Polymorphism in the major histocompatibility complex (MHC class II B) genes of the Rufous-backed Bunting (Emberiza jankowskii)

Abstract

Genetic diversity is one of the pillars of conservation biology research. High genetic diversity and abundant genetic variation in an organism may be suggestive of capacity to adapt to various environmental changes. The major histocompatibility complex (MHC) is known to be highly polymorphic and plays an important role in immune function. It is also considered an ideal model system to investigate genetic diversity in wildlife populations. The Rufous-backed Bunting (Emberiza jankowskii) is an endangered species that has experienced a sharp decline in both population and habitat size. Many historically significant populations are no longer present in previously populated regions, with only three breeding populations present in Inner Mongolia (i.e., the Aolunhua, Gahaitu and Lubei557 populations). Efforts focused on facilitating the conservation of the Rufous-backed Bunting (Emberiza jankowskii) are becoming increasingly important. However, the genetic diversity ofE. jankowskiihas not been investigated. In the present study, polymorphism in exon 2 of the MHCIIB ofE. jankowskiiwas investigated. This polymorphism was subsequently compared with a related species, the Meadow Bunting (Emberiza cioides). A total of 1.59 alleles/individual were detected inE. jankowskiiand 1.73 alleles/individual were identified inE.cioides. The maximum number of alleles per individual from the threeE. jankowskiipopulations suggest the existence of at least three functional loci, while the maximum number of alleles per individual from the threeE. cioidespopulations suggest the presence of at least four functional loci. Two of the alleles were shared between theE. jankowskiiandE. cioides. Among the 12 unique alleles identified inE. jankowskii, 10.17 segregating sites per allele were detected, and the nucleotide diversity was 0.1865. Among the 17 unique alleles identified inE. cioides, eight segregating sites per allele were detected, and the nucleotide diversity was 0.1667. Overall, compared to other passerine birds, a relatively low level of MHC polymorphism was revealed inE. jankowskii, which was similar to that inE. cioides. Positive selection was detected by PAML/SLAC/FEL analyses in the region encoding the peptide-binding region in both species, and no recombination was detected. Phylogenetic analysis showed that the alleles fromE. jankowskiiandE. cioidesbelong to the same clade and the two species shared similar alleles, suggesting the occurrence of a trans-species polymorphism between the twoEmberizaspecies.