Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA.
Proc Natl Acad Sci U S A. 2011 Oct 4;108(40):16705-10. doi: 10.1073/pnas.1106893108. Epub 2011 Sep 26.
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.
新兴的两栖动物疾病壶菌病是由真菌病原体蛙壶菌（Batrachochytrium dendrobatidis，Bd）引起的。两栖动物种群和物种对 Bd 的易感性存在差异，但我们对这种自然变异的遗传基础知之甚少。MHC 基因座编码在脊椎动物中引发获得性免疫的肽，这使它们成为确定疾病易感性的候选基因。然而，MHC 基因在壶菌病的背景下从未被描述过。在这里，我们对从五个表现出 Bd 易感性自然变异的种群中收集的实验室饲养的青蛙进行了实验性 Bd 感染。我们发现，一个表达的 MHC 类 IIB 基因座的等位基因与 Bd 感染后的存活有关。在不同的种群中，MHC 杂合性是存活的重要预测因子。在种群内部，MHC 杂合子和携带 MHC 等位基因 Q 的个体死亡风险显著降低，并且我们在导致等位基因 Q 的进化谱系中检测到了显著的正选择信号。我们的研究结果表明，免疫遗传变异在受控的实验条件下影响壶菌病的存活，证实宿主遗传多态性有助于对抗壶菌病。
