Reproduction and Resistance to Stress: When and How

Abstract

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

Individual variation in baseline and stress-induced corticosterone and prolactin levels predicts parental effort by nesting mourning doves

“…At least one previous study indicates that breeding birds may modulate the decline in PRL level when facing acute stressors when compared to nonbreeders , indicating that the PRL stress response may have important consequences for breeding birds. The CORT stress response is better studied in birds, but ambiguity exists in whether and when birds modulate the stress response (Shultz and Kitaysky, 2008;Romero, 2002;Wingfield and Sapolsky, 2003). Given the dramatic effects of SI CORT level on subsequent parental effort we found in this study, it is somewhat surprising that we did not find evidence that parents modulated the response in relation to their own current conditions or that of their young.…”

“…The potential for SI CORT secretion to affect the life-history tradeoff between the immediate needs of an individual for survival and their investment in reproductive output has led to a focus on factors that cause individuals to modulate their stress response (Wingfield et al, 1998;Romero, 2002;Wingfield and Sapolsky, 2003). There is mixed evidence that birds suppress their CORT response to acute stressors during breeding (Romero, 2002;Wingfield and Sapolsky, 2003) or that different populations of the same species vary their response to reflect different conditions during breeding (Kitaysky et al, 2007;Shultz and Kitaysky, 2008).…”

“…There is mixed evidence that birds suppress their CORT response to acute stressors during breeding (Romero, 2002;Wingfield and Sapolsky, 2003) or that different populations of the same species vary their response to reflect different conditions during breeding (Kitaysky et al, 2007;Shultz and Kitaysky, 2008). Differences among species in reproductive value of offspring predict differences in SI CORT responses (Bókony et al, 2009), indicating that life-history predictions may be important in driving variation in the response.…”

Differential investment into testes and sperm production in alternative male reproductive tactics of the African striped mouse (Rhabdomys pumilio)

“…Philopatric males thus showed clear signs of being reproductively suppressed, 510 supporting a previous study (Schradin et al, 2009b). Compared to their singly-housed 511 brothers, they had higher corticosterone levels, which is regarded as an indicator of 512 physiological reproductive suppression (Reyer et al, 1986;Wingfield and Sapolsky, 2003). 513…”

How should the psychological well‐being of zoo elephants be objectively investigated?

“…A well-documented effect of chronic stress in humans, research rodents, and many other species [see reviews by e.g., Wingfield and Sapolsky 2003;von Borell et al, 2007;Clubb et al, 2009] is reduced fertility. In adult females, this can be manifest as impaired cycling/reduced estrous periods, low libido, premature reproductive senescence, reduced conception rates, increased pre-term fetal losses, prolonged parturitions, smaller birth weights, asymmetrical infant development, increased offspring stress responsiveness, poor maternal care (or infanticide), and/or increased infant mortality.…”