The role of physical geography and habitat type in shaping the biogeographical history of a recent radiation of Neotropical marsupials (Thylamys: Didelphidae)

Aim: In this study, we reconstructed the biogeographical history of species within the sister-genera Thylamys and Lestodelphys, Neotropical marsupials that primarily inhabit open biomes. We used this reconstruction to test the extent to which physical geography (e.g. mountains and rivers) and habitat type (e.g. biomes) shaped patterns of diversification. Location: Central and southern South America. Methods: A fossil-calibrated ultrametric tree for all species within Thylamys and Lestodelphys, along with relevant marsupial outgroups, was reconstructed using sequences from 23 nuclear loci and three mitochondrial loci. Using two biogeographical area schemes (based on biomes and physical barriers, respectively), the biogeographical history of this clade was reconstructed using Lagrange, a maximum-likelihood approach. Results: Thylamys and Lestodelphys originated during the Pliocene in the lowland areas east of the Andes and later expanded their range into and across the Andes. Rivers are implicated in speciation events that occurred in the lowlands, whereas differentiation among habitat types may have led to increased in situ speciation within the Andes. Main conclusions: Biogeographical area schemes based on biomes and physical geographical barriers offered largely complementary results, supporting the hypothesis that both physical geography and ecological differences among habitats drive speciation in continental fauna. Invasion of high-elevation grasslands may have been the impetus for further diversification in montane habitats, eventually seeding the adjacent lowland areas with additional species.