Gut Microbiota Colonization and Transmission in the Burying Beetle Nicrophorus vespilloides throughout Development

Abstract

Carrion beetles in the genus Nicrophorus rear their offspring on decomposing carcasses where larvae are exposed to a diverse community of decomposer bacteria. Parents coat the carcass with antimicrobial secretions prior to egg hatch (defined as prehatch care) and also feed regurgitated food, and potentially bacteria, to larvae throughout development (defined as full care). Here, we partition the roles of prehatch and posthatch parental care in the transmission and persistence of culturable symbiotic bacteria to larvae. Using three treatment groups (full care, prehatch care only, and no care), we found that larvae receiving full care are predominantly colonized by bacteria resident in the maternal gut while larvae receiving no care are colonized with bacteria from the carcass. More importantly, larvae receiving only prehatch care were also predominantly colonized by maternal bacteria; this result indicates that parental treatment of the carcass, including application of bacteria to the carcass surface, is sufficient to ensure symbiont transfer even in the absence of direct larval feeding. Later in development, we found striking evidence that pupae undergo an aposymbiotic stage, after which they are recolonized at eclosion with bacteria similar to those found on the molted larval cuticle and on the wall of the pupal chamber. Our results clarify the importance of prehatch parental care for symbiont transmission in Nicrophorus vespilloides and suggest that these bacteria successfully outcompete decomposer bacteria during larval and pupal gut colonization.IMPORTANCE Here, we examine the origin and persistence of the culturable gut microbiota of larvae in the burying beetle Nicrophorus vespilloides. This insect is particularly interesting for this study because larvae are reared on decomposing vertebrate carcasses, where they are exposed to high densities of carrion-decomposing microbes. Larvae also receive extensive parental care in the form of carcass preservation and direct larval feeding. We find that parents transmit their gut bacteria to larvae both directly, through regurgitation, and indirectly via their effects on the carcass. In addition, we find that larvae become aposymbiotic during pupation but are recolonized apparently from bacteria shed onto the insect cuticle before adult eclosion. Our results highlight the diverse interactions between insect behavior and development on microbiota composition. They further suggest that competitive interactions mediate the bacterial composition of Nicrophorus larvae together with or apart from the influence of beetle immunity, suggesting that the bacterial communities of these insects may be highly coevolved with those of their host species.KEYWORDS Nicrophorus, parental care, symbiosis, microbiota, transmission A nimals are colonized by a diverse community of bacterial symbionts that play crucial roles in their ecology and evolution (1-3). This has been especially well studied in insects, whose bacterial symbionts can influence traits ranging from mate

Burying beetles regulate the microbiome of carcasses and use it to transmit a core microbiota to their offspring

“…Interestingly, Wohlfahrtiimonas and Morganella morganii , both detected in N. vespilloides guts in this study, were previously found to be resistant to the antibiotics produced by Myroides (Dharne et al., ), indicating that the N. vespilloides microbiota may be shaped by organisms that have evolved resistance against the antimicrobial action of other bacterial members constituting its core microbiome. Vagococcus , Myroides , Providencia and Morganella have also been detected in culture‐dependent studies (Wang & Rozen, ) to be transmitted by N. vespilloides adults to their larvae. Given their prevalence in meat (either fresh or decomposing) and in the gut of flesh‐feeding insects, and their diverse digestive and antimicrobial properties, these bacteria could play important roles in carcass digestion and preservation.…”

Gut microbiota in the burying beetle, Nicrophorus vespilloides, provide colonization resistance against larval bacterial pathogens

“…Nicrophorus larvae are exposed to a highly diverse microbiota in their breeding environment, first from the soil where they hatch and next from the microbes proliferating on and within their carrion resource. In the absence of parental care, larvae become colonized with these bacteria (Wang & Rozen, ) which reduces their weight and survival (Rozen et al., ) and also leads to reduced brood mass when these larvae reproduce as parents (Figure ). However, when larvae are reared with parental care, their gut microbiome resembles that of their parent, even if parental care is limited to carcass preparation prior to larval hatch (Wang & Rozen, ).…”

“…To determine if “endogenous” bacteria can outcompete foreign strains during larval colonization, we competed bacterial strains against one another within the larval gut, focusing on four different bacterial species. The bacterial species Providencia rettgeri and Morganella morganii are abundant N. vespilloides gut symbionts throughout development and are considered “endogenous” species (Vogel et al., ; Wang & Rozen, ). By contrast, S. marcescens and Escherichia coli , which are found commonly in both soil and on decomposing carcasses, colonize larvae that are reared without parental care in NC broods (Wang & Rozen, ).…”

“…The bacterial species Providencia rettgeri and Morganella morganii are abundant N. vespilloides gut symbionts throughout development and are considered “endogenous” species (Vogel et al., ; Wang & Rozen, ). By contrast, S. marcescens and Escherichia coli , which are found commonly in both soil and on decomposing carcasses, colonize larvae that are reared without parental care in NC broods (Wang & Rozen, ). Serratia marcescens is also a known insect pathogen in several insect species (El Sanousi et al., ; Nehme et al., ; Renoz et al., ), including N. vespilloides .…”

“…In addition, we found that the core members of this microbiota could even be transmitted to larvae indirectly, by bacteria deposited onto the carcass by parents (Wang & Rozen, ). This unexpected result suggested that these core bacterial species were outcompeting the numerous microbes living on and inside the carcass within the larval gut, thus giving rise to the stable endogenous Nicrophorus microbiome (Vogel et al., ; Wang & Rozen, ). However, the mechanisms of their increased competitiveness remained unclear as were the consequences of their colonization.…”