Ecological theory suggests that closely-related, competing species occurring in sympatry differ in a way that helps them coexist, a concept called niche partitioning. One important way species may differ in sympatry is in their microbiome, which has been shown to affect physiological functions such as metabolism and thermal tolerance. However, little is known about microbiome variation among closely-related, sympatric species. Here we investigated variation in the gut microbiota of two sympatric sister species of dung beetle, Phanaeus vindex and P. difformis, which have the same diet but prefer different soil types, to see whether they shared a common gut microbiome.
Phanaeus dung beetles reproduce by burying a ball of dung, called a brood ball, with a single egg below the soil. The gut microbiome is vertically-transmitted to offspring via the brood ball and aids in cellulose digestion, nitrogen fixation, and thermal tolerance, which enhances offspring growth and development. Phanaeus difformis reproduces on sand whereas P. vindex buries brood balls on various soil types, including clay. Brood balls buried in clay are exposed to warmer temperatures and greater temperature variation. Because gut microbiota affect thermal tolerance, we predict that P. vindex will have gut microbiome that is distinct from that of P. difformis, possibly allowing P. vindex offspring to withstand warmer and more variable temperature conditions underground.
To examine the gut microbiomes of these two species, we sampled one sympatric population of P. vindex and P. difformis and fed them autoclaved dung to control for differences in diet prior to capture. We prepared and sequenced gut bacterial/archaeal 16S rDNA to recover operational taxonomic units (OTUs) and investigated how species identity correlated with observed patterns of microbial diversity.
Results/Conclusions
Phanaeus vindex and P. difformis showed species-specific patterns of bacterial and archaeal diversity. Three of the fifteen most abundant genera, including those in the Enterobacteriaceae and Flavobacteriaceae families, differed by at least twelve-fold between Phanaeus species. Importantly, these observed genera have members that break down cellulose and fix nitrogen in the guts of other insect species, physiological functions which would enhance Phanaeus survival on their nutrient-poor diet of dung. Our results suggest that despite being sister species, sharing food resources, and overlapping in range, P. vindex and P. difformis have distinct gut microbiota. It is possible that these differences reflect different selective pressures experienced by developing larvae. In future work we will test the role of the gut microbiome in offspring survival and fitness.