Environmental sex determination, alternative male morphs, and the biological basis of personality

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My lab is focused upon understanding the biological basis of personality-like traits in general, and aggressiveness in particular. We examine the evolution, development and neuroendocrinological mechanisms underlying such individual variation. We aim to understand the evolutionary costs and benefits maintaining variation in behaviour.Variation in prenatal testosterone exposure during development is thought to permanently organize many behaviours throughout adulthood, particularly those that show sex differences, creating a spectrum of brain sex. Empirical evidence from both human and non-human animals suggests that the strength of sexual differentiation can variably masculinize eventual adult morphology and behaviour alike. Most of this work is purely correlational. Experimental manipulations, such as hormone treatments during development, do not necessarily inform us about the selective pressures on variation if the phenotypes produced are outside the range seen in recent ancestral history.To create such real-world range variation, I shall experimentally manipulate sex in an ecologically realistic manner by manipulating water chemistry in a species of cichlid fish with environmental sex determination. The intent is to create variation in the degree of mascuilinization of individuals. Lower pH during the first 30 days produces more males in adulthood, and more of those males are of the more aggressive, haremic-tending morph, and fewer are of the monogamy-tending morph. Work in many other species with environmental sex determination suggests that methylation of the aromatase gene promoter is associated with the environmental factor and a key part of sex determination. My preliminary data suggests that early pH manipulations influence the methylation of CpG sites in the promoter for both the brain and gonadal version of the aromatase genes. I shall extend this work to examine whether this sex determination pathway is also involved in determining male morph, and individual differences within morphs and sexes. I will examine the effects of these manipulations, and differences between alternative male morphs, in terms of both behaviour and brain. The brain's social behaviour network is a set of brain circuits which is highly conserved across vertebrates. We can experimentally induce changes in these brain regions, then study the effects on social behaviour in fish that should be of direct relevance to humans. That the sex of the brain lies on a continuous spectrum between a male and female extreme is an idea with very broad applicability and relevance. Many aspects of autism can be understood as a pathological hypermasculinization of the brain, as many aspects of psychosis can be understood as a pathological hyperfeminization of the brain. Between these extremes lies a continuous range of cognitive abilities and behavioural tendencies, each one with it's strengths and weaknesses.