Association between the skin microbiome and MHC class II diversity in an amphibian

Microbiomes play an important role in determining the ecology and behaviour of their hosts. However, questions remain pertaining to how host genetics shape microbiomes, and how microbiome composition influences host fitness. We explored the effects of geography, evolutionary history and host genetics on the skin microbiome diversity and structure in a widespread amphibian. More specifically, we examined the association between bacterial diversity and composition and the major histocompatibility complex class II exon 2 diversity in 12 moor frog (Rana arvalis) populations belonging to two geographical clusters that show signatures of past and ongoing differential selection. We found that while bacterial alpha diversity did not differ between the two clusters, MHC alleles/supertypes and genetic diversity varied considerably depending on geography and evolutionary history. Bacterial alpha diversity was positively correlated with expected MHC heterozygosity and negatively with MHC nucleotide diversity. Furthermore, bacterial community composition showed significant variation between the two geographical clusters and between specific MHC alleles/supertypes. Our findings emphasize the importance of historical demographic events on hologenomic variation and provide new insights into how immunogenetic host variability and microbial diversity may jointly influence host fitness with consequences for disease susceptibility and population persistence.

Historical gene flow and profound spatial genetic structure among golden pheasant populations suggested by multi-locus analysis

Major histocompatibility complex (MHC) is a good marker system for geographical genetics since they are functional genes in the immune system that are likely to affect the fitness of the individual, and the survival and evolutionary potential of a population in a changing environment. Golden pheasant (Chrysolophus pictus) is a wild Phasianidae distributed in central and north China. In this study, we used a locus-specific genotyping technique for MHC IIB genes of golden pheasant. Combining with microsatellites (simple sequence repeat, SSR) and mitochondrial DNA (mtDNA) D-loop region, we investigated the demographic history and illuminate genetic structure of this bird in detail. SYR (south of Yangtze river) - NYR (north of Yangtze river) lineages, separated by Yangtze River, were defined in genetic structure of MHC IIB. NYR was supposed as refuge during glacial period, suggested by diversity parameters and more ancient alleles in this region. Based on this hypothesis, there was gene flow from NYR to SYR, which was proved by three pieces of evidence: (1) distinct demographic histories of SYR (kept stable) and NYR (experienced expansion); (2) specific affiliation of LC in genetic structure of SSR and MHC genes; (3) significant gene flow from NYR to SYR. Moreover, we also found balancing selection by combination of three Grouping A2's regions (SC, QL and North) into one in Grouping B4 (NYR) and no pattern of isolation by distance (IBD) found in MHC IIB, whereas for SSR we found a relatively strong and significant IBD. Several mechanisms in the evolution of MHC IIB genes, including recombination, historically positive selection, trans-species evolution and concerted evolution, were shown by molecular and phylogenetic analysis. Overall these results suggest the Yangtze River was inferred to be a geological barrier for this avian and NYR might experience population expansion, which invaded into a neighboring region. This study contributes to the understanding of the effects of geographic features on contemporary patterns of genetic variation in the golden pheasant in China, and helps us to define the adaptive unite (AU) for this avian.