Across the animal kingdom, social behaviour has been shown to be both a driver of and a response to selection. The question of how social interactions within the family contribute to evolutionary change has received much attention from behavioural ecologists and evolutionary biologists alike, with the former largely focussing on how these interactions are adaptive, and how they impose selection on each member of the partnership, and the latter focussing more on the specific mechanisms of inheritance and how social behaviours of one partner induce the evolution of traits in others. The aim of this thesis is to unite these approaches by asking how adaptive social behaviour (i.e. parental care) can potentially influence evolution: by providing a mechanism for non-genetic inheritance, by constructing the environment in which further social interactions play out, and by influencing trait loss and trait evolvability.

The burying beetle Nicrophorus vespilloides represents an excellent system for investigating these consequences of parental care. This species exhibits elaborate but variable biparental care, whereby both parents prepare an edible nest for their young from a small vertebrate carcass. They then defend the larvae from predators and competitors and feed them trophallactically with oral fluids. Larvae can survive without any post-hatching care – in the lab at least.

I begin in Chapter 2, by examining how burying beetles inherit their gut microbiome, in collaboration with Dr Rahia Mashoodh and Dr Helen Leggett at the University of Cambridge. Previous work suggests this is achieved by two routes: directly from the parents via oral trophallaxis and indirectly via the carcass, through the deposition by parents of oral and anal exudates, which larvae then consume. I eliminated the former mechanism of inheritance, by breeding beetles with and without post-hatching care for two generations, and analysed the resulting gut bacteria of grand-offspring using 16S sequencing. I found that different bacteria are inherited by each route but that gut bacterial communities are just as diverse when vertical transmission happens via the carcass alone. In future work it would be interesting to determine whether beetles have reduced fitness when vertical transmission of the gut bacterial community during post-hatching is prevented.

In Chapters 3-6, I extended this approach of comparing populations that had and had not experienced post-hatching care. I analysed replicate experimental burying beetle populations that had evolved for 40 or more generations in the Kilner lab either with or without post-hatching care, respectively the ‘Full Care’ and ‘No Care’ populations. In Chapters 3 and 4, I focused on traits linked to the preparation of the carrion nest. In Chapter 3, I conducted breeding experiments that investigated whether nest construction had evolved divergently between the Full Care and No Care populations. I found that faster nest building in the No Care populations did not compensate for poorer post-hatching care. There was evidence of within-family co-adaptation for nest construction, but the extent of co-adaptation did not diverge between ‘Full Care’ and ‘No Care’ populations. In Chapter 4, in collaboration with Prof. Adria LeBoeuf at the University of Fribourg, Switzerland, I analysed the proteins in oral fluids produced by parents and offspring, which are deposited on the carrion nest. We found that No Care parents had evolved to deposit proteins that could assist their larvae in their absence, but found no evidence of equivalent change in the No Care larvae.

Finally, to look at the longer-term evolutionary consequences of parental care, in Chapter 5 I investigated whether traits for supplying and receiving care can persist when they are no longer expressed (as experienced by the No Care populations). I found that No Care fathers and larvae had lower expression of post-hatching care-related traits than their Full Care counterparts, but similar trait loss was not found in mothers. In Chapter 6, I investigated whether evolving with or without care conferred greater resilience when beetles were exposed to increased temperatures during sexual maturation. I found that founder effects were a far better predictor of a population’s resilience than social evolutionary history. I conclude that long-term consequences of social evolution are unpredictable and that the resilience of a population will largely be predicted by the standing genetic variation of its founders.