Testosterone mediates life-history trade-offs in female mammals.

Hormones mediate life-history trade-offs. In female mammals, such trade-offs have been studied predominantly in the contexts of oestrogen, progesterone and prolactin. We evaluate the hypothesis that prenatal and postnatal testosterone levels structure and regulate trade-offs in females involving components of reproduction and survival. This hypothesis is predicated on the observation that testosterone confers competition-related and survival-related benefits, but also reproduction-related costs, to female mammals. The hypothesis is supported by field and laboratory data from diverse non-human animals, and data from healthy women. Most broadly, relatively low testosterone level in females has been associated with earlier, faster and higher offspring production, greater attractiveness to males, and reduced dominance or competitiveness, whereas higher testosterone level is associated with delayed and reduced reproduction but increased dominance, status, aggression, and resource accrual. The magnitude of testosterone-mediated trade-offs is expected to depend upon the strength of female-female competition, which represents some function of species-specific ecology, behaviour and mating system. Testosterone-associated trade-offs have, until now, been virtually ignored in studies of female life history, reproductive physiology, evolutionary endocrinology, and female-limited disease, probably due to researcher biases towards conceptualizing androgens as hormones with effects mainly restricted to males.