Aridification drove repeated episodes of diversification between Australian biomes: Evidence from a multi-locus phylogeny of Australian toadlets (Uperoleia: Myobatrachidae)

- We investigated the phylogeny of the Uperoleia genus of frogs.
- We found substantial geographic structure within the genus.
- Genetic data supports the role of aridity cycles in the diversification of the genus.
- Monsoonal, mesic and arid biomes do not have monophyletic groups of species.
- Mitochondrial and nuclear genetic markers suggests a history of introgression.

Australia is a large and complex landmass that comprises diverse biomes ranging from tropical rainforests to harsh deserts. While Australian biotic diversity has evolved in response to landscape and climate changes, evidence of Miocene or later biome shifts are few. The Australo-Papuan endemic frog genus Uperoleia is widely distributed across mesic, monsoonal tropic and arid regions of Australia. Thus, it represents an ideal system to evaluate biome shifts as they relate to known landscape and climate history. We comprehensively sampled the distributional range of 25 described Uperoleia species and generated a detailed molecular phylogeny for the genus based on one mitochondrial and five nuclear loci. Our results support a single origin of monsoonal tropic taxa, followed by diversification within the region under the influence of the Australian monsoon. Molecular dating analyses suggest the major divergence between eastern mesic and monsoonal species occurred in the Miocene approximately 17 million years ago, with repeated evolution of species from monsoonal biomes to arid or mesic biomes in the later Miocene, early Pliocene and at the beginning of the Pleistocene. Our detailed sampling helps to clarify the true distributions of species and contributes to on-going work to improve the taxonomy of the genus. Topological differences between nuclear and mitochondrial phylogenies within major clades suggest a history of mitochondrial introgression and capture, and reduce the ability to resolve close interspecific relationships.

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