Abstract
BackgroundNicrophorus vespilloides eggs are deposited into the soil in close proximity to the decomposing vertebrate carcasses that these insects use as an obligate resource to rear their offspring. Eggs in this environment potentially face significant risks from the bacteria that proliferate in the grave-soil environment following nutrient influx from the decomposing carcass. Our aims in this paper are twofold: first, to examine the fitness effects of grave-soil bacteria to eggs, and second, to quantify egg immunocompetence as a defence against these bacteria.ResultsOur results provide strong evidence that grave-soil microbes significantly reduce the survival of Nicrophorus eggs. Females provided with microbe rich carcasses to rear broods laid fewer eggs that were less likely to hatch than females given uncontaminated carcasses. Furthermore, we show that egg hatch success is significantly reduced by bacterial exposure. Using a split-brood design, which controlled for intrinsic differences in eggs produced by different females, we found that eggs washed free of surface-associated bacteria show increased survival compared to unwashed eggs. By contrast, eggs exposed to the entomopathogen Serratia marcescens show decreased survival compared to unexposed eggs. We next tested the immune competence of eggs under challenge from bacterial infection, and found that eggs lacked endogenous production of antimicrobial peptides, despite well-developed responses in larvae. Finally, we found that despite lacking immunity, N. vespilloides eggs produce an extraembryonic serosa, indicating that the serosa has lost its immune inducing capacity in this species.ConclusionsThe dependency on ephemeral resources might strongly select for fast developing animals. Our results suggest that Nicrophorus carrion beetles, and other species developing on ephemeral resources, face a fundamental trade-off between egg immunity and development time.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0208-x) contains supplementary material, which is available to authorized users.
Highlights
Nicrophorus vespilloides eggs are deposited into the soil in close proximity to the decomposing vertebrate carcasses that these insects use as an obligate resource to rear their offspring
As we have previously shown that the eggs of Tribolium castaneum can induce antimicrobial peptide genes upon infection [15], induction of antimicrobial peptides might increase survival in adverse conditions for the eggs of N. vespilloides
We show that egg hatching success is a direct function of bacterial exposure; eggs washed free of surface-associated bacteria show increased survival compared to unwashed eggs (Figure 1B) while eggs washed in a bacterial solution show decreased survival compared to unexposed eggs (Figure 1C)
Summary
Nicrophorus vespilloides eggs are deposited into the soil in close proximity to the decomposing vertebrate carcasses that these insects use as an obligate resource to rear their offspring. Microbial defence in animals that develop externally is provided by barrier protection from the egg surface, from maternally provided antimicrobials or through intrinsic immunity coordinated by the developing embryo [4]. These modes of protection have been eggs [9,14,15]. Pre-hatch reductions in fitness as a consequence of microbial exposure have not been studied; it remains unknown how or if eggs respond to the adverse environment in which they are laid
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
