MHC class I genes of birds of prey: isolation, polymorphism and diversifying selection

The threat of emerging infectious diseases encourages the investigation of functional loci related to host resilience, such as those belonging to the major histocompatibility complex (MHC). Through careful primer design targeting to conserved regions of MHC class I sequences in birds, we successfully amplified a genomic fragment spanning exons 2-4 in three birds of prey. The identification of a highly conserved region within intron 2 allowed cross-amplifying complete exon 3 sequences in diurnal raptors, owls and New World vultures. We found evidence through PCR and cloning for 1-2 polymorphic class I loci, although this is almost certainly an underestimate. Inferences of diversifying selection in the kestrel MHC revealed that the two major regions of exon 3 exhibiting positive selection mostly agree with those described for the human HLA-A2 molecule. In contrast to passerines, where a high incidence of gene duplications and pseudogenes has been commonly documented, birds of prey emerge as nice model species for the investigation of the evolutionary significance and conservation implications of MHC diversity in vertebrates.