Meeting Abstract
The fungal pathogen Batrachochytrium dendrobatidis (Bd) has caused population declines and extinctions in hundreds of amphibian species globally. The American bullfrog (Rana catesbeiana) has been implicated as a vector species responsible for the global spread of Bd, however little is known about the genetic mechanism behind pathogen tolerance in this species. Many amphibian species experience natural selection acting on the Major Histocompatibility Complex (MHC) class II gene, a vertebrate immune gene that binds to foreign antigen proteins, facilitating T-cell recognition, and subsequent acquired immune response. Here we compared populations of R. catesbeiana with other well-studied populations to determine if MHC class II polymorphism could be responsible for the widespread tolerance to Bd expressed by R. catesbeiana. We collected genetic samples from three populations of the American bullfrog from across its North American range. We also collected samples of the lowland leopard frog (Rana yavapaiensis), a species with intermediate Bd susceptibility that varies among populations. R. yavapaiensis samples were taken from two populations; one population that had developed tolerance to Bd via MHC class II, and another that had not. We amplified, and sequenced MHC class II genes from all populations, and quantified the number of beneficial alleles shared between species. The proportion of MHC class II beneficial alleles was determined in each R. catesbeiana population and was compared against the proportions found in the tolerant and non-tolerant populations of R. yavapaiensis. Determining if phenotypically divergent species evolve the same way in response to disease remains an important question for amphibian conservation. Our study aims to broaden our understanding of the immunogenetic evolution of species that appear to be ubiquitously tolerant to Bd.
