Genomic Evidence for Elevational Segregation and Adaptive Introgression in Prunellidae Radiation

Heterogeneous mountainous environments and climate fluctuations during glacial periods can accelerate speciation and adaptive evolution in mountainous species. However, the interplay between these processes and their collective impact on mountainous diversity remains poorly understood, particularly across broad geographic scales. We conducted a comparative genomic study of Prunellidae (accentors), an avian family distributed across Eurasian mountain chains. Our analyses revealed low genetic divergence among species (D_XY ranging from 0.631 × 10^-2 to 2.665 × 10^-2). When separated by elevation, high-elevation species (> 2500 m) exhibited greater genetic diversity than mid- (1000-2500 m) and low-elevation species (< 1000 m). Demographic reconstructions showed distinct response to Last Glacial Maximum: high-elevation species experienced population declines, mid-elevation species maintained stable population sizes, while low-elevation species underwent expansions. High-elevation species also showed signatures of divergent selection in genes involved in blood vessel development and DNA break repair, suggesting adaptation to extreme environments. Despite these differences, we detected widespread interspecific introgression, with the most pronounced event occurring between low-elevation P. montanella and the ancestor of high/mid-elevation species. The introgressed regions showed evidence of positive selection and reduced genetic load, potentially facilitating P. montanella's recent expansion into higher elevations. Our findings demonstrate how elevational segregation drives montane diversity and underscore the importance of adaptive introgression in the evolution of the montane species.