Genetic diversity of the major histocompatibility complex of cotton rats (Sigmodon hispidus) inhabiting an oil refinery complex.

We examined genetic diversity of an immune-response gene within the major histocompatibility complex in cotton rats (Sigmodon hispidus) inhabiting an oil refinery complex. Genetic diversity of MHC-DQA exon-2 was examined within and among contaminated and noncontaminated reference grids. The level of gene diversity within contaminated grids (0.748) was lower than within reference grids (0.818), but the difference was not statistically significant (p > 0.5). Analysis of molecular variance, pairwise FST values, and hierarchical clustering failed to reveal population genetic structure related to contamination. Results of this study indicate either that the level of contaminant-induced selection is insignificant at this major histocompatibility complex (MHC) locus or that gene flow from surrounding areas has obliterated the effects of selection.