Species Limits and Hybridization in Andean Leaf-Eared Mice ().

Leaf-eared mice (genus ) are among the most widespread and abundant small mammals in the Andean Altiplano, but species boundaries and distributional limits are often poorly delineated due to sparse survey data from remote mountains and high-elevation deserts. Here, we report a combined analysis of mitochondrial DNA variation and whole-genome sequence (WGS) variation in mice to delimit species boundaries, to assess the timescale of diversification of the group, and to examine evidence for interspecific hybridization. Estimates of divergence based on data suggest that most diversification of occurred during the past 3 million years. Consistent with the Pleistocene Aridification hypothesis, our results suggest that diversification of largely coincided with climatically induced environmental changes in the mid- to late-Pleistocene. Contrary to the Montane Uplift hypothesis, most diversification in the group occurred well after the major phase of uplift of the Central Andean Plateau. Species delimitation analyses revealed surprising patterns of cryptic diversity within several nominal forms, suggesting the presence of much undescribed alpha diversity in the genus. Results of genomic analyses revealed evidence of hybridization between the sister species and , suggesting that the contemporary zone of range overlap between the two species represents a hybrid zone.