Polymorphism and signature of selection in the MHC class I genes of the three-spined stickleback Gasterosteus aculeatus

Authors

  • H. Schaschl,

    Corresponding author
    1. * Department of Evolutionary Ecology, Max-Planck Institute for Limnology, August-Thienemann-Str. 2, 24306 Ploen, Germany, Konrad Lorenz Institute for Ethology, Austrian Academy of Sciences, Savoyenstrasse 1a, A-1160 Vienna, Austria and §ETH Zürich, Institute of Integrative Biology, Experimental Ecology, CHN H72, Universitätstrasse 16, 8092 Zurich, Switzerland
      ‡Tel.: +43 151581 2738; fax: +43 151581 2800; email: h.schaschl@gmx.net
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  • K. M. Wegner

    1. * Department of Evolutionary Ecology, Max-Planck Institute for Limnology, August-Thienemann-Str. 2, 24306 Ploen, Germany, Konrad Lorenz Institute for Ethology, Austrian Academy of Sciences, Savoyenstrasse 1a, A-1160 Vienna, Austria and §ETH Zürich, Institute of Integrative Biology, Experimental Ecology, CHN H72, Universitätstrasse 16, 8092 Zurich, Switzerland
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‡Tel.: +43 151581 2738; fax: +43 151581 2800; email: h.schaschl@gmx.net

Abstract

The role and intensity of positive selection maintaining the polymorphism of major histocompatibility complex (MHC) class I genes in the three-spined stickleback Gasterosteus aculeatus was investigated. The highly polymorphic set of MHC class I genes found was organized in a single linkage group. Between 5 and 14 sequence variants per individual were identified by single-stranded conformation polymorphism (SSCP) analysis. Segregation analysis studied in 10 three-spined stickleback families followed the expected pattern of Mendelian inheritance. The gamete fusion in three-spined stickleback thus seems to be random with respect to the MHC class I genes. The DNA sequence analyses showed that the expressed MHC class I loci are under strong selection pressure, possibly mediated by parasites. Codons that were revealed to be under positive selection are potentially important in antigen binding. MHC class I sequences did not form significant supported clusters within a phylogenetic tree. Analogous to MHC class II genes, it was not possible to assign the class I sequences to a specific locus, suggesting that the class I genes may have been generated by recent gene duplication.

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