A microbial view on secondary contact between two Alpine butterflies

Background Coexistence between sibling species can be limited if they are ecologically too close, leading to the formation of often narrow zones of secondary contact. While the ecological niche is commonly estimated using abiotic factors, the potential for differentiation in gut microbial communities is less well studied. We address this gap in research, focusing on two Alpine butterfly species of the genus Erebia that form a stable and very narrow contact zone. Results Using a metabarcoding approach to sequence the adult gut microbial communities of our two focal species as well as capturing the microbial diversity found on three nectar plant species, we found that the microbial community i) significantly differed between species but not between sexes, that ii) the abundance of the endosymbiont Wolbachia differed between species, where its high abundance resulted in the presence of fewer other microbial taxa, and that iii) microbes found on flowers largely overlap with the ones found in the butterfly hosts, suggesting that intestinal environmental filtering occurs only to some degree. Conclusions Unlike for abiotic environmental factors, we uncovered significant species specific differences in the gut microbial communities of our focal species, further highlighting the complex interactions between host biology and environmental factors in shaping the gut microbiota. The observed microbial differences could reflect potential adaptive mechanisms and evolutionary processes at play. Overall, our study highlights the utility to study cryptic niche differentiation during secondary contact, advancing our understanding of the ecological dynamics of alpine butterflies.