Inter Kindgom Competition for Rare and Ephemeral Resources

Abstract

All animals interact in some way with microbes during their growth anddevelopment. These interactions often prove harmful as animals find themselves exposedto pathogens or the harmful by-products of microbial growth. For many animals avoidanceof microbes is difficult or impossible, particularly for species that obligately utilisemicrobe-laden resources during reproduction. Larvae of the carrion beetle Nicrophorusvespilloides are significantly harmed by the bacteria they encounter during theirdevelopment on decomposing vertebrate carcasses. However, these effects can be partiallyameliorated by parental investment into behaviours which reduce the effects of microbialexposure.In this thesis I focus on two aspects of N. vespilloides response to microbialcompetition. First I investigate the composition and fitness effects of the application ofexogenous secretions by parents and larvae to their breeding resource. This behaviourin parents has long been hypothesized to form an important part of the antimicrobialcomponent of parental care, but this has not been rigorously tested. Nor, prior to my work,has any experimental attention been given to the possibility that larvae also contributeto antimicrobial production while on the carcass. Second I investigate the late-life andintergeneration effects of microbial exposure during development on a range of beetle lifehistory traits including larval body size, brood size and immune function and survival inresponse to bacterial challenge.My results demonstrate the following: i) that larval N. vespilloides suffersignificant harm from microbial competition during development that manifests itself inseveral ways, e.g. reduced body size, increased susceptibility to infection, or reducedability of mothers to provide post hatch maternal care; ii) that the effects of microbialcompetition can be mitigated by parental behaviours that reduce the level of microbialcontamination on a resource. Specifically, mothers apply antimicrobial secretionscontaining lysozyme to the carcass which kills bacteria and significantly increases larvalsurvival; iii) that larvae are not totally reliant on their parents for antimicrobial protectionbecause they too can secrete exogenous antimicrobial compounds similar in activity totheir parents and which significantly increase larval fitness; iv) the effects of microbialcompetition can result in transgenerational effects that reduce offspring fitness but whichcan also provide context-dependent benefits by increasing larval survival when post-hatchparental care is poor and following challenge with pathogenic infection.By developing on and consuming carrion Nicrophorus larvae and other specialistscavengers experience an extreme example of the challenges faced by opportunistic carrionusers or animals that for any reason utilise microbially contaminated resources. This makesthem ideal model organisms to study adaptations to the presence of complex microbialcommunities that may contain both pathogens and toxin producers.

Date of Award	31 Dec 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Richard Preziosi (Supervisor) & Daniel Rozen (Supervisor)