Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, New York, United States of America.
PLoS One. 2012;7(11):e50108. doi: 10.1371/journal.pone.0050108. Epub 2012 Nov 28.
Animals facing seasonal variation in food availability experience selective pressures that favor behavioral adjustments such as migration, changes in activity, or shifts in diet. Eclectic omnivores such as many primates can process low-quality fallback food when preferred food is unavailable. Such dietary flexibility, however, may be insufficient to eliminate constraints on reproduction even for species that live in relatively permissive environments, such as moist tropical forests. Focusing on a forest-dwelling primate with a flexible diet (Cercopithecus mitis) we investigated whether females experience seasonal energetic stress and how it may relate to reproductive seasonality. We used fecal glucocorticoids (fGCs) as an indicator of energetic stress, controlling for the potentially confounding effects of social interactions and reproductive state. We modeled within-female fGC variation with General Linear Mixed Models, evaluating changes in feeding behavior and food availability as main effects. Regardless of reproductive state, fGCs increased when females shifted their diet towards fallback foods (mature leaves and other non-preferred items) and when they spent more time feeding, while fGCs decreased with feeding time on preferred items (insects, fruits, young leaves) and with the availability of young leaves. Changes in fruit availability had no general effects on fGCs, likely because fruits were sought out regardless of availability. As predicted, females in the energetically demanding stages of late pregnancy and early lactation showed greater increases in fGCs between periods of low versus high availability of fruits and young leaves than females in other reproductive states. Potential social stressors had no measurable effects on fGCs. Preliminary evidence suggests that seasonal energetic stress may affect the timing of infant independence from mothers and contribute to unusually long inter-birth intervals compared to closely related species of similar body size. Our findings highlight how the study of stress responses can provide insights into the proximate control of reproductive strategies.
动物在面对食物供应季节性变化时，会面临选择压力，这些压力有利于行为上的调整，如迁徙、活动变化或饮食变化。许多灵长类动物等杂食性动物在缺乏首选食物时，可以处理低质量的备用食物。然而，这种饮食灵活性可能不足以消除对繁殖的限制，即使对于生活在相对宽松环境中的物种也是如此，例如潮湿的热带雨林。我们专注于一种具有灵活饮食的森林栖息灵长类动物（Cercopithecus mitis），研究雌性动物是否会经历季节性能量压力，以及这种压力如何与繁殖季节性相关。我们使用粪便皮质醇（fGCs）作为能量压力的指标，控制社交互动和繁殖状态的潜在混杂影响。我们使用广义线性混合模型来模拟雌性个体内的 fGC 变化，评估摄食行为和食物可获得性的主要影响。无论繁殖状态如何，当雌性动物转向备用食物（成熟叶子和其他非首选食物）时，以及当它们花更多时间进食时，fGCs 会增加，而当它们花更多时间进食首选食物（昆虫、水果、嫩叶）时，以及当嫩叶供应增加时，fGCs 会减少。水果供应的变化对 fGCs 没有普遍影响，这可能是因为无论供应情况如何，水果都会被寻找。正如预测的那样，处于妊娠后期和哺乳期能量需求较高阶段的雌性动物，在果实和嫩叶供应较低与较高时期之间，fGCs 的增加幅度大于其他繁殖状态的雌性动物。潜在的社会压力源对 fGCs 没有可测量的影响。初步证据表明，季节性能量压力可能会影响婴儿从母亲独立的时间，并导致与体型相似的近亲物种相比，生育间隔异常长。我们的研究结果强调了研究应激反应如何为研究生殖策略的近因控制提供见解。
