Richter-Boix, A. | bioRxiv Science

bioRxiv2023

The Major Histocompatibility Complex modulates Batrachochytrium dendrobatidis and Ranavirus infections in three amphibian species

Genetic variation of immune genes is an important component of genetic diversity. Major histocompatibility complex (MHC) genes have been put forward as a model for studying how genetic diversity is maintained and geographically distributed in wild populations. Pathogen-mediated selection processes (i.e., heterozygosity advantage, rare-allele advantage or fluctuating selection) and demography are believed to generate and maintain the extreme diversity of MHC genes observed. However, establishing the relative importance of the different proposed mechanisms has proved extremely difficult, but heterozygote advantage is expected to be more detectable when multiple pathogens are considered simultaneously. Here, we test whether MHC diversity in three amphibian species (Ichthyosaura alpestris, Pleurodeles waltl, and Pelophylax perezi) is driven by pathogen-mediated selection. We examined the relationship between the individual MHC class II exon variability with individual infection status (infected or not), infection intensity, and co-infection of two main amphibian pathogens: Batrachochytrium dendrobatidis (Bd) and Ranavirus sp. (Rv). We found higher MHC class II exon 2 allelic diversity in I.alpestris and P. perezi than in P.waltl but no significant differences in allele frequencies between infection groups. We also observed significant differences in Bd infection intensity between Bd infected individuals and co-infected individuals depending on the number of MHC loci that an individual carries. For I. alpestris, we show stronger evidence for MHC associations with infection intensity and status when individuals carry specific alleles and supertypes. Our results suggest that studying the association between MHC genes and single and co-infected individuals might provide new insights into host-parasite evolution and a better understanding of evolutionary mechanisms driven by MHC diversity.

evolutionary biology↗

bioRxiv2023

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

It has become clear that the microbiome plays an important role in determining host health, diseases, and phenotypic variation. There is increasing evidence that the microbiome influences host fitness and its adaptation to the environment is changing our thinking on host-microbe interactions. However, it remains unclear how a host genotype shapes its microbiome. Here, we explored how genetic background and evolutionary history influence associated microbiome in amphibian populations. We studied how skin bacterial diversity is associated with the Major Histocompatibility Complex (MHC) class II exon 2 diversity in 12 moor frog populations belonging to two geographical clusters that show signatures of past and ongoing differential selection patterns. We found that bacterial alpha-diversity remained similar between the two clusters, while MHC haplotype-supertypes and genetic diversity differed between the clusters. Bacterial alpha-diversity was positively correlated with expected MHC heterozygosity and negatively with MHC nucleotide diversity. We also found that bacterial community composition differed significantly between the two geographic clusters and between specific MHC supertypes. These findings further suggest that population historical demographic events influence 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.

evolutionary biology↗