Sociality and reproductive tactics in ground-dwelling squirrels: cooperation, tolerance and reproductive skew

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Life-history theory assumes animals have finite energy to invest in growth, maintenance and reproduction and predicts that investment in one trait will come at a cost to another (trade-offs). The trade-off between reproduction and survival is a major focus of research, especially between species with slow (large-bodied, long-lived) and fast (small-bodied, short-lived) life histories. Examining these trade-offs in species that do not follow the usual patterns, and where harsh environments magnify constraints, will broaden our understanding of the evolution of life history strategies. My research program focuses on understanding the selective forces influencing the evolution of sociality and reproductive strategies. We will test fundamental hypotheses on life-history, alternative reproductive tactics and cooperative breeding in an arid-adapted African ground squirrel, using behavioural, molecular and endocrine techniques. My long-term study of this species has been a productive system for examining social complexity because females are cooperative breeders living in family groups with multiple breeders, and males live in all-male bands. Both male and female groups are non-territorial, lack dominance hierarchies and display little aggression (rare in mammals). They are long-lived, despite a small body size, and have few offspring, similar to a large mammal. Males have two alternative tactics - they either delay dispersal and stay with their family, or disperse and join all-male bands. Tactics do not differ in reproductive success but less than 30% of males of either tactic sire offspring. Examining this skewed reproductive success, delayed dispersal and longevity in males is one focus of my program. In complex animal societies, females usually live with their close kin but these close kin are also their closest competitors. Thus sociality can be seen as a tug-of-war between cooperation and competition among groupmates. In female Cape ground squirrels, most breeding attempts fail to wean offspring, but the reasons for this reproductive skew are unclear. Reproductive conflict within the family group is not apparent, so such skew is unexpected. Testing hypotheses related to life-history and social complexity in family groups that appear to be egalitarian is the second focus of my program. Cooperative breeding, where individuals care for offspring that are not their own, is usually explained as helping kin, but male carers in Cape ground squirrels provide care as a form of rent. The question is, do male carers increase the reproductive success or survival of breeders? Or do breeders pay the cost in terms of infections from grooming male carers? Understanding the benefits and costs of male care to females is another focus of this work. Results of this research will have theoretical and applied implications to evolutionary biology, and human and veterinary medicine, and will train HQP in crucial laboratory and fieldwork skills for these fields.