Do maternal effects influence phenotypic traits in a cooperatively breeding mammal?

Abstract

Animals within populations show considerable variation in physiological and behavioural traits. These phenotypic differences can be profoundly influenced by the ecological and social conditions experienced in early life. Usually, adverse early life conditions, such as low food availability, will constrain offspring development. However, recent studies suggest that in some contexts suboptimal developmental conditions may be associated with fitness benefits. In this thesis I consider the ultimate and proximate mechanisms underlying individual variation in a cooperatively breeding mammal. I use hormone samples and the long-term dataset from the banded mongoose research project to investigate the social factors that influence early life stress and how patterns of reproductive investment change with maternal age. In chapter one I review current theories on the function of glucocorticoid (GC) hormones and give an overview of maternal stress and its effect on offspring development and physiology. In addition, I discuss the influence of maternal effects on cooperatively breeding systems. In chapter two, I introduce the study population and provide a general outline of the methods used in data collection and analysis. In chapter three, I test how maternal effects, specifically maternal rank, influence GC concentrations in banded mongoose pups and whether elevated early life GC is associated with mortality risk. I also consider whether the amount of cooperative care received by offspring in early life affects their GC concentrations. In chapter four, I use a larger dataset to consider how maternal effects influence adult life- history traits. I examine the influence that maternal age has on offspring survival, longevity and reproductive success and consider whether any effects might be sex- specific. I also ask whether age-related optimal maternal investment strategies can influence offspring sex ratios. In chapter five, I synthesis my findings and attempt to draw on the wider implications and make suggestions for future study.