Beetlejuice, Beetlejuice, Beetlejuice: The role of antimicrobial secretions in competition in the burying beetle, Nicrophorus orbicollis

Abstract

An organism’s ability to survive and reproduce is often related to its ability to compete for resources. Competition can be intense for organisms that rely on temporally or spatially limited or unpredictable resources. Carrion is often both limited and unpredictable, and is particularly valuable because it is nutrient rich. Animals that use carrion face intense competition from microbes, which can make the carcass unpalatable or inhospitable. I investigated adaptations to competition with microbes in the burying beetle, Nicrophorus orbicollis. Burying beetles require vertebrate carcasses to reproduce, and use anal secretions containing antimicrobial components and beneficial gut microbes to protect a carcass during breeding. Anal secretions might delay carcass decay and prevent pathogenic competitor microbes from colonizing the carcass during larval rearing. However, the proximate mechanisms by which these antimicrobial effects occur, whether through endogenous immune defenses of the beetle and/or direct competition between gut and carcass microbes, remain unknown. Fungal gut symbionts might play a critical role in competition with harmful carrion consuming microbes, and until now the direct effects of fungal gut symbionts on competition between burying beetles and carcass microbes have not been tested. I determined the competitive consequences of experimentally disrupting fungal symbionts from the gut microbiome of N. orbicollis by measuring treatment effects on carcass preparation behaviours, anal secretion antimicrobial potency, and carcass decomposition rate. Results demonstrate the importance of the gut microbiome in behavioural plasticity, but suggest that fungal microbial symbionts might not produce antimicrobial compounds to directly compete with other carrion consuming microbes or impact the rate of carcass decomposition. Our findings contribute to our understanding of symbiotic relationships organisms have with their gut microbes, and the complex strategies some organisms use to compete for scarce resources.