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Abstract
BackgroundIn evolutionary and conservation biology, parasitism is often highlighted as a major selective pressure. To fight against parasites and pathogens, genetic diversity of the immune genes of the major histocompatibility complex (MHC) are particularly important. However, the extensive degree of polymorphism observed in these genes makes it difficult to conduct thorough population screenings.MethodsWe utilized a genotyping protocol that uses 454 amplicon sequencing to characterize the MHC class I in the endangered loggerhead sea turtle (Caretta caretta) and to investigate their evolution at multiple relevant levels of organization.ResultsMHC class I genes revealed signatures of trans-species polymorphism across several reptile species. In the studied loggerhead turtle individuals, it results in the maintenance of two ancient allelic lineages. We also found that individuals carrying an intermediate number of MHC class I alleles are larger than those with either a low or high number of alleles.ConclusionsMultiple modes of evolution seem to maintain MHC diversity in the loggerhead turtles, with relatively high polymorphism for an endangered species.
Highlights
In evolutionary and conservation biology, parasitism is often highlighted as a major selective pressure
The loggerhead turtle shows major histocompatibility complex (MHC) alleles that display closer allelic relationships between species than within species - suggesting trans-species polymorphism over a large range of reptile species and/or a duplication event prior to speciation
Phylogeny of MHC in the Cape Verde rookery The phylogenies within the loggerhead turtle population from Cape Verde based on mtDNA and MHC class I alleles were discordant
Summary
In evolutionary and conservation biology, parasitism is often highlighted as a major selective pressure. To fight against parasites and pathogens, genetic diversity of the immune genes of the major histocompatibility complex (MHC) are important. In vertebrates, growing evidence suggests that genetic diversity is especially important at the level of the major histocompatibility complex (MHC, [2,3,4]). Since the primary function of MHC molecules is to present parasite-derived peptides to T-lymphocytes, it has been argued that parasites and pathogens are major selective pressures acting on the evolution of MHC genes [1,2,5,6]. The MHC polymorphism is especially high in the region that encodes for the peptide-binding domain. The residues of the α1 and α2 domains of the MHC class I molecules form the peptide-binding region. Antigenic peptides are anchored at specific residues called antigen binding sites, which are commonly found to be evolving under positive selection in natural populations (e.g. [8])
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