title: Evidence for selection maintaining MHC diversity in a rodent species despite strong density fluctuations.
abstract: Strong spatiotemporal variation in population size often leads to reduced genetic diversity limiting the adaptive potential of individual populations. Key genes of adaptive variation are encoded by the immune genes of the major histocompatibility complex (MHC) playing an essential role in parasite resistance. How MHC variation persists in rodent populations that regularly experience population bottlenecks remains an important topic in evolutionary genetics. We analysed the consequences of strong population fluctuations on MHC class II DRB exon 2 diversity in two distant common vole (Microtus arvalis) populations in three consecutive years using a high-throughput sequencing approach. In 143 individuals, we detected 25 nucleotide alleles translating into 14 unique amino acid MHC alleles belonging to at least three loci. Thus, the overall allelic diversity and amino acid distance among the remaining MHC alleles, used as a surrogate for the range of pathogenic antigens that can be presented to T-cells, are still remarkably high. Both study populations did not show significant population differentiation between years, but significant differences were found between sites. We concluded that selection processes seem to be strong enough to maintain moderate levels of MHC diversity in our study populations outcompeting genetic drift, as the same MHC alleles were conserved between years. Differences in allele frequencies between populations might be the outcome of different local parasite pressures and/or genetic drift. Further understanding of how pathogens vary across space and time will be crucial to further elucidate the mechanisms maintaining MHC diversity in cyclic populations.
authors.affiliation: Department of Comparative Zoology, Institute for Evolution and Ecology, Eberhard Karls University Tuebingen, Auf der Morgenstelle 28, 72076, Tuebingen, Germany.|Animal Ecology, Institute of Biochemistry and Biology, University of Potsdam, Maulbeerallee 1, 14469, Potsdam, Germany.
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Schuster
authors.affiliation: Animal Ecology, Institute of Biochemistry and Biology, University of Potsdam, Maulbeerallee 1, 14469, Potsdam, Germany.|Department of Plant Ecology and Nature Conservation, Institute of Biochemistry and Biology, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Herde
authors.affiliation: Evolutionary Genetics, Leibniz-Institute for Zoo and Wildlife Research (IZW), Alfred-Kowalke-Straße 17, 10315, Berlin, Germany.|Berlin Center for Genomics in Biodiversity Research, Koenigin-Luise-Straße 6-8, 14195, Berlin, Germany.
authors.forename: Camila J
authors.initials: CJ
authors.lastname: Mazzoni
authors.affiliation: Animal Ecology, Institute of Biochemistry and Biology, University of Potsdam, Maulbeerallee 1, 14469, Potsdam, Germany.
authors.forename: Jana A
authors.initials: JA
authors.lastname: Eccard
authors.affiliation: Evolutionary Genetics, Leibniz-Institute for Zoo and Wildlife Research (IZW), Alfred-Kowalke-Straße 17, 10315, Berlin, Germany. Simone.Sommer@uni-ulm.de.|Institute of Evolutionary Ecology and Conservation Genomics, University of Ulm, Albert-Einstein Allee 11, 89069, Ulm, Germany. Simone.Sommer@uni-ulm.de.
authors.forename: Simone
authors.initials: S
authors.lastname: Sommer
mesh_terms: D000818:Animals; D003411:Arvicolinae / Q000235:genetics*; D005787:Gene Frequency; D040961:Genetic Drift; D014644:Genetic Variation / Q000235:genetics*; D005828:Genetics, Population; D008285:Major Histocompatibility Complex / Q000235:genetics*; D010802:Phylogeny; D012641:Selection, Genetic / Q000235:genetics*
keywords: Common vole; High-throughput next-generation sequencing; MHC diversity; Microtus arvalis; Population cycle; Selection