Repeated biome transitions in the evolution of Australian rodents.

Transitions between disparate biomes (e.g. arid and mesic) are expected to be rare, but few systems provide the taxonomic sampling and geographic scope to test these expectations. The Pseudomys division comprising 5 genera and 41 historically extant species are the most diverse group of rodents to evolve from a single colonisation of Australia and are widely distributed across biomes. With a species-level phylogeny we show that repeated biome transitions were required to achieve the distributions of extant taxa in this group with half of all transitions originating from the arid biome. Transitions to the monsoon and arid biomes occurred early, but transition to the temperate mesic biome occurred up to 2 MY later. Early evolving genera remained primarily restricted to a single biome with few transitions among biomes. In contrast, transitions between biomes were associated with most speciation events in a phylogenetically-nested clade of the genus Pseudomys. Our results suggest that, at the broad environmental scale of biome transitions, evolutionarily labile niche divergence can evolve in lineages descended from niche conservative taxa.