Meeting Abstract

P1.167  Saturday, Jan. 4 15:30  Positive selection and recombination in the MHC of mainland and island killifish WHITE, ME*; COHEN, CS; Macalester College; Romberg Tiburon Center, Biology, San Francisco State University mwhite2@macalester.edu

Analyses of genetic variation at the antigen-binding sites of the adaptive immune loci in vertebrates often show strong signals of positive diversifying selection, and the study of wild populations subject to differing environments can be used to examine the processes that generate and maintain this diversity. We compared genetic variation in 10 Fundulus populations from Bermuda and from mainland locations in southern New England. The 3 mainland populations are associated with a strong pollution gradient, while 5 island F. heteroclitus populations, and a narrowly distributed island endemic F. relictus (2 populations) show evidence of genetic bottlenecks. Intron analysis revealed two phylogenetically distinct lineages that are interpreted to reflect distinct loci allowing estimation of recombination rates in exon sequence within and between duplicated loci. Mainland and bottlenecked island populations of F. heteroclitus show strong signals of positive selection in the PBR region of Class II MH DB. All populations of both species show higher variation in the exon in comparison to the intron, however island F. heteroclitus show lower exon and intron haplotype and allelic diversity than mainland populations. Comparison of recombination rate estimates among populations suggests recombination as an important contributor to MHC diversity. In particular, higher recombination rates and non-synonymous substitution rates are associated with higher pollution levels in a comparison among the three mainland populations studied. These results suggest that the bottleneck event experienced by the Bermuda fish resulted in a significant lack of diversity, a diversity which is generated and maintained in a large part by microrecombination and gene conversion.