. The biology of the amphibia. Amphibians. SPEC I AT I ON AND ADAPTATION 91 in young metamorphosed individuals. Some of these color patterns appear again in species of Plethodon and Eurycea. It is thus clear that D. f. carolinensis is able to produce in a single locality many of the patterns of the Plethodontidae, and while some of these patterns may appear with intergrades such as the reddish-cheeked variant of the Great Smokies, others may show little intergradation. If any of these well-marked color variants of Durbin could isolate themselves in a distinctive range or ecological niche, few
. The biology of the amphibia. Amphibians. SPEC I AT I ON AND ADAPTATION 91 in young metamorphosed individuals. Some of these color patterns appear again in species of Plethodon and Eurycea. It is thus clear that D. f. carolinensis is able to produce in a single locality many of the patterns of the Plethodontidae, and while some of these patterns may appear with intergrades such as the reddish-cheeked variant of the Great Smokies, others may show little intergradation. If any of these well-marked color variants of Durbin could isolate themselves in a distinctive range or ecological niche, few systematists would hesitate in calling them species. The case of reddish-cheeked Plethodon and Desmognathus occurring together in the Great Smokies and nowhere else in the United States has been considered an instance of mimicry. The phenomenon may be compared with the parallel modification of bent terminal phalanges in certain African ranids (Fig. 30). Why the only species of Rana having claw-shaped terminal phal- anges actually perforating the integument of the digit tips should be found in the only FlG- f -Th° African Gampsosteo- J nyx batesi with recurved terminal part of the World where this phalanges which normally protrude modification OCCUrS in Other through the skin of the toes to form claws. genera not closely related to it is difficult to account for on the basis of natural selection, since neither this modification nor the reddish cheeks seem to have a survival value. It is possible that parallel modifica- tions in unrelated genera are linked with physiological muta- tions having such a value, but at present there is no evidence for such an assumption. Function in Phylogeny.—Structural characters may also exhibit in some cases an apparent gradual change, in others an apparent sudden modification. Various genera of frogs differ from their closest relatives merely by a loss of teeth, but tooth loss in some bufonids such as Batrachophrynus was brought on gradually.
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
