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.

Genetic variability in geographic populations of the natterjack toad (Bufo calamita).

Across altitudinal and latitudinal gradients, the proportion of suitable habitats varies, influencing the individual dispersal that ultimately can produce differentiation among populations. The natterjack toad (Bufo calamita) is distributed across a wide geographic range that qualifies the species as interesting for a geographic analysis of its genetic variability. Five populations of B. calamita in the Sierra de Gredos (Spain) were studied in an altitudinal gradient ranging from 750 to 2270 m using microsatellite markers. In addition, we analyzed the latitudinal genetic variation in B. calamita within a global European distribution using genetic diversity parameters (mean number of alleles per locus [M(a)] and expected heterozygosity [H(E)]) obtained from our results and those published in the literature. The low level of genetic differentiation found between populations of B. calamita (F(st) ranging from 0.0115 to 0.1018) and the decreases in genetic diversity with altitude (M(a) from 13.6 to 8.3, H(E) from 0.82 to 0.74) can be interpreted by the combined effects of discontinuous habitat, produced mainly by the high slopes barriers and geographic distance. In the latitudinal gradient, genetic diversity decreases from south to north as a consequence of the colonization of the species from the Pleistocene refugium. We conclude that the genetic variability in B. calamita along its wide altitudinal and latitudinal geographic distribution mainly reflects the colonization history of the species after the last glacial period.