Decoding the symbiotic dynamics of the wood-degrading bess beetles (Coleoptera: Passalidae) and their gut microbiomes: Evolutionary and ecological insights

Beetles of the family Passalidae are an important group of wood-decomposing (saproxylophagous) insects, spending their entire life cycle living inside and feeding on rotten logs. Decaying wood is an abundant resource; however, it is nutritionally poor and challenging to digest. This digestion is facilitated through essential symbiotic relationships between the insects and their gut microbiomes, highlighting the critical roles of these symbionts in the evolution of wood-decomposing insects. Despite their ecological importance, the evolution of passalids and their microbiomes remains poorly understood, limiting our understanding of this relationship and its potential influence on passalid diversification. Using high-throughput sequencing of the bacterial 16S rRNA and the fungal ITS regions to comparatively analyze the distribution and abundance of symbiont lineages in the anterior hindguts of two independent mountain systems of passalid beetles in the Colombian Caribbean region. Our data sheds light on important questions in the evolution of the symbiotic relationships within wood-decomposing insects and their microbiomes, such as whether the gut microbiomes of closer phylogenetic relatives are more similar than those of distantly related ones, and whether passalid species in the same habitat are more similar than those in different habitats, regardless of phylogenetic relatedness.