Wood fibers are a crucial microhabitat for cellulose- and xylan- degrading bacteria in the hindgut of the wood-feeding beetle Odontotaenius disjunctus

IntroductionWood digestion in insects relies on the maintenance of a mosaic of numerous microhabitats, each colonized by distinct microbiomes. Understanding the division of digestive labor between these microhabitats- is central to understanding the physiology and evolution of symbiotic wood digestion. A microhabitat that has emerged to be of direct relevance to the process of lignocellulose digestion is the surface of ingested plant material. Wood particles in the guts of some termites are colonized by a specialized bacterial fiber-digesting microbiome, but whether this represents a widespread strategy among insect lineages that have independently evolved wood-feeding remains an open question.MethodsIn this study, we investigated the bacterial communities specifically associated with wood fibers in the gut of the passalid beetle Odontotaenius disjunctus. We developed a Percoll-based centrifugation method to isolate and enrich the wood particles from the anterior hindgut, allowing us to access the wood fibers and their associated microbiome. We then performed assays of enzyme activity and used short-read and long-read amplicon sequencing of the 16S rRNA gene to identify the composition of the fiber-associated microbiome.ResultsOur assays demonstrated that the anterior hindgut, which houses a majority of the bacterial load, is an important site for lignocellulose digestion. Wood particles enriched from the anterior hindgut contribute to a large proportion of the total enzyme activity. The sequencing revealed that O. disjunctus, like termites, harbors a distinct fiber-associated microbiome, but notably, its community is enriched in insect-specific groups of Lactococcus and Turicibacter.DiscussionOur study underscores the importance of microhabitats in fostering the complex symbiotic relationships between wood-feeding insects and their microbiomes. The discovery of distinct fiber-digesting symbionts in O. disjunctus, compared to termites, highlights the diverse evolutionary paths insects have taken to adapt to a challenging diet

Historical biogeography of New World passalid beetles (Coleoptera, Passalidae) reveals Mesoamerican tropical forests as a centre of origin and taxonomic diversification

Aim: The fauna of Mesoamerica is extraordinarily species rich and exhibits a high degree of local, regional and high-elevation endemism. Traditionally, this area has been seen as a transition zone between the Nearctic and Neotropical regions; in contrast, new data suggest that Mesoamerica is a centre of origin and taxonomic diversification. For example, the diversity of species and genera of Passalidae in Mesoamerica is concentrated in montane environments and there are many locally endemic taxa; thus, Mesoamerica has been suggested as a centre of origin and taxonomic diversification for the group. However, this hypothesis has not been formally tested. Location: New World tropics, with an emphasis on Mesoamerica. Taxon: Coleoptera, Passalidae (tribes Passalini and Proculini). Methods: We studied timing and geographic patterns in the taxonomic diversification of Neotropical Passalidae. We used DNA sequence data from 3 genes (CAD, Wingless, 28S) for 93 species of Passalidae, along with information from the fossil record, to generate a time-calibrated phylogeny for the group. Additionally, we performed Ancestral Area Estimation and Ancestral State Reconstruction of the altitudinal distribution niche. Results: The divergence time analyses recovered a much older estimated timing of origin and diversification events in Passalidae than previously proposed. We recovered the origins of the New World Passalidae in the late Jurassic and the split between Passalini and Proculini during the mid-Cretaceous. Moreover, we observed congruence between timing and patterns of clade diversification and major paleogeographical events; for example, the origin and crown diversification of montane genera during the uplift and emergence of Mesoamerica from the sea. Main conclusions: Orogenic events throughout the Paleogene and Neogene played a major role in the diversification of New World Passalidae. Moreover, Nuclear and Southern Mesoamerica are centres of origin and taxonomic diversification for Proculini