Variation at the MHCI and MHCII gene regions in Squalus acanthias : evidence for selection.

Abstract

Determining levels of adaptive molecular variation can be important in understanding the long-term viability of a population and can provide essential information for conservation efforts. High levels of molecular variation are found at Major Histocompatibility Complex (MHC) genes, which code for cell-surface molecules that bind pathogen-derived peptides and help activate an adaptive immune response. The goal of this study was to determine the level of variation at the peptide binding region (PBR) of MHC molecules by comparing it to other coding and non-coding regions in hopes of determining a footprint of selection. Squalus acanthias, commonly known as spiny dogfish, was the species of interest in this study, and spiny dogfish populations all over the world have been declining due to overfishing. These dramatic population declines have the ability to decrease molecular variation throughout the spiny dogfish genome; however, data showed that variation at the MHC loci in the form of nucleotide substitutions, substitutions leading to amino acid changes and heterozygosity was able to persist at levels much greater than in other coding and non-coding regions. This suggests that balancing selection and heterozygote advantage are some of the selective mechanisms acting on the MHC.