Abstract
We tested how variation at a gene of adaptive importance, MHC class I (UBA), in a wild, endemic Salmo trutta population compared to that in both a previously studied non-native S. trutta population and a co-habiting Salmo salar population (a sister species). High allelic diversity is observed and allelic divergence is much higher than that noted previously for co-habiting S. salar. Recombination was found to be important to population-level divergence. The α1 and α2 domains of UBA demonstrate ancient lineages but novel lineages are also identified at both domains in this work. We also find examples of recombination between UBA and the non-classical locus, ULA. Evidence for strong diversifying selection was found at a discrete suite of S. trutta UBA amino acid sites. The pattern was found to contrast with that found in re-analysed UBA data from an artificially stocked S. trutta population.
Highlights
Genes of adaptive importance are of growing interest to conservation genetics [1]
These studies were based on a MH class I marker and, it is of clear interest to examine allelic diversity, sequence polymorphism and selection at class I itself in S. trutta
How do patterns of allelic diversity, divergence and codon-level selection differ between the wild and artificial stock? A previous study examined MH class I in S. salar which share the same Irish river and similar exposure to pathogens over time [36], and here we investigate how the native brown trout compare with these? it was felt that the new data from wild brown trout might reveal important phylogenetic novelties and help identify whether patterns of selection vary amongst salmonid species
Summary
Genes of adaptive importance are of growing interest to conservation genetics [1]. Major Histocompatibility Complex loci are critical to immune function and highly polymorphic. Variation at MHC affects their ability to bind different types of peptide and is adaptive in helping to resist disease [2,3,4,5]. Populations which lose this variation [6,7] may be of conservation concern [1]. MHC class I showed lower population differentiation than neutral markers across trout populations while variation at class I was maintained in populations isolated above waterfalls where it was lost at neutral markers [8] Both of these phenomena are expected for a gene under balancing selection. These studies were based on a MH class I marker and, it is of clear interest to examine allelic diversity, sequence polymorphism and selection at class I itself in S. trutta
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