MHC genotypes associate with resistance to a frog-killing fungus

Abstract

The emerging amphibian disease chytridiomycosis is caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd). Amphibian populations and species differ in susceptibility to Bd, yet we know surprisingly little about the genetic basis of this natural variation. MHC loci encode peptides that initiate acquired immunity in vertebrates, making them likely candidates for determining disease susceptibility. However, MHC genes have never been characterized in the context of chytridiomycosis. Here, we performed experimental Bd infections in laboratory-reared frogs collected from five populations that show natural variation in Bd susceptibility. We found that alleles of an expressed MHC class IIB locus associate with survival following Bd infection. Across populations, MHC heterozygosity was a significant predictor of survival. Within populations, MHC heterozygotes and individuals bearing MHC allele Q had a significantly reduced risk of death, and we detected a significant signal of positive selection along the evolutionary lineage leading to allele Q. Our findings demonstrate that immunogenetic variation affects chytridiomycosis survival under controlled experimental conditions, confirming that host genetic polymorphisms contribute to chytridiomycosis resistance.emerging infectious disease | experimental infection | major histocompatibility complex | molecular evolution | Ranidae

The other white‐nose syndrome transcriptome: Tolerant and susceptible hosts respond differently to the pathogen Pseudogymnoascus destructans

“…A resistant and susceptible pair of frog species exposed to the fungal pathogen Batrachochytridium dendrobatidis upregulated the same biological processes, but experienced different disease outcomes (Rosenblum et al., 2012). Similarly, survival following exposure to B. dentrobaditis is correlated with particular MHC allele sequences in red‐eyed tree frogs ( Agalychnis callidryas ; Savage & Zamudio, 2011), implying that these alleles may confer tolerance to the pathogen. In the second scenario, tolerant/resistant and susceptible hosts upregulate different biological responses to infection.…”

Extensive diversification of MHC in Chinese giant salamanders Andrias davidianus (Anda-MHC) reveals novel splice variants

“…Compelling evidence showing high similarity in MHC structure and complexity between amphibians and mammals, and also close associations between MHC diversity and diseases resistance (Savage and Zamudio, 2011;Teacher et al, 2009). However, little information has so far been available about the functional role of MHC in the Chinese giant salamander.…”

MHC influences infection with parasites and winter survival in the root vole Microtus oeconomus

“…Among fish species, MHC genotype influenced the survival of embryos that had been exposed to bacterial infection (Wedekind et al 2004), and individuals with homozygous MHC genotypes survived better when infected with flukes than did heterozygotes (Hedrick et al 2001). In frogs, alleles from the MHC class IIB locus were associated with increased survival following experimental infection with chytridiomycosis, an emerging disease (Savage and Zamudio 2011). In contrast, although MHC heterozygosity increased survival in male chamois, there was no evidence for an MHC-related survival advantage in populations exposed to scabies (Schaschl et al 2012).…”