Conflict and Cooperation in Vertebrate Societies
Sanderson, Jennifer Louise
Thesis or dissertation
University of Exeter
Within animal societies, individuals often differ greatly in their level of investment in cooperative activities. Individuals are predicted to show high cooperative investment if high levels of relatedness lead to large indirect fitness benefits, or if differences in individual characteristics such as age, sex, rank, or body condition increase the direct fitness benefits of helping. However, individual differences often persist after these differences are controlled for; a residual variation that remains unexplained. Understanding the proximate mechanisms underlying variation in behaviour can give novel insights into the selection pressures shaping behavioural differences. This suggests that a research focus onto the proximate mechanisms underpinning cooperative behaviours is needed to further our understanding of why individuals behave differently within social groups. In this thesis, I address this shortfall in understanding by investigating hormonal variation alongside individual differences in cooperative investment in the banded mongoose (Mungos mungo). Banded mongooses are a highly social carnivore with two highly conspicuous forms of cooperative offspring care that are easily measurable and show large inter-individual variation. In chapter 3, I demonstrate a negative carry-over effect of investment in offspring care in consecutive breeding attempts. I show that this carry-over effect is mediated by variation in glucocorticoid concentrations, which may be attributable to the energetic costs of helping. Glucocorticoids predict investment in offspring care, suggesting that this mechanism may drive inter-individual variation in cooperative investment. In chapter 4, I find evidence for a testosterone mediated trade-off between offspring care and mating effort, which suggests that inter-individual differences may also be driven by variation in the costs of helping attributable to missed mating opportunities. In chapter 5, I use simulated territorial intrusions to show that there is unlikely to be a trade-off between offspring care and territory defence in banded mongoose societies. However, carers and non-carers show a differential physiological response to territorial intrusion, suggesting that there may be a more subtle behavioural trade-off that occurs post-intrusion. In chapter 6, I find evidence for consistent individual differences in both cooperative and competitive behaviours, which suggests that individual differences in adult behaviour may be determined by early-life effects. Individual differences in cooperative investment are positively correlated, suggesting that individuals are not specialised to different cooperative activities, but are consistently either helpful or selfish. Together, these results give insights into the selection pressures shaping individual differences and highlight endocrine research as a valuable tool in understanding the evolution of cooperative societies.
PhD Biological Sciences