B ULLETIN OF THE FLORIDA STATE MUSEUM BIOLOGICAL SCIENCES Volume 5 Number 6 COLOR PATTERN VARIATION AMONG SNAILS OF THE GENUS LIGUUS ON THE FLORIDA KEYS Frank N. Young 0 \/811/ UNIVERSITY OF FLORIDA Gainesville 1960 The numbers of THE BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES, are published at irregular intervals. Volumes contain about 800 pages and are not necessarily completed in any one calendar year. WILLIAM J. RIEMER, Managing Editor OLIvER L. AusTIN, JR., Editor All communications concerning purchase or exchange of the publication should be addressed to the Curator of Biological Sciences, Florida State Museum, Seagle Building, Gainesville, Florida. Manuscripts should be sent to the Editor of the BULLETIN, Flint Hall, University of Florida, Gainesville, Florida. Published 21 October 1960 Price for this issue $0.20 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: Castropoda, 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 axjal coloration„ banding, pigmentation, and other characters. A new form from Little Torch Key, Liguus fasciatus vonpaul- seni new subspecies, combining many of the 06lor 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 combilia- tions 6f 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 fbrm 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, f6r 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, graphicus, and possibly others now lost. Other colonies on the Lower Keys were also mixed, and the rality 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 i Frank Young completed his doctoral work at the University of Florida in 1942. His principal contributions haye been 6n aquatic beetles, but he has main- tained a steady interest in the distribution, genetics, and evolution of the tree anails 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. 688 from the Zoological Laboratories of Indiana University, Bloomington, Indiana. Manuscript submitted 4 May 1960. 260 BULLETIN FLORIDA STATE MUSEUM Vol. 5 colonies. The great destruction of the hammocks in recent years by burning and clearing has increased the isolati6n of the 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 origineil 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, (8) sutural banling, (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 resiilt 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 cdor 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. graphicus), 1-2-3-4-5-6-0 (pictus), 1-2-0-0-5-6-7 (oAmed- ti), and 0-8-4-0-0-7 (solidulus) survive today or have been preserved by ' Dr. W. J. Clench of the Museum of Comparative Zoology does »not believe that parthenogenesis in Ligtms is probable. It is true that Liguus like other pulmonates. is hermaphroditic, but if the repfoductive behavior is comparable to tliat in Cepaed 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- "Non. Self-fertilization a16ne would not insure a "pure colony except in the case of homozygous individuals. 1960 ¥OUNG: COLOR PATTERN IN LIGUUS 261 transfer to the Everglades National Park area,3 The c6mbination 1-2-0-4-0-0-0 (dryas) occurs on Little Pine Key in a nearly pure colony, but there is an atea in which it occurs with graphicus. Other com- binatiens appear in pure colonies on the mainland, including 1-2-8- 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 suturaI 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 ''shggesting that translocation may have occurred. Erwin Winte of the Everglades National Park staff made some interesting artificial crosses of snails from the Lowei 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. The5e snails which are associated with Orthalicus #oridensis (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 discoverets I take pleasure in naming it: Liguus fasciatus uonpaulseni new subspecies DIAGNOSIS: Similiar to Liguus fasciatus graphicus, ·but differing in the presence on the periphery of numerous periostracal green lines »'The project of transferring and preserving the Lower Key snails is being conducted by Ralph Humes, Archia L. Jones, C. C. Von Paulsen of Miami, and Erwin Winte of the National Park Service with cooperation of th¢ Everglades National Park authorities. Snails are 1*ing 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 preser.ved 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 hot be known for some time. L: E r ---1 4 - 551F . -/ I '--- - . B U LLE T IN F LO R ID A S TATE A U S E U M Vol. 5