Data from: MHC selection dynamics in pathogen-infected túngara frog (Physalaemus pustulosus) populations

Pathogen-driven selection can favour major histocompatibility complex (MHC) alleles that confer immunological resistance to specific diseases. However, directional selection should deplete genetic variation necessary for maintaining resistance to other pathogens. Robust immune function thus requires balancing as well as directional selection on the MHC. We examined selection dynamics at one MHC class II locus across Panamanian populations of the túngara frog, Physalaemus pustulosus, infected by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). We compared the pathogen’s effects on western highland túngara frog populations, where amphibian communities experienced declines due to Bd, with those in the central lowland region that have shown no evidence of decline. Highland region frogs had MHC variants known to confer resistance against Bd. MHC-II genetic variation was higher than expected under neutrality assumptions, suggesting directional selection for the advantageous variants. In Bd-infected lowland sites, however, heterozygous individuals with only one Bd-resistance allele appeared to accrue selective advantage. Environmental conditions in lowlands should be less favourable for Bd infection, which may reduce selection for specific Bd resistance in hosts. Our results suggest that Bd differentially impacts MHC selection dynamics in its amphibian hosts depending on its infection history within populations and environmental conditions which modulate its virulence.