Nearly all organisms alter physiological and behavioral activities across the twenty-four-hour day. Endogenous timekeeping mechanisms, which are responsive to environmental and internal cues, allow organisms to anticipate predictable environmental changes and time their daily activities. Among-individual variation in the chronotype, or phenotypic output of these timekeeping mechanisms (i.e. timing of daily behaviors), is often observed in organisms studied under naturalistic environmental conditions. The neuroendocrine system, including sex steroids, has been implicated in the regulation and modulation of endogenous clocks and their behavioral outputs. Numerous studies have found clear evidence that sex steroids modulate circadian and daily timing of activities in captive animals under controlled conditions. However, little is known about how sex steroids influence daily behavioral rhythms in wild organisms or what, if any, implication this may have for survival and reproductive fitness. Here we review the evidence that sex steroids modulate daily timing in vertebrates under controlled conditions. We then discuss how this relationship may be relevant for the reproductive success and fitness of wild organisms and discuss the limited evidence that sex steroids modulate circadian rhythms in wild organisms.

几乎所有有机体都会在一天二十四小时内改变生理和行为活动。对环境和内部线索作出反应的内源性计时机制使生物体能够预测可预测的环境变化并为其日常活动计时。在自然环境条件下研究的生物体中，经常观察到这些计时机制（即日常行为的时间）的计时型或表型输出的个体差异。神经内分泌系统，包括性类固醇，与内源性时钟及其行为输出的调节和调节有关。许多研究已经发现明确的证据表明，在受控条件下，性类固醇调节圈养动物的昼夜节律和日常活动时间。然而，关于性类固醇如何影响野生生物的日常行为节律，或者这可能对生存和生殖健康有什么影响（如果有的话），我们知之甚少。在这里，我们回顾了性类固醇在受控条件下调节脊椎动物每日时间的证据。然后我们讨论这种关系如何与野生生物的繁殖成功和健康相关，并讨论性类固醇调节野生生物昼夜节律的有限证据。