Phylogeographic parallelism: Concordant patterns in closely related species illuminate underlying mechanisms in the historically glaciated Tasmanian landscape

Aim Knowledge of species responses to past environmental change provides a basis to predict and mitigate the outcomes of future environmental change. While paradigm studies of comparative phylogeography have surveyed dissimilar taxa as a means to identify generalities of species responses to past environmental change, the fact that such taxa are dissimilar also raises the chances that any shared patterns reflect coincident responses from different processes (‘phylogeographic convergence’). Here we advocate for and demonstrate the value of examining closely related, ecologically similar co‐distributed species in comparative phylogeographic studies aimed at inferring the environmental processes driving distributional change. Closely related species with similar environmental requirements represent valid phylogeographic replicates, meaning that shared historical distributional responses can more confidently be attributed to the operation of the same process (‘phylogeographic parallelism’). Location Tasmania, temperate south‐east Australia. Taxa We compared phylogeographic patterns observed in two closely related, co‐distributed skink species ( Carinascincus ) sharing similar ecological and physiological tolerances. Methods Using mitochondrial and nuclear DNA, we reconstructed relationships between populations across the known range of C. metallicus and compared it with those of C. ocellatus . We also compared dated phylogenies inferred using Bayesian approaches, and analyses of population structure and genetic diversity. Results We found remarkably similar geographic patterns of genetic diversity in these two species, suggesting they responded similarly to Plio‐Pleistocene climate cycling. We infer that glacial cold and aridity forced these species into similar lowland refugial regions throughout Tasmania and the Bass Strait Islands. Main conclusions Examining phylogeographic patterns in closely related, ecologically similar co‐distributed species allows for confident inference of mechanisms driving historical distributional changes. This is an important step towards generating robust predictions of species responses to future environmental change.