SPECIATION IN EASTERN NORTH-AMERICAN SALAMANDERS OF THE GENUS PLETHODON

Studies on allozyme variation in eastern plethodontid salamanders of the woodland genus Plethodon have revealed a large number of cryptic species. Genetic variation within and among species reveals patterns of speciation. In the late Miocene and early Pliocene there appear to have been only five clades of eastern North American Plethodon that still survive today. A burst of speciation took place in the Pliocene, so there are now at least 35 species in four species groups in eastern North America. It is hypothesized that the arid climates of the Pliocene isolated many populations in wetter forested mountainous areas where in isolation allopatric speciation occurred. With the return of wetter climates, many of these species dispersed and a large number of parapatric contact zones may now be studied where closely related species are interacting. Hybridization between closely related species is frequent in these contact zones.