Balancing selection,sexual selection and geographic structure in MHC genes of Great Snipe |
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Authors: | Robert Ekblom Stein Are Sæther Peder Fiske John Atle Kålås Jacob Höglund |
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Institution: | 1.Population Biology, Evolutionary Biology Center,Uppsala University,Uppsala,Sweden;2.Department of Animal and Plant Sciences,University of Sheffield,Sheffield,UK;3.Centre for Ecological and Evolutionary Synthesis, Department of Biology,University of Oslo,Blindern, Oslo,Norway;4.Norwegian Institute for Nature Research,Trondheim,Norway |
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Abstract: | Signatures of balancing selection are often found when investigating the extremely polymorphic regions of major histocompatibility
complex (MHC) genes, and it is generally accepted that selective forces maintain this polymorphism. However, the exact nature
of the selection is controversial. Theoretical studies have mainly focused on overdominance and/or frequency dependent selection
while laboratory studies have emphasised the role of mate choice. Empirical field data, on the other hand, have been relatively
scarce. Previously we have found that geographic structure in MHC class II genes of the Great Snipe (Gallinago media) is too pronounced to be explained by neutral forces alone. Here we test the hypothesis that sexual selection on MHC alleles
may be influencing this geographic structure between mountain and lowland populations. We found evidence of balancing selection
acting on MHC genes in the form of a higher rate of amino-acid changing substitutions compared to silent substitutions in
the peptide binding regions. Not only natural selection but also sexual selection may influence MHC polymorphism in this bird
because certain MHC alleles have been found to be associated with higher male mating success. Contrary to predictions from
negative frequency dependent selection, males carrying locally rare alleles did not have a mating advantage. Instead, the
mating success of alleles in a mountain population was positively correlated to their relative frequency in the mountains
compared to the lowlands, implying that locally adapted MHC alleles may also be favoured by sexual selection. |
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