FLORIDA STATE MUSEUM
COLOR PATTERN VARIATION AMONG SNAILS
GENUS LIGUUS ON THE FLORIDA KEYS
Frank N. Young
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Published 21 October 1960
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COLOR PATTERN VARIATION AMONG SNAILS OF THE
GENUS LIGUUS ON THE FLORIDA KEYS
FRANK N. YOUNG 1
SYNOPSIS: The basic color patterns of Florida tree snails of the genus Liguus
(Mollusca: Gastropoda, Bulimulidae) show little correlation with environmental
conditions. The occurrence of distinctive variants in "pure colonies" suggests that
the basic pattern and pigments are directly controlled by a relatively few genes.
The segregation of various elements of the basic patterns among the colonies of
the Lower Florida Keys and mainland can be used as the basis for an hypothesis
concerning the genetic control of axial coloration, banding, pigmentation, and
other characters. A new form from Little Torch Key, Liguus fasciatus vonpaul-
seni new subspecies, combining many of the color pattern elements previously
known from the Florida Keys is described and figured. This form is presumably
close to the ancestral form that migrated to Florida from Cuba. A key to the
described forms of Liguus from the Florida Keys illustrates the known combina-
tions of color pattern elements.
Clench's description of Liguus fasciatus osmenti (1942) suggests
the possibility that the color forms of Liguus occurring on the Lower
Florida Keys represent segregates derived from some ancestral form
with a complex color pattern. This supposed ancestor may have come
to Florida from Cuba directly or have been produced by the combina-
tion of a number of forms coming to the islands separately and inter-
breeding. In the early days of settlement, the large colonies on the
Lower Keys apparently contained a number of different color forms.
Key West, for example, supported three or more, including L. f.
solidus, solidulus, and pictus. Big Pine Key supported several mixed
colonies which, in addition to the forms known from Key West, in-
cluded L. f. crassus, graphics, and possibly others now lost. Other
colonies on the Lower Keys were also mixed, and the rarity of cer-
tain color patterns suggests that they appeared only as chance homo-
zygotes in large panmictic populations.
Since these tree snails can live only in the tropical jungle hammock
vegetational association, they were always segregated into separate
1 Frank Young completed his doctoral work at the University of Florida in
1942. His principal contributions have been on aquatic beetles, but he has main-
tained a steady interest in the distribution, genetics, and evolution of the tree
snails of Florida. The present paper is based on detailed studies of material in
the Charles Torrey Simpson collection at the University of Miami, the material
in the University of Michigan Museum of Zoology, and.specimens and notes from
the active group of collectors in southern Florida. It represents contribution
No. 683 from the Zoological Laboratories of Indiana University, Bloomington,
Indiana. Manuscript submitted 4 May 1960.
BULLETIN FLORIDA STATE MUSEUM
colonies. The great destruction of the hammocks in recent years by
burning and clearing has increased the isolation of tle colonies, and
today, most of the known colonies on the Pine Islands of the Lower
Keys are each composed of a single variant. Such colonies may be
essentially pure clones produced from single snails which possibly
reproduced parthenogenetically.2 The resulting genetic screening
against lethal and detrimental genes together with the intense se-
lective action of the environment may account for the success of
the Lower Key colonies under apparently hopeless conditions of
drought, burning, and human intervention.
If the colonies of Liguus composed of single variants on the Keys
and the Florida mainland represent the segregates of the characters
of an original stock plus accumulated mutations in pure form, we may
make certain assumptions about the genetics of the color pattern of
these snails. The following seem to be unit characters: (1) colored
apex and columella, (2) peripheral banding, (3) sutural banding, (4)
yellow pigments, (5) dark pigments, (6) brown or brownish-red periph-
eral or sutural lines or both, (7) periostracal green lines on periphery
of whorls. Each of these characters may be due to the action of only
a single gene or the result of combined action of several genes, but
the way in which they segregate in different colonies suggests that
single genes or very small groups of genes are involved. Each of
these positive characters is matched by a negative character. The
latter may be assumed to be recessive, but there are certainly ex-
ceptions. Many other elements of the color pattern must also be
genetically controlled, but cannot be distinguished from environmental
effects under field conditions.
On the Lower Keys pure colonies showing the combinations 1-2-
0-4-5-6-0 (L. f. graphicss, 1-2-3-4-5-6-0 (pictus), 1-2-0-0-5-6-7 (osmen-
ti), and 0-3-4-0-0-7 (solidulus) survive today or have been preserved by
2 Dr. W. J. Clench of the Museum of Comparative Zoology does not believe
that parthenogenesis in Liguus is probable. It is true that Liguus like other
pulmonates is hermaphroditic, but if the reproductive behavior is comparable
to that in Cepaea and other land snails which have been studied in detail. in
this regard self-fertilization is very rare. Observations on Liguus in captivity
suggest, in fact, that mutual fertilization does not normally occur. Snails may
be alternately male in one mating and female in another. If these observations
hold generally and Liguus has devices to prevent self-fertilization, such as those
in Cepaea, parthenogenesis in isolated individuals is as probable as self-fertiliza-
tion. Self-fertilization alone would not insure a "pure" colony except in the
case of homozygous individuals.
YOUNG: COLOR PATTERN IN LIGUUS
transfer to the Everglades National Park area.3 The combination
1-2-.0-4-0-0-0 (dryas) occurs on Little Pine Key in a nearly pure colony,
but there is an area in which it occurs with graphics. Other com-
binations appear in pure colonies on the mainland, including 1-2-3-
4-5-6-7 and 0-0-0-0-0-0-0. Certain combinations are rare, however,
suggesting, as might be expected, linkage and crossing over and other
genetic complications. For example, colored apex, colored columella,
and peripheral banding frequently occur together. Banded forms
with white tips are rare as are washed forms (combining peripheral
and sutural banding) with pink tips. In some cases where the latter
condition occurs as in pictus and some ornatus (Simpson, 1929) the
apex is colored but not the columella suggesting that translocation
may have occurred.
Erwin Winte of the Everglades National Park staff made some
interesting artificial crosses of snails from the Lower Keys with some
of the mainland forms. Unfortunately, exact data could not'be pre-
served under the conditions of the experiment, but the progeny of
the cross that were retrieved suggest that the first generation shows
only characters of the Lower Key parent while the second shows seg-
regation. Modification of the shell shape and texture in the hybrids
also indicates genetic influences.
Recently, C. C. Von Paulsen, William Osment, and Erwin Winte
have discovered an interesting colony on Little Torch Key, one of
the Pine Islands, in which all the shells are 1-2-0-4-5-6-7. These snails
which are associated with Orthalicus floridensis (Pilsbry) in a small,
dry hammock represent a distinctive color form. I wish to thank
Erwin Winte and Archie L. Jones for calling this discovery to my
attention, and with the permission of the discoverers I take pleasure
in naming it:
Liguus fasciatus vonpaulseni new subspecies
DIAGNOSIS: Similiar to Liguus fasciatus graphics, but differing
in the presence on the periphery of numerous periostracal green lines
SThe project of transferring and preserving the Lower Key snails is being
conducted by Ralph Humes, Archie L. Jones, C. C. Von Paulsen of Miami, and
Erwin Winte of the National Park Service with cooperation of the Everglades
National Park authorities. Snails are being colonized in formerly barren ham-
mocks, and the results to date are most gratifying. It is hoped that all of the sur-
viving pure colonies of Florida Liguus can be preserved and thus be available for
future research. A number of experimental crosses to test genetic assumptions
have already been made in other separated hammocks, but the result of these will
not be known for some time.
BULLETIN FLORIDA STATE MUSEUM
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YOUNG: COLOR PATTERN IN LIGUUS
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BULLETIN FLORIDA STATE MUSEUM
and in having the lip of the shell crenate at the juncture of the peri-
ostracal green lines. The distinction of the subspecies vonpaulseni
from the other forms now found or formerly occurring on the Lower
Keys is given in the key following the description.
DESCRIPTION: Shell-Moderately elongate, heavy in texture, vary-
ing from shining in younger examples to dull in older specimens;
whorls not inflated, slightly flattened; columella straight; outer lip
crenate at juncture of periostracal green lines even in old specimens,
but not crenate at juncture of sutural or peripheral brown-red lines;
lip moderately thickened internally. Color-In younger specimens,
including the type, richly banded with yellow as in the subspecies
graphics; apex and columella pink; peripheral and sutural brown-
red lines well developed; dark pigments in form of blotches on periph-
eral bands of upper whorls and as small spots along upper border,
and as elongate streaks along the lower border of the bands on the
intermediate and lower whorls; in very young shells these elongate
streaks form nearly continuous lines, but in older specimens the streaks
separate into elongate spots of varying lengths; old specimens fade
until there is a superficial resemblance to the form L. f. osmenti, but
yellow pigment and the periostracal green lines are retained in the
bands on at least the last two whorls even in the largest shells seen,
and the outer lip is crenate at the juncture of the periostracal green
lines; periostracal green lines well developed, up to six reaching the
lip above the brown-red peripheral line.
TYPE MATERIAL: Holotype, University of Florida Collections (UF)
18865. Collected on Little Torch Key, Monroe County, Florida, by
C. C. Von Paulsen, William Osment, and Edwin Winte, during the
summer 1959. The type is a mature shell with eight visible whorls in
dorsal view. Length 55 mm., greatest width 27 mm., distance from su-
ture to tip of columella 21 mm. Smallest shell seen, 30 x 18 x 12 mm.;
largest seen, 65 x 32 x 24 mm. Paratypes, 70 in all are distributed as
follows: University of Florida Collections (UF) 18866 (5), Museum
of Comparative Zoology (4), University of Michigan Museum of Zool-
ogy (4), and the private collections of Captain Von Paulsen, and
Messrs. Winte, Humes, Osment, and Jones (56).
The form L. f. vonpaulseni falls in the Clench and Fairchild classi-
fication of Florida Liguus (1939) under Liguus fasciatus solidus (Say).
As indicated in the following key it should be placed next to graphics.
Three abberrant shells collected by William Osment are not des-
ignated as paratypes. One of these is abnormally elongate with the
suture deeply indented. Otherwise it seems to be typical. Another
YOUNG: COLOR PATTERN IN LIGUUS
shell shows most of the characteristics but has the green periostracal
lines reduced or fused. The third shows the green lines only at the
base of the shell on the new growth, although the yellow pigment is
not at all bleached as it is in older shells.
A KEY TO THE DESCRIBED FORMS OF Liguus fasciatus (Miiller)
FROM THE LOWER FLORIDA KEYS
1. Apex of shell and usually the columella pink . . . . . 2
Apex of shell and columella colorless or white . . . . 7
2. Yellow pigment present in bands or whorls or as a general wash
over the shell . .. . .. . 3
Yellow pigment lacking; periostracal green lines present, but lip of shell
not or only feebly crenate at their juncture; shell relatively heavy;
dark pigment in blotches on upper whorls, and in elongate streaks
along brown-red peripheral lines on lower whorls; peripheral and
sutural brown-red lines present, usually strongly developed even in
old shells . . . . .. . osmenti Clench
3. Blotches of dark pigments on upper whorls and as elongate streaks or
squarish blotches along the peripheral brown lines . . . 4
Dark pigment lacking or greatly reduced; yellow pigment intense, often
appearing orange in fresh specimens, confined to regular bands from
near the apex to the lip; peripheral and sutural brown lines lacking
..................... dryas Pilsbry
4. Yellow piment present in definitely restricted peripheral bands on the
whorls; both apex and columella usually pink; dark pigment seldom,
if ever, in the form of squarish blotches along the peripheral brown
lines, if so within these lines not crossing them . . . . 5
Yellow pigment present as a wash over shell; columella pale pink or white,
usually white; dark pigment present as blotches on upper whorls and
as squarish blotches along peripheral brown lines to lip, the blotches
crossing peripheral lines or above and below them rather than con-
fined to area between them on each whorl as in graphics pictus (Reeve)
5. Shell thin, translucent, resembling form lignumvitae Pilsbry from Lower
Matecumbe and adjacent keys; periostracal green lines developed on
lower whorls at least; lip not create; dark pigment in blotches on
upper whorls, but intensely dark elongate streaks on lower whorls
reduced;, extinct form from No Name Key . . innominatus Pilsbry
Shell relatively thick, not translucent; elongate dark streaks along periph-
eral brown lines often intense . .. . . . .6
6. Periostracal green lines fully developed as in typical fasciatus, up to six
reaching the lip of shell between the peripheral brown-red lines in
unfaded examples and some green lines evident even in old shells,
although in the latter the yellow pigments fade so that they resemble
osmenti; lip of shell crenate at juncture of periostracal green lines
BULLETIN FLORIDA STATE MUSEUM
(but not at juncture of brown-red peripheral lines) in young specimens,
moderately create on new growth in old shells; shell shape and col-
umellar form similar to graphics; body of snail lighter brown than
in graphics . . ... .. .vonpaulseni new subspecies
Periostracal green lines lacking; lip of shell not crenate; size sometimes
very large, up to 72 mm. in length . . . graphics Pilsbry
7. Yellow pigment absent; shell heavy, inflated, ground color ivory white
with bronzy peripheral line (or lines) present or absent; presumably
extinct, known only from figure of type from Big Pine Key and a
doubtful specimen from Ramrod Key (heavy ridge inside lip of type
and Ramrod Key specimen of doubtful significance) crassus Simpson
Ground color of shell white, cream, or straw yellow; yellow pigment
present, either as a general wash over shell or in restricted bands .. 8
8. Shell with a broad basal and supraperipheral pale yellow band (prob-
ably with periostracal green lines in young specimens); presumably
extinct, but once widely distributed over the Lower Keys solidus (Say)
Shell with two narrow yellow peripheral bands and one at the suture,
presenting essentially a photographic-type negative of solidus; young
shells with periostracal green lines . . .. solidulus Pilsbry
Clench, W. J.
1942. A new race of Liguus from the Lower Keys of Florida. Proc. New
England Zool. Club, vol. 19, pp. 69-71.
Clench, W. J., and G. B. Fairchild
1939. The classification of Florida Liguus. Proc. New England Zool. Club,
vol. 17, pp. 77-86.
Pilsbry, H. A.
1912. A study of the variation and zoogeography of Liguus in Florida. Jour.
Acad. Nat. Sci. Philadelphia, vol. 2, no. 15, pp. 427-471, pls. 37-40.
Simpson, C. T.
1929. The Florida tree snails of the genus Liguus. Proc. U.S. Natl. Mus.,
vol. 73, no. 2, pp. 1-144, 4 pls.
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