A morphologically cryptic salamander reveals additional hidden diversity: evidence for ancient genetic divergence in Webster’s salamander, Plethodon websteri

We investigated the genetic diversity and phylogenetic structure of Webster’s salamander (Plethodon websteri), an understudied species of conservation concern and one of the first morphologically cryptic salamander species described solely on the basis of molecular techniques. Using a combination of mitochondrial and microsatellite data, we discovered significant genetic differentiation across the known distribution (ɸST > 0.868 and FST = 0.261−0.652, p < 0.001), and identified at least two highly divergent clades. These clades, referenced herein as the Semlitsch and Type Locality clades, are of late Miocene origin (approximately 5.3 million years old) and are composed of several geographically and genetically distinct populations. Together, our observations suggest that previously unrecognized species-level diversity may exist in P. websteri, with populations potentially representing distinct but undescribed taxa. We hypothesize that divergence within P. websteri likely resulted from a culmination of radical changes in climate, hydrology, and geology over deep time. Moreover, our results add to mounting evidence suggesting that P. websteri does not belong within the P. welleri group, but instead forms its own discrete species complex separate and genetically distant from P. welleri. This study provides a starting point for future work and reiterates that relationships among, and species-level diversity within, eastern species of Plethodon require additional investigation and potential reevaluation.