Sexual selection and the evolution of the Major Histocompatibility Complex

The genes of the major histocompatibility complex (MHC) are a key component of the adaptive immune system and among the most variable loci in the vertebrate genome. Pathogen-mediated natural selection and MHC-based disassortative mating are both thought to structure MHC polymorphism, but their effects have proven difficult to discriminate in natural systems. Using the first model of MHC dynamics incorporating both survival and reproduction, we demonstrate that natural and sexual selection produce distinctive signatures of MHC allelic diversity with critical implications for understanding host–pathogen dynamics. While natural selection produces the Red Queen dynamics characteristic of host–parasite interactions, disassortative mating stabilizes allele frequencies, damping major fluctuations in dominant alleles and protecting functional variants against drift. This subtle difference generates a complex interaction between MHC allelic diversity and population size. In small populations, th...主要组织相容性复合体（MHC）基因是适应性免疫系统的核心组成部分，亦是脊椎动物基因组中多态性最高的基因座之一。学界普遍认为，病原体介导的自然选择与基于MHC的异型交配共同塑造了MHC的多态性，但二者在自然种群中的作用效应难以区分。本研究首次采用整合了存活与繁殖过程的MHC动态模型，证实自然选择与性选择可产生具有独特特征的MHC等位基因多样性模式，这对解析宿主-病原体动态具有关键意义。自然选择会催生宿主-寄生虫互作中典型的红皇后动态，而异型交配则可稳定等位基因频率，抑制优势等位基因的剧烈波动，并保护功能变异体免遭遗传漂变的影响。这种细微差异会引发MHC等位基因多样性与种群大小之间的复杂相互作用。在小型种群中，……