title: Sexual selection and the evolutionary dynamics of the major histocompatibility complex.
abstract: 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.
authors.affiliation: 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.
authors.forename: Maciej
authors.initials: M
authors.lastname: Jan Ejsmond
authors.affiliation: Institute of Environmental Biology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznan, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Radwan
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland Department of Biology, Brooklyn College and The Graduate Center, City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA twilson@brooklyn.cuny.edu.
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Wilson
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003247:Conservation of Natural Resources; D005787:Gene Frequency; D014644:Genetic Variation; D054884:Host-Pathogen Interactions / Q000235:genetics; D008285:Major Histocompatibility Complex / Q000235:genetics*; D052586:Mating Preference, Animal; D008957:Models, Genetic; D011156:Population Density; D012098:Reproduction
keywords: adaptive immunity; disassortative mating; genetic drift; natural selection; pathogen-mediated selection; sexual selection