Diversity of the Major Histocompatibility Complex Region Among Seven Founders of the Crested Ibis Nipponia nippon in Japan.

The Crested Ibis Nipponia nippon is a critically threatened avian species. The current Japanese population originates from only seven founders introduced from China. The major histocompatibility complex (MHC) is a highly polymorphic genomic region that plays a central role in the immune system. We previously reported that only three MHC class II haplotypes (HP1-3) with one to three copies of MHC-IIA/IIB gene pairs (one copy of DAA/DAB locus and 0-2 copies of DBA/DBB loci) were detected among the five older founders, and four MHC-IIB exon 2 alleles (Type I-IV) were identified. In this study, MHC class II haplotypes in two novel founders, and MHC class IA genotypes at UAA locus in the seven founders were investigated. Of the two novel founders, while one possessed known HP1 and HP2, another possessed known HP1 and a novel haplotype (HP4) with the combination of type II and type I in DAB and DBB exon 2 s, respectively. Analysis of the linkage between MHC class II haplotypes and UAA alleles revealed five distinct MHC haplotypes against seven founders. These results strongly suggested that the founders might be considerably closely related, and the novel HP4 was produced by recombination between HP1 and HP2.