Amphibians have undergone catastrophic declines worldwide and the major histocompatibility complex (MHC) is an
attractive candidate for investigating the link between adaptive variation and individual fitness. Nonetheless, little research
has been conducted to study the amphibians MHC genes. Thus, MHC class Ia of Odorrana margaretae, a representative
species of the Odorrana, was isolated and used to analyze the adaptive mechanism. We isolated alleles and determined
evolution patterns of MHC class Ia in O. margaretae. The phylogenetic tree of MHC class Ia was reconstructed to
understand the evolutionary relationship of Anura. In O. margaretae of MHC class Ia: there were more non-synonymous
mutations compared to synonymous mutations; there are at least two loci; the recombination alleles took place for a
large proportion (55.56%) of the alleles and recombination usually took place between whole exon of Ia genes of MHC
class; positive selection sites were detected and most (10 of 19) located at the α1 and α2 domains belonged to the
presumed ABS. The diversity of genes of MHC class Ia was led by recombination, gene duplication and positive selection.
Trans-species polymorphisms of anuran genes of MHC class Ia were evident in anurans. Therefore, the MHC class Ia
present demonstrative candidates for investigating the link between adaptive variation and individual fitness. We argue
that knowledge of the MHC of other anuran lineage, especially focusing a genus such as O. margaretae, should provide
an overall more complete picture of the organization of MHC in anurans.