Front Cover
 Table of Contents
 Distribution and habitats
 Historical perspective
 Materials and methods
 Literature cited
 Specimens examined
 Back Cover

Group Title: Bulletin of the Florida State Museum
Title: A Zoogeographic analysis of variation in recent Geomys Pinetis (Geomyidae) in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00095800/00001
 Material Information
Title: A Zoogeographic analysis of variation in recent Geomys Pinetis (Geomyidae) in Florida
Series Title: Bulletin - Florida State Museum ; volume 30, number 1
Physical Description: 28 p. : ill., maps ; 23 cm.
Language: English
Creator: Wilkins, Kenneth T.
Florida Museum of Natural History
Publisher: Florida State Museum, University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1987
Copyright Date: 1987
Subject: Geomys pinetis -- Florida   ( lcsh )
Mammals -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 23-25).
General Note: Cover title.
General Note: Summary in English and Spanish.
Statement of Responsibility: Kenneth T. Wilkins.
 Record Information
Bibliographic ID: UF00095800
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 15998269

Table of Contents
    Front Cover
        Page i
        Page ii
    Table of Contents
        Page 1
        Page 2
    Distribution and habitats
        Page 3
    Historical perspective
        Page 4
        Page 5
        Page 6
    Materials and methods
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Literature cited
        Page 23
        Page 24
    Specimens examined
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
    Back Cover
        Page 30
Full Text

B, [ L TIN

of the
Biological Sciences
Volume 30 1987 Number 1





ENCES, are published at irregular intervals. Volumes contain about 300 pages and are not
necessarily completed in any one calendar year.

S. DAVID WEBB, Associate Editor
RHODA J. BRYANT, Managing Editor

Consultants for this issue:


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 FL 32611; U.S.A.

This public document was promulgated at an annual cost of $2880.00 or
$2.88 per copy. It makes available to libraries, scholars, and all interested
persons the results of researches in the natural sciences, emphasizing the
circum-Caribbean region.

Publication date: 12 March 1987

Price: $2.90


ABSTRACT: Cranial characters were used to assess phenetic relationships of Geomys pi-
netis populations in Florida. The observed pattern of geographic variation is examined in
light of rivers and patchy distribution of suitable habitats that influence dispersal of pocket
gophers and the effects of sealevel changes on isolation of populations. Phenetic breaks in
the pattern of geographic variation correspond to the Apalachicola and, to a lesser extent,
the Suwannee rivers. Several features of these river corridors explain their relative effec-
tiveness as barriers: (1) potential for gene flow around river headwaters, (2) effective width
of the river corridors, and (3) various streamflow parameters. The barrier effects of the
Apalachicola and Suwannee rivers on other vertebrate and invertebrate taxa are dis-

RESUMEN: Caracteristicas craniales de Geomys pinetis fueron utilizadas para establecer
relaciones fen6ticas en poblaciones de esta especie en Florida. Los patrons observados
de variaci6n geogrdfica fueron examinados en base a rios y distribuci6n fragmentada ("en
parche") de habitats favorables que influencian la dispersi6n de las tuzas de bolsillo, asi
como los efectos de cambios del nivel del mar sobre sislamiento de poblaciones. Rupturas
feneticas en los patrons de variaci6n geografica correspondent al rio Apalachicola y, en
menor grado, al rio Suwannee. Varias caracteristicas de estos corredores de rios explican
su relative eficacia como barreras: (1) potential para flujo de genes alrededor de cabeceras
de rios; (2) ancho efectivo de corredores, y (3) parimetros de flujo de corriente. Se discute
tambi6n los efectos de barrera de los rios Apalachicola y Suwannee sobre otros taxones de
vertebrados e invertebrados.


Acknowledgm ents........... ............................................ 2
Distribution and Habitats ......... .. ................................... 2
Historical Perspective ............ ....................................... 4
M materials and M ethods ............... .................................... 7
Results................... ..... ........................................ 9
Non-geographic Variation ........... ..................................... 9
Geographic Variation .............. .................................. 12
Discussion .......................... ... ...... ........................ 17
Riverine Barrier M echanisms ........ .................................. 19
Riverine Barrier Effects on Other Taxa .................................... 21
Literature Cited ................. .......................................... 23
Appendix: Specimens Examined ......... ................................ 25

IThe author is Assistant Professor of Biology, Baylor University, Waco, Texas 76798 (formerly a Postdoctoral Research
Associate of the Florida State Museum, Gainesville, Florida, 32611).
Wilkins, K. T. 1987. A zoogeographic analysis of variation in Recent Geomys pinetis
(Geomyidae) in Florida. Bull. Florida State Mus., Biol. Sci. 30(1):1-28.



Geographic isolation is a key component in many speciation models
(Wiley 1981). Fragmentation of populations is important in the differen-
tiation process because it may serve to reduce the amount of gene flow
between populations (Wright 1943). The degree of divergence between
populations may depend on many factors including distance between
populations, duration of isolation, effective population sizes, vagility of
the organism, and others (Patton and Feder 1981). Because of their fos-
sorial lifestyle, low vagility, skewed sex ratio of breeding adults, and low
effective population sizes, pocket gophers (Rodentia: Geomyidae) exem-
plify the effects of geographic isolation in terms of recognizable morpho-
logical and chromosomal variability. For example, over 200 subspecies of
Thomomys bottae have been recognized (Hall and Kelson 1959).
Like many pocket gopher species, the southeastern pocket gopher
(Geomys pinetis) is patchily distributed because of its restriction to soils
of suitable friability and moisture content. Hubbell and Goff (1939:131)
recognized the discontinuous distribution of pocket gophers in Florida
as the result of the patchy occurrence of deep, well-drained soils ele-
vated slightly above surrounding wetter habitats which are unsuitable
and impassable to pocket gophers. They (1939:134) stated that "it would
not be surprising . to find that specific or racial differentiation corre-
sponding to the degree of isolation had occurred" in Geomys pinetis. This
study utilizes craniometric data from over 800 specimens to examine
geographic variation in Recent Geomys pinetis in Florida. The pattern of
variation found is interpreted in the light of both the relative roles of
river valleys as dispersal barriers and the effects of past sealevel changes
on isolation of pocket gophers during the Quaternary Period.
This paper represents part of a doctoral dissertation in the Department of Zoology,
University of Florida. I thank S. David Webb and Charles A. Woods for their guidance
throughout the study. I sincerely thank curators from the museums and collections listed
in the Appendix for permission to examine specimens. S. D. Webb, B. J. MacFadden, A.
Berta, J. W. Hermanson, and G. S. Morgan critically read earlier drafts of this manu-
script. This paper further benefited from comments made by J. L. Patton. Grants from
National Geographic Society, Southern Regional Education Board, and Sigma Xi sup-
ported this work. Northeast Regional Data Center (University of Florida) provided com-
puter facilities for data analyses and text editing.


Geomys pinetis occurs along the Atlantic and Gulf coastal plains of
Alabama, Florida, and Georgia (Hall 1981:505). Figure 1 shows the de-
tailed distribution of G. pinetis in Florida. Specimens are known from all

VOL. 30 NO. 1




0 25 50 I00

Figure 1.-Recent distribution of Geomys pinetis (dots) overlaid by general distribu-
tion of sandhill habitat (outlined stippled areas) in Florida. The Apalachicola (central pan-
handle) and Suwannee (eastern panhandle) rivers are indicated by darkened lines.

panhandle counties except Gulf County. The range extends through the
northern two-thirds of the peninsula to a southern tier of counties (Man-
atee, DeSoto, Highlands, Osceola, and Brevard). Thus, the occurrence
of G. pinetis in Florida is much more extensive than depicted in Hall
(1981:505) or in Hamilton and Whitaker (1979:173), but less extensive
than indicated by Williams and Genoways (1980). The latter extension of
its range into St. Lucie County probably originated as an error in geo-
graphic terminology. Pocket gophers do not occur in St. Lucie County as
cited by Williams and Genoways (1980). Walton (St. Lucie Co.) is about
90 km south of the southernmost record of living Geomys along the At-
lantic coast (Melbourne, Brevard Co.). Rather, these specimens are
probably from Ft. Walton (Okaloosa Co.) in the Florida panhandle.
The occurrence of pocket gophers in Florida is controlled by geomor-


phological and habitat features. Prime pocket gopher habitat is the sand-
hill ecosystem characterized by two codominant tree species, longleaf
pine (Pinus palustris) and turkey oak (Quercus laevis). Geomys selects its
diet from the grasses, forbs, and sedges that comprise the fire-perpetu-
ated ground cover. Terrain in the sandhill ecosystem is rolling and the
soils are well-drained (Monk 1968). A second habitat occupied by G.
pinetis is the xeric hammock ecosystem that commonly occurs in associa-
tion with the sandhill community. Xeric hammocks are dominated by live
oaks (Q. virginiana) and other hardwood species; soils are slightly mois-
ter and contain more organic material than soils of the sandhill (Monk
1968). Geomys pinetis occurs less commonly in longleaf pine flatwoods
and sand pine scrub habitats.
A close correspondence exists between museum specimen localities
and the distribution of suitable habitat. In Figure 1, known locality rec-
ords of pocket gophers are superimposed on the distribution of the sand-
hill ecosystem as mapped by Davis (1980). Over 125 of the more than
150 plotted localities coincide with (or are at the edges of) parcels of
sandhill habitat. Most of the remaining localities do in fact correspond to
patches of sandhill habitats that were too small to be included on the
large-scale map, although a few populations do occupy other habitats
such as sand scrub or longleaf pine flatwoods. Hence, Florida pocket
gopher populations occur in a mosaic of islands of suitable habitats within
a sea of unsuitable habitats, primarily the excessively moist pine flat-
woods. The opportunity for allopatric differentiation exists for pocket go-
phers in Florida despite what appears to be fairly uniform topography.
The correspondence of pocket gopher occurrence with geomorphol-
ogy is particularly evident towards range limits in the southern penin-
sula. Suitable habitats predominate along such higher-elevation features
as the Polk Upland, DeSoto Plain, and Lake Wales Ridge (see White
1970). At the escarpment of the DeSoto Plain, habitats abruptly change
to pine flatwoods, cypress swamps, and others too moist for pocket go-
phers. For example, pocket gophers range to the DeSoto Plain escarp-
ment in Manatee County, but are unknown in adjacent lowland Sarasota


Geomys pocket gophers are first known in Florida from the early Ir-
vingtonian (earliest Pleistocene) Inglis IA site dated at about 1.8 million
years before present (mybp; Webb 1974). Fossil evidence suggests a con-
tinuous occupation of the Florida peninsula since then with probable in
situ evolution of the Inglis IA Geomys propinetis into G. pinetis by about
1 mybp (Wilkins 1984). It is of interest to note here that previous mor-

VOL. 30 NO. 1


phological and genic studies show G. pinetis and G. bursarius to have
diverged from a common ancestor about 300,000 ybp during the early
Rancholabrean (Russell 1968, Penney and Zimmerman 1976). While
agreeing that the G. pinetis and G. bursarius complexes are distantly
related, Heaney and Timm (1983, citing Kurten and Anderson 1980) re-
ported origination of these two species groups as "no later than the late
Irvingtonian." My own morphological studies of Quaternary Florida Geo-
mys, wherein pocket gophers statistically indistinguishable from modern
Geomys pinetis extend back to the late Irvingtonian Coleman IIA de-
posit, corroborates the latter opinion (Wilkins 1984).
Because of Florida's low and gentle topographic relief (maximum ele-
vation of 105 m), sealevel changes during the last several million years
have drastically altered the configuration of the emergent Florida land
mass (Healy 1975). During the high sea stands of earlier interglacials (i.e.
the Miocene and Pliocene Coharie, Okefenokee, and Wicomico shore-
lines; see Alt and Brooks 1965) seas covered much of the present state,
leaving only an archipelago of islands to represent the present-day pe-
ninsula. The body of water separating the mainland from the peninsular
archipelago was the Suwannee Straits. Pleistocene transgressions, though
less severe than those previous, undoubtedly affected pocket gopher bio-
geography. Approximately 22 glacial-interglacial cycles (rather than the
traditional four cycles) characterized the last 870,000 years of the two
million year long Pleistocene epoch (Shackleton and Opdyke 1973).
A scenario by which sealevel changes influence the pattern of geo-
graphic variation among populations of pocket gophers may be devel-
oped in accordance with the allopatric model of speciation. This model
holds that gene flow occurring between populations will lead to homo-
geneity of these populations; conversely, restriction of gene flow leads to
inbreeding within isolated populations and resultant divergence of pop-
ulations via differential selection regimes, founder effect, or genetic drift.
Pocket gopher populations, if present on such islands at these times,
were isolated from other insular populations and from the mainland, and
thereby were afforded opportunities to differentiate. During ensuing gla-
cials, however, sealevel fell well below the present level (by 100 m or
more), thereby reconnecting islands with each other. With sea barriers
removed, islands and suitable parcels of pocket gopher habitat tended to
regain contact. Concomitantly, formerly restricted pocket gopher popu-
lations expanded and probably established breeding connections be-
tween populations throughout the peninsula. During such intervals, pocket
gopher populations would have been characterized by their greatest
phenotypic homogeneity, with any differentiation achieved during for-
mer isolation (if not already secured by reproductive isolation) being ob-
literated through panmixia.



The preceding direct-inundation mechanism of population isolation is
accompanied by a second mechanism: Levels of water tables in inland
areas of the Florida peninsula tend to track changes in sealevel. Effects
of water table variation can affect pocket gophers directly through soil
regimes unsuitably wet or dry. Changes in soil moisture conditions also
determine which plant communities can occupy given tracts of land. Be-
cause pocket gopher distribution is closely linked with that of suitable
habitats, it is apparent that changes in soil moisture conditions affect
Geomys distribution.
According to this scenario, the current pattern of geographic variation
presumably reflects the influence of the most recent glacial-interglacial
cycle. The Pamlico Shoreline (about 9 m above present mean sealevel)
apparently was formed by the latest high sea stand about 125,000 years
before present during the late Sangamonian interglacial.
MacNeil (1950) mapped the shorelines of Florida resulting from ocean
transgressions in the Pleistocene (including Pamlico) and earlier in the
late Tertiary. The emergent peninsular landmass during Pamlico times
consisted of a more-or-less connected spine of uplands in the central
peninsula, numerous islands east of the present St. Johns River, and a
few isolated uplands in present day south Florida and in the Tampa re-
gion. Sangamonian fossil sites abound along this central peninsular spine:
Geomys pinetis is known from Arredondo, Sabretooth Cave, Reddick,
several Haile sites, and several others (Wilkins 1984). No Sangamonian
sites have as yet been found in the coastward Pamlico emergent islands.
Yet, during earlier and later glacial times, Geomys occurred in similar
areas which are now at (e.g. early Irvingtonian Inglis IA, Citrus Co.) or
below present sealevel (e.g. late Wisconsinan vertebrate fauna in the
Atlantic Ocean about 100 m offshore from Ft. Pierce, St. Lucie Co.).
The fact that Geomys distributions have changed drastically through nearly
two million years by tracking sealevel changes is well-documented (Wil-
kins 1984). Although the Pamlico transgression did not isolate the penin-
sula from the mainland, it almost certainly increased the degree of frag-
mentation of pocket gopher populations. But any divergence that might
have been achieved between these populations during late Sangamonian
fractioning of ranges could well have been swamped during the subse-
quent range re-extensions that accompanied the late Wisconsinan return
to lower sealevels. At the height of the late Wisconsinan (about 19,000
ybp), seas fell to about 90 m to 130 m below present (Bloom et al. 1974,
Harmon et al. 1978). Since then, glaciers have been melting and the sea
continuously rising towards its present level. During the last 19,000 years,
therefore, the degree of isolation between Geomys populations in pen-
insular Florida presumably has again increased with increasing sea and
ground water levels.

VOL. 30 NO. 1


However, it should be noted here that, in light of recent research, the
scenario proposed above may not be tenable. Study of genetic structure
of pocket gopher (Thomomys bottae) populations in California has dem-
onstrated that, despite moderate rates of gene flow, differentiation at-
tained during isolation is maintained via non-random breeding and drift
(Patton and Feder 1981). Hence, enhanced gene flow accompanying re-
union of once-separated areas need not lead to genetic homogeneity over
geography for animals of low vagility.

Locality data from 1123 skin and skull specimens of Florida Geomys pinetis were used
to construct the distribution map (Fig. 1). The Appendix lists specimens examined. Cran-
iometric analysis was restricted to the 854 adult specimens which were divided into two
age classes on the basis of three osteological features: (1) degree of fusion of the basisphe-
noid and basioccipital bones, (2) development of the temporal ridges, and (3) degree of
porosity of the palatine bone and of the maxillary process of the zygoma. In younger adults
(age class 1) the basisphenoid-basioccipital suture is closed with no intervening gap, but
yet is not obliterated by accumulated bone as in old adults (age class 2). The temporal
ridges in old adults (especially males) are highly rugose and usually meet to form the
sagittal ridge. Rarely, if ever, is such a sagittal ridge found in females, although (as in
males) the distance between temporal ridges decreases and their degree of development
increases with age. In both sexes, porosity in the palatine and maxillary bones decreases
with age.
Twenty cranial characters were measured to the nearest 0.1 mm with Helios dial cali-
pers for all adults. Descriptions and abbreviations of these characters follow: greatest
length of skull (GLS), from exoccipital to anterior surface of incisors; greatest zygomatic
width (ZYGO); width across mastoid processes (WMAST); depth of cranium (DCRAN),
dorsoventral distance from top of cranium to ventral surface of auditory bullae; depth of
rostrum (DROST), least dorsoventral distance from dorsal surface of nasals to ventral sur-
face of premaxillae; width of rostrum (WROST), greatest width across rostrum usually at
level of premaxillary-maxillary suture; least interorbital constriction (IOC); least distance
between temporal ridges (TEMP), generally at or anterior to the anterior width of inter-
parietal; anterior width of interparietal (AWINT); posterior width of interparietal (PWINT):
length of interparietal (LINT), taken along midsagittal axis; least width across nasals
(LWNAS); greatest width across nasals (GWNAS); length of premaxillary extensions
(PMEXT), distance that premaxillaries extend posterior to posterior tip of nasals; length
of upper diastema (LUDIAST); alveolar length of maxillary toothrow (LMXTR); width of
upper incisor (WUINC); length of lower diastema (LLDIAST); alveolar length of mandib-
ular toothrow (LMNDTR); width of lower incisor (WLINC). Geomys pinetis crania are
illustrated in Merriam (1895), Pembleton and Williams (1978), and Hall (1981).
In order to analyze geographic variation it was necessary to combine specimens from
adjacent localities into larger samples. The state was divided into 13 partial to multi-
county natural regions delimited by rivers (Fig. 2). The intent was to define objectively
geographic units containing populations that might be morphometrically distinguishable
because of their histories of isolation. Because rivers are known to influence movements
of pocket gophers (Udvardy 1969, Lowery 1974), care was taken not to group into the
same samples specimens from opposite sides of boundary rivers. Further details defining
these natural regions are available in Wilkins (1982).
Additionally, three geographic areas were recognized to permit assessment of the roles


1 2 3

Apalachicola River Suw e


- AREA III o0I25
AREA III 01025 50



100 / f
I, 0adP~ ~

Figure 2.-Areas (I-III) and component natural regions (A-M) of Florida divided by
rivers (heavy black lines). The unshaded portion of the southern peninsula lies outside
the range of Geomys pinetis. Codes for inter-region boundary waterways are: (1) Escambia
R., (2) Yellow R., (3) Choctawhatchee R., (4) Ocklockonee R., (5) Aucilla R., (6) Withla-
coochee R., (7) Alapaha R., (8) Withlacoochee R., (9) Peace R., (10) Prairie Creek, (11)
Fisheating Creek, (12) Kissimmee R., and (13) St. Johns R.

of Florida's two largest rivers (Apalachicola and Suwannee, respectively) in pocket gopher
zoogeography (Fig. 2). Area I includes regions (A, B, C, and D) west of the Apalachicola
River. Regions E, F, G, H, and I between the Apalachicola and Suwannee rivers comprise
area II. The peninsular regions J, K, L, and M of area III are separated from area II by
the Suwannee River.
ANALYSES CONDUCTED.-Intrapopulation variation was examined for Geomys pinetis
from Gainesville (Alachua Co.), the largest available local sample (n = 209). The MEANS
and TEST procedures of the Statistical Analysis System (SAS, Helwig and Council 1979)
evaluated sex, age, and individual character variation in each sex/age category.
Multivariate analyses were used first to explore phenetic relationships among regional

VOL. 30 NO. 1


samples (cluster analyses) and then to test for differences among regional or area samples
(multivariate analyses of variance and canonical analyses). All multivariate analyses were
conducted separately for each of the four sex/age categories. For cluster analyses, input
data were the standardized regional mean character values for each of 16 cranial charac-
ters. Regions represented by one or no specimens were omitted from multivariate analy-
ses. Data sets standardized to zero mean and unit standard deviation were submitted to
the Ward's method algorithm (Ward 1963) of the CLUSTAN multivariate statistical pack-
age (Wishart 1975). Multivariate analyses of variance (MANOVA's) were used to test the
null hypotheses of no significant differences (1) among all regional samples and (2) among
area samples. Using character measurements of individual specimens as input, MANO-
VA's were computed by the GLM procedure of SAS. MANOVA results are graphically
presented in canonical variates projections. Character loadings and other details pertain-
ing to MANOVA's are available in Wilkins (1982).



Coefficient of variation (CV) values were used to assess within-sample
variation in the 20 cranial characters. Because of extremely large CV
values (Table 1), four characters (TEMP, AWINT, PWINT, LINT) were
omitted from further analyses. Others with relatively large CV values
were retained because of their previous usage in systematic studies of
southeastern United States pocket gophers. Variation in character means
due to sex and age was evaluated using t-tests. For age class 1, males
were larger than females in all of the remaining 16 characters; LWNAS
was the only character for which the sexes were not different (P>0.05).
For the older adults (age 2), females were slightly, but not significantly,
larger than males only in GWNAS. The sexes were similar in size for
IOC, LWNAS, and PMEXT. Males were significantly larger than females
in the remaining measurements.
The means for male Geomys pinetis of both age categories were simi-
lar in four characters: IOC, LWNAS, GWNAS, and PMEXT. Old adult
males were significantly larger than younger adult males in all other fea-
tures examined. For females, mean values for IOC in both age groups
were equal. In the remaining characters, older adult females were larger
than younger adult females; these differences were significant for all fea-
tures except LWNAS, GWNAS, and PMEXT. Because the Gainesville
sample of Geomys pinetis demonstrated such marked sex and age varia-
tion, subsequent analyses of geographic variation entailed comparisons
of subsamples of like sex and age. The four subsamples recognized are
(1) males of age class 1, (2) males, age 2, (3) females, age 1, and (4) fe-
males, age 2.

Table 1-Non-geographic variation in 20 cranial characters for Recent Geomys pinetis from Gainesville, Alachua County, Florida. Univariate
statistics presented for each of four sex/age categories. Each entry contains the mean and standard deviation (first line) and extreme
values and coefficient of variation (second line). Measurements are in millimeters; coefficient of variation is expressed as a percentage.

Male (N = 87) Female (N = 122)

Character Age 1 (N = 53) Age 2 (N = 34) Age 1 (N= 84) Age 2 (N = 38)

Skull Length (GLS)

Zygomatic Width (ZYGO)

Mastoid Width (WMAST)

Depth of Cranium
Depth of Rostrum
Width of Rostrum
Interorbital Constriction
Distance between
Temporal Ridges (TEMP)
Anterior Width of
Interparietal (AWINT)
Posterior Width of
Interparietal (PWINT)
Length of Interparietal

49.6, 2.53
44.2-54.8, 5.1
29.6, 1.74
26.0-33.6, 5.9
25.5, 2.98
20.1-28.8, 11.7
14.9, 0.59
13.8-16.4, 4.0
7.4, 0.51
6.2-9.0, 6.9
10.5, 0.58
9.1-11.8, 5.6
7.0, 0.33
6.3-7.7, 4.7
4.0, 1.25
1.7-7.7, 30.9
2.2, 1.14
0.1-6.1, 51.3
5.7, 1.13
2.0-8.0, 19.7
4.7, 0.84
3.5-7.2, 17.7

52.5, 1.69
48.4-55.7, 3.2
32.1, 1.33
29.7-35.6, 4.1
27.1, 1.56
20.1-28.9, 5.7
15.2, 0.51
14.2-16.1, 3.4
7.7, 0.44
6.9-8.6, 5.7
11.0, 0.50
9.9-12.1, 4.6
6.9, 0.45
6.0-7.8, 6.4
2.5, 1.62
0.7-7.6, 63.3
1.4, 0.79
0.2-3.2, 55.9
5.6, 0.92
3.5-7.6, 16.4
4.8, 0.65
3.6-6.6, 13.3

44.6, 1.77
40.0-50.7, 4.0
26.3, 1.33
23.5-30.3, 5.1
23.6, 1.47
14.5-28.9, 6.3
14.0, 0.47
12.8-15.5, 3.4
6.6, 0.40
5.7-7.8, 6.1
9.6, 0.51
8.2-10.9, 5.4
6.9, 0.33
6.1-7.7, 4.8
5.8, 1.43
1.9-12.4, 24.7
3.65, 1.15
6.2, 0.66
4.0-8.2, 10.6
4.5, 0.64
3.0-6.7, 14.2

46.3, 2.75
40.1-55.1, 5.9
28.0, 1.68
25.1-34.3, 6.0
24.9, 1.30
22.5-28.9, 5.2
14.4, 0.49
13.4-16.2, 3.4
7.0, 0.49
6.1-8.2, 7.0
10.0, 0.49
9.3-11.4, 5.0
6.9, 0.30
6.4-7.7, 4.4
4.7, 1.64
2.5-7.8, 30.9
3.1, 1.09
1.4-6.3, 35.2
5.7, 0.87
3.3-7.4, 15.3
4.3, 0.52
3.3-5.7, 12.2

Least Width of Nasals
Greatest Width of Nasals
Maxillary Extension
beyond Nasals (PMEXT)
Length of Upper Diastema
Length Maxillary Toothrow
Width of Upper Incisor
Length of Lower Diastema
Length Mandibular
Toothrow (LMNDTR)
Width of Lower Incisor

2.2, 0.32
1.3-3.0, 14.3
2.8, 0.34
2.1-3.6, 12.3
3.1, 0.74
1.5-4.4, 23.9
19.5, 1.50
16.2-22.7, 7.7
10.1, 0.51
9.1-11.6, 5.1
2.3, 0.23
1.9-3.0, 10.0
12.0, 1.33
7.2-14.9, 11.1
8.7, 0.43
7.6-9.7, 4.9
2.2, 0.22
1.7-2.9, 10.2

2.2, 0.39
1.4-3.2, 17.5
2.7, 0.38
1.9-3.4, 14.0
2.9, 0.65
1.4-4.6, 22.0
21.2, 1.01
18.9-23.0, 4.8
10.5, 0.60
9.3-11.7, 5.7
2.4, 0.15
2.2-2.7, 6.2
13.1, 1.00
11.7-16.1, 7.6
9.1, 0.42
7.9-10.0, 4.6
2.3, 0.13
2.1-2.6, 5.7

2.1, 0.26
1.5-2.8, 12.3
2.6, 0.28
2.0-3.3, 10.8
2.7, 0.65
1.2-4.2, 24.1
16.4, 1.25
10.2-20.1, 7.6
9.7, 0.70
5.2-11.6, 7.3
2.1, 0.14
1.8-2.6, 6.7
10.2, 0.81
8.5-13.2, 7.9
8.3, 0.47
6.1-9.3, 5.7
1.9, 0.12
1.7-2.3. 6.3

2.2, 0.86
1.6-7.2, 37.7
2.8, 0.84
2.2-7.6, 29.9
2.9, 0.62
1.2-4.6, 21.5
17.8, 1.45
15.3-23.2, 8.2
10.0, 0.46
9.3-11.6, 4.6
2.2, 0.16
1.8-2.6, 7.2
11.1, 1.02
9.2-14.5, 9.2
8.6, 0.39
7.8-9.6, 4.6
2.0, 0.18
1.6-2.6, 8.9



In this study phenetic similarities between samples of like sex and age
are assumed to reflect the degree of past or present gene flow between
populations in adjacent regions (sensu Pounds and Jackson 1981). An al-
ternative argument for high phenetic resemblances between populations
is that of highly similar selection regimes operating in populations not
experiencing gene flow (Ehrlich and Raven 1969). Cluster composition
in the following analyses addresses the relative importance of the various
boundaries (principally rivers) in inhibiting pocket gopher dispersal (Fig.
MALES, AGE 1.-In the dendrogram depicting similarities between
samples of young adult males, the four peninsular regions (area III) clus-
ter tightly with each other, yet distantly from all other area I and II
regions (Fig. 3). The only two area I regions (C and D) represented in
this comparison comprise a discrete cluster. Regions G and F (area II)
form two single-member branches.
MALES, AGE 2.-The separation of samples by area is less clear in
this comparison due to positioning of the area II regions F and H (Fig.
3). G bears little resemblance to any region, whereas F is included with
area III. The two regions from area I (C and D) form a distinct cluster.
Three of the four peninsular regions comprise another highly similar group;
the fourth peninsular region (L) occurs in the same major cluster as re-
gions J, K, and M.
FEMALES, AGE 1.-Two primary clusters are evident in the dendro-
gram generated for females of age class 1 (Fig. 3). One of these clusters
contains all four peninsular regions (J, K, L, and M). The remaining
regions, all west of the Suwannee River, are split into three groups. One
group contains only panhandle forms (B, C, and D) from west of the
Apalachicola River (area I). Of the three area II regions included in this
analysis, two (F and G) are closely united in one cluster. Region H, how-
ever, is distant from both area I and II clusters.
FEMALES, AGE 2.-The dendrogram for age class 2 females resembles
that for old age males (Fig. 3). Regions A, C, and D form a discrete
cluster containing regions from no other areas. A second major cluster
includes regions J, K, and M (all peninsular) plus region F (area II); these
same four regions formed a group in the age 2 male comparison. The
remaining two regions (E and L) in this analysis are similar to each other
but different from all other regions.
In each of the four cluster analyses, all area I regions were consistently
and exclusively grouped together. In the two age 1 dendrograms the four

VOL. 30 NO. 1


0 1 2 3 4

0 1 2 3 4

0 1 2 3 4 5

Figure 3.-Results of cluster analyses of the four sex/age categories of Recent Geomys
pinetis in Florida. Dendrograms were computed from distance matrices using Ward's
method. Letters identify natural regions; associated numbers indicate sample size. Hori-
zontal scales are a dissimilarity measure.

peninsular regions formed exclusive, highly similar clusters, while in the
age 2 dendrograms three peninsular regions grouped with an area II
region. In all four comparisons, area II regions were placed either alone,
or with another area II region, or with peninsular regions. These data
support the hypothesis that both the Apalachicola and Suwannee rivers
are barriers to gene flow in pocket gophers, with the Apalachicola being
the more effective of the two rivers.


The occurrence of statistically significant morphometric differences
(P<0.0002) among samples characterizing different natural regions was
demonstrated for each sex/age category (Table 2).
MALES, AGE 1.-For age 1 males, the first three canonical variates

5 6

1 2 3



Table 2-Results of multivariate analyses of variance for differences among regional samples
and among area samples of Recent Geomys pinetis from Florida. Included are
statistics for three tests for significant differences between samples plus Roy's
test for significance of the first canonical vector. Presented separately for each
sex/age category.

Males Females

Statistics Age 1 Age 2 Age 1 Age 2

Variation Among Regions

Hotelling-Lawley Trace
Pillai's Trace
Wilk's Criterion
Roy's Maximum Root

Hotelling-Lawley Trace
Pillai's Trace
Wilk's Criterion
Roy's Maximum Root





Variation Among Areas













VOL. 30 NO. 1


Age 1 Males

9 11

- 3

-2 7


Age 2 Males


Age 1 Females
TT -4
I' T

Age 2 Females

I -


Figure 4.-Canonical variates projections showing relationships among regional samples
separately for the four sex/age categories of Florida Geomys pinetis. Bars represent one
standard deviation to either side of sample means (indicated by position of letters). Sample
sizes indicated in text.

represent 30.31%, 25.87%, and 19.94% of the variation, respectively;
the other vectors each entail less than 8% of the total variation. GLS
(18.14%) and LMXTR (16.23%) contributed most to separation of samples
along variate I; the only other characters on variate I with more than 8%
influence were IOC and DROST. Over 70% of the dispersion along var-
iate II stemmed from five characters: WMAST, LUDIAST, IOC, LMXTR,
and DCRAN. GLS, WMAST, and LMNDTR were the most important
discriminators for variate III.
The plot of sample centroids and corresponding 1 standard deviation
bars on axes I vs II shows two sample clusters where regions C and D
(area I) form one group and regions from areas II and III collectively
form the other (Fig. 4). In this plot, regions C and D broadly overlap
each other but do not overlap other samples. Area II samples (F and G)
are intermediate between those of areas I and III and broadly overlap
various of the area III regions. Regional sample sizes are as follows: A, 1;
C, 4; D, 7; E, 1; F, 8; G, 4; I, 1; J, 104; K, 34; L, 6; and M, 17.
MALES, AGE 2.-Variates I, II, and III individually represent 33.24%,
25.69%, and 17.65% of the inter-sample variation, collectively explaining




76.58%. Less than 10% of the variation accompanies each of the remain-
ing axes. The five most influential variables for variate I (LMXTR, GLS,
IOC, LUDIAST, and DROST) individually explained greater than 9%
(and collectively the majority) of the observed variability. Three-quarters
of the dispersion along axis II was attributable to five characters: WROST,
GLS, DROST, WMAST, and DCRAN. Along variate III five characters
(LUDIAST, WMAST, GLS, ZYGO, and DCRAN) accounted for more
than 56% of the variation.
Two distinct sample clusters are evident in the scatter plot of regional
sample centroids along variates I and II (Fig. 4). Samples C and D (area
I) variously overlap, but are widely separated from the cluster composed
of area II and III samples. Overlap of confidence bars of region F (area
II) with those of J, K, L, and M (area III) is extensive. Regional sample
sizes are as follows: B, 1; C, 6; D, 5; E, 1; F, 8; G, 2; J, 95; K, 26; L, 6;
and M, 24.
FEMALES, AGE 1.-Over 78% of the variation between regional samples
corresponds to the first three canonical variates which individually entail
51.60%, 16.56%, and 10.26% of the variation, respectively. Eight other
roots each account for less than 8% of the variation. Along variate I,
about 60% of the dispersion occurred through five characters, each with
greater than 9% influence: IOC, DCRAN, LUDIAST, ZYGO, and
WMAST. Over 57% of the dispersion along variate II is shared between
ZYGO, LMNDTR, IOC, WMAST, and DCRAN. The five most impor-
tant characters along variate III were DROST, ZYGO, LMNDTR,
WUINC, and IOC; the first two of these together exert nearly 50% of
the discriminating ability of this vector. In the plot of regional sample
centroids on axes I and II (Fig. 4), area I samples (B, C, and D) group
closely together and are separate from area II and III samples. Regional
sample sizes are as follows: A, 1; B, 2; C, 15; D, 23; E, 1; F, 12; G, 5; H,
3; J, 161; K, 39; L, 9; and M, 27.
FEMALES, AGE 2.-Variates I, II, and III entail 49.99%, 16.86%, and
10.38% of the overall variation, respectively, and 77.23% collectively.
Less than 8% of the variation is explained by each of the remaining vec-
tors. The five most influential characters along variate I (LMNDTR, LU-
DIAST, DCRAN, GWNAS, and LMXTR) accounted for 49% of its dis-
persion. WMAST, GLS, IOC, LMNDTR, and DROST were the five
most important characters along variate II. Three attributes (LMXTR,
WMAST, and ZYGO) on variate III explained 61% of the variation. The
canonical variates plot on axes I and II shows area I regions A, C, and D
to form an overlapping cluster separate from the area II and III regions
(Fig. 4). Regional sample sizes are as follows: A, 3; B, 1; C, 5; D, 3; E, 5;
F, 7; G, 1; J, 93; K, 34; L, 5; and M, 27.

VOL. 30 NO. 1



The preceding MANOVAs and canonical variates plots suggest a pat-
tern of variation wherein phenetic breaks among regional samples cor-
respond to the three geographic areas defined by the Apalachicola and
Suwannee rivers. A final series of MANOVAs tested the null hypothesis
of no differences among joint means of samples representing areas I, II,
and III. For each of the four sex/age categories, the hypothesis of equal
means was rejected for all test statistics at P<0.0002 (Table 2). Hence,
Geomys pinetis from the three areas of Florida differ significantly in cra-
nial dimensions. Plots of centroid means 1 standard deviation (Fig. 5)
as developed from plots of individual specimens show the same pattern
of overlap as in Figure 4. In all cases area I is distinct from areas II and
III; areas II and III overlap variously with each other.

Age 1 Males



Age 1 Females

__ T


Age 2 Males

02 1
03 -


0 1 -
5 75 10

Age 2 Females


-3' r

Figure 5.-Canonical variates projections showing relationships among areas sepa-
rately for the four sex/age categories of Florida Geomys pinetis. Bars represent one stan-
dard deviation to either side of sample means (indicated by position of letters).


Pocket gophers in Florida occur in two major zoogeographic units: the
panhandle west of the Apalachicola River (area I), and the remainder of

I -"

0 75

-0 75



the state, which may be further subdivided. The areas east of the Apa-
lachicola River are separated by the Suwannee River into the eastern
panhandle (area II) and the peninsula (area III). MANOVA and canonical
variate analyses show slight to extensive overlap of samples from the
peninsula and eastern panhandle, but no overlap of these with the west-
ern panhandle samples. Hence, the Apalachicola River apparently com-
prises a more effective barrier to pocket gopher dispersal and gene flow
than the Suwannee River.
This study clearly indicates that interruption of gene flow to varying
degrees by rivers of different magnitudes is manifest in the pattern of
geographic variation in cranial characters of Geomys pinetis in Florida.
Study of southeastern United States fence lizards (Sceloporus undulatus)
demonstrating direct correlation between river size and amount of differ-
entiation of populations on opposite sides of such rivers is highly sup-
portive of results of this pocket gopher investigation (Pounds and Jackson
1981). The findings of both of these studies contradict Ehrlich and Ra-
ven's (1969) contention that populations lacking gene flow will remain
undifferentiated when similar selection regimes are acting on both pop-
ulations. It is hard to imagine that different selective forces operate on
G. pinetis populations in seemingly identical habitats separated by as
little as a few hundred meters on opposite banks of the Suwannee River
or by a few kilometers on opposite sides of the Apalachicola River. Rather,
phenetic divergence seems dependent on degree of gene flow across
these rivers.
Avise et al. (1979) studied genetic variation of the entire Geomys pi-
netis complex using mitochondrial DNA and electrophoretic techniques
and demonstrated a similar pattern of geographic variation correspond-
ing to these rivers. They acknowledged a significant role for the Apalach-
icola-Chattahoochee-Flint river system in separating eastern and west-
ern "forms" of Geomys pinetis. Further, geographic distribution of
electromorph frequencies of 6-phosphogluconate dehydrogenase (PGD)
hints that the Suwannee River might separate peninsular populations
from mainland populations (Avise et al. 1979:6697).
In the latest published revision of Geomys pinetis, Williams and Gen-
oways (1980) found no subspecific breaks in Florida Geomys pinetis nor
did they recognize any barriers to gene flow in Florida. They viewed the
complex as one species with two subspecies: G. p. piletis representing
the entire species range except for the isolated colony of G. p. fontanelus
(formerly G. fontanelus) near Savannah, Georgia. Evaluation of the im-
portance of the Suwannee River was precluded by their method of
grouping samples because their samples 14 and 20 each included speci-
mens from both sides of the Suwannee River (Williams and Genoways

VOL. 30 NO. 1



It is of some interest to consider why the Apalachicola appears to serve
(or have served) as a more important barrier to pocket gopher gene flow
than has the Suwannee. Three different features are evaluated in this
analysis of the effectiveness of these river valleys as barriers to animal
to flow between populations on opposite sides of a river, individuals need
not actually cross the waterway. An alternative is for genes to be ex-
changed with adjacent colonies thereby facilitating flow up one side of
the river, around the headwaters, and then down the opposite side of
the river. For this mechanism to function, pocket gopher populations
must be appropriately distributed. The entire Suwannee River water-
shed is contained within the range of Geomys pinetis. Therefore, popu-
lations on opposite sides of the Suwannee River are potentially in genetic
communication, albeit indirectly. However, this scheme of gene flow is
not presently possible for Apalachicola-Chattahoochee-Flint river basin
populations because these rivers originate in the Appalachian Mountains
far beyond the northernmost extent of the range of Geomys pinetis.
wannee rivers also differ importantly in their effective widths. Effective
width includes width of the watercourse and the distance between suit-
able habitats on opposite sides of the rivers. Actual width of the Suwan-
nee in most places can be measured in a few tens of meters. Suitable
sandhill and xeric hammock habitats extend to river's edge along much
of the Suwannee River (Davis 1980). In many places (e.g. in Suwannee-
Lafayette and Columbia-Hamilton counties) active pocket gopher colo-
nies occur on opposite sides of the Suwannee within a few hundred me-
ters of each other (pers. obs.).
The effective width of the Apalachicola River is much greater-on the
order of several kilometers. Actual width of this river approaches (and
near the mouth exceeds) 100 m. Unlike the Suwannee, the Apalachicola
has cut a deep valley occupied by habitats (e.g. swamp hardwood flood-
plain forests) excessively wet for Geomys. These forests are very broad
(several km) in Gulf and Franklin counties (along the Gulf coast) and in
southern parts of Calhoun and Liberty counties. Sandhill habitat suitable
for pocket gophers approaches the river to within as little as 2 or 3 km
only in northwestern Liberty and western Gadsden counties (pers. obs.)
STREAMFLOW PARAMETERS.--Various streamflow measurements also
demonstrate the larger size of the Apalachicola River (Heath and Wim-
berly 1971:466, 531). Average discharge of the Suwannee at Branford
(Suwannee Co.) is 192 cubic meters per second (cms) in contrast to 709


cms for the Apalachicola at Blountstown (Calhoun Co.). Recorded maxi-
mum and minimum discharges (and associated water gage heights) for
the Suwannee are 2374 cms (10.38 m) and 43 cms (0.60 m); those values
for the Apalachicola are 2773 cms (6.77 m) and 152 cms (0.73 m).
Because both rivers are subject to vast fluctuations in water height
and discharge, the possibility exists that pocket gophers could swim or
conceivably even walk across the waterway during drought periods. Bar-
rington (1940) experimentally showed G. pinetis capable of swimming in
quiet water a distance of 23 m in 8 min. For this to be effective, however,
pocket gophers must be in residence in the immediate vicinity. Because
of the greater proximity of colonies and suitable habitat to the Suwannee
than to the Apalachicola, this mode of interchange appears feasible only
for the Suwannee. For the same reason, rivercourse changes and oxbow-
ing could enhance cross-channel gene flow only for the Suwannee River
BIOGEOGRAPHIC CONSIDERATIONS.-The pattern of geographic var-
iation in modern Florida pocket gophers can be examined with respect
to two opposing biogeographic hypotheses. A vicariant explanation in-
volves a widespread population that is later dissected by the Apalachicola
and Suwannee rivers. Conversely, the dispersalist view has pocket go-
phers invading a Florida theater already having these rivers and asso-
ciated riparian corridors well-entrenched. Both the Apalachicola and, as
noted above, Suwannee rivers have geological histories antedating the
earliest documented (early Irvingtonian) and the earliest conceivable
(Blancan) arrival of Geomys in Florida (White 1970). The means and tim-
ing of movements of Geomys from the western to eastern sides of the
Apalachicola remain an enigma, although meandering and oxbowing when
sandy soils of delta regions were exposed during lowered sealevels seem
to be plausible mechanisms.
Whereas the Apalachicola has probably always been a continuously
flowing surficial stream (because its bed is of rock types generally imper-
vious to water flow), the Suwannee River has a highly intermittent his-
tory because it (and most other peninsular Florida streams) flows through
a region of karst limestone. During moister interglacial periods, piezo-
metric surfaces were high and peninsular rivers flowed at the ground
surface. Crossing the Suwannee at such times would involve swimming
of shallow waters during seasonal dry periods or even travel across dry
river beds during extreme droughts. During the drier glacial intervals,
however, water table levels dropped substantially, and surficial river beds
were abandoned in favor of subterranean flow through karst limestone.
A surficial Suwannee River was, at least along portions of its course, non-
existent during certain glacial intervals, and movement across deserted
river corridors was surely unimpeded. It is apparent, then, that the dis-

VOL. 30 NO. 1


persalist hypothesis applies to the Apalachicola River and that dispersal-
ist and vicariance hypotheses alternatively apply to the Suwannee River.


APALACHICOLA RIVER. -The effect of the Apalachicola River as a zo-
ogeographic barrier has been widely recognized in many animal groups
in addition to Sceloporus undulatus fence lizards as noted above (Pounds
and Jackson 1981). Two genera (Mycotrupes and Gronocarus) of beetles
(Scarabaeidae: Geotrupinae) occur on opposite sides of the Apalachicola
River system (Hubbell 1954, Howden 1963). Neill (1957) noted that the
Apalachicola and other rivers of the panhandle mark the eastern distri-
butional limits of many western fishes and the western limits of eastern
The mutually exclusive distributions of two species of pocket gopher
lice (Mallophaga: Trichodectidae) bear directly on Geomys pinetis zo-
ogeography (Price 1975). Geomydoecus mobilensis has been found only
on southeastern pocket gophers collected from west of the Apalachicola
River. A closely related species (Geomydoecus scleritus) fills this ectopar-
asitic niche in Geomys populations east of Apalachicola River. The exis-
tence of this variation pattern in species so closely connected to pocket
gophers supports the interpretation that the Apalachicola River has influ-
enced gene flow between Florida Geomys populations.
Not all mammalian species, however, are significantly restricted by
the Apalachicola River. Hall (1981:505) figured this river as the division
between a western subspecies and two eastern subspecies of Geomys
pinetis. Survey of range maps in Hall (1981) of all mammal species occur-
ring in Florida reveals Neotomafloridana to be the only other mammal
with subspecies boundaries coinciding with the Apalachicola River. The
entire range of Neofiber alleni lies east of Apalachicola River. Of the ap-
proximately 70 species of native land mammals in Florida (Stevenson
1976), the distributions of about 48 species span the Apalachicola River.
Hence, this river seems to pose a barrier of some recognizable magni-
tude to only about 6% of the more widely distributed Florida mammal
species. Similarly, Christman (1980) found that geographic variation pat-
terns in none of 15 species of Florida snakes corresponded with the Apa-
lachicola River.
SUWANNEE RIVER.-The Suwannee Straits, the former salt water
channels between the United States mainland and peninsular Florida
that existed to various extents during the Neogene interglacials, occu-
pied that area now drained by the Suwannee and St. Marys rivers and
their tributaries (Neill 1957:188). During these interglacials, the Suwan-
nee Straits apparently barred movement of many species between the


mainland and the "peninsula." The effectiveness of these straits as a bar-
rier is evidenced by the lengthy list of subspecies and species of verte-
brates and invertebrates presently restricted to peninsular Florida (Neill
1957:189-194). The ranges of several mainland species of mollusks do
not extend south or east of the Suwannee River (Dall 1890-1903, Clench
and Turner 1956). Additionally cyprinid, sucker, and darter fishes, groups
which occur abundantly in the southeastern United States, are very poorly
represented in the Florida peninsula (Neill 1957:193). One of the most
important patterns of geographic variation observed in 15 species of Florida
snakes, the Suwannee Straits pattern, demonstrates the zoogeographic
effect of the Suwannee River (Christman 1980). Review of species and
subspecies boundaries of the approximately 48 species of Florida mam-
mals with distributions spanning the Suwannee River reveals five species
(Sciurus niger, Oryzomys palustris, Neofiber alleni, Mustela vison, and
Spilogale putorius), or about 10%, that have subspecies limits approxi-
mating the Suwannee River. No Florida mammals have species bounda-
ries coinciding with this river.
A further probable reason that the phenetic break in Geomys corre-
sponding to the Suwannee River is of lesser significance pertains to the
antiquity and persistence of the Suwannee Straits as compared to the
Apalachicola as a barrier to Geomys gene flow in the Florida peninsula.
The Suwannee Straits existed intermittently during the Miocene and Pli-
ocene, an interval spanning from about 25 mybp to 5 mybp. The Straits'
last occurrence corresponds to the 30 m to 52 m marine shorelines: Sun-
derland shoreline (Cooke 1945) and Okefenokee shoreline (MacNeil 1950).
Alt and Brooks (1965) and most subsequent researchers recognize Mio-
cene and Pliocene ages for these and earlier (higher) shorelines. Later
transgressions produced lower shorelines (Wicomico, 21 m to 30 m; Pen-
holoway, 13 m to 21 m; Talbot, 8 m to 13 m; and Pamlico, 3 m to 8 m;
see Healy 1975), none of which were of sufficient elevation to isolate the
peninsula from the mainland. These lower shorelines are of Pliocene and
Pleistocene age (Alt and Brooks 1965).
The first appearance of the genus Geomys in the fossil record was in
the mid-Pliocene at the beginning of the Blancan Land Mammal Age,
some 3.5 mybp (Lindsay et al. 1975). The earliest known occurrence of
geomyids in Florida is from the early Irvingtonian Inglis IA deposit (Cit-
rus Co.), an early Pleistocene site about 1.8 million years old (Wilkins
1984). The actual time of arrival of geomyids in Florida is as yet uncer-
tain, but could have been during the Blancan. The Pleistocene is gener-
ally regarded as beginning about 2 million years ago. Therefore, the his-
toric importance of the Suwannee Straits seemingly has no bearing on
pocket gopher distribution because geomyids could not have entered
Florida until after the mid-Pliocene. Hence, the Suwannee River valley

VOL. 30 NO. 1


as a terrestrial feature has played a role in occluding gene flow in pocket
gophers in Florida only during the Quaternary.
This study underscores the role that river valleys can serve as disper-
sal barriers to various taxa. It may be noted, however, that under other
circumstances pocket gophers may not find river systems to be barriers.
An example includes Geomys arenarius in the Rio Grande valley (Wil-
liams and Genoways 1978). In such semiarid to arid settings the only
friable soils and suitable vegetation occur within the riparian corridor.
Smith and Patton (1980) demonstrated that gene flow in Thomomys bot-
tae occurs across the lower Colorado River between the Palo Verde and
Cibola valleys and between the Imperial and Yuma valleys, but that bar-
riers to north-south gene flow along both river banks exist. Pocket go-
phers presumably crossed these rivers on occasions when water flow had
diminished or ceased altogether, thus maintaining gene flow along both
sides of the river.

Alt, D., and H.K. Brooks. 1965. Age of Florida marine terraces. J. Geol. 73:406-411.
Avise, J.C., C. Giblin-Davidson, J. Laerm, J.C. Patton, and R.A. Lansman. 1979. Mito-
chondrial DNA clones and matriarchal phylogeny within and among geographic pop-
ulations of the pocket gopher, Geomys pinetis. Proc. Natl. Acad. Sci. 76:6694-6698.
Barrington, B.A. 1940. The natural history of pocket gophers. M.S. thesis, Univ. Florida,
Gainesville, 49 p.
Bloom, A.L., W.S. Broecker, J.M.A. Chappell, R.K. Matthews, and K.J. Mesolella. 1974.
Quaternary sea level fluctuations on a tectonic coast: 230Th/23U dates from the Huon
Peninsula, New Guinea. Quaternary Res. 4:185-205.
Christman, S.P. 1980. Patterns of geographic variation in Florida snakes. Bull. Florida
State Mus., Biol. Sci. 25(3):157-256.
Clench, W.J., and R.D. Turner. 1956. Freshwater mollusks of Alabama, Georgia, and
Florida from the Escambia to the Suwannee River. Bull. Florida State Mus., Biol. Sci.
Cooke, C.W. 1945. Geology of Florida. Bull. Florida Geol. Survey 29:1-339.
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VOL. 30 NO. 1


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Specimens Examined

The 1123 specimens of Geomy pinetis examined in this study are listed below by re-
gion. The number of specimens and the museum in which they are deposited for each
locality are enclosed in parentheses. Collection acronyms are as follows: American Mu-
seum of Natural History (AMNH); Carnegie Museum of Natural History (CMNH); Dela-
ware Museum of Natural History (DMNH); Field Museum of Natural History (FMNH);
University of Florida, Florida State Museum (UF); University of South Florida (USF);
Florida State University (FSU); University of Georgia (UGA); Harvard University, Mu-
seum of Comparative Zoology (MCZ); University of Illinois, Museum of Natural History
(UIMNH); University of Kansas, Museum of Natural History (KU); Michigan State Uni-
versity, The Museum (MSU); University of Michigan, Museum of Zoology (UMMZ); Al-
bert Schwartz private collection (AS); Shippensburg State College, Vertebrate Museum
(SSC); Tall Timbers Research Station (TTRS); Texas Tech University, The Museum (TTU);
and United States National Museum of Natural History (USNM).
REGION A (10 specimens).-Escambia Co.: Century (1, AMNH); Gonzales (3, AMNH);
7 mi N, 2 mi W Gonzales (1, AMNH); Pensacola (1, UF; 1, MCZ; 3, USNM).
REGION B (12 specimens).-Santa Rosa Co.: Milton (12, USNM).
REGION C (44 specimens).-Holmes Co.: Ponce de Leon (1, AMNH; 1, USNM); West-
ville (1, USNM). Okaloosa Co.: Crestview (7, AMNH; 4, USNM); 4.5 mi N, 1 mi W Fort
Walton (1, AMNH); 5 mi N, 0.5 mi E Fort Walton (1, AMNH); Shalimar (2, AMNH); 0.5
mi W Co. line, Hwy 90 (2, TTU). Walton Co.: Argyle (1, AMNH; 1, USNM); 3 mi E
Bruce (3, USNM); 1 mi W Bruce (1, USNM); 20 mi E Crestview (2, USNM); 6.5 mi SE
DeFuniak Springs (2, USNM); 5 mi NW DeFuniak Springs (2, UF); 10.6 mi W DeFuniak
Springs (1, AS; 3, USNM); 1.2 mi N Freeport, Rt. 331 (2, UGA); 1.3 mi N Freeport, Rt.
331 (1, UGA); Rockhill (5, USNM).
REGION D (55 specimens).-Bay Co.: Highland Park (1, USNM); 5 mi E Inlet Beach
(1, USNM); 5 mi E Saunders (1, USNM); Saunders (Park) (3, USNM); Southport (1, AMNH);
5 mi S Youngstown (1, USNM); 1.4 mi S Rt. 79 on Rt. 98 (1, UGA); 1.6 mi N Rt. 98 on


Rt. 79 (1, UGA). Calhoun Co.: Blountstown (4, AMNH; 1, USMN); 1 mi W Blountstown
(1, UF); 1.4 mi W Blountstown (1, UF); 3.5 mi W Blountstown (1, UF). Jackson Co.: 0.7
mi S Butler (1, UF); Cypress (1, USNM); Marianna (1, UF; 3, USNM); Sneads (2, USNM);
4 mi N Snead (2, UF); 7 mi N Snead (1, UF). Walton Co.: Grayton Beach (1, USNM); 1.2
mi E Point Washington (2, USNM); 2.5 mi E Point Washington (1, USNM); 4 mi E Point
Washington, Rt. 98 (1, USNM); Seagrove Beach, Rt. 395 (1, UF; 3, USNM); Rt. 30A near
Seagrove Beach (1, UF); Rt. 30A between (Hwy.) 98 and Seagrove Beach (3, UF); 6.2 mi
E Rt. 395 on US 98 (1, UGA); 6.6 mi E Rt. 395 on US 98 (1, UGA); 8.3 mi E Rt. 395 on
US 98 (2, UGA). Washington Co.: Chipley (1, UF); 2 mi E Chipley (1, USNM); Crystal
Lake (1, AMNH); Redbay (1, AMNH); Vernon (2, AMNH); 2 mi N Vernon (1, USNM); 4
mi N Vernon (1, USNM); 10 mi SW Vernon, Miller's Ferry (1, USNM).
REGION E (11 specimens).-Franklin Co.: St. James Island (1, UF). Gadsen Co.: Chat-
tahoochee (2, USNM); E of Concord, 1 mi W Ochlockonee River along Hwy. 12 (2, TTRS;
2, USNM); 5 mi W, 2 mi N Havana (=0.2 mi W Ochlockonee River on Hwy. 12) (2, UGA).
Liberty Co.: Hosford (1, UF); Rock Bluff (1, TTRS).
REGION F (51 specimens).-Jefferson Co.: 3 mi S Lloyd (1, UF); Monticello (1, USNM);
2.8 mi W Monticello (1, UF); Waukeenah (1, UF); 2 mi N Waukeena (1, UF). Leon Co.:
Tallahassee, West Campus (1, FSU); FSU Dairy Farm Pasture (Tallahassee) (7, FSU); 3
mi E Tallahassee (1, UF); 1/4 mi N Hwy. 371, 1 mi W on 371A (1, FSU); 2 1/2 mi N
Tallahassee (2, FSU); 10 mi S Tallahassee, on Adams St. (1, FSU); 10.2 mi S, 4.3 mi E
Tallahassee (1, FSU); 7.4 mi SW Tallahassee (1, AS); 7.8 mi SW Tallahassee (2, AS); 5 mi
WSW Tallahassee (1, FSU); 1.5 mi N Wakulla, Rt. 363 (1, UGA); 5 mi W Wakulla (1, UF);
1 mi N Wakulla Co. line, Hwy. 61 (1, UF); 6 mi E Wakulla Springs Hwy. 61 (1, FSU);
Woodville (4, UF); 4 mi E Woodville (1, AMNH); 2.5 mi E Woodville on Natural Bridge
Rd. (4, UF). Wakulla Co.: Crawfordsville (1, UF); Panacea (1, UIMNH); 1.7 mi N Wakulla
(=0.9 mi S Co. line) (1, UGA); 1 mi S Wakulla Gate (2, FSU); near Wakulla Springs (1,
FSU); 0.5 mi S Wakulla Springs (4, FSU); 2 mi S Leon Co. line, Rt. 61 (1, FSU); 3.5 mi
S Leon Co. line (2, FSU); US 319 and SR 61 (1, FSU); Unknown (1, FSU).
REGION G (24 specimens).-Dixie Co.: Jena (2, UF); Old Town (4, UF; 3, USNM).
Lafayette Co.: 4 mi E Alton (1, UF); 3 mi W Branford (1, UF); 1 mi W Suwannee River,
SH 27, near Branford (1, UF); 0.5 mi S jet. Hwys. 250 and 251, near Day (1, UF). Madison
Co.: Lee (2, USNM); Madison (2, USMN); 2 mi W Madison (2, AS). Taylor Co.: 3 mi E
Perry (1, UF); 4 mi NNW Perry (2, AMNH); 5 mi SSE Perry (1, UF); 3.5 mi SW Perry
(1, AMNH).
REGION H (3 specimens).-Hamilton Co.: 1 mi E Blue Spring (2, UF); 3 mi E Blue
Spring (1, UF).
REGION I (1 specimen).-Hamilton Co.: White Springs (1, UF).
REGION J (588 specimens).-Alachua Co.: Archer (6, UF); 4.7 mi E Archer (1, UF);
Gainesville (12, AMNH: 201, UF; 1, MCZ; 1, UMMZ; 4, USNM); 5 mi SW Gainesville
(2, UF); 8 mi SW Gainesville (2, UF); Kanapaha (2, UF); 6 mi E LaCrosse (1, UF); 3 mi
E Newberry (1, UF); 1 mi W Newnan's Lake (3, UF); Payne's Prairie (1, UF); San Felasco
(1, USNM); Unknown (9, UF). Baker Co.: Glen St. Mary (1, USNM). Bradford Co.: 0.1
mi S Keystone Heights SR 21 (1, UGA); 2.1 mi S Keystone Heights, SR 21 (2, UGA); 2.2
mi S Keystone Heights, SR 21 (1, UGA); 1.9 mi N Co. line, SR 21 (1, UGA); 3.2 mi N
Co. line, SR 21 (1, UGA). Clay Co.: 6 mi NE Camp Blanding (1, UF); Green Cove Springs
(2, UF); 0.7 mi N Keystone Heights (1, UF); 5.8 mi N Keystone Heights, SR 21 (1, UGA);
2.2 mi NE Keystone Heights (1, UF); 1 mi NW Keystone Heights (1, UF); 2 mi NW
Keystone Heights (1, UF); 2.5 mi NW Keystone Heights (1, UF); 1 mi W Keystone Heights
(1, UF); Kingsley Lake (6, UF); 3 mi SW Middleburg (1, UF). Columbia Co.: Ellisville
(1, UF); 0.9 mi E Fort White (1, UGA); 1.0 mi E Fort White, SR 18 (1, UGA); 1.1 mi E
Fort White, SR 18 (1, UGA); 4 mi NW Fort White (1, UF); 14 mi N Lake City (1, UF);

VOL. 30 NO. 1


16 mi N Lake City, US 441 (15, UGA); 5 mi S Lake City (1, UF); 4.7 mi N Santa Fe River
US 41 (1, UF); 1 mi N Co. line, US 27 (1, UGA); 2.3 mi N Co. line, US 27 (1, UGA); 3.5
mi N Co. line, US 41 (1, UGA). Duval Co.: Jacksonville (3, FMNH); Jacksonville, N along
US Rt. 17 (6, USNM); New Berlin (27, MCZ); Oceanway, US 17 (8, USNM); 0.6 mi N
firetower, US Rt. 17 (Tisonia) (1, USNM); 13 mi S, 2 mi W Yulee, 1-95 (3, UGA). Gilchrist
Co.: 1 mi S Bell (1, UF); Trenton (1, UF). Lake Co.: Leesburg (27, UF); Mascotte (2, UF);
Mt Dora (1, UMMZ); 1 mi W Okahumpka (1, UGA); Tavares (10, UF); 3.1 mi S Tavares
(2, AS); 2 mi W Tavares (6, UF); 2 mi NW Lake Yale (Umatilla) (4, UF). Levy Co.: Bronson
(2, UF); 2.2 mi NE Bronson (1, UF); 9 mi S Chiefland (2, UF); Lebanon Station (1, UF);
18 mi SW Otter Creek, Rt. 24 (1, UF); Sumner (9, UF); 2 mi NE Williston (1, UF); Wylly
(2, UF); 6 mi SW Wylly (1, UF). Marion Co.: Camp Roosevelt, Ocala National Forest (3,
UF); 1.5 mi E Dunnellon (2, UF); 1.6 mi E Dunnellon (1, UF); 4.4 mi E Dunnellon (1,
UF); 4.5 mi E Dunnellon (1, UF); 4.6 mi E Dunnellon (2, UF); 4.9 mi E Dunnellon (2,
UF); 5 mi E Dunnellon (1, UF); 5.3 mi E Dunnellon (2, UF); 5.7 mi E Dunnellon (1,
UF); 9.3 mi E Dunnellon (3, UF); Lake Bryant Ranger Sta., Ocala Natonal Forest (18,
USNM); 1.3 mi W Lynne (3, AS); 3 mi W Orange Springs, Hwy. 318 (3, UF); 7 mi W Salt
Springs (1, UF); 7 mi E Silver Springs (1, UF); E of Withlacoochee River (3, UF). Nassau
Co.: Chester (1, USNM); Crandall (11, USNM); 6 mi NW Hilliard (1, UF); Raser's Bluff
(7, AMNH); Reed's Bluff (1, AMNH); Rose Bluff, St. Mary's River (2, MCZ); 1.6 mi S St.
Mary's River, US 1 (2, UF); Yulee (1, UF); 1.0 mi E Yulee, Rt. 200A (1, USNM); 1.8 mi
E Yulee, Rt. A1A (1, USNM); 1.2 mi E Yulee, Rt. 200A (1, USNM); 2 mi E Yulee (2,
UGA); 2.4 mi E Yulee, Rt. 200A (1, USNM); 2.5 mi E Yulee, Rt. 200A (1, USNM); 3 mi
E Yulee (1, UGA); 3.6 mi E Yulee (1, UGA); Yulee, 1.35 mi NE A1A, C220A (2, UGA);
Yulee, 1.4 mi NE A1A, C220A (1, UGA); 2 mi S Yulee (4, AS). Orange Co.: 1 mi N Fort
Christmas (1, UF); Lockhart (1, UF); 1.5 mi NE Lockhart (1, UF); 1.5 mi SE Lockhart (1,
UF); Orlando (2, MCZ; 1, USNM); Tangerine (2, UF); Winter Park (1, UF); Zellwood,
Bay Ridge Blvd. (2, MSU). Osceola Co.: 5 mi N Kenansville (2, AMNH); 7 mi N Kenans-
ville (2, AMNH; 2, UF); 9 mi N Kenansville (2, UF); 11 mi N Kenansville (2, UF); Nittaw
(1, UF); St. Cloud (2, UF). Putnam Co.: 5 mi NE Hawthorne (1, UF); W side Levy Prairie
(1, UF); 2.5 mi S Melrose (1, UF); Palatka (2, UF; 1, MCZ); 5 mi W Palatka (1, UF).
Seminole Co.: Fern Park (1, UF); Forest City (1, UF); Geneva (2, USNM). Sumter Co.:
Wildwood (14, AMNH; 1, UMMZ); 9 mi S Wildwood (1, UGA); SR 470, 3.5 mi W US
301 (1, UGA); SR 470, 4 mi W US 301 (1,UGA); SR 470, between SR 33 and US 301 (2,
UGA). Suwannee Co.: 0.4 mi E Suwannee River, SH 27 (near Branford) (1, UF); 0.8 mi
E Suwannee River, SH 27 (near Branford) (2, UF); Falmouth (5.7 mi E Suwannee RR
Sta., Rt. US 90) (1, UF); Live Oak (1, UF); 12 mi W Live Oak, US 90 (1, UGA); 2.5 mi W
co. line, US 90 (1, UGA); 24 mi W co. line, US 90 (2, UGA); 25 mi W co. line, US 90 (4,
UGA). Union Co.: E Lake Butler (3, UF); 3 mi E Lake Butler (1, UF); 0.9 mi N co. line,
SR 100 (2, UGA).
REGION K (165 specimens).-Citrus Co.: Citronelle (2, MCZ); 3.4 mi E Dunnellon (2,
UF); 5 mi E Dunnellon (1, UF); 1.4 mi SE Dunnellon (1, UF); 1.7 mi SE Dunnellon (1,
UF); 2 mi SE Dunnellon (1, UF); 2.2 mi SE Dunnellon (1, UF); 2.3 mi SE Dunnellon (1,
UF); 2.6 mi SE Dunnellon (2, UF); 4.2 mi SE Dunnellon (2, UF); 5.2 mi SE Dunnellon
(1, UF); 5.3 mi SE Dunnellon (1, UF); 9 mi SW Dunnellon (1, UF); 6 mi W Dunnellon,
SR 488 (2, UGA); 7 mi W Dunnellon, SR 488 (1, UGA); Inverness (1, USNM); 7 mi S
Inverness (1, UF); Trenton (1, UF); S of Withlacoochee River (1, UF). DeSoto Co.: 4 mi
NW Arcadia (1, AS); 8 mi NW Arcadia (1, AS). Hardee Co.: Wauchula (2, AMNH; 1, UF).
Hernando Co.: Bayport (1, UF); Coogler's Camp (1, UF); Weekiwachee Springs (2, AMNH);
1.4 mi W US 19 and Fla. 50 (1, UF). Hillsborough Co.: Dug Creek (1, UF); Plant City (3,
UF); Tampa, Univ. of South Florida Campus (5, UF; 26, USF); 19.5 mi N Tampa, SR 587
(5, UGA); Wimauma (4, AMNH). Manatee Co.: Sullivan's Bridge (1, UF); Jct. Hwys. 64


and 675, N side Manatee River (1, UF); Unknown (1, UF). Pasco Co.: New Port Richey
(5, AMNH); 5 mi E New Port Richey (9, USNM); SW corner of co. (3, UF). Pinellas Co.:
Bellaire (5, UF; 2, MCZ); Clearwater (8, UF); 9 mi N Clearwater, Wall Springs (1, UF); 1
mi N Davis Causeway (3, UF); Dunedin (2, UF; 1 UMMZ); Safety Harbor (2, UF); St.
Petersburg (4, MCZ; 1, USMN); Tarpon Springs (4, AMNH; 1, UMMZ; 12, USNM);
Tarpon Springs Golf Course (2, AS); 1/2 mi N, 1 mi E Tarpon Springs (1, AMNH); 2 mi
N, 1 mi E Tarpon Springs (1, AMNH); Unknown (1, UF). Polk Co.: Auburndale (1, UF;
7, USNM); 3.2 mi N Bartow (2, UGA); 1 mi NE Davenport (8, AMNH); 1.5 mi NE
Davenport (12, AMNH); Along Hwy. 27, 0.6 mi N jet. Rd. 547, near Davenport (1, UF);
Along Hwy. 27, 0.6 mi S jet. Rd. 547, near Davenport (1, UF); Along Rd. 547, 0.3 mi E
jet Hwy 27, near Davenport (1, UF); Along Rd. 547, 0.6 mi Wjct. Hwy. 27 near Daven-
port (1, UF); Fort Meade (1, AMNH); Frostproof (3, UF); Lake Juliana (1, USNM); 2 mi
S Lake Wales, US 27 (1, UGA); 1 mi S Polk City (1, UF); 5 mi S Winter Haven (1, UF).
REGION L (37 specimens).-DeSoto Co.: Arcadia (3, USNM); N of Arcadia (1, UF);
Fort Ogden (1, UF). Hardee Co.: S Zolfo Springs (1, UF); 5.4 mi W co. line, Hwy. 66, E
of Zolfo Springs (3, UF); 5.5 mi W co. line (5, UGA). Highlands Co.: DeSoto City (13,
AMNH); 7 mi N Lake Placid (1/4 mi N Josephine Creek) (2, UF); Sebring (5, CMNH); 1
mi N Sebring (1, SSC); SE corner (T34S, R29E, Sec 20) (2, SSC).
REGION M (122 specimens).-Brevard Co.: Eau Gallie (5, AMNH; 1, DMNH; 4, UF;
1, KU; 12, MCZ; 2, AS). Duval Co.: 4 mi W Atlantic Beach (1, UF); 1 mi NW Bayard,
Hwy. 1 (3, TTU); 2 mi W Bayard (1, UF); 6 mi SE Jacksonville (1, UF); Mandarin (1, UF);
1/2 mi N St. Johns-Duval Co. line (= 1 mi E Mandarin) (1, UF). Flagler Co.: 0.3 mi S St.
Johns Co. line, US 1 (1, UF); 0.5 mi S St. Johns Co. line, US 1 (1, UF). Putnam Co.: S of
Crescent City, US 17 (2, UGA); 13 mi S Palatka, US 17 (2, UGA); Pomona (Park?) (4,
USNM); San Mateo (8, UF); 2 mi E San Mateo (1, USNM); 5 mi NE San Mateo (5,
USNM); Satsuma (6, UF); 8 mi S Satsuma (1, UGA); Silver Lake (2, AS; 2, UMMZ);
Welaka (7, UF); Welaka, Univ. Conservation Reserve (2, UF). St. Johns Co.: 13 mi N
Bunnell (2, AMNH); 14 mi N Bunnell (1, AMNH); Carterville (21, MCZ); St. Augustine
(3, UF); 4 mi S St. Augustine (1, UF); 6 mi S St. Augustine (1, UF); Switzerland (1, UF);
1 mi N Flagler Co. line (1, UF); 1.75 mi N Flagler Co. line (1, UF). Volusia Co.: Barber-
ville (1, AMNH; 1, UF); DeLand (1, UF); DeLeon Springs (3, AMNH); Enterprise (1,
AMNH); New Smryna (1, DMNH); Pierson city limits, US 17 (4, UGA); S of Seville, US
17 (1, UGA).

VOL. 30 NO. 1

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ceptance of the manuscript.
All illustrations are referred to as figures. They must comply with the following
standards: Photographs should be sharp, with good contrast, and printed on glossy paper. If the
background of photographs (especially those of specimens) is not desired, amberlith should be cut
out and used to cover the background. Drawings should be made with dense black waterproof ink
on quality paper or illustration board. All illustrations should have a cover sheet. All lettering will
be medium weight, sans-serif type (e.g. Futura Medium, News Gothic) in cutout, dry transfer, or let-
tering guide letters. Make allowance so that after reduction no lower case letter will be less than 1
mm high (2 mm is preferred) nor any capital letter greater than 5 mm high. The maximum size for
illustrations is 9" x 14" (twice BULLETIN typepage size); illustrations should not be less than type-
page width (41/2"). With soft lead pencil on the back of each illustration, designate the top and iden-
tify each by author's name, manuscript title, and figure number.
All manuscripts not submitted in BULLETIN format will be returned to the
author for retyping.

Manuscripts and all editorial matters should be addressed to:

Managing Editor of the BULLETIN
Florida State Museum
University of Florida
Gainesville FL 32611

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