Jan Ejsmond Maciej, Radwan Jacek, Wilson Anthony B
Institute of Environmental Sciences, Jagiellonian University, ul. Gronostajowa 7, 30-387 Krakow, Poland Department of Arctic Biology, The University Centre in Svalbard, Box 156, 9171 Longyearbyen, Norway.
Institute of Environmental Biology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznan, Poland.
Proc Biol Sci. 2014 Dec 7;281(1796):20141662. doi: 10.1098/rspb.2014.1662.
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, the stabilizing effects of sexual selection moderate the effects of drift, whereas pathogen-mediated selection accelerates the loss of functionally important genetic diversity. Natural selection enhances MHC allelic variation in larger populations, with the highest levels of diversity generated by the combined action of pathogen-mediated selection and disassortative mating. MHC-based sexual selection may help to explain how functionally important genetic variation can be maintained in populations of conservation concern.
主要组织相容性复合体（MHC）的基因是适应性免疫系统的关键组成部分，也是脊椎动物基因组中变化最大的基因座之一。病原体介导的自然选择和基于MHC的异交均被认为构成了MHC多态性，但在自然系统中，它们的影响很难区分。通过使用第一个同时纳入生存和繁殖的MHC动态模型，我们证明自然选择和性选择产生了MHC等位基因多样性的独特特征，这对理解宿主-病原体动态具有关键意义。虽然自然选择产生了宿主-寄生虫相互作用特有的红皇后动态，但异交使等位基因频率稳定，抑制了优势等位基因的主要波动，并保护功能变体不被漂变。这种细微的差异在MHC等位基因多样性和种群大小之间产生了复杂的相互作用。在小种群中，性选择的稳定作用缓和了漂变的影响，而病原体介导的选择加速了功能重要的遗传多样性的丧失。自然选择在较大种群中增强了MHC等位基因变异，病原体介导的选择和异交的联合作用产生了最高水平的多样性。基于MHC的性选择可能有助于解释如何在受保护关注的种群中维持功能重要的遗传变异。
