Genetic potential for disease resistance in a critically endangered frog decimated by chytridiomycosis

Abstract

Southern corroboree frogs (Pseudophryne corroboree) have been driven to functional extinction in the wild after the emergence of the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) in southeastern Australia in the 1980s. This species is currently maintained in a captive assurance colony and is managed to preserve the genetic diversity of the founding populations. However, it is unlikely that self-sustaining wild populations can be re-established unless Bd resistance increases. We performed a Bd-challenge study to investigate the association between genetic variants of the major histocompatibility complex class IA (MHC) and genome-wide single nucleotide polymorphisms (SNPs). We also investigated differences in Bd susceptibility among individuals and populations, and the genetic diversity and population genetic structure of four natural P. corroboree populations. We found several MHC alleles and SNPs associated with Bd infection load and survival, provide evidence of significant structure among populations, and identified population-level differences in the frequency of influential variants. We also detected evidence of positive selection acting on the MHC and a subset of SNPs as well as evidence of high genetic diversity in P. corroboree populations. We suggest that low interbreeding rates may have contributed to the demise of this species by limiting the spread of Bd resistance genes. However, our findings demonstrate that despite dramatic declines there is potential to restore high levels of genetic diversity in P. corroboree. Additionally, we show that there are immunogenetic differences among captive southern corroboree frogs, which could be manipulated to increase disease resistance and mitigate the key threatening process, chytridiomycosis.