Sexual steroids can play an important role as life-history organizers. In males, high circulating testosterone levels induce physiological/behavioral costs and benefits, leading to trade-offs. However, studies simultaneously testing the impact of these levels in both fitness components (survival and fecundity) during lifetime are scarce and limited to wild birds. To determine the mortality causes or hormonal manipulation impacts on male fertility is, nonetheless, a difficult task in free-ranging animals that could be easier in captivity. We longitudinally monitored captive red-legged partridges (Alectoris rufa) and exposed males to high exogenous testosterone levels, anti-androgens, or a control treatment during each breeding period throughout their lives. Theory predicts that individuals maintaining high androgen levels should obtain higher fitness returns via reproduction, but suffer reduced longevity. Testosterone-treated male partridges, accordingly, lived shorter compared to controls, since they were more prone to die from a natural bacterial infection. However, the same birds seemed to have a lower capacity to fertilize eggs, probably due to endocrine feedback reducing testicular mass. These results show that exogenous testosterone can exert unpredicted effects on fitness parameters. Therefore, caution must be taken when drawing conclusions from non-fully controlled experiments in the wild. Males treated with the androgen-receptor blocker flutamide did not outlive controls as predicted by the life-history trade-off theory, but their mates laid eggs with higher hatching success. The latter could be due to mechanisms improving sperm quality/quantity or influencing maternal investment in egg quality. Testosterone receptor activity/amount could thus be as relevant to fitness as testosterone levels. It has repeatedly been hypothesized that high testosterone levels induce a cost in terms of reduced lifetime reproductive success. This can be due to reduced fecundity or via shorter lifespan. This is, however, only supported by a handful of studies, mostly in wild birds. We tested this in captive male red-legged partridges, which allowed us to determine reproductive success and mortality causes. We increased testosterone levels or blocked its action with antiandrogens throughout life. High testosterone levels reduced the survival by making birds more prone to die by infection. The eggs produced by their mates also showed lower hatching success, a probable manipulation artifact that should be considered in avian studies in the wild. Interestingly, the androgen-receptor blocker flutamide increased lifetime hatching success compared to controls, suggesting that androgen receptor amounts/activity are even more relevant to fitness than testosterone levels.

中文翻译：

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终生睾酮和抗雄激素治疗影响圈养雄性红腿鹧鸪 (Alectoris rufa) 的存活和繁殖

性类固醇可以作为生活史的组织者发挥重要作用。在男性中，高循环睾酮水平会导致生理/行为成本和收益，从而导致权衡。然而，同时测试这些水平在一生中两个健康组成部分（生存和繁殖力）的影响的研究很少，并且仅限于野生鸟类。尽管如此，确定死亡原因或荷尔蒙操纵对雄性生育力的影响对于自由放养的动物来说是一项艰巨的任务，而圈养起来可能更容易。我们纵向监测圈养红腿鹧鸪 (Alectoris rufa)，并在其一生的每个繁殖期将雄性暴露于高外源性睾酮水平、抗雄激素或对照治疗。理论预测，维持高雄激素水平的个体应该通过繁殖获得更高的健康回报，但寿命会缩短。因此，与对照组相比，接受睾酮治疗的雄性鹧鸪寿命更短，因为它们更容易死于自然细菌感染。然而，同样的鸟类似乎具有较低的受精能力，这可能是由于内分泌反馈减少了睾丸质量。这些结果表明外源性睾酮可以对健身参数产生不可预测的影响。因此，在从非完全受控的野外实验中得出结论时必须谨慎。正如生活史权衡理论所预测的那样，用雄激素受体阻滞剂氟他胺治疗的雄性没有比对照寿命长，但它们的配偶产卵的孵化成功率更高。后者可能是由于提高精子质量/数量的机制或影响母体对卵子质量的投资。因此，睾酮受体活性/数量可能与睾酮水平一样与健康相关。一再假设高睾酮水平会导致终生生殖成功率降低的成本。这可能是由于繁殖力降低或寿命缩短。然而，这仅得到少数研究的支持，主要是在野生鸟类中。我们在圈养的雄性红腿鹧鸪中对此进行了测试，这使我们能够确定繁殖成功率和死亡原因。我们在一生中增加了睾酮水平或用抗雄激素阻断了它的作用。高睾酮水平使鸟类更容易因感染而死亡，从而降低了存活率。由它们的配偶产生的卵也显示出较低的孵化成功率，这可能是在野外鸟类研究中应该考虑的操纵人工制品。有趣的是，与对照相比，雄激素受体阻滞剂氟他胺提高了终生孵化成功率，这表明雄激素受体的数量/活性比睾酮水平更与健康相关。