Bulletin of the National Speleological Society - ISSN 0146-9517
Volume 33 Number 1: 1-21 - January 1971
A publication of the National Speleological Society
North American Troglobitic
Salamanders: Some Aspects of Modification in Cave Habitats, with Special Reference
to Gyrinophilus palleucus
Ronald A. Brandon
Seven of the eight known species of troglobitic salamanders are found in North America. Of these seven, all closely related within the family Plethodontidae, only Typhlotriton spelaeus normally undergoes metamorphosis. There is ample evidence that the others, Eurycea troglodytes, Gyrinophilus palleucus, Haideotriton wallacei, Typhlomolge rathbuni, Typhlomolge tridentifera, and probably Eurycea latitans, are paedogenetic and reproduce while retaining larval body morpology. Of the last six, only G. palleucus is known to undergo major metamorphic change readily in response to experimentally administered thyroxin. The most highly specialized species tend to have more rigid control of paedogenesis, increased numbers of teeth, fewer trunk vertebrae, more reduced eyes, more reduced integumentary pigmentation, broader heads, flatter snouts, and more elongateand attenuate limbs. All of these features, except number of trunk vertebrae, are considered selectively adventageous to salamanders living under cave conditions; they probably evolved in response to food requirements and food availablity and result in more efficient energy utilization by the population. Probable mechanisms in the evolution of these features are general neotenic trends and allometric growth changes. The number of trunk vertebrae seems related not to degree of specialization to cave habitats, but rather to the ancestry of the species.
Gyrinophilus palleucus, in several ways, seems to be the least specialized troglobitic salamander. It responds readily to thyroxin, its eyes are not greatly reduced, members of some populations are quite heavily pigmented, and in most regards it is similar to larvae of the epigean species Gyrinophilus porphyriticus. It is highly variable geographically, and has a range which is on the periphery of that of G. porphyriticus, from which species it may have arisen under changing climatic conditions of the Pleistocene.
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