Causes and consequences of plasticity in parental and offspring behaviour in the burying beetle Nicrophorus vespilloides

Behavioural plasticity, the environmentally induced change in behaviour, is a reversible response that allows a rapid switch in activity to best match the environment. Behavioural plasticity is a widespread mechanism influencing the ability to find resources, reproduce and survive. Behavioural plasticity is particularly important in parent-offspring interactions because it allows parents and offspring to finely tune costly behaviours, such as parental care or offspring begging, to avoid unnecessary expenditure and obtain the highest returns from the interaction. In this thesis, I examined the role of plasticity in parental and offspring behaviour in response to changes in various aspects of in the intrinsic and environmental conditions in the burying beetle Nicrophorus vespilloides: energetic costs, infection status, resources availability, and parent’s body size. I first showed how females unexpectedly increase parental care with higher energetic costs and that females do so irrespectively of variation in brood size. Next, I showed that infected females maintain their level of care despite suffering from high mortality. I further showed that resource availability has a positive effect on biparental cooperation over care, as males tend to provide care for longer when resources are more abundant. I also showed how larvae preferentially beg towards larger females as they spend more time associating with larger females over smaller ones. I focused the final part of the thesis on the consequences of behavioural plasticity and tested whether inbreeding can alter plasticity in adult and larval behaviour, and how parent-offspring and male-female interactions mediate the effects of inbreeding depression. I found evidence that inbreeding can increase plasticity in offspring behaviour. Moreover, I found that maternal inbreeding has detrimental effects on offspring survival, and that these effects remain regardless of the presence or the inbreeding status of the male parent. Collectively, these findings confirm that behavioural responses oftentimes allow balancing the costs and benefits of a behaviour, but that the direction of behavioural adjustments can also change unexpectedly depending on prospects for survival and future reproduction. These findings provide further evidence indicating that the intrinsic and environmental conditions not only shape the behavioural responses and fitness of focal individual, but also influence the behavioural responses and fitness of social partners. Overall, these studies provide additional support to the idea that behavioural plasticity might be a key step in the emergence of complex behavioural phenotypes and a major source of behavioural diversit

Carry on caring:Infected females maintain their parental care despite high mortality

Parental care is a key component of an organism’s reproductive strategy that is thought to trade-off with allocation toward immunity. Yet, it is unclear how caring parents respond to pathogens: do infected parents reduce care as a sickness behavior or simply from being ill or do they prioritize their offspring by maintaining high levels of care? To address this issue, we investigated the consequences of infection by the pathogen Serratia marcescens on mortality, time spent providing care, reproductive output, and expression of immune genes of female parents in the burying beetle Nicrophorus vespilloides. We compared untreated control females with infected females that were inoculated with live bacteria, immune-challenged females that were inoculated with heat-killed bacteria, and injured females that were injected with buffer. We found that infected and immune-challenged females changed their immune gene expression and that infected females suffered increased mortality. Nevertheless, infected and immune-challenged females maintained their normal level of care and reproductive output. There was thus no evidence that infection led to either a decrease or an increase in parental care or reproductive output. Our results show that parental care, which is generally highly flexible, can remain remarkably robust and consistent despite the elevated mortality caused by infection by pathogens. Overall, these findings suggest that infected females maintain a high level of parental care, a strategy that may ensure that offspring receive the necessary amount of care but that might be detrimental to the parents’ own survival or that may even facilitate disease transmission to offspring

Parental care buffers against effects of ambient temperature on offspring performance in an insect

Understanding how animals respond to and cope with variation in ambient temperature is an important priority. The reason for this is that ambient temperature is a key component of the physical environment that influences offspring performance in a wide range of ectotherms and endotherms. Here, we investigate whether post-hatching parental care provides a behavioral mechanism for buffering against the effects of ambient temperature on offspring in the burying beetle Nicrophorus vespilloides. We used a 3×2 factorial design where we manipulated ambient temperature (15, 20 or 25°C) and parental care (presence or absence of a female parent after hatching). We found that the effect of ambient temperature on offspring performance was conditional upon the presence or absence of a caring female. Fewer larvae survived in the absence than in the presence of a caring female at 15°C whilst there was no difference in larval survival at 20 and 25°C. Our results show that parental care buffers against some of the detrimental effects of variation in ambient temperature on offspring. We suggest that post-hatching parental care may buffer against such effects by creating a more benign environment or by boosting offspring resilience towards stressors. Our results have important implications for our understanding of the evolution of parental care because they suggest that the evolution of parental care could allow species to expand their geographical range to colonize areas with harsher climatic conditions than they otherwise would tolerate

Male assistance in parental care does not buffer against detrimental effects of maternal inbreeding on offspring

<p>The severity of inbreeding depression often varies across environments and recent work suggests that social interactions can aggravate or reduce inbreeding depression. For example, stressful interactions such as competition can exacerbate inbreeding depression, whereas benign interactions such as parental care can buffer against inbreeding depression in offspring. Here, we test whether male assistance in parental care can buffer against the detrimental effects of maternal inbreeding on offspring fitness in the burying beetle Nicrophorus vespilloides. Our results confirm that maternal inbreeding had detrimental effects on offspring survival. However, we found no evidence that male assistance in parental care buffered against those effects on offspring fitness. Outbred females benefitted from male assistance, gaining more weight over the breeding attempt when assisted by a male. In contrast, inbred females did not benefit from male assistance, gaining as much weight regardless of whether they were assisted by a male or not. Surprisingly, we find that males gained more weight during the breeding attempt when mated to an inbred female, suggesting that males benefitted from assisting an inbred female partner in terms of their weight gain. Overall, our findings suggest that parental care or other benign social interactions may not always buffer against detrimental effects of inbreeding depression.</p