Electronic Thesis and Dissertation Repository


Master of Science




Dr. Bryan Neff


Research suggests an androgen mediated trade-off between nurturing and defensive behaviour during parental care. This research, however, comes from species with biparental care, where changes in behaviour of one parent can be compensated for by the other parent. I tested the validity of this trade-off by manipulating androgen levels in bluegill sunfish (Lepomis macrochirus), a species where males provide sole parental care. I implanted males with testosterone, 11-ketotestosterone or flutamide, an androgen receptor blocker, and tested their nurturing behaviour and aggressiveness towards a brood predator. Males implanted with 11-ketotestosterone were 64% more aggressive and 71% less nurturing than controls. In contrast, males implanted with flutamide were 7% less aggressive and 126% more nurturing. Males with elevated testosterone levels showed marginally higher aggression, but no reduction in nurturing behaviour. This study is among the first to confirm an androgen mediated trade-off in aggression and nurturing in a uniparental care system.