Population genetics, systematics, biogeography, and evolution of the southeastern central Texas Eurycea clade Blepsimolge (Plethodontidae)


Nathan Bendik


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The central Texas Eurycea are a diverse group of perennibranchiate salamanders which inhabit the Edwards Plateau. Although several studies have addressed the systematics and taxonomy of this group, little is known about species boundaries within the southeastern Blepsimolge. Here I assess genetic variation and phylogenetic relationships both within and among species of the southeastern Blepsimolge. Using mitochondrial DNA sequences of the control region, I examine the population structure and genetic variation of Eurycea nana as well as the evolution of the control region within Eurycea and other salamanders. I compared levels of genetic variation among 24 E. nana from San Marcos Springs (Hays Co.), individuals from ageographically proximate population at Comal Springs (Comal Co.), and representatives of several other central Texas Eurycea. No population structure was found among the three E. nana localities sampled and haplotype diversity in E. nana was lower than in E. sp. Comal Springs, which is consistent with previous results. To examine species boundaries and evolutionary patterns among the southeastern Blepsimolge, I used three mitochondrial DNA products (control region, cytochrome b, and partial ND2), totaling 3,252 base pairs, to reconstruct phylogenetic relationships. The combined data set consisted of 58 ingroup populations or taxa from 43 different localities sampled from caves and springs throughout the eastern portion of the Edwards Plateau, south of the Colorado River. Several species boundaries recovered in this study do not appear to be wholly consistent with previous designations. Eurycea latitans is paraphyletic and appears to be conspecific with E. tridentifera. Populations of Eurycea pterophila form a weakly-supported monophyletic group and the range of this species extends beyond springs and caves in the Blanco River basin, contrary to previous inferences. Deep divergences within the southeastern Blepsimolge among taxa distributed along the Edwards fault zone aquifer suggest that formation of the Edwards Aquifer and compartmentalization within it may have been integral to the early diversification of this group. Subsequent dispersal and diversification probably ensued when the Lower Glen Rose limestone in the central portion of their distribution was exposed. Aquifer and cavern development in the region provided access to novel habitat that was exploited by salamanders. Finally, phylogenetic analysis revealed recurring patterns of morphological convergence among hypogean populations with cave-associated morphologies.

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