Phylogenetic and Taxonomic Issues Relating to Salamanders of the Family Plethodontidae
Total Page:16
File Type:pdf, Size:1020Kb
Herpetologica, 49(2), 1993, 229-237 0 1993 by The Herpetologists’ League, Inc PHYLOGENETIC AND TAXONOMIC ISSUES RELATING TO SALAMANDERS OF THE FAMILY PLETHODONTIDAE DAVIDB. WAKE Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, CA 94720, USA THE occasion of the third decennial spects, but he chose not to recognize any Conference on the Biology of Plethodontid taxa between genus and family. Dunn en- Salamanders, and the first publication of visioned two “main groups” of genera the proceedings of the conference, is a pro- along the lines of Cope’s groups-a Pleth- pitious time to take stock concerning di- odon group with attached tongues and a verse phylogenetic and taxonomic issues. Eurycea group with free tongues, “con- As background, the monograph of Cope nected by three intermediate genera which (1889)is used as a point of departure. Cope hardly belong to either group” (Dunn, recognized a family Desmognathidae (for 1926:22)-Stereochilus, Typhlotriton, and Desmognathus) and a family Thoriidae Typhlomolge. Apart from the recognition (for Thorius),both distinguished from the of many more species and a few novel new Plethodontidae by having opisthocoelous genera, the largest difference between the vertebrae. Within the Plethodontidae he taxonomy of today and that of Dunn is his recognized two groups of genera: Pletho- treatment of tropical salamanders. He rec- dontae [Plethodon, Hemidactylium, Bat- ognized only 31 tropical species (about 44% rachoseps, Stereochilus, and Autodax (= of the total number of species of pletho- Aneides)], and Spelerpes [Geotriton (= dontids; tropical species constitute more Hydromantes), G yrinophilus, Manculus than 65% today), all placed in Oedipus. (now included in Eurycea),Spelerpes (Eu- While workers such as Noble (1927, rycea and Pseudotriton), Oedipina, and 1931) quibbled with some of Dunn’s ideas, Oedipus (supergenus Rolitoglossa, minus the monograph remained authoritative for Oedipina and Thorius)].The fundamental several decades. Taylor (1944) described distinction was that the Plethodontae ha5 many tropical species and sorted them into a tongue attached anteriorly, while Spe- a number of genera. Several new genera lerpes has a free tongue. Cope thought that (e.g., Phaeognathus, Haideotriton) and “The generic relationships of the above- many new species were named in North named groups are exceedingly simple, and America as well, but it was not until my the ease with which the animals can be comparative osteological study (Wake, analyzed renders the case free from the 1966) that there was a major change in doubts which constantly arise in discus- taxonomy and phylogenetic perspective. sions of generic relationships as to the That work was published on the eve of the probable omission of characters from the cladistic revolution, and while most taxa argument” (Cope, 1889:121-1 22). are monophyletic and based on shared de- The famous monograph of Dunn (1926) rived character states, there are some in- remains useful today. Dunn documented consistencies with respect to modern cla- the unique features of the family, dis- distic methodology (e.g., in the brief cussed relationships to other families, and discussion of familial relationships) The included a lengthy treatment of relation- main results of that study have remained ships of species within some of the genera surprisingly robust and find wide accep- (e.g., Desmognathus), and of the genera tance to this day. to each other. Only 16 genera and 72 spe- Wake (1966)thought that plethodontids cies were recognized. Dunn noted that were derived from an ambystomatid an- Desmognathus and Leurognathus dif- cestral stock (in 1966 the Ambystomatidae fered from the other genera in many re- included the three subfamilies Ambysto- 229 230 HERPETOLOGICA [Vol. 49, No. 2 matinae, Dicamptodontinae, and Rhyaco- with the hyobranchial apparatus and the tritoninae, all currently recognized as fam- nervous system, and there are unique fea- ilies), that the genera of plethodontids could tures of courtship. Recently Larson and be placed in two subfamilies, Desmogna- Wilson (1989) and Larson (1991) have pro- thinae and Plethodontinae, both with an- vided characters from rRNA sequences that cestral and derived characters, and that further support the monophyly of the fam- the Plethodontinae could be segregated ily, and Sever (1991) has presented some into three tribes, the Hemidactyliini, the characters from the morphology of the clo- Plethodontini, and the Bolitoglossini. A acal region. major departure from prior work was the When I argued for a phylogenetic re- grouping of Hydromantes, Batrachoseps, lationship between the plethodontids and and all of the tropical salamanders (su- the ambystomatids (Wake, 1966), I had pergenus Bolitoglossa) as a monophyletic Rhyacotriton very much in mind. With tribe Bolitoglossini. Another novel feature the breakup of the Ambystomatidae, the was the placement of Hemidactylium with possibility of a sister taxon relationship with the Eurycea group of genera of Dunn the Rhyacotritonidae (fide Good and Wake, (1926). I envisioned the Hemidactyliini as 1992) must be seriously considered. Larson the central evolving stock, giving rise first and Wilson (1989) and Larson (1991) have to the desmognathines, next to the boli- shown that plethodontids are very distinct toglossines, then to the plethodontines, and from other families, and occupy a rather finally to Hemidactylium on the one hand basal position. Rhyacotritionids also are and the remaining hemidactyliines on the rather basal, and remote from both am- other, but I was uncertain on the place- bystomatids and dicamptodontids (Good ment of Hemidactylium, which ended up and Wake, 1992; Larson, 1991; Sever, 1991, with the Eurycea group mainly by default. 1992). The rRNA sequence data have sup- 1 use the 1966 taxonomy and phylogenetic ported some traditional groupings (notably interpretation as a point of departure for the monophyly of the Hynobiidae + Cryp- my re-evaluation. tobranchidae), while they have challenged others (the widely accepted grouping of FAMILYPLETHODONTIDAE the Plethodontidae with the Ambystomati- There has been no proposal to include dae, or alternatively with the Salamandri- plethodontids as members of any other dae). Further resolution of relationships of currently recognized family of salaman- the families of salamanders is likely to come ders since the admission of Typhlomolge with additional sequence data, and by to the Plethodontidae (Fowler and Dunn, combining sequence data with traditional 1917). Dunn (1926) showed that Typhlo- characters (such work is in progress, Lar- molge was a plethodontid; his conclusions son and Dimmick, personal communica- were foreshadowed by Emerson’s (1905) tion). demonstration that the genus was not a proteid. There have been no shifts of gen- SUBFAMILYDESMOGNATHINAE era from other families into the Pletho- This is a well supported, monophyletic dontidae since that time. While Soler (1950) group (Schwenk and Wake, 1993; Soler, proposed recognition of a family Desmog- 1950; Wake, 1966). Phaeognathus has nathidae, he acknowledged close relation- many autapomorphies, and it seems to be ship with the Plethodontidae. a basal derivative within the subfamily. All The Plethodontidae is well supported by remaining species fit well within Desmog- character data-lunglessness is universal, nathus, although Leurognathus, which all metamorphosed individuals have a na- contains a single species with a few autapo- solabial groove, only adult plethodontids morphies, is universally recognized. This lack an ossified pterygoid bone, pletho- may well render Desmognathus paraphy- dontids have a unique arrangement of vo- letic. This problem may be solved by DNA merine and postvomerine teeth, there are sequence data (Titus, 1992).A special phy- a number of unique features associated logenetic puzzle of the subfamily is the June 19931 HERPETOLOGICA 23 1 number of times that direct development called global) heterochrony could affect has evolved. Direct development is found many characters at once, leading to an in- in Phaeognathus, D. aeneus, and D. flated impression of the extent of homo- wrighti. It seems unlikely that aquatic lar- plasy, but so far it has not proven possible vae have re-evolved in the subfamily (for to sort coevolving complexes of characters one thing, a more ancestral hyobranchial that might be unconnected functionally system is present in desmognathine larvae from independently evolving characters. I than in the remaining plethodontids: Wake, personally like to use new data sets to test 1966). However, Phaeognathus is a sister hypotheses based on old data, and so I have taxon of Desmognathus, and if one or both long advocated the use of molecular and of the species of Desmognathus that have other kinds of data. Linda Maxson and I direct development should prove to be bas- started a collaboration with the goal of test- al within the genus, that possibility must ing alternative morphologically based be considered. phylogenetic hypotheses, but the taxa are too differentiated for microcomplement SUBFAMILYPLETHODONTINAE fixation of albumin to be effective. Protein Wake (1966) recognized three tribes of electrophoresis is useful for comparing genera: Plethodontini (for Plethodon, closely related species and even genera, Aneides, and Ensatina),Bolitoglossini (for but the higher taxa are beyond the limit Bolitoglossa, Chiropterotriton, Lineatri- of effectiveness of the technique. On the