title: Contrasting evolutionary histories of MHC class I and class II loci in grouse--effects of selection and gene conversion.
abstract: Genes of the major histocompatibility complex (MHC) encode receptor molecules that are responsible for recognition of intracellular and extracellular pathogens (class I and class II genes, respectively) in vertebrates. Given the different roles of class I and II MHC genes, one might expect the strength of selection to differ between these two classes. Different selective pressures may also promote different rates of gene conversion at each class. Despite these predictions, surprisingly few studies have looked at differences between class I and II genes in terms of both selection and gene conversion. Here, we investigated the molecular evolution of MHC class I and II genes in five closely related species of prairie grouse (Centrocercus and Tympanuchus) that possess one class I and two class II loci. We found striking differences in the strength of balancing selection acting on MHC class I versus class II genes. More than half of the putative antigen-binding sites (ABS) of class II were under positive or episodic diversifying selection, compared with only 10% at class I. We also found that gene conversion had a stronger role in shaping the evolution of MHC class II than class I. Overall, the combination of strong positive (balancing) selection and frequent gene conversion has maintained higher diversity of MHC class II than class I in prairie grouse. This is one of the first studies clearly demonstrating that macroevolutionary mechanisms can act differently on genes involved in the immune response against intracellular and extracellular pathogens.
authors: Department of Teacher Training and Biodiversity Studies, University of Łódź, Łódź, Poland.|Behavioral and Molecular Ecology Group, Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA.
authors: P
authors: P
authors: Minias
authors: Behavioral and Molecular Ecology Group, Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA.
authors: Z W
authors: ZW
authors: Bateson
authors: Behavioral and Molecular Ecology Group, Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA.
authors: L A
authors: LA
authors: Whittingham
authors: Department of Biological Sciences, Institute of Applied Sciences, University of North Texas, Denton, TX, USA.
authors: J A
authors: JA
authors: Johnson
authors: Fort Collins Science Center, US Geological Survey, Fort Collins, CO, USA.
authors: S
authors: S
authors: Oyler-McCance
authors: Behavioral and Molecular Ecology Group, Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA.
authors: P O
authors: PO
authors: Dunn
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D046094:Galliformes / Q000145:classification / Q000235:genetics*; D005785:Gene Conversion; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010802:Phylogeny; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA