Susceptibility of amphibians to chytridiomycosis is associated with MHC class II conformation

Author(s):  Bataille, Arnaud; Cashins, Scott D., et. al.

Publication: The Royal Society Publishing

Publication Date: 10/3/15

Abstract: The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) can cause precipitous population declines in its amphibian hosts. Responses of individ- uals to infection vary greatly with the capacity of their immune system to respond to the pathogen. We used a combination of comparative and exper- imental approaches to identify major histocompatibility complex class II (MHC-II) alleles encoding molecules that foster the survival of Bd-infected amphibians. We found that Bd-resistant amphibians share common amino acids in three binding pockets of the MHC-II antigen-binding groove. More- over, strong signals of selection acting on these specific sites were evident among all species co-existing with the pathogen. In the laboratory, we exper- imentally inoculated Australian tree frogs with Bd to test how each binding pocket conformation influences disease resistance. Only the conformation of MHC-II pocket 9 of surviving subjects matched those of Bd-resistant species. This MHC-II conformation thus may determine amphibian resistance to Bd, although other MHC-II binding pockets also may contribute to resistance. Rescuing amphibian biodiversity will depend on our understanding of amphi- bian immune defence mechanisms against Bd. The identification of adaptive genetic markers for Bd resistance represents an important step forward towards that goal.