The Evolutionary Ecology of Mayor Histocampability Complex

School of Biological Sciences, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, UK.
Heredity (Impact Factor: 3.81). 02/2006; 96(1):7-21. DOI: 10.1038/sj.hdy.6800724
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The major histocompatibility complex (MHC) has become a paradigm for how selection can act to maintain adaptively important genetic diversity in natural populations. Here, we review the contribution of studies on the MHC in non-model species to our understanding of how selection affects MHC diversity, emphasising how ecological and ethological processes influence the tempo and mode of evolution at the MHC, and conversely, how variability at the MHC affects individual fitness, population dynamics and viability. We focus on three main areas: the types of information that have been used to detect the action of selection on MHC genes; the relative contributions of parasite-mediated and sexual selection on the maintenance of MHC diversity; and possible future lines of research that may help resolve some of the unanswered issues associated with MHC evolution.

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Available from: Matthew K Oliver, Oct 13, 2015
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    • "Thus, the specific MHC class II allele setting of an individual determines directly its capability to resist or defend specific parasitic infections. The extraordinary high genetic diversity of the MHC genes is believed to be maintained by a number of non-neutral mechanisms (Bernatchez and Landry 2003; Piertney and Oliver 2006). Three major mechanisms have been hypothesized, based on heterozygote advantage, negative frequency-dependent selection, and fluctuating selection (Spurgin and Richardson 2010). "
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    ABSTRACT: Genes that play key roles in host immunity such as the major histocompatibility complex (MHC) in vertebrates are expected to be major targets of selection. It is well known that environmental conditions can have an effect on host–parasite interactions and may thus influence the selection on MHC. We analyzed MHC class IIß variability over 35 years in a population of perch (Perca fluviatilis) from the Baltic Sea that was split into two populations separated from each other. One population was subjected to heating from cooling water of a nuclear power plant and was isolated from the surrounding environment in an artificial lake, while the other population was not subjected to any change in water temperature (control). The isolated population experienced a change of the allelic composition and a decrease in allelic richness of MHC genes compared to the control population. The two most common MHC alleles showed cyclic patterns indicating ongoing parasite–host coevolution in both populations, but the alleles that showed a cyclic behavior differed between the two populations. No such patterns were observed at alleles from nine microsatellite loci, and no genetic differentiation was found between populations. We found no indications for a genetic bottleneck in the isolated population during the 35 years. Additionally, differences in parasitism of the current perch populations suggest that a change of the parasite communities has occurred over the isolation period, although the evidence in form of in-depth knowledge of the change of the parasite community over time is lacking. Our results are consistent with the hypothesis of a selective sweep imposed by a change in the parasite community.
    Ecology and Evolution 02/2015; 5(7). DOI:10.1002/ece3.1426 · 2.32 Impact Factor
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    • "Advance Access publication December 4, 2014 lineage-specific bouts of adaptive evolution may dominate the dynamics of vertebrate TLRs (Tschirren et al. 2011, 2012; Quach et al. 2013; Grueber et al. 2014). Thus, although adaptive changes in TLR genes may be subtle in comparison to other components of the immune system (Piertney and Oliver 2006; Downing et al. 2010; Quintana-Murci and Clark 2013), these genes should be incorporated into research aiming to understand associations between genetic variation and susceptibility to pathogens in natural populations (Tschirren et al. 2013). "
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    ABSTRACT: Acute die-offs of amphibian populations worldwide have been linked to the emergence of viral and fungal diseases. Inter- and intra-specific immunogenetic differences may influence the outcome of infection. Toll-like receptors (TLRs) are an essential component of innate immunity and also prime acquired defenses. We report the first comprehensive assessment of TLR gene variation for urodele amphibians. The Lissotriton newt TLR repertoire includes representatives of 13 families and is compositionally most similar to that of the anuran Xenopus. Both ancient and recent gene duplications have occurred in urodeles, bringing the total number of TLR genes to at least 21. Purifying selection has predominated the evolution of newt TLRs in both long (~70 million years ago) and medium (~18 mya) timescales. However, we find evidence for both purifying and positive selection acting on TLRs in two recently diverged (2-5 mya) allopatric evolutionary lineages (L. montandoni and L. vulgaris graecus). Overall, both forms of selection have been stronger in L. v. graecus, while constraint on most TLR genes in L. montandoni appears relaxed. The differences in selection regimes are unlikely to be biased by demographic effects because these were controlled by means of a historical demographic model derived from an independent dataset of 62 loci. We infer that TLR genes undergo distinct trajectories of adaptive evolution in closely related amphibian lineages, highlight the potential of TLRs to capture the signatures of different assemblages of pathogenic microorganisms, and suggest differences between lineages in the relative roles of innate and acquired immunity. © The Author(s) 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.
    Genome Biology and Evolution 12/2014; 7(1). DOI:10.1093/gbe/evu266 · 4.23 Impact Factor
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    • "The most accepted ones refer to the effects of specific alleles in parasite and pathogen resistance ('rare allele advantage hypothesis', 'negative frequency-dependent selection') (Clarke and Kirby 1966), 'heterozygote advantage' (Doherty and Zinkernagel 1975) and 'fluctuating selection' ('selection that varies in space or time') (Hill 1991; Hedrick 2002). Indeed, growing evidence of associations between specific MHC alleles/haplotypes and parasites/disease supports the view that pressure from pathogens is the primary source of selection on MHC polymorphism (reviewed by Sommer 2005; Piertney and Oliver 2006; Radwan et al. 2009). However, fully separating pathogenmediated selection mechanisms like e.g. "
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    ABSTRACT: Empirical evidence is accumulating that pathogens drive selection and explain common patterns of high immune gene (major histocompatibility complex, MHC) polymorphism. While most previous studies have identified that selection has acted over large time scales on the MHC, there still is a paucity of information in mammal species that demonstrates how processes operate on MHC genes in extant generations. Here we investigated 439 striped mouse individuals (Rhabdomys pumilio), trapped across seven different locations along a climatic gradient in southern Africa. Data from a previous study, conducted in the same study system, revealed that gastro-intestinal nematode infections were higher in individuals from study sites located within wetter climates compared to those from drier ones. In order to improve our understanding about the role of parasite-driven selection on the MHC in contemporary generations we tested for population divergences based on seven neutral microsatellite markers and the MHC DRB exon II locus. If divergences exist, we wanted to know if they are influenced by the spatial variation in parasite pressure mediated by different climatic conditions along the study site transect. Our analysis revealed an extensive polymorphism of 249 different MHC alleles and isolation-by-distance showed significant correlations at the microsatellite loci but not at the MHC. Nematode pressure was lowest at the driest site (Fish River Canyon, Namibia) and specifically this population revealed the highest divergence between MHC and microsatellite loci. We conclude that spatial variation in parasite pressure can facilitate local immune gene adaptations and thus mediate interactions of directional and balancing selection shaping MHC polymorphism in contemporary generations.
    Evolutionary Ecology 11/2014; 28(6):1169-1190. DOI:10.1007/s10682-014-9731-x · 2.52 Impact Factor
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