Spatial diversity of MHC class II DRB exon2 sequences in North African cape hares (Lepus capensis): positive selection and climatic adaptation signals

The genes of the major histocompatibility complex (MHC) are among the best candidates for studying adaptive variation driven often by pathogen-mediated selection. However, diversity of these genes might be differently shaped by selective and non-selective evolutionary mechanisms. In this study, we assessed the spatial distribution of MHC class II DRB exon 2 gene diversity in hares from Tunisia (Lepus capensis) across a steep ecological gradient and tried to disentangle the driving mechanisms shaping the observed diversity. We also compared the current data with previous results from the MHC class II DQA and DQB loci of the same individuals. We found a relatively high level of diversity and spatial differentiation similar to that observed earlier for DQA and DQB. We also detected clear evidence of positive selection acting on the DRB gene. Nevertheless, recombination was considered as a more important process shaping the evolution of the DRB locus. Our information theory-based models revealed statistically meaningful climate effects on the occurrence of some alleles (i.e., protein variants), regardless of their geographical distribution patterns, supposedly reflecting adaptation to spatial pathogen variation.