Allelic characterization of the second DRB locus of major histocompatibility complex class II in Ussuri sika deer (Cervus nippon hortulorum): highlighting the trans-species evolution of DRB alleles within Cervidae

摘要

MHC (major histocompatibility complex)-DRB variability reflects evolutionarily relevant and adaptive processes within and between populations, and is suitable for the investigation of a wide range of questions in evolutionary ecology. Using motif-specific polymerase chain reaction (PCR), single-stranded conformation polymorphism (SSCP) analyses and direct sequencing, 15 DRB-2 alleles were identified from 43 Ussuri sika deer. Extensive sequence variation was detected at peptide-binding region (PBR) or positively selected sites (PSS) sites among DRB loci, which were proved to be maintained by positive selection. DRB-2 loci of the Ussuri sika deer were strikingly similar to those of red deer after comparing sequences. In phylogenetic analysis, DRB-2 alleles of Ussuri sika deer were not monophyletic with respect to red deer, white-tailed deer, fallow deer, and roe deer sequences. Two DRB-2 alleles of the species tended to cluster together with those of white-tailed deer or red deer with high bootstrap values, respectively. Considering that sika and red deer are closely related, and their hybridization is occasionally seen in areas of range overlap, and their mtDNAs are paraphyletic to white-tailed deer, fallow deer, and other Cervus species, we suggested that these similarities result from trans-species evolution rather than convergent evolution.