Diversification across the Australian Monsoonal Tropics: Comparing phylogeographic and demographic patterns within and between species of Cryptoblepharus skinks

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Organisms vary in their ability to cope with environmental perturbations, and even closely related species can differ in their resilience to climate change. For example, generalists may be better at accommodating environmental change than specialists with a narrow ecological niche. However, many species are difficult to classify as "specialist" or "generalist", and may be merely adapted to distinct ecological niches. Furthermore, climate resilience may vary between ecological specialists if consequences are more profound for one ecological niche than another. In this study, we employ a multi-locus exon-capture approach and combine phylogeographic and population genetic methods to compare the evolutionary history of four species of Australian Cryptoblepharus lizards. These skinks co-occur in the Australian Monsoonal Tropics (AMT), have persisted despite major changes in Pleistocene climate, and have adapted to arboreal or rock substrates (two arboreal, two rock specialists). We find that phylogeographic structure is idiosyncratic between species and ecomorphs, likely shaped by the complex topography and heterogeneous environment of the AMT. In contrast, demographic analyses recovered largely congruent signals of expansion across populations, suggesting shared responses to past environmental change independent of ecomorph type. These results show that ecological specialization per se is not always a good predictor of demographic history or phylogeographic structure, and highlight the complex interplay between topography and climate history in promoting diversification. Thus, while ecological specialization, niche breadth, and other species-specific characteristics remain of interest, major landscape features that serve as biogeographic barriers or refugia may mask idiosyncratic responses between ecomorphs from the same adaptive radiation.

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