Meeting Abstract
Genes of the vertebrate Major Histocompatibility Complex (MHC) defend against disease by making cell-surface proteins that display pathogen peptides to the immune system. Class II MHC proteins are heterodimers encoded by two different genes, but most studies of natural selection or sexual selection have focused only on the II B genes which encode the beta subunit. Here, we characterize MHC Class II A genes in Leach’s storm-petrels and then synthesize data across vertebrate species to examine the evolutionary dynamics of these understudied II A genes. Leach’s storm-petrels fit the dogma that II A genes are oligomorphic, but our meta-analysis shows that several other species have more than 40 II A alleles within a single population. In many species, allelic polymorphism was similar between II A and II B genes. Less surprisingly, the number of alleles found per species was positively related to sampling effort. However, there was an additional effect of taxonomic group, with fish having more alleles per species than mammals. We found no support for the hypothesis that gene duplication and proliferation of allelic diversity are negatively correlated, that is, that they could be alternative routes to generating a consistently high level of functional diversity in the alpha subunit of the protein. Analyses are in progress to compare signatures of selection at these two groups of genes, to test the hypothesis that II A should show more purifying selection in comparison to the common finding of diversifying selection at II B. Overall results will help determine whether studies of pathogen-mediated selection should continue to neglect the alpha subunit of the protein.
