Range-wide Phylogeography of the Four-toed Salamander (Hemidactylium scutatum): Out of Appalachia and into the Glacial Aftermath

Herman, Timothy

Due to its limited vagility, deep ancestry, and broad distribution, the four-toed salamander (Hemidactylium scutatum) is well suited to track biogeographic patterns across eastern North America. The range of the monotypic genus Hemidactylium is highly disjunct in its southern and western portions, and even within contiguous portions is highly localized around pockets of preferred nesting habitat. Over 330 Hemidactylium genetic samples from 79 field locations were collected and analyzed via mtDNA sequencing of the cytochrome oxidase 1 gene (co1). Phylogenetic analyses showed deep divergences at this marker (>10% between some haplotypes) and strong support for regional monophyletic clades with minimal overlap. Patterns of haplotype distribution suggest major river drainages, both ancient and modern, as boundaries to dispersal. Two distinct allopatric clades account for all sampling sites within glaciated areas of North America yet show differing patterns of recolonization. High levels of haplotype diversity were detected in the southern Appalachians, with several members of widely ranging clades represented in the region as well as other unique, endemic, and highly divergent lineages. Bayesian divergence time analyses estimated the common ancestor of all living Hemidactylium included in the study at roughly 8 million years ago, with the most basal splits in the species confined to the Blue Ridge Mountains. This pattern of radiation from the southern Appalachians parallels that of the “Out of Appalachia” hypothesis of the geographic origin of the lungless salamanders, and lends further support to the importance of this region as a generator of biodiversity in eastern North America.

Range-wide Phylogeography of the Four-toed Salamander (Hemidactylium scutatum): Out of Appalachia and into the Glacial Aftermath

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