The MHC Class Ia Genes in Chenfu's Treefrog ( Zhangixalus chenfui ) Evolved via Gene Duplication, Recombination, and Selection

The molecular mechanisms underlying the evolution of adaptive immunity-related proteins can be deduced by a thorough examination of the major histocompatibility complex (MHC). Currently, in vertebrates, there is a relatively large amount of research on MHCs in mammals and birds. However, research related to amphibian genes and knowledge about the evolutionary patterns is limited. This study aimed to isolate the genes from Chenfu's Treefrog ( and reveal the underlying evolutionary processes. A total of 23 alleles spanning the coding region of genes were identified in 13 individual samples. Multiple approaches were used to test and identify recombination from the 23 alleles. Amphibian alleles, from NCBI, were used to construct the phylogenetic relationships in MEGA. Additionally, the partition strategy was adopted to construct phylogenetic relationships using MrBayes and MEGA. The sites of positive selection were identified by FEL, PAML, and MEME. In Chenfu's Treefrog, we found that: (1) recombination usually takes place between whole exons of genes; (2) there are at least 3 loci for , and (3) the diversity of genes in can be attributed to recombination, gene duplication, and positive selection. We characterized the evolutionary mechanisms underlying genes in Chenfu's Treefrog, and in so doing, broadened the knowledge of amphibian MHC systems.