Meeting Abstract
The amphibian disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has contributed to the decline of the Federally threatened Chiricahua leopard frog (Lithobates chiricahuensis). We characterized immunogenetic variability in L. chiricahuensis by sequencing an expressed Major Histocompatibility Complex (MHC) class II gene across 16 natural populations in Arizona, USA, as well as from 250 individuals that were reared in captivity. We recovered a total of five class II MHC alleles, compared to 83 alleles previously characterized in 11 natural populations of the Arizona congener L. yavapaiensis, demonstrating reduced MHC diversity in L. chiricahuensis. One allele was fixed in four populations, higher MHC diversity was found at higher latitudes, and none of the L. chiricahuensis alleles were closely related to L. yavapaiensis allele Q, which is significantly associated with resistance to chytridiomycosis. Twelve L. chiricahuensis populations were Bd positive, and Bd prevalence was significantly lower among individuals with homozygous compared to heterozygous MHC genotypes. Three class II alleles were recovered from captive reared individuals, which were released to natural populations for recapture surveys to assess MHC-based survival over winter when chytridiomycosis outbreaks are most severe. All recaptures were of the same MHC genotype, indicating that immunogenetics are important for survival under natural conditions. We conclude that the limited MHC variation in L. chiricahuensis is nonetheless important for driving survival in the face of Bd, and may reflect selective sweeps that have removed susceptibility alleles from populations.
