The biological basis of individual differences in aggressiveness

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The long term goal of my research is to understand the causes, both evolutionary and developmental, of individual differences in aggressiveness and other social behaviours. At present the proximate and developmental causes of individual differences in such personality traits are not well understood. One factor thought to influence adult personality in mammals is uterine environment. Psychologists and biologists believe that variation in fetal exposure to testosterone has an important organizing effect on subsequent aggressiveness, brain lateralization and other traits among adults. In a parallel tradition, it is thought that maternal stress hormones may adaptively program offspring into developing a behavioural stress coping style best suited to the environment they will grow up and live in. I will experimentally manipulate both these effects in fish, not by artificially dosing them with hormones during early development (a biologically unrealistic manipulation which may produce biologically unrealistic results) but by manipulating their environment in as biologically realistic, yet simple, a method as possible. The cichlid fish Pelvicachromis pulcher shows pH-dependent sex determination. Lower pH water produces more males, and a higher proportion of males with a tendency to haremic breeding. I will use these pH manipulations in the 30 first days of life to vary the masculinization/feminization of fish. I will also expose developing fish to a chemical alarm pheromone, a natural stressor indicating elevated predator risk. I will examine the effects of these manipulations on growth rates and adult body shape, as well as effects on the hypothalamus, amygdala and hippocampus (brain areas involved in aggression and stress coping), behavioural traits (including fearfullness and aggressiveness), and epigenetic effects. I will measure the evolutionary costs and benefits of these differences by testing how fish fare in social situations. This programme ties together questions at the mechanistic level, the developmental level, and the ultimate level to understand how different personalities develop and function to serve individuals to better survive and reproduce.