Unearthing carrion beetles' microbiome: characterization of bacterial and fungal hindgut communities across the Silphidae

Abstract C arrion beetles ( C oleoptera, S ilphidae) are well known for their behaviour of exploiting vertebrate carcasses for nutrition. While species in the subfamily Silphinae feed on large carcasses and on larvae of competing scavengers, the N icrophorinae are unique in monopolizing, burying and defending small carrion, and providing extensive biparental care. As a first step towards investigating whether microbial symbionts may aid in carcass utilization or defence, we characterized the microbial hindgut communities of six N icrophorinae ( N icrophorus spp.) and two S ilphinae species ( O iceoptoma noveboracense and N ecrophila americana ) by deep ribosomal RNA amplicon sequencing. Across all species, bacteria in the family X anthomonadaceae, related to I gnatzschineriao larvae , were consistently common, and several other taxa were present in lower abundance ( E nterobacteriales, B urkholderiales, B acilli, C lostridiales and B acteroidales). Additionally, the N icrophorinae showed high numbers of unusual C lostridiales, while the S ilphinae were characterized by F lavobacteriales and R hizobiales ( B artonella sp.). In addition to the complex community of bacterial symbionts, each species of carrion beetle harboured a diversity of ascomycetous yeasts closely related to Y arrowia lipolytica . Despite the high degree of consistency in microbial communities across the S ilphidae—specifically within the N icrophorinae—both the fungal symbiont phylogeny and distance‐based bacterial community clustering showed higher congruence with sampling locality than host phylogeny. Thus, despite the possibility for vertical transmission via anal secretions, the distinct hindgut microbiota of the S ilphidae appears to be shaped by frequent horizontal exchange or environmental uptake of symbionts. The microbial community profiles, together with information on host ecology and the metabolic potential of related microorganisms, allow us to propose hypotheses on putative roles of the symbionts in carcass degradation, detoxification and defence.