Limited polymorphism of the functional MHC class II B gene in the black‐spotted frog (Pelophylax nigromaculatus) identified by locus‐specific genotyping

Abstract

Amphibians can be more vulnerable to environmental changes and diseases than other species because of their complex life cycle and physiological requirements. Therefore, understanding the adaptation of amphibians to environmental changes is crucial for their conservation. Major histocompatibility complex (MHC) presents an excellent tool for the investigation of adaptive variations and the assessment of adaptive potential because it can be under strong diversifying selection. Here, we isolated the MHC class II B (MHCIIB) gene from cDNA sequences of the black‐spotted frog (Pelophylax nigromaculatus), a widespread amphibian species in China, and designed locus‐specific primers to characterize adaptive variability of this amphibian. Ten alleles were identified from 67 individual frogs of three populations and no more than two alleles were present in each individual animal. Furthermore, none of the sequences had indels or/and stop codons, which is in good agreement with locus‐specific amplification of a functional gene. However, we found low polymorphism at both nucleotide and amino acid levels, even in the antigen‐binding region. Purifying selection acting at this locus was supported by the findings that the dN/dS ratio across all alleles was below 1 and that negatively selected sites were detected by different methods. Allele frequency distributions were significantly different among geographic populations, indicating that physiographic factors may have strong effect on the genetic structure of the black‐spotted frog. This study revealed limited polymorphism of three adjacent black‐spotted frog populations at the functional MHCIIB locus, which may be attributed to region‐specific differences. The locus‐specific genotyping technique developed in this study would provide a foundation for future studies on adaptive divergence among different frog populations.

Conserved Evolution of MHC Supertypes among Japanese Frogs Suggests Selection for Bd Resistance

“…The other species included for MHC-II supertyping were: (a) B. orientalis and B. gargarizans (resistant) from South Korea [ 16 ]; (b) L. catesbeiana (transcriptome data, DRA accession number SRP051787); (c) L. yavapaiensis from North America [ 18 ]; (d) Z. omeimontis from China [ 45 ]; (e) representative sequences from Epidalea calamita (low susceptibility), Nanorana parkeri (susceptibility unclear), Rhinella marina (tolerant), and Quasipaa spinosa (susceptibility unclear) available in GenBank; and (f) L. verreauxii alpina (susceptible) from Australia but with some resistant populations or individuals [ 16 ]. MHC-IIb sequences from Chinese populations of P. nigromaculatus [ 46 ] were initially included but formed a very distinct ST cluster and thereby excluded.…”

Cape Feather Coloration Signals Different Genotypes of the Most Polymorphic MHC Locus in Male Golden Pheasants (Chrysolophus pictus)

“…The heterozygote advantage hypothesis suggests that heterozygous genotypes have a higher relative fitness than homozygous genotypes. The diversity mechanism of MHC is a classic example of heterozygote advantage selection, as MHC heterozygous genotypes can potentially provide resistance to a wider range of antigens [ 9 , 10 ]. Many studies have found direct evidence for MHC-based mate choice [ 4 , 6 , 11 , 12 , 13 ].…”