Abstract
The Nicrophorus genus lives and breeds in a microbe rich environment. As such, it would be expected that strategies should be in place to counter potentially negative effects of the microbes common to this environment. In this study, we show the response of Nicrophorus vespilloides to the common soil bacterium, Bacillus subtilis. Phenoloxidase (PO) levels are not upregulated in response to the challenge and the bacteria are observed to multiply within the haemolymph of the host. Despite the growth of B. subtilis, survival is not affected, either in virgin or in breeding beetles. Some limit on bacterial growth in the haemolymph does seem to be occurring, suggesting mechanisms of resistance, in addition to tolerance mechanisms. Despite limited detrimental effects on the individual, the challenge by Bacillus subtilis appears to act as a cue to increase reproductive investment. The challenge may indicate a suite of negative environmental conditions that could compromise future breeding opportunities. This could act as a cue to increase parental investment in the current bout.
Highlights
Trade-offs between life-history traits are widely studied in evolutionary biology
This study shows that N. vespilloides is tolerant to B. subtilis, the presence of bacteria appears to act as a cue for increasing reproductive investment
PO is involved in wound healing so the effects observed across the wounded, injected with nutrient broth, injected with dead bacteria and injected with bacteria are likely due to the wound healing process alone
Summary
Trade-offs between life-history traits are widely studied in evolutionary biology. Costs of reproduction are well documented [1,2,3] and recently attention has focused on ecological immunology, providing evidence for the costliness of immune function. Resistance may arise through behavioural traits, e.g., avoidance of the parasites, physical traits, e.g., the exoskeleton in insects, or internal immune or physiological factors, e.g., a powerful immune response or specific gene-gene interactions between parasite and host involving recognition, which may result in resistance without having to further employ immune function [42] Variation in tolerance, both across and within taxa can be driven by different mechanisms, such as nutrition, efficient tissue repair, the ability to detoxify by-products of bacterial replication and the use of commensal/mutualistic bacteria [43,44]. It is likely that longevity will be affected by the challenge, either through the costs of dealing with an infection, or direct bacteria-induced mortality
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