-
tween Lower Keys victa and S. storerioides.
The immediate common ancestor of the taxa in question was a snake
much like S. storerioides and occurred in what is today Mexico and
southern United States including Florida, although not necessarily at any
one point in time. This snake was characterized by 15 scale rows and 2
preoculars. Geographic variation coupled with geographic isolation led
ultimately to genetically isolated populations in Mexico (S. oc-
cipitomaculatum hidalgoensis and S. storerioides). The former differen-
tiated into S. o. occipitomaculatum in the eastern United States, and S. o.
obscura on the Florida peninsula. Storeria storerioides meanwhile con-
tinued to differentiate on the American continent. Differentiation pro-
ceeded relatively more slowly on the Florida peninsula owing to reduced
gene flow with continental populations (peninsular effect), a likely re-
duced population size resulting in slower rates of recombination and
mutation, and also a weaker selective pressure in the climatically more
stable Florida peninsula. Consequently Storeria on the Florida peninsula
retain more primitive characters than do populations from the mainland


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1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 229

where evolution proceeded more rapidly. Populations on the Lower Keys
retain still more primitive characters, being isolated from the center of the
range even more. Brown (1957) called this type of evolution, "centrifugal
speciation."
The differentiation between mainland dekayi and Florida victa was
probably speeded by further reduction in gene flow brought about by the
periodic insulation of Florida caused by rising sea levels.
S. d. victa is considered autochthonous in Florida and descended from
the same ancestor as S. d. wrightorum but with less differentiation. No
evidence suggests that S. d. wrightorum and S. d. victa are members of
the same biological species. Storeria on the Lower Florida Keys are dif-
ferentiated even less than peninsular victa and could realistically be
assigned subspecific status.
Thamnophis sirtalis.-Ventral and subcaudal counts are generally
higher in the south. A general pattern involving the characters, dorsal
spotting and parietal spots sees higher character states in the
geographically disjunct regions of the western Panhandle, Central
Highlands, southern Everglades, and southwestern coast of the peninsula.
Very little previous work has been done on geographic variation in
this species beyond the naming and delimitation of subspecies. Rossman
(1965) described the race T. sirtalis similis from the Gulf Hammock
region of peninsular Florida. None of the characters investigated in the
present study is diagnostic of similis, which is characterized by its distinc-
tive color in life. Pattern and meristic variation reported here vary discor-
dantly with color; thus it is not possible to discern the range of similis in
any of my maps.
Garter snakes with dorsal checks (ordinatus phase) apparently occur
in several areas within the range of T. sirtalis. Many individuals from the
Panhandle have no stripes, with instead a dorsal pattern of small black
checks. Snakes from the Everglades have the checks, but still retain the
longitudinal stripes. The color phase is also known from the Carolinas. In
view of the scattered geography of the spotted phenotype, it seems un-
likely that it represents a monophyletic stock. In all likelihood, spotting in
T. sirtalis has arisen several times, perhaps in response to similar environ-
mental selective pressures.
On the other hand, Blaney (1971b) suggested that the spotted phase in
this species may once have been continuous along the coast, and the pre-
sent disjunct nature of the phenotype a result of more recent fragmenta-
tion. This may be true. The pattern of geographic variation in this
character (Fig. 13) suggests a coastal distribution. When much of the Gulf
continental shelf was exposed during former periods of lower sea level, a
spotted sirtalis may have occupied this region. Subsequent rise in sea level
has left scattered colonies of spotted garter snakes in coastal regions and







BULLETIN FLORIDA STATE MUSEUM


throughout most of the Everglades. If this interpretation is correct, it of-
fers a clue to the nature of the habitat on the now submerged coastal
plain: It was probably treeless, and similar to the present Everglades,
where the spotted phenotype is common today.
The evolutionary history of the garter snakes is certainly a subject of
interest, but one that has not been investigated since Ruthven (1908).
Based on patterns in other species, I predict that the populations of T. sir-
talis in Florida will be found to share conservative characteristics with
populations considered closest to the ancestral stock. Like other species for
which we have better information, garter snakes have probably evolved
more slowly in Florida, and also in Mexico. Indeed, Ruthven (1908) con-
sidered Mexico to be the "center of origin" of the entire genus. Although
the concept of center of origin is of little theoretical value (Croizat et al.
1974), the fact that the most primitive garter snakes occur there today im-
plies that evolution has proceeded more slowly there than in the rest of
North America. It is anticipated that future studies will show that
divergence has also proceeded relatively more slowly in Florida garter
snakes.
Thamnophis sauritus.-Ventral and subcaudals increase clinally to
the south on the Florida peninsula, although the patterns are not espe-
cially well-developed. T. sauritus from the Florida peninsula differ
markedly in the number of supralabials from snakes inhabiting the
Panhandle and regions north of Florida. The nature of the paired parietal
light spots varies in a pattern like that noted in several other species with
specimens from the southern edge of the Okefenokee Swamp, the area
east of Tampa Bay, and the southern tip of the peninsula forming a
phenetic entity. Finally, the subspecies, T. s. nitae of the Gulf Hammock
region is identified in the geographic variation of dorsal ground color.
The evolutionary history of the ribbon snake complex as envisioned
here is largely in agreement with that proposed by Rossman (1963): The
ancestral ribbon snake, very much like present day T. proximus, became
widespread across the North American continent including Mexico and
Florida. The Mississippi embayment provided a barrier to gene flow, and
differentiation occurred between the snake populations on either side,
resulting in, among other things, reproductive isolation (Rossman 1962).
Phenotypically the snakes on the east side of the Mississippi were probably
still a lot like proximus characterized by eight supralabials. Another
vicariation occurred when snakes on the Florida peninsula became
relatively isolated owing either to the peninsula effect or actual insulation
during high sea level periods. Because of presumed climatic stability,
smaller population sizes, and decreased gene flow with the mainland
populations, the Florida snakes changed less and more slowly than their
mainland relatives. As eastern mainland ribbon snakes differentiated into


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 231

the sauritus phenotype with seven supralabials, the Florida populations
remained like the original stock, including the retention of the ancestral
eight supralabials.
We have no reason to believe that reproductive isolation between
proximus and sauritus occurred before the evolution of a reduced
supralabial count in sauritus. Thus the development of the present
sauritus phenotype in eastern North America may have occurred before,
during, or after the events that led to reproductive isolation between pro-
ximus and sauritus. Furthermore, the differences between Florida sackeni
and eastern North American sauritus, although not including reproduc-
tive isolation (Rossman 1963), may predate the divergence of the eastern
from the western species. The species concept relies only on reproductive
incompatibility, not on degree of divergence nor time since divergence.
Thus the phenotypic resemblance between western proximus (pre-
sumed primitive) and Florida sackeni is due to the fact that they have
each differentiated less from their common ancestor than has the sauritus
stock in geographically intermediate eastern North America. Superficially
(i.e. in color and pattern), sackeni from the Lower Florida Keys are even
more like western proximus, indicating that evolution has proceeded even
more slowly on the isolated Lower Keys than on the peninsula.
The Gulf Hammock subspecies, nitae, is presumed antochthonous in
that region, having vicariated with sackeni.
Coluber constrictor.-Ventral and subcaudal numbers increase in a
dine southward on the Florida peninsula, although the subcaudal dine is
poorly defined. Coluber tend to have lighter colored venters in the
southern peninsula and northward along both coasts, but the darkest
venters are seen in the Lower Keys. Gular brown is the best single
character for differentiation of the subspecies C. c. helvigularis, found
only in the Apalachicola River Valley, especially the lower valley (Auf-
fenberg 1955). Snakes from that area also have the most brown pigment
on their supralabial scales, but specimens from the Everglades and parts
of the southern peninsula also have brown supralabials. Gular black,
supralabial black pigment, and supralabial-loreal contact vary in a man-
ner observed in several other species: Racers from extreme northern
Florida, the area east of Tampa Bay, and the Lower Keys share a com-
mon state for these characters. Because this pattern of geographic varia-
tion occurs so frequently, the hypothesis of an independent origin of these
characteristics in each of the three regions must be rejected in favor of a
monophyletic origin followed by change in the intervening populations.
Thus at the level of infraspecific variation, black supralabials and little or
no white ventrally are considered primitive to the condition in which
snakes have more white pigment.
Ortenburger (1928) believed that light dorsal coloration was







BULLETIN FLORIDA STATE MUSEUM


primitive, and the darker black dorsum and labials of eastern and Florida
C. constrictor was derived. This difference can be resolved in the follow-
ing possible evolutionary scheme. The original ancestor of Coluber con-
strictor probably looked much like present day C. c. flaviventris or
oaxaca. Geographic variation is the rule in natural systems, and such
variation in a wide-ranging species such as the racers must have led to the
geographic differentiation we see today. The Mississippi Embayment
may have helped reduce gene flow between populations on either side
as these differentiated. Coluber east of this barrier became dark black in
color, and with black gulars and supralabials. This is the condition in
most C. c. constrictor today. Differentiation in the northeastern parts of
its range (east of the Mississippi and north of Florida) included the loss
of the enlarged hemipenial basal spines (hooks), as well. Coluber from
the remainder of the range retain the enlarged basal spines (Auffenberg
1955). Evidence based on present hybridization between adjacent pheno-
types (subspecies) suggests that reproductive isolation has never been
achieved. Nevertheless we can reconstruct the subsequent history of east-
ern populations alone if evolution there proceeded relatively independent
of evolution in western populations. The effect of distance on gene flow
(Huxley 1942) probably has insured that evolution in (for example) Flor-
ida populations has proceeded independent of any differentiation in pop-
ulations west of the Mississippi River.
Geographic variation in Florida led eventually to the loss of the black
supralabials and gulars in most populations, but for some reason Coluber
from three separate regions in Florida failed to change in this direction,
and today still retain black supralabial and gular scales. Black snakes
from extreme northern Florida, the area east of Tampa Bay, and the
Lower Florida Keys retain the primitive gular and supralabial pigmenta-
tion. Evolution in these characteristics apparently has proceeded more
slowly in these three regions.
The difference between Ortenburger's (1928) and my own conclusion
regarding black supralabials and dorsal color now disappears: a light dor-
sum and labials are primitive for the group as a whole, but a darker dorsal
and labial pattern is primitive if we consider only populations east of the
original vicariating border (Mississippi River). Therefore most Florida C.
c. priapus with white supralabials and southern Florida C. c. paludicola
with much white ventrally and lighter dorsal color are considered derived
with respect to these characters, and the latter's similarity with western
flaviventris a result of either convergent evolution (= adaptation to
similar environments) or of more recent gene flow with western forms via
some past land connection (e.g. the Gulf Coast Corridor).
Another pattern of geographic variation in this species offers a clue as
to which alternative seems more likely. Snakes from the Apalachicola


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 233

region have brown or tan supralabials and gulars (C. c. helvigularis). This
condition is also approached in most specimens of southern Florida
paludicola. The two forms are readily distinguishable on the basis of
ground color, but the similarity in supralabial pigmentation suggests a
common ancestry. The occurrence of this phenotype in the Everglades
and the Apalachicola River Valley suggests a once continuous distribution
of brown-chined racers along the west coast of Florida. As the occurrence
of three disjunct populations of black-chinned racers on the Florida
peninsula and Keys necessitates calling that phenotype ancestral in
Florida, the brown-chinned form must be of more recent derivation. The
most reasonable interpretation of the data has a Coluber stock in Florida
characterized by black supralabials and gular scales. Geographic varia-
tion led to lighter colored snakes in southern and coastal Florida and to a
loss of the black throat and labial pigmentation in all populations save the
three already mentioned. The lighter dorsal and ventral color may be
more adaptive near the coasts and in prairie situations such as the
Everglades. Thus during the Wisconsin, when sea levels dropped as much
as 100 meters (Fairbridge 1960), additional habitat along the Gulf Coast
of Florida was inhabited by Coluber with light-colored dorsums and ven-
trums, and probably brown supralabials as well. Today all that remains
of this once-continuous population are remnants in the Everglades and
the lower Apalachicola Valley, and certain coastal areas of Florida.
Probably the similarity in dorsal and ventral color between south
Florida paludicola and western flaviventris results from similar responses
to similar selective pressures. On the other hand, the similarity in labial
coloration between Panhandle helvigularis and south Florida paludicola
may be a remnant of a once continuous interbreeding stock that has since
become extinct leaving relicts in disjunct regions.
Both Auffenberg (1955) and Wilson (1970a) implied that southern
Florida paludicola may be closely related to western flaviventris. This
could be true because the emergent Gulf Coast Corridor would have pro-
vided the opportunity for gene flow between coastal western populations
flaviventriss) and coastal Florida populations (paludicola and helvigu-
laris), but the important point is that the Gulf Coast Corridor was
inhabited by Coluber adapted to the conditions present at that time. If
south Florida paludicola and western U.S. flaviventris have experienced
more recent contact along the Gulf Coast, it would imply that the habitat
there at the time of contact was treeless, probably similar to the present
Everglades. A more detailed study of variation, perhaps at the
biochemical level, might establish a closer relationship between these
taxa, but evidence available at this time does not.
Brown pigment on the supralabials may have originated separately in
paludicola and helvigularis. If this were true, recourse to the Gulf Coast







BULLETIN FLORIDA STATE MUSEUM


Corridor hypothesis would be unnecessary, but for the present all
available evidence points to the development through differential selec-
tion acting on coastal populations of a phenotype of Coluber constrictor
characterized by light dorsal and ventral colors and brown-pigmented
supralabials. Snakes sharing these characters occur today in the
Everglades, coastal situations, islands, and (without the lighter dorsal
color) the lower Apalachicola River Valley. Blaney (1971b) was correct in
interpreting his light-colored Coluber from islands off the Apalachicola
River mouth as representatives of this coastal phenotype, but his state-
ment that they represent relicts of an ancestral population "which dis-
persed eastward along the Gulf Coast migration route during a period of
lower sea level, ultimately giving rise to C. c. paludicola" (Blaney
1971b:422) cannot be defended with available data.
Masticophis flagellum.--Ventral and subcaudal counts tend to be
higher in the Panhandle and western peninsula, but no dine is evident.
Relative tail length also varies in this manner.
Wilson (1970b) noted the disjunct nature of the color phase variation
in Florida Masticophis. Blaney (1971b) suggested that the light phase
might indicate a closer relationship with the western M. f. testaceus. I
agree with Blaney's thesis and envision an evolutionary history of the
Florida populations as follows:
The ancestral Masticophis flagellum was a light-colored snake,
phenotypically similar to present day testaceus in the west and hatchling
and juvenile flagellum in the east. Evolution east of the Mississippi River
in the form of geographic variation led to a phenotype of coachwhip
characterized by increased dark pigment, especially anteriorly. In some
areas this differentiation proceeded more slowly, and light colored
coachwhips are still the common phenotype. It is noteworthy that the
center of this region of slower differentiation is again located in Florida.
Nothing suggests that testaceus-like coachwhips invaded Florida along a
now-submerged land bridge while darker coachwhips were already pre-
sent north of Florida. The pattern of geographic variation in this
character suggests merely that differentiation proceeded relatively more
slowly in parts of Florida than in other parts of the species' distribution.
Thus the darker individuals in the northeastern parts of the range repre-
sent populations more derived than Floridian and western populations
with respect to color pattern.
Opheodrys aestivus.--Although no well-developed dine is evident,
green snakes do tend to have more ventral scales in the southern parts of
Florida, and caudal scale counts are highest in Panhandle specimens.
Snakes from the Panhandle and west coast of the peninsula have darker
supralabial scales than those from the rest of the state. The lightest
supralabials are on snakes from the Florida Keys and the peninsula, ex-


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 235

elusive of the west coast. Opheodrys from northern Florida and the
Panhandle tend to have little or no keeling on the scales of the second dor-
sal scale row. Specimens from the southern half of the peninsula have
well-developed keels on these scales. Green snakes from the Lower Keys
may be sexually dimorphic for this trait, but more specimens should be ex-
amined.
Little previous variational work has been done on this species. It is a
wide-ranging form with a distribution fragmented in the north and west,
suggesting a shrinking range to the southeast with relictual colonies re-
maining in scattered areas to the north and west of the main range (see
Conant 1975 for range maps). This is an unusual pattern in North
America where most species with disjunct distributions appear to be
shrinking to the north, following post-Wisconsin extirpation in southern
regions in the wake of a warming climate, but the distribution of
Opheodrys aestivus cannot be explained in these terms. The disjunct col-
onies to the north and west of the main range may be remnants of a
former distribution during the post-Wisconsin Xerothermic Interval
(Deevey 1949).
A study currently in progress by Grobman and Markezich (pers.
comm.) shows that the keeling character of the second dorsal scale row is
highly developed only in central and southern Florida. Furthermore Carr
(1940) and I have noticed that green snakes from central and southern
Florida have yellow venters, while specimens from the rest of the range
have white bellies. I believe that green snakes from the southern half of
the Florida peninsula are more highly evolved with respect to these two
characters, and probably represent fairly recent adaptations to something
in the South Florida environment. Specimens from the Lower Keys have
white venters (Carr 1940). The Lower Keys thus stand out as refugia for
ancestral character states, as in other species of snakes studied.
Elaphe guttata. -Both ventrals and subcaudals increase clinally to the
south in Florida, as do blotches on the body and the tail. A coastal pattern
is evident in the geography of several characters. Corn snakes from coastal
parts of the peninsula including offshore islands tend to have less dark pig-
ment ventrally, and that pigment confined to smaller square blotches. In
addition, coastal corn snakes have higher ventral counts than their inland
relatives. These trends find their maximum expression on the Lower
Florida Keys, where the populations are also noteworthy for their lighter
dorsal color, absent or very narrow dorsal blotch borders, very high ven-
tral and subcaudal counts, and a more slender body.
Geographic variation in the corn snake has not been studied in detail
until very recently (Mitchell 1977; Thomas 1974). The distinctive Lower
Keys population, which display characteristics not shared by any other
population, was once recognized subspecifically, but was synomized by







BULLETIN FLORIDA STATE MUSEUM


Duellman and Schwartz (1958). The corn snakes from the Lower Florida
Keys are more like specimens from west of the Mississippi River in ventral
pigment amount and shape, as well as dorsal blotch counts. These snakes
very likely retain ancestral states for these characters, while populations
on peninsular Florida and elsewhere in the east have developed more ven-
tral pigment, fewer blotches, and wider dorsal blotch borders. The evolu-
tionary history of this species probably involved a differentiating se-
quence on opposite sides of the Mississippi which included a change to red
dorsal blotches from the original brown. Further evolution in the east and
north involved a reduction in number of blotches and an increase in
darker pigmentation. The reduction of ventral pigment may be an adap-
tation to coastal climates, the epitome of which would be in off-shore in-
sular situations.
Where E. guttata occurs in the absence of its congener, E. obsoleta, as
on the Lower Keys and Gulf Coast islands, the former demonstrates a
phenotype more closely approaching that of E. obsoleta than anywhere
else within its range. Such "ecological release" has been suggested for
many species (see for example, Ricklefs 1973) and may help explain the
reduced ventral pigment, paler dorsal pattern, more slender and elongate
body form, and increased arboreal tendencies (personal observations) of
corn snakes from the Lower Keys and Florida Gulf Coast islands. Where
it occurs syntopically with E. obsoleta, E. guttata is stockier, more boldly
marked both ventrally and dorsally, and more confined to a terrestrial or
fossorial existence.
Occasional specimens of Elaphe guttata from southwestern Florida
(especially Lee County) have brown dorsal blotches, and ventral patterns
very reminiscent of E. guttata emoryi in the western United States, sug-
gesting retention of ancestral characteristics in these specimens.
Elaphe obsoleta.-The currently recognized subspecies E. o. spiloides
is clearly defined by the geographic variation in stripe development,
blotch development, ventral pigmentation, and supralabial pigmenta-
tion. The subspecies williamsi appears in an area where both spots and
stripes are fairly well-developed. Specimens from the Gulf Hammock
region also have darker labials and venters, more like northern spiloides
than quadrivittata. Another subspecies, rossalleni (Neill 1949) is not de-
fined by any of the characters investigated in the present study. The sub-
species E. o. deckerti (synomized by Duellman and Schwartz 1958) shows
up as a disjunct population with stripes and blotches, and dark supra-
labial pigmentation on the extreme south Florida mainland and Upper
Keys.
The evolutionary history of the rat snakes is currently under investiga-
tion by Richard Blaney (pers. comm.), but some preliminary speculations
can be made here. The juveniles of all subspecies and the adults of the


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 237

western forms are blotched. Thus I believe this to be the ancestral condi-
tion, most clearly matched by present day E. o. lindheimeri. Geographic
variation in most of Florida has led to the development of the striped pat-
tern seen in quadrivittata and rossalleni, and in the eastern parts of the
United States to the solid-colored snake known as E. o. obsoleta. Popula-
tions from extreme southern Florida have probably diverged less from the
ancestral condition, and still retain the darker pigmentation and blotched
phenotype. More recent geographic variation on the Florida peninsula
has led to the reduction in ground color dark pigment along the coasts and
in the Everglades region.
The development of the striped phenotype in peninsular Florida was
probably expedited by a reduction in gene flow brought about by the in-
sulation of parts of Florida during periods of higher sea level. Populations
(E. o. williamsi) in the Gulf Hammock region probably represent hybrids
from a subsequent contact between mainland blotched and peninsular
striped forms. The fact that all combinations of striped and blotched
phenotypes can be found in the Gulf Hammock region today suggests a
pattern of recombinants such as would be observed when isolated popula-
tions come secondarily into contact. Rat snakes with both stripes and
blotches occur along a narrow band from the Gulf Hammock region to
coastal South Carolina (W. Auffenberg, pers. comm.) providing addi-
tional evidence for the hybrid origin of the phenotype.
Lampropeltis getulus. -Kingsnakes from the southern regions have a
weakly developed tendency to more ventrals and subcaudals, as in most
snake species studied. The Suwannee Valley shows up again as a major
transition zone in kingsnakes, this time for a rapid change in number of
dorsal scale rows. Kingsnakes from the extreme southern peninsula have
the longest tails relative to their body length. An extremely well-
developed clinal increase in cross band counts is evident for both sexes.
Dorsal color pattern reflects the taxonomy as recognized by Blaney
(1971a) with lighter colored individuals (Blaney's floridana) occurring in
southern Florida, the extreme northern peninsula, and the Apalachicola
River Valley.
Blaney (1971a) discussed the evolutionary history of the North
American Lampropeltis getulus complex. His speculations, relying chiefly
on an eastward migration of early getulus stock from the west into an
unoccupied Florida peninsula during the Pleistocene, seem unduly com-
plex. Sea levels change gradually. There is no evidence that a Gulf Coast
migration route appeared overnight to allow dispersal into unoccupied
habitats. On the contrary, the accumulation of continental ice and
resulting sea level drop occurred slowly, allowing the gradual establish-
ment of continental organisms seaward as suitable terrestrial habitats
became available.







BULLETIN FLORIDA STATE MUSEUM


Blaney (1971a) suggested that the higher scale row counts seen in the
subspecies splendid are probably ancestral. He attributes the same high
counts in peninsular Florida kingsnakes to invasion of Florida from the
west by splendida-like snakes while getulus-like kingsnakes with fewer
scale rows remained to the north. I believe that kingsnakes in peninsular
Florida have retained the ancestral condition for scale row numbers (as
has splendid) while populations to the north diverged by reduction of
scale rows. I agree that the higher counts in splendid and peninsular
Florida kingsnakes represent an ancestral condition. The northern
populations of getulus evolved a reduction in scale rows while populations
to the west splendidd) and south (Florida forms) remained unchanged in
this character. Peninsular Florida thus emerges once again as a place
where evolutionary change in some characters proceeds more slowly than
in continental areas to the north.
The presence of light-colored kingsnakes reminiscent of south Florida
brooks (Blaney's floridana) in extreme northern Florida and the
Apalachicola Valley suggest that this phenotype was once more
widespread in Florida. Evolution elsewhere has led to an increase in dark
pigment dorsally, with relict populations remaining disjunct in these two
regions. The extreme northern peninsular region and the Apalachicola
Valley seem to be refugia for ancestral character states in other species as
well (e.g. Coluber constrictor, Thamnophis sauritus).
Contrary to Blaney's (1971a) interpretation, I view the very wide in-
tergrade zone between light-colored south Florida kingsnakes and darker
northern snakes as evidence of recent differentiation in the northern
populations, and not of secondary hybridization following differentiation
in isolation. Whether or not complete geographic isolation accompanied
the differentiation of getulus is not important. What is important is that
the kingsnakes in peninsular Florida, and especially southern peninsular
Florida have remained relatively unchanged with respect to dorsal color
pattern and number of midbody scale rows while populations to the north
have differentiated.
Lampropeltis triangulum.-Ventrals and caudals appear to decrease
southward on the peninsula, but the trend is probably more complex than
that. Scarlet kingsnakes tend to have proportionately longer tails in the
southern parts of the peninsula. The area east of Tampa Bay, northern
Florida, and a small region in southeastern Florida are set off with similar
character states for red cross band counts.
This species may have the widest distribution of any terrestrial snake
species in the world, and one recent authority recognized 23 distinct
subspecies (Williams 1970). Williams' evolutionary speculations are based
on the premise that the group has had a center of origin and each of the
subspecies has developed from another subspecies and dispersed into its


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 239

present range. He decided that the area of greatest subspecific diversity
represents the "point of origin," and identified central Mexico as the
ancestral home of L. triangulum. I view the 23 distinguishable
phenotypes of L. triangulum as localized populations adapted to en-
vironmental conditions where they exist. Their differentiation can be ac-
counted for by responses to differential selective pressures brought about
by different environments. If central Mexico has more subspecies than
other areas of comparable size, the reason must lie in the environmental
heterogeneity of that part of Mexico, coupled to an unknown extent with
a tendency for reduced gene flow between the populations. If central
Mexico is the present home of the subspecies retaining the most primitive
character states, we can definitely state that evolution (= change) has
proceeded relatively more slowly in that part of Mexico than in other
regions for the characters in question.
The milk snakes in peninsular Florida are closer to what Williams
(1970) believed to be the ancestral phenotype than are those from north of
Florida. Thus Florida has been acting as a refugium for preservation of
certain ancestral character states.
Within Florida, the pattern of geographic variation suggests that dif-
ferentiation in the southern half of the peninsula has led to a reduction in
number of cross bands in all areas except the Central Highlands and the
southeastern part of the peninsula. Alternatively, cross bands could have
increased in these two regions while remaining lower in the rest of the
southern peninsula.
According to Williams (1970) the ancestral midbody scale row
number was probably 21. Southwestern milk snakes typically have 19
scale rows. Many Florida specimens have reduced this still further to 17
dorsal scale rows at midbody.
Cemophora coccinea.-The patterns of variation of C. coccinea in
Florida are apparently more complex than previous workers have
recognized. Correlation analyses (Christman, unpubl.) seem to show two
rather distinctive morphotypes in Florida characterized by a combination
of features. Generally speaking, Cemophora with high ventral counts are
frequently larger, have more infralabials, more dorsal scale rows both
anteriorly and posteriorly and more subcaudals. Without additional
material it is difficult to determine the significance of this variation, but
apparently Cemophora that tend to be larger and have more ventrals and
subcaudals, more infralabials, and more dorsal scale rows, occur most
frequently in the central part of the peninsula; snakes of a contrasting
phenotype occur in North Florida, the Panhandle, and to the south in the
Everglades regions. Additionally, the central peninsular snakes usually
have 14 supralabials, while Cemophora to the north and south have 12.
Previous studies (Neill 1950b, Duellman and Schwartz 1958, Williams







BULLETIN FLORIDA STATE MUSEUM


and Wilson 1967) have failed to notice this pattern. Current taxonomy
(Williams and Wilson 1967) recognizes the snakes from the northern
peninsula and Panhandle as C. coccinea copei and assigns all C. coccinea
from the peninsula south of Marion County to the nominate race.
The scarlet snakes may represent another example of the mor-
phological similarity between North and South Florida populations with
divergent populations in the geographically intermediate region.
Diadophis punctatus.--Unlike most snake species investigated, D.
punctatus tend to have lower ventral counts southward. Variation of sub-
caudal numbers shows no obvious trend. Like other species, ringnecks
usually have proportionately longer tails in the south. Many of the
characters concerned with the nuchal ring and labial pigmentation show
a relationship between the Gulf Hammock region and the extreme
southern peninsula including the Lower Keys. Superimposed upon this
pattern is frequently the Suwannee Straits break in phenotype as seen in
other species and evident in Diadophis in number of supralabials, labial
spots, and ring width.
Most of the previous work on variation in Diadophis has concerned the
validity and distribution of the various taxonomic entities within the
genus (Conant 1946, Paul 1967, and others). A recent study by Gehlbach
(1974) speculated on the evolutionary history within the species.
Gehlbach believes that the smaller body size in populations called arnyi is
probably ancestral. The larger Diadophis in the southwestern United
States reflect adaptation to present conditions there. He further speculates
that the tail-coiling habit and distinctive subcaudal coloration (Myers
1965), seen in Florida populations and in arnyi is ancestral, and that more
northeastern populations have lost these characteristics. I agree with these
speculations and add the following comments on the species' color pat-
tern.
The lack of a nuchal ring in Lower Keys populations may be ancestral
and imply that Diadophis there have failed to evolve a complete neck
ring. The fact that some populations of ringnecks in the southwestern
U.S. also lack a neck ring (Stebbins 1966) lends credence to this
hypothesis. The development of discrete pigment spots on the labial scales
in northern populations has proceeded relatively more thoroughly there
than in Keys populations. The Lower Florida Keys may be acting as a
refugium for such ancestral character states as presence of subcaudal
black spots, a reduced labial pigmentation pattern, and a reduced neck
ring.
Ringneck snakes from the peninsula generally differ from their
mainland relatives in the nature of the nuchal ring. Snakes from south of
the Suwannee River frequently have a narrower neck ring that is inter-
rupted middorsally and displaced farther posteriorly than specimens to


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 241

the north and west. This phenotype may represent an intermediate condi-
tion between the virtually ringless populations on the Keys and the typical
ringed Diadophis north and west of Florida.
Alternatively, the Keys populations may be more derived with respect
to the nuchal ring and labial pigmentation, perhaps a relatively recent
adaptation to conditions there. The disjunct nature of the variation seen
in number of subcaudal black spots suggests that these spots have been lost
in peninsular populations while they were retained by both northern
Florida and Lower Keys populations. This pattern has been observed in
several other species (Duellman and Schwartz 1958; this study) and does
not support the suggestion that the Keys might harbor more advanced
phenotypes.
The number of subcaudal black spots, labial pigmentation, and
absence of the nuchal ring suggest a relationship between Diadophis
populations in the Gulf Hammock Region and the Lower Keys. Again
these areas may be refugia for ancestral character states while evolu-
tionary change has proceeded more thoroughly in geographically in-
termediate areas.
Tantilla sp.-Ventral and subcaudal counts tend to decrease clinally
to the south on the Florida peninsula. Specimens from the Miami and Key
Largo populations are an exception to this, having generally high ventral
and caudal counts. Tantilla from the west coast of the peninsula and the
Suwannee River Valley usually have proportionately longer tails than
specimens from elsewhere in the state.
Geographic variation in most of the characters examined is complex.
Populations from Miami and the Suwannee River Valley are more closely
related phenetically than geographically intermediate populations.
Telford (1966) noted this when he described T. oolitica from Miami. The
disjunct nature of this pattern suggests a retention of ancestral character
states in these regions while adaptation in geographically intermediate
regions led to partial differentiation. I cannot agree with Telford (1966)
that this disjunct pattern implies the existence of a former gene corridor
connecting the two regions while "strongly dissimilar, evolutionary older
populations" (op. cit.: 300) existed alongside the corridor. Rather, I
believe the similarity between northern and extreme southern populations
is more easily explained by assuming moderate differentiation in inter-
mediate populations and less differentiation in the two disjunct regions.
Geographic variation in crowned snakes on the peninsula has led to
the complex picture Telford treated taxonomically in 1966. The different
phenotypes are probably restricted to particular ecological situations, as
suggested by Telford. Whether the phenotypes have or have not achieved
reproductive isolation cannot be determined by a phenetic study.
Sistrurus miliarius.-Ventrals and caudals appear to increase clinally







BULLETIN FLORIDA STATE MUSEUM


to the south. The Coastal Pattern describes the variation in several
characters: Coastal populations have higher dorsal scale row counts,
higher dorsal blotch counts, and larger, rounder dorsal blotches. The
Panhandle west of the Ochlockonee River and the Everglades seem to be
set apart phenetically from geographically intermediate regions. Sistrurus
from these two disjunct regions share character states for ventral pigmen-
tation, dorsal contrast, spot shape, spot-space ratio, and ventrals and
caudals.
Gloyd (1940) commented on phylogenetic relationships in the genus
Sistrurus. He pointed out that the Florida subspecies barbouri has more
primitive character states than either of the other two subspecies. He
went on to speculate that barbouri must therefore have given rise to the
other two following its isolation in Pleistocene Florida. If barbouri does
retain more primitive characteristics (and I agree that it probably does),
the implication is that it has changed less than the others, not that it is
ancestral to them. Populations of Sistrurus miliarius are adapted to local
conditions wherever they exist. If the populations on peninsular Florida
retain presumed ancestral states for some characters, while populations to
the north and west demonstrate character states believed to be derived, it
follows that something about the Florida environment has allowed
populations there to remain unchanged, while populations elsewhere
have been forced to differentiate. The location of the area of least evolu-
tionary change is not the center of origin, center of dispersal, or anything
but the area where evolution has proceeded more slowly.
Just as Florida appears to be acting as a refuge for ancestral character
states with respect to the remainder of North America, parts of Florida
seem to preserve primitive characters with respect to the rest of the state.
The morphological similarities between Sistrurus from the Everglades
and the widely disjunct western Panhandle cannot be denied. These
snakes with their narrow, crossband-like dorsal blotches, increased dorsal
contrast, and increased ventral white are more similar to the western
subspecies, streckeri, than to any other Florida populations. This
phenotype is probably ancestral, with populations in other parts of the
range having differentiated more from this condition. The alternative
hypothesis suggests that this phenotype has arisen independently in the
several remote regions where it occurs today.
Crotalus adamanteus.-Variation in ventral and subcaudal counts for
Florida Crotalus show no obvious trends except that Keys specimens have
higher ventral counts. The number of infralabial scales varies in such a
way that Keys rattlesnakes are closer to more northern specimens than
to those from the adjacent mainland. Pigmentation of the labials and
ventral surface shows a similarity between specimens from the Lower
Keys and the Central Ridge.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 243

Gloyd (1940) believed that Crotalus adamanteus was derived from
western atrox, which he suggested was closest to the ancestral type for the
atrox group of rattlesnakes. The implication, although not noticed by
Gloyd, is that adamanteus in Florida has diverged less from the ancestral
phenotype than have other members of the group. The fact that atrox is
the most primitive and occurs today in the southwestern United States im-
plies not that it arose there as Gloyd believed, but that it has changed less
there. The southwestern United States has acted as a refuge, preserving
ancestral character states while other regions have dictated evolutionary
change in their rattlesnake populations. Similarly, Florida has been a
refuge where rattlesnakes have evolved more slowly. There is no reason to
suppose that adamanteus arose on the Mexican Plateau and dispersed into
Florida.
Within Florida Crotalus adamanteus has differentiated in response to
different selective regimes, with this differentiation no doubt effected by
variations in gene flow. The phenotypic resemblance between disjunct
populations on the Keys and in northern Florida suggests that these forms
share a common history. Evolution in the intermediate parts of the penin-
sula has produced a phenotype somewhat distinct from that still persisting
both northward and southward.

SUMMARY
Much of the morphological variation in 15 species of snakes occurring
in Florida can be summarized by seven major patterns of geographic
variation. Totally unrelated characters of unrelated species often vary
geographically in remarkably similar ways. Such patterns of geographic
variation must reflect the history of these species in Florida including the
present as well as past selective regimes.
Peninsular Florida has been widely cited as the center of origin for a
number of plant and animal species, largely because the most primitive
members of the various groups now occur there. As pointed out by
Croizat et al. (1974) the concept of a center of origin is of little theoretical
value. A new species forms when another species splits into isolated
populations that receive different selective pressures and have reduced
genetic mixing with each other. The center of origin is thus the entire
range of each isolated population.
The reason so many primitive species and primitive character states
occur in Florida is simply that these populations have diverged less from
their ancestral stocks than have populations elsewhere. The geographic
location of the most primitive species of a group or the most primitive
character state for a species tells us nothing about the origin of that group
or species, but it does tell us that, for some reason, evolution has been pro-
ceeding more slowly in these areas.







BULLETIN FLORIDA STATE MUSEUM


Evolution has proceeded more slowly on the Florida Peninsula than
elsewhere in the eastern United States for two important reasons. The first
involves a consideration of gene flow. Because Florida is a peninsula (and
from time to time in the past was an archipelago), gene flow between con-
tinental populations and Florida populations has been reduced below that
for other areas of similar size. This means simply that evolutionary
changes that occurred in the central continental parts of a species' range
(where they are most likely to occur anyway) were not always as fully in-
corporated into the genotypes of the partially isolated peninsular popula-
tions. The phenomenon of centrifugal speciation, discussed theoretically
by Brown (1957), is demonstrated clearly in Florida where many species
retain more primitive characteristics at the periphery of their distribu-
tions.
The second reason that evolution has proceeded relatively more slowly
in Florida involves natural selection. Paleoecologic data suggest that
Florida has been climatically more stable since the Pliocene than have
areas to the north. Obviously organisms living in a more stable climatic
region will be under less selective pressure to change their morphology.
Species inhabiting the continent north of Florida during the Pleistocene
were faced with changing climatic regimes to which they responded with
extinction or adaptation. Thus there are today fewer species in the north,
and those that are still present are often quite divergent from ancestral
stocks.
Although little is to be gained from speculating on centers of origin,
the position of the barrier that somehow reduced gene flow and allowed
the differentiation process to proceed is of interest. In Florida the most
important vicariating barrier was certainly the base of the peninsula or
Suwannee Straits region. Species that today range across the region of the
present Suwannee River often demonstrate abrupt shifts in character
states on either side of this region. I can think of no selective pressure now
operating that might maintain such well defined phenotypes on opposite
sides of the Suwannee Valley, and must conclude that the pattern is a
remnant of past genetic barriers and selective pressures no longer visible.
The present Suwannee Valley is, of course, the very region where Florida
becomes a peninsula, and the region that was at least partially inundated
during higher sea levels, even while parts of the peninsula were still
emergent. Thus populations on opposite sides of the Suwannee Straits
have had a history of at least partial isolation and therefore independent
evolution.
Even within Florida evolutionary rates have varied geographically in
response to varying degrees of isolation. Lower Keys populations have
been relatively isolated from peninsula populations and today usually re-
tain more primitive characteristics.


Vol. 25, No. 3







1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 245

One of the most interesting patterns of geographic variation in Florida
organisms is the Lower Keys-North Florida Pattern. In this pattern,
species that range throughout Florida frequently demonstrate mor-
phological similarities in three disjunct regions: the extreme northern
peninsula, the Lower Keys, and the Central Highlands just east of Tampa
Bay. Conspecific individuals from these three widely separated regions
are often more similar to each other than they are to individuals living be-
tween them. The three regions probably represent islands of slower evolu-
tionary rates. The northernmost peninsula, the Central Highlands and
the Lower Keys may have been islands of terrestrial habitat when much of
the remainder of the peninsula was submerged (see Fig. 101 for elevations
in Florida), and their populations probably shared common ancestors.
When the rest of the peninsula became available for colonization, the
stocks moving in from the three islands were plastic enough in their
genotypes to respond differentially to selective pressures in the lower
elevations.
Variations in present day selective pressures have also contributed to
the patterns of morphologic variation in Florida snakes. Many popula-
tions living in open, largely treeless environments differ phenotypically
from conspecifics in more forested habitats, even when the treeless
habitats are disjunct. Similarly the two regions of highest annual
precipitation (the Everglades and the Panhandle), although widely dis-
junct, support populations of some species that are more similar to each
other than either is to geographically intermediate populations. The uni-
que habitat afforded by the Central Highlands ridge of scrub and sand-
hills often supports populations somewhat divergent from other Florida
populations, and the same can be said for the Gulf Hammock Region.
The striking north-south dines running the length of the peninsula in
nearly all species examined parallel mean annual temperature and most
other temperature-related climatic measurements, which also vary clin-
ally down the peninsula. This suggests a cause and effect relationship,
although its adaptive significance is not clear.
A dine would also be maintained by the peninsula or gene-flow effect.
The base of the peninsula is a partial barrier to most species' gene flow.
Adaptations occurring north of Florida would spread (if they remained
adaptive) southward onto the peninsula. A picture of such dynamic varia-
tion at one point in time (i.e. this study) would be a dine.
Some of the variation in Florida snakes may be explained in terms of
release from competition with ecologically related species. Where Elaphe
guttata occurs in the absence of E. obsoleta (the Lower Keys and several
Gulf Coast islands), the former is generally more slender, less distinctly
patterned ventrally and dorsally and more arboreal in habits, all
characteristics of E. obsoleta. Many authors (Carr 1940, Duellman and







BULLETIN FLORIDA STATE MUSEUM


Schwartz 1958) have noted that Storeria dekayi victa is essentially an
aquatic snake, but this species is terrestrial on the Lower Keys where such
potential competitors and predators as Tantilla, Rhadinaea flavilata, and
Lampropeltis triangulum are absent. It seems possible that the distinctive
morphology of Lower Keys Storeria might reflect its use of habitats not
used on the mainland.
In several instances a coastal pattern of geographic variation is
manifest where populations demonstrate a unique phenotype typical only
of coastal localities. These snakes may be better adapted to coastal en-
vironments, which are often more open (i.e. less forested) and subject to
less extreme temperature fluctuations.
For several of the species examined, the analysis of geographic varia-
tion revealed patterns of potential taxonomic significance. Although I
withhold formal taxonomic judgments, the data suggest the following
conclusions:
(1) Storeria dekayi wrightorum and S. d. victa are apparently
allopatric, are morphologically and behaviorally distinct, and are prob-
ably evolving independently. The population on the Lower Keys is
distinctive and could probably be considered a subspecies of the penin-
sular form, victa.
(2) The population of Coluber constrictor on the Lower Keys is as
distinctive as any of the currently recognized subspecies.
(3) Elaphe guttata on the Lower Keys is distinctive and could also be
recognized taxonomically.
(4) Cemophora coccinea may consist of two rather distinctive mor-
photypes on the Florida peninsula.
(5) The validity of Tantilla relicta or T. oolitica is not supported (or
denied) by any of the data used in this study.

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Bull. Florida St. Mus., Biol. Sci. 7(3):99-178.
1965. A new subspecies of the common garter snake, Thamnophis sirtalis, from
the Florida Gulf Coast. Proc. Louisiana Acad. Sci. 27:67-73.
Ruthven, A. G. 1908. Variation and genetic relationship of the gartersnakes. Bull. U.S. Natl.
Mus. 61:1-201.
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Schmidt, K. P., and D. D. Davis. 1941. Field Book of Snakes of the United States and Can-
ada. G. P. Putnam's Sons, New York. 13 + 365 p.


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1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 249

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APPENDIX A
CHARACTERS EXAMINED
ALL SPECIES
NUMBER OF VENTRALS. Unless otherwise noted, this count includes the first anterior ventral
scute that is wider than long, through the last scute anterior to the anal plate. This method,
recommended by Schmidt and Davis (1941), is less time-consuming to determine, and thus
more efficient in terms of information gathered than the more complicated method advocated
by Dowling (1951).
NUMBER OF SUBCAUDALS. Only those specimens with a terminal spine were counted. Unless
otherwise stated, the spine was included and the anal plate was not.
NUMBER OF SUPRALABIALS. Counts were made on both sides.
NUMBER OF INFRALABIALS. Counts were made on both sides.
DORSAL SCALE ROWS. Scale rows around the body were counted in three places: one head
length posterior to the head, at midbody, and one head length anterior to the anal plate.
SNOUT-VENT LENGTH. This was measured from the tip of the snout to the posterior margin of
the anal plate.
TAIL LENGTH. The length of the tail from the posterior margin of the anal plate to the tip of
the terminal spine was recorded only for specimens with complete tails.
SEX. In snakes without everted hemipenes, sex was determined by dissecting the base of the
tail.
QUALITATIVE CHARACTERS. Aspects of carination, pattern, and pigmentation were ranked on
qualitative scales and assigned numerical character states. For pattern analysis line drawings








BULLETIN FLORIDA STATE MUSEUM


on the data-collection forms were filled in, and numerical scores assigned only after all the
material had been examined. For carination or pigmentation characters, a preliminary in-
vestigation determined the range of variation, and a scale was constructed beforehand.
"Voucher" specimens were used as models for the character states while the scoring was in
process. In this manner, the specimens could be compared with the models, and assigned the
appropriate character state value.

Storeria dekayi
NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
DORSAL SCALE ROWS.
NUMBER OF PREOCULARS. The preocular scales were counted on each side of the head. Scales
divided incompletely were counted as half scales.
NUMBER OF POSTOCULARS. These scales were counted in the same manner as the preoculars.
VENTRAL DARK PIGMENTATION. The general extent of ventral dark pigment was ranked on a
scale of zero (venter immaculate) to five (venter with much dark pigment).
TEMPORAL PIGMENT AMOUNT. The amount of black pigment on the temporal scale was noted
and assigned values from zero for no such pigment to five when the entire temporal is
pigmented.
TEMPORAL PIGMENT SHAPE. The orientation of the tear-drop-shaped temporal blotch (when
present) was noted. This blotch has been used by previous workers (Anderson 1961 and
Sabath and Sabath 1969) but has always been confusing. Noting merely in which direction
the blotch seems to point provides a more manageable character. Specimens in which tem-
poral pigment appeared to enter the temporal at its posterior margin were given values of
one; those in which pigment entered at the anterior margin were scored as two. Specimens
whose temporal pigment was entirely confined within the scale and specimens without tem-
poral pigment were given missing values for this character.
SUBOCULAR PIGMENTATION. This is the number of supralabial scales covered by the large
subocular spot. If pigment covered more than half a supralabial it was counted. Only the
right side was examined.
BLACK SUPRALABIALS. The number of supralabial scales with black pigment was recorded for
the right side.
BLACK INFRALABIALS. The number of infralabial scales with black pigment was recorded for
the right side.
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.
Thamnophis sirtalis
NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
DORSAL SCALE ROWS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
PARIETAL SPOTS. The distinctiveness and size of the parietal spots were ranked on a scale of one
to three.
DORSAL SPOTTING. The degree of dorsal spotting ("ordinatus" phase, discussed by Rossman
1965) was ranked on a scale of one to three.
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.


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1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 251


Thamnophis sauritus

The data for this species were supplied by Douglas A. Rossman.
NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
PARIETAL SPOT SIZE. The small paired light spots near the medial margin of the parietal scales
were scored for presence or absence as well as size when present. The smallest spots were
assigned values of one; the largest, values of 2. Specimens lacking the parietal spot received
scores of zero for this character.
PARIETAL SPOT. The spots were scored zero for absent, one for faint or indistinct, and two for
distinct.
GROUND COLOR. Rossman described the brown in the dorsal ground color as light, medium,
dark, very dark, or black. I assigned numbers from one to five to these qualitative
assessments.
DORSAL GRAY. The presence of gray in the dorsal ground color was scored one, its absence
zero.
DORSAL STRIPE EDGE. The black border of the dorsal stripe may be absent, weak and irregular,
present but narrow, or up to 11 V scales wide. Values of zero to three were assigned for these
conditions.
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.

Coluber constrictor

NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
BLACKNESS. Adult specimens (>70 cm) were scored one, two, or three, based on how dark
they appeared in preservative.
VENTRAL WHITE. The amount of white pigment on the ventral surface was assigned values
ranging from zero (no white on any part of the venter) to five (venter completely white).
GULAR BROWN PIGMENTATION. The amount of brown pigment in the gular region was assigned
values ranging from zero for no pigment to five for much pigment.
GULAR BLACK PIGMENTATION. Like gular brown, the values for this character ranged from
zero to five.
SUPRALABIAL BROWN PIGMENTATION. The amount of brown pigment on the supralabial scales
was assigned values from zero for no pigment to five for much pigment.
SUPRALABIAL BLACK PIGMENTATION. The amount of black pigment on the supralabial scales
was scored with values from zero to five.
SUPRALABIAL-LOREAL CONTACT. This character, introduced by Auffenberg (1955), was ex-
amined on both sides of the head. The first supralabial is either in contact with the loreal, or it
is not.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
FRONTAL MEASUREMENTS. Linear measurements were made on three aspects of the frontal
plate. The anterior width is the straight line distance between the junction of the left pre-
frontal, the left supraocular, and the frontal, and the junction of the right prefrontal, the
right supraocular, and the frontal. The posterior width is the straight line distance between
the junction of the left supraocular, the left parietal and the frontal and the junction of the
right supraocular, the right parietal, and the frontal. The frontal length is the straight line
distance from the junction of the two prefrontals and the frontal to the junction of the two
parietals and the frontal.









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SIZE. Specimens were categorized as either large, medium, small, or hatchling.
SEX.

Masticophis flagellum

Data for this species were supplied by Larry David Wilson.
NUMBER OF VENTRALS. Ventrals were counted by the method proposed by Dowling (1951).
NUMBER OF SUBCAUDALS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
COLOR PHASE. On the basis of overall color and pattern, the specimens were assigned to either
a light phase (1), intermediates (2), or dark (3).
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.

Opheodrys aestivus

NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
DORSAL SCALE ROWS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
SUPRALABIAL PIGMENTATION. The amount of dark pigment on the supralabials was scored
from zero (immaculate) to five (completely pigmented).
KEELING OF THE SECOND DORSAL SCALE ROW. A value of zero was assigned to specimens showing
no keel on this scale row and a maximum of three when the keel was developed to the same ex-
tent as the adjacent third row; intermediate conditions were scored as one or two. This charc-
ter was introduced by Cope (1900).
FRONTAL MEASUREMENTS. Three dimensions of the frontal plate were recorded as in C. con-
strictor.
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.
Elaphe guttata

NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
NUMBER OF BODY BLOTCHES. This includes only the precaudal blotches.
NUMBER OF TAIL BLOTCHES.
DORSAL SCALE ROWS.
FRONTAL MEASUREMENTS. Linear measurements were made on three aspects of the frontal
plate, as in C. constrictor.
LATERAL BLOTCH SHAPE. The lateral series of spots was examined and scored for presence or
absence, and (when present) whether the surrounding border was complete or incomplete.
BLOTCH BORDER. The black border surrounding a typical midbody dorsal blotch was scored for
width and distinctiveness on a scale of zero (no border) to four (border very well developed
and more than two scales in width).
VENTRAL PIGMENTATION. The general totality of dark pigment in a typical midbody ventral
section was scored on a scale of zero (venter immaculate) to five (venter with black pigment
over more than 3/ of surface).
VENTRAL CHECK SHAPE. The general shape of the ventral checks in a typical midbody section
was scored on a scale of one (ventral pigment consisting mainly of small spots) to five (ventral
pigment usually covering entire ventral scales).








1980 CHRISTMAN: PATTERNS OF GEOGRAPHIC VARIATION 253


SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.

Elaphe obsoleta

The data for this species were supplied by Walter Auffenberg.
NUMBER OF DORSAL BLOTCHES. This includes only the precaudal blotches.
STRIPE DEVELOPMENT. This qualitative assessment of the degree to which the dorsal stripes are
evident ranged from zero for no stripes to five for very well-developed stripes.
BLOTCH DEVELOPMENT. The degree of development of the dorsal blotches was ranked on a
scale like that for stripe development.
GROUND COLOR. The dorsal ground color was compared with a series of color chips showing
increasing melanism scaled from zero to 3.5.
VENTRAL PIGMENTATION. The totality of dark pigment on the ventral surface was scored from
one to four with increasing darkness.
SUPRALABIAL PIGMENTATION. The values for supralabial pigmentation ranged from one to four
with increasing darkness.
SIZE. The head length was recorded to obtain rough size correlations and for grouping the
specimens.

Lampropeltis getulus

Data for this species were supplied by Richard M. Blaney.
NUMBER OF VENTRALS. These were counted by Dowling's (1951) method.
NUMBER OF SUBCAUDALS.
NUMBER OF CROSS BANDS. This includes only the precaudal bands.
NUMBER OF INFRALABIALS.
DORSAL SCALE ROWS AT MIDBODY.
DORSAL PATTERN. This character attempts to describe the relative amount of light pigment in
the dorsal pattern. The three states for this character (1-3) correspond in part to Blaney's
(1971a) Figure 13.
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.

Lampropeltis triangulum

Data for this species were supplied by Kenneth Williams.
NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
DORSAL SCALE ROWS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
NUMBER OF LOREALS. These were counted on each side.
RED BODY BANDS. This is a count of precaudal red bands.
RED TAIL BANDS.
TOTAL LENGTH.
TAIL LENGTH.
SEX.

Cemophora coccinea

Data for this species were provided by Kenneth Williams and Larry David Wilson.
NUMBER OF VENTRALS.








BULLETIN FLORIDA STATE MUSEUM


NUMBER OF SUBCAUDALS.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
DORSAL SCALE ROWS.
NUMBER OF RED BODY BANDS. This is the number of precaudal red saddles.
NUMBER OF RED TAIL BANDS.
LENGTH OF FIRST RED BAND. This is the number of scale lengths in the first red dorsal saddle.
LENGTH OF FIFTH RED BAND.
LENGTH OF FIRST WHITE BAND.
LENGTH OF FIFTH WHITE BAND.
TOTAL LENGTH.
TAIL LENGTH.
SEX.
Diadophis punctatus
NUMBER OF VENTRALS.
NUMBER OF SUBCAUDALS.
NUMBER OF PAIRED GULARS. This is the number of paired scales in the throat region between
the posterior chin shields and the first ventral scales.
NUMBER OF ANAL PLATES. Of the specimens examined, 23% had the last ventral scale enlarged
and patterned like the adjacent anal plate, giving the appearance of two anal plates.
NUMBER OF SUPRALABIALS.
NUMBER OF INFRALABIALS.
SUBCAUDAL SPOTS. The number of black spots on the underside of the tail was recorded for
each specimen.
VENTRAL PIGMENTATION. The amount of black pigment at a typical midbody section was
ranked on a scale of zero (venter immaculate) to five (venter very heavily pigmented).
VENTRAL SPOT SHAPE. The shape of the ventral spot was assigned values from zero (slightly
higher than wide) to five (as wide as the whole ventral scale). This character measures the
degree to which the ventral spot is elongated into a bar.
CONNECTED SPOTS. The state for this character is three if most of the ventral spots are con-
nected anterior-posteriorly, one if none is, and two if some are.
VENTRAL SPOT DISTINCTIVENESS. The snakes were given values of one, two, or three depending
on how clear-cut and distinct the ventral spots were.
NUMBER OF IMMACULATE VENTRALS. The number of ventral scales lacking black spots was
recorded.
RING SEPARATION. The width of the break in the nuchal ring was scored using a scale of zero
for no break to five for a break more than one scale wide. A value of six was assigned to those
specimens in which the ring was reduced to a pair of dorso-lateral dots or lacking altogether.
RING POSITION. This is the number of scales between the parietal and the anterior margin of
the nuchal ring.
RING WIDTH. The width of the nuchal ring was measured in number of scales at its widest dor-
sal part.
LABIAL PIGMENTATION. Specimens with diffuse labial pigment were assigned a value of zero,
those with clear, distinct labial spots or with no pigment were given three, intermediate
specimens one or two.
PIGMENTED SUPRALABIALS. The number of supralabial scales with black spots was recorded for
the right side.
PIGMENTED INFRALABIALS. The number of infralabial scales with black spots was recorded for
the right side.
SNOUT-VENT LENGTH.
TAIL LENGTH.
SEX.


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