Genetic polymorphisms

Female mate choice has been proposed to be a major force acting to maintain the polymorphism of the MHC, the most genetically variable genes known. I genotyped seventy-two individuals from a free-living population of the parrot, Forpus passerinus, in order to determine whether disassortative mating is the mode of selection acting at this locus. Both the high rate of nonsynonymous amino acid changes at the peptide binding regions of exon 2 of the class II beta gene and the unprecedented number of alleles found in this population provided strong evidence for the operation of selection. Despite this, a chi-square test revealed no evidence of disassortative mating for this sample, X2=0.569, n.s. I propose that natural selection, not sexual selection, must be operating at this locus to maintain the degree of variation found in 270 base-pairs of this gene.

The Major Histocompatibility Complex class II B (MHC II B) gene encodes a protein that is part of the adaptive immune system and critical for the non-self recognition ability of immune cells. This gene has been characterized in the Bald Eagle, ten unique alleles were found in two subpopulations at the geographic extremes of the range margins. Geographic genetic variation is suggested by the presence of population specific alleles. The results showed considerable divergence of groups of Bald Eagle alleles when compared to alleles from other birds of prey. Particular codons within the exon II show signs of balancing selection driving the evolution of the MHC II B. Transcription data showed statistically significant differential expression of alleles. This can be interpreted as meaning a particular locus is being preferentially expressed in blood. The analysis of the polymorphism of this adaptive marker may aid managers of wildlife during this age of global climate change and the biodiversity crisis.