Body size, inbreeding, and family interactions in the burying beetle Nicrophorus vespilloides

There are three social dimensions within a family: parent-parent interactions, parent-offspring interactions, and offspring-offspring interactions. All of these interactions are subject to evolutionary conflict, which occurs whenever interacting individuals have divergent evolutionary interests. Family interactions and family conflict are often influenced by phenotypic and genotypic traits of the parents and the offspring. An important phenotypic trait is body size, which can affect fecundity, mating success, and fighting ability. An important genotypic trait is inbreeding status (i.e., whether an individual is outbred or inbred), which can influence its overall quality or condition. In this thesis, I investigate the independent and interactive effects of inbreeding and parental body size on family interactions in the burying beetle Nicrophorus vespilloides. I first show that the body size of the two parents influences the resolution of sexual conflict over the amount of parental care (Chapter 2) and over the consumption of a shared resource (Chapter 3). Here, the shared resource refers to the carcass from which both the parents and the offspring feed over the course of the breeding attempt. I then show that females that won or lost a fighting contest provide more care to their offspring compared to beetles with no fighting experience (Chapter 4). This indicates that female burying beetles make parental investment decisions based on their experience with a contest (which is independent of body size) rather than the outcome of that contest (which is dependent on body size):. In the second half of my thesis, I examine whether family interactions also influence and are influenced by inbreeding depression (Chapters 5–8). I find that a female's mating preference for an outbred versus an inbred male is conditional on her own inbreeding status: inbred females preferentially mate with outbred males, whereas outbred females are equally likely to mate with an outbred or an inbred male (Chapter 5). Even though sibling competition does not appear to have an effect on the offspring's inbreeding depression (Chapter 6), the presence of the mother during larval development can reduce the severity of inbreeding depression (Chapter 7), and this effect depends on the mother's body size (Chapter 8). In Chapter 9, I discuss the broader implications of these findings for evolutionary biology, ecology, and conservation biology