The gut microbiome mediates adaptation to scarce food in cave Coleoptera
Beetles are ubiquitous cave invertebrates worldwide and cave colonization involves a drastic transition from abundant nutrient sources on the surface to the subterranean scarce resources. We investigated the potential role of gut microbiota in cave adaptation of beetles in Carpathian caves from different climatic regions of Romania. The sediment microbiota was relatively constant in taxonomic structure across all seasons and was similar between all five caves. Uncultured phyla Patescibacteria and GAL15 were highly represented. In comparison, the beetles' microbiota was host specific, reflecting both phylogenetic and nutritional adaptation. The microbial community structure further resolved conspecific beetles by caves suggesting microbiota-host coevolution and influences by local environmental factors. The detritivore Leiodidae hosted a variety of bacterial taxa known to decompose and ferment organic matter including in other animal guts, suggesting turnover and host cooperative digestion of the sedimentary microbiota and allochthonous derived nutrients. The Carabidae represented by Duvalius, beetles with strong mandibulae adapted to predation and scavenging of animal and plant remains, had distinct microbiota dominated by symbiotic lineages of Spiroplasma or Wolbachia. Interestingly, all beetles had relatively high levels of fermentative Carnobacterium and Vagococcus involved in lipid accumulation and a reduction of metabolic activity, both features characterizing cave beetles.