1. Role of androgens and glucocorticoids in parental care

A parental male bluegill tends his nest, which contains thousands of tiny eggs that are greyish in colour. Our research suggests that in bluegill androgens may not inhibit care behaviour as previous research in other species has suggested.

2. Role of androgens and glucocorticoids in life histories

A parental male bluegill (left) spawns with a female mimic (right) and a true female (centre).

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Endocrinology has become a powerful tool used by behavioural ecologists to study the proximate costs of parental care. This work focuses on androgens because of their role in mediating aggressive behaviour and the potentially detrimental effects of elevated concentrations on other systems critical for survival, such as immune function. The CHALLENGE HYPOTHESIS purports that increased circulating concentrations of testosterone during periods of heightened male-male aggression (e.g. territory establishment and courtship) and decreased androgen concentrations during periods of paternal care reflect the general incompatibility of androgens and the expression of parental caring behaviour. Conflicting results, however, have suggested that androgens may not be responsible for regulating parental care, but rather may decrease during the care period due to other factors such as the termination of physiological processes required for the production of sperm or associated secretions. Another group of hormones that is likely important in regulating reproductive behaviour are the glucocorticoids, which play a central role in the vertebrate stress response and in mobilizing the energy reserves through the regulation of metabolism. In collaboration with Dr Rosemary Knapp at the University of Oklahoma we are investigating the roles of these hormones on behaviour during parental care.

The alternative life histories of bluegill also provide an exceptional opportunity to understand the endocrinological basis of behavioural and morphological variations, and specifically to detail the proximate mechanisms mediating the male polymorphism. This work in part examines the morphology and distribution of steroid receptors in the brains of females, parentals, and cuckolders. Of particular interest is detailing the specific regions of the brain that develop within maturing cuckolders that could explain the observed larger brain size as compared to same aged (but immature) parentals. These data will also provide refined information as to when the male life histories first diverge ontogenetically.

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