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Exogenous testosterone increases the audience effect in healthy males: evidence for the social status hypothesis.

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Environmental and social stresses have deleterious effects on reproductive function in vertebrates. Global climate change, human disturbance and endocrine disruption from pollutants are increasingly likely to pose additional stresses that could have a major impact on human society. Nonetheless, some populations of vertebrates (from ®sh to mammals) are able to temporarily resist environmental and social stresses, and breed successfully. A classical trade-off of reproductive success for potential survival is involved. We de®ne ®ve examples. The stress-response plays a key role in allowing an organism to survive the acute challenge to homeostasis that constitutes the typical stressor. Energy is mobilized from storage sites and diverted to exercising muscle, cardiovascular tone is enhanced, long-term and costly anabolism is suppressed until a more auspicious time, and cognition is sharpened. However, following the pioneering work of Hans Selye in the 1930s, it is clear that an excess of stress can have pathogenic effects on metabolism, vascular function, growth, tissue repair, immune defences, and even the health of some neurones.Among the most consistently adverse consequences of prolonged stress is disruption of reproductive physiology and behaviour (Figs 1 and 2). Whether one is a clinician trying to understand a patient's loss of libido, a wildlife biologist grappling with how habitat degradation translates into decreased fertility of wild populations, or a conservationist faced with an endangered species refusing to mate in a zoo enclosure, stress must be considered in the equation. As a result of considerable research, a great deal is known about the neuroendocrine bases by which the stress-response can impair reproduction (Figs 1 and 2).In this review, we consider the general mechanisms by which such suppression occurs. More importantly, we provide examples where this yoking of stress and reproductive impairment does not occur. Such exceptions to the broad physiological effects of stress are not restricted to the reproductive axis. As an interesting recent precedent, socially subordinate mice subject to numerous bite wounds during ®ghting become resistant to the immunosuppressive effects of stress and glucocorticosteroids. The authors

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