Evaluating hypotheses of expansion from refugia through comparative phylogeography of south-eastern Coastal Plain amphibians

Aim: Early genetic studies in the south-eastern United States provided the foundation for ideas in the field of comparative phylogeography, but few direct comparisons with consistent sampling across taxa exist for this region. We investigate the influence of historical processes and species-level characteristics on phylogeographic structure within four anuran species, evaluate previously described biogeographic patterns, and test three hypotheses of expansion from putative glacial refugia. Location: South-eastern United States Coastal Plain. Methods: We sampled four anuran species from the same 36 localities, assembled mitochondrial genomes from Illumina sequence data and estimated phylogenetic relationships and divergence times within each species. We used spatially explicit phylogeographic analyses and ecological niche models (ENMs) to test predictions about expansion from putative glacial refugia and estimate species-specific parameters including dispersal, migration direction and centre of origin. ENMs for four different time periods were compared within species to assess niche stability. Results: Species differ in patterns of mitochondrial divergence, with only one species displaying a pattern consistent with the previously described Alabama suture zone. Few predictions for hypotheses of expansion from putative glacial refugia were met. ENMs suggest that species have responded differently to historical changes in climate, possibly contributing to discordant genetic patterns. Two species with deep mitochondrial divergences (>2.5 Ma) had low niche stability through time and potentially isolated regions of suitable habitat, whereas the two species with relatively stable, continuous niches exhibit less genetic structure. Main conclusions: These Coastal Plain anurans appear to have been affected by historical climate change, but were not necessarily isolated in glacial refugia. Different natural history characteristics have likely produced discordant patterns in these species, with more generalist, ephemeral breeders exhibiting greater niche stability and lower phylogeographic structure.