Genetic variation of major histocompatibility complex genes in the endangered red-crowned crane

Populations that have drastically decreased in the past often have low genetic variation, which may increase the risk of extinction. The genes of major histocompatibility complex (MHC) play an important role in the adaptive immune response of jawed vertebrates. Maintenance of adaptive genetic diversity such as that of MHC genes is important for wildlife conservation. Here, we determined genotypes of exon 3 of MHC class IA genes (MHCIA) and exon 2 of MHC class IIB genes (MHCIIB) to evaluate genetic variation of the endangered red-crowned crane population on Hokkaido Island, Japan, which experienced severe population decline in the past. We identified 16 and 6 alleles of MHCIA and MHCIIB, respectively, from 152 individuals. We found evidence of a positive selection at the antigen-binding sites in MHCIA exon 3 and MHCIIB exon 2. The phylogenetic analyses indicated evidence of trans-species polymorphism among the crane MHC genes. The genetic variability in both classes of MHC genes at the population level was low. No geographic structure was found based on the genetic diversity of microsatellite and MHC genes. Our study provides useful data for the optimal management of the red-crowned crane population in Hokkaido and can contribute to future studies on MHC genes of the continental populations of the red-crowned crane and other crane species.