Costs, consequences and context-dependency of intrafamilial conflict

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The environment that an individual experiences during growth and development has profound implications for the future health and fitness of that individual during adulthood. In species that provide parental care offspring are usually reared together in broods, so close relations often provide the social environment in which growth and development takes place. However, because parental care is costly to parents (in time and energy), and availability of environmental resources essential for growth and development of young varies unpredictably, offspring demand for food and other resources often exceeds parental supply. As a consequence there may be conflicts of interest among family members over the supply of these parental resources (parental investment; PI), which affects the amount of resources available to individual offspring. The consequences of such conflicts within families can be pervasive, and have important effects for the diversity and evolution of life-history traits and behaviours such as growth rates, clutch size, sexual attractiveness and begging behaviour. The amount of resources available to individual offspring depends upon the amount of conflict, which is determined by the relatedness of family members and the availability of key resources in the environment. However, although the importance of within-family conflicts for growth, development and fitness is increasingly being recognised, very little is known about the mechanisms that underpin such conflicts, or the interrelationships between resource availability, conflict over these resources and the mechanisms that determine the costs and consequences of conflict. Previous work on zebra finches by the author showed that, although receiving less food, offspring reared under conditions of higher within-family conflict had faster growth compared to siblings reared under lower levels of conflict. As a result these offspring were less attractive as adults, indicating a substantial costs of rapid growth and of family conflict. These costs are most probably a consequence of increased oxidative stress, which occurs when high levels of free radicals, which are by-products of normal metabolic processes, cause damage to various cell components. Antioxidants provide protection against the damaging effects of free radicals. An important component of total antioxidant defence is provided by fat-soluble antioxidants, such as carotenoids and vitamin E, which are derived from the diet. The interaction between dietary availability of antioxidants and within-family conflicts has not previously been considered, but is likely to be important as variation in antioxidant availability determines the trade-off between self-maintenance and investment in growth and reproduction, and hence fitness. This project plans to use brood size manipulations, hand-rearing and parent removal experiments and cross-fostering to tease apart the effects of sexual conflict and sibling competition on growth and fitness of offspring, examine the cost basis of growth through the measurement of oxidative stress and manipulation of dietary antioxidant availability, and establish the behavioural mechanisms that underlie the allocation of PI in relation to the social and environmental context in which they are operating. The work integrates nutrition, reproductive ecophysiology and environmental uncertainty with behavioural ecology in examining the costs and consequences of variation in social and environmental effects early in life on adult health and fitness. If funded, the project would be conducted at the Institute of Biological and Life Sciences at the University of Glasgow, using zebra finches Taeniopygia guttata as a model species.