Generic Boundaries in Texas Cave Salamanders, and a Redescription of Typhlomolge robusta (Amphibia: Plethodontidae) Author(s): Floyd E. Potter, Jr. and Samuel S. Sweet Reviewed work(s): Source: Copeia, Vol. 1981, No. 1 (Feb. 10, 1981), pp. 64-75 Published by: American Society of Ichthyologists and Herpetologists (ASIH) Stable URL: http://www.jstor.org/stable/1444041 . Accessed: 10/01/2012 14:25 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Society of Ichthyologists and Herpetologists (ASIH) is collaborating with JSTOR to digitize, preserve and extend access to Copeia. http://www.jstor.org 64 COPEIA, 1981, NO. 1 RIVAS,L. R. 1964. A reinterpretationof the concepts Wauchope and R. C. West (eds.). Univ. Texas "sympatric"and "allopatric"with proposal of the Press, Austin. additional terms "syntopic"and "allotopic."Syst. TURNER,B. J., AND R. K. LIU. 1977. Extensiveinter- Zool. 13:42-43. specific genetic compatabilityin the New World SOLTZ, D. L., AND R. J. NAIMAN. 1978. The natural killifishgenus Cyprinodon.Copeia 1977:259-269. history of native fishes in the Death Valley system. Nat. Hist. Mus. L.A. Co. Sci. Ser. 30. MUSEUM OF ZOOLOGYAND DIVISION OF BIOLOG- TAMAYO,J. L., ANDR. C. WEST. 1964. The hydrog- ICAL SCIENCES, THE UNIVERSITY OF MICHI- 84-121. In: Hand- raphy of Middle America, p. GAN, ANN ARBOR, MICHIGAN 48109. Accept- book of Middle American Indians, Vol. 1. R. ed 18 Dec. 1979. Copeia, 1981(1), pp. 64-75 Generic Boundaries in Texas Cave Salamanders, and a Redescription of Typhlomolgerobusta (Amphibia: Plethodontidae) FLOYD E. POTTER, JR., AND SAMUEL S. SWEET Confusion presently surrounds the systematics of the salamanders of the gen- era Eurycea and Typhlomolgeof the Edwards Plateau of central Texas. Existing morphological evidence is reviewed and found to be inadequate to resolve the status of the genus Typhlomolge.New data on skull morphology supports the continued recognition of this genus. The advanced troglobite Typhlomolgerobusta Longley, 1978, is redescribed and shown to share the features which distinguish T. rathbunifrom the Texas Eurycea.Typhlomolge rathbuni and T. robustamay be parapatricin the San Marcos Pool of the Balcones Aquifer. of parallelism and convergence characters are known or suspected to be sus- PROBLEMSare acute in the systematics of troglobitic ceptible of convergence. animals, resulting from a common tendency for Recent systematic treatments of the hemidac- cave colonization to occur repeatedly through- tyliine plethodontid salamanders of the Ed- out the range of ancestral populations, and wards Plateau of central Texas exemplify these from an apparent similarity in selective regimes difficulties of interpretation. The caves of the which characterizes the cave environment. The Edwards Plateau contain a diverse assemblage narrow circumscription of successful adaptive of troglobitic salamanders, comprising numer- modes in the evolution of troglobites is evi- ous independently-derived populations which denced by the existence of striking conver- display varying degrees of specialization in pig- gences in morphology, physiology and life-his- mentation, eye size and structure, relative limb tory features among diverse taxa of troglobitic length and head size, head shape and numbers animals (Poulson, 1964; Barr, 1968; Poulson of trunk vertebrae and teeth (Mitchell and Red- and White, 1969). For these reasons most meth- dell, 1965; Brandon, 1971; Sweet, 1978b). At ods of phylogenetic reconstruction are difficult present, each of three alternative taxonomic to apply in the resolution of systematic ques- arrangements of this group of six species has tions involving troglobitic taxa; even a large set a degree of acceptance in the literature. Conant of apparently synapomorphic character states (1975), Sweet (1977a, b, 1978a) Thomas (1976) may fail to demonstrate convincingly mono- and Collins et al. (1978) retain the generic des- phyly when a significant percentage of the ignations of the original authors (Eurycea nana ? 1981 by the American Society of Ichthyologists and Herpetologists POTTER AND SWEET-TYPHLOMOLGE ROBUSTA DESCRIPTION 65 Bishop, 1941, E. neotenes Bishop and Wright, conclusions through an examination of a new 1937, E. latitans Smith and Potter, 1946, E. trog- troglobitic species which seems to be superfi- lodytes Baker, 1957, E. tridentifera Mitchell and cially intermediate between Eurycea tridentifera Reddell, 1965, and Typhlomolgerathbuni Stejne- and Typhlomolgerathbuni. The major method- ger, 1896, in order of increasing troglobitic ad- ological assumption in this investigation is that aptation). Following Mitchell and Reddell evidence of convergent adaptation to the cave (1965) and Mitchell and Smith (1972), Typhlo- environment among the Edwards Plateau molge has been widely considered to be a junior hemidactyliines would require the rejection of synonym of Eurycea: Reddell (1967, 1971), Bo- an hypothesis of monophyly in the group. gart (1967), Blair (1968), Raun (1971), Hen- dricks (1973), Thomas (1974), Tupa and Davis MATERIAL EXAMINED (1976), Russell (1976) and Longley (1978). Wake (1966) redefined and expanded the ge- In the course of this work 95 specimens of nus Typhlomolgeto include both E. tridentifera T. rathbuni ranging from 7.4 to 73.2 mm in and T. rathbuni; this arrangement has been ac- standard length (SL, tip of snout to posterior cepted by Brame (1967), Brandon (1968, 1971), margin of cloaca), and 144 specimens of E. tri- Leviton (1971), Raun and Gehlbach (1972), dentifera ranging from 14.0 to 46.0 mm SL have Dundee (1973), Gorham (1974), Besharse and been examined externally and by high resolu- Holsinger (1977) and Smith (1978). In addi- tion radiographs. Five T. rathbuni (28.5-54.0 tion, Longley (1978) has employed the desig- mm SL) and 32 E. tridentifera (14.0-45.0 mm nations Eurycea (=Typhlomolge) rathbuni and SL) were available as cleared and stained prep- Typhlomolge(=Eurycea) rathbuni (sic), apparent- arations. In addition, 42 (7 cleared and stained) ly without intending to establish subgeneric sta- specimens of E. troglodytes(22.5-43.6 mm SL), tus for Typhlomolge. 21 (1 cleared and stained) specimens of E. la- At issue are the status and content of the ge- titans (9.5-47.8 mm SL), and 153 (17 cleared nus Typhlomolge,and the zoogeographic inter- and stained) specimens of E. neotenes(15.0-53.0 pretations of Wake (1966) and Mitchell and mm SL) representing 13 troglobitic populations Smith (1972). Wake suggested that Typhlomolge have been available, together with approxi- is a relict of a Miocene radiation of salamanders mately 3500 specimens representing about 115 ancestral to the genus Eurycea, a radiation also epigean populations of E. neotenesand two pop- represented by the troglobites Typhlotritonspe- ulations of E. nana. The repositories of this laeus and Haideotriton wallacei; in Wake's view, material are listed by Sweet (1978b). Cleared the Texas Eurycea derive from a subsequent and stained representative series of all genera (probably Plio-Pleistocene) invasion of the Ed- and the majority of species of the hemidacty- wards Plateau. Citing geologic evidence on the liine plethodontids have been available as ref- age of the plateau (discussed below), Mitchell erence material. and Smith (1972) interpreted the history of the The following abbreviations are employed in Texas hemidactyliines to date from Pleistocene the text: FEP, personal collection of the senior time. author; MVZ, Museum of Vertebrate Zoology, The question at the root of this disagreement University of California, Berkeley; TNHC, seems to be the following: is there a morpho- Texas Natural History Collection, University of logical dichotomy among the Edwards Plateau Texas, Austin; TTU, uncatalogued material hemidactyliines which is of sufficient magni- loaned by R. W. Mitchell and J. R. Reddell, tude to indicate their derivation from disparate Texas Tech University. ancestral stocks? In other words, does this as- consist of in semblage solely lineages evolving RESULTS AND DISCUSSION parallel (and thus properly congeneric under an operating assumption of monophyly), or is Status of Typhlomolge.-Had representatives of there some combination of parallel and con- the range in troglobitic specialization now vergent lineages? The present work has two known in the Texas Eurycea been available to objectives: to reevaluate existing evidence on Stejneger it is doubtful that the genus Typhlo- the status of the genus Typhlomolgein terms of molge would have been established. The histor- the likelihood of convergent origin for shared ical accident of the discovery of T. rathbuni long character states; and to test our phylogenetic before other paedogenetic troglobites were 66 COPEIA, 1981, NO. 1 known from the Edwards Plateau resulted in in E. tridentifera, but are nearly always present action, which is now viewed from a very differ- in large specimens, though they are uniformly ent perspective. The discovery of increasingly absent in T. rathbuni; this feature is presumably specialized troglobitic species of the Texas Eu- related to the reduced need