Data from: Interbirth intervals in wild baboons: environmental predictors and hormonal correlates

Objectives: Interbirth intervals (IBIs) are a key metric of female reproductive success; understanding how they are regulated by environmental, social, and demographic factors can provide insight into sources of variance in female fitness. Materials and Methods: Using 36 years of reproductive data on 490 IBIs for 160 wild female baboons, we identified sources of variance in the duration of IBIs and of their component phases: postpartum amenorrhea (PPA), sexual cycling, and pregnancy. We also examined how body fat and fecal hormone concentrations varied during female IBI. Results: We found that IBIs tended to be shorter (reproduction was accelerated) when female traits and environmental variables promoted energy acquisition, but with different specific effects for different component phases of the IBI. We also found that females lost a substantial amount of body fat during PPA, indicating that PPA imposes accumulating energetic costs as it progresses. Prior to cycle resumption females began to regain body fat; body fat was stable across the cycling phase and increased throughout most of pregnancy. However, body fat scores per se were not associated with the duration of any of the component phases. Finally, we found that fecal glucocorticoid concentrations decreased as PPA progressed, suggesting a decline in energetic stress over this phase. Fecal progestogen and estrogen concentrations changed over time during sexual cycling; the direction of these changes depended on the phase of the sexual cycle (luteal versus early or late follicular phases). Discussion: Our study lends insight into the energetic constraints on female primate reproduction, revealing how female environments, changes in body fat, and steroid hormone concentrations relate to IBI duration and to reproductive readiness.研究目的：产间期（Interbirth Intervals, IBIs）是衡量雌性繁殖成功的关键指标；解析其受环境、社会及人口统计学因素调控的机制，可为理解雌性适合度变异的来源提供重要视角。 材料与方法：本研究基于针对160只野生雌性狒狒的36年繁殖数据，共包含490条产间期记录，我们分析了产间期时长及其各组成阶段——产后闭经（Postpartum Amenorrhea, PPA）、性周期恢复阶段与妊娠阶段——的变异来源；同时探究了雌性在产间期内体脂含量与粪便激素浓度的变化规律。 研究结果：当雌性自身性状与环境变量有利于能量获取时，产间期通常更短（即繁殖进程得以加速），但该效应对产间期的不同组成阶段存在特异性影响。此外，我们发现雌性在产后闭经阶段会流失大量体脂，表明该阶段随时长增加会累积能量消耗；在性周期恢复前，雌性开始恢复体脂，性周期阶段体脂保持稳定，而妊娠阶段的体脂则在多数时期呈上升趋势。不过，体脂水平本身与各组成阶段的时长并无关联。最后，我们观察到粪便糖皮质激素浓度随产后闭经阶段推进而降低，提示该阶段的能量压力随时间推移有所缓解；在性周期阶段，粪便孕激素与雌激素浓度随时间发生变化，其变化方向取决于性周期所处的阶段（黄体期与卵泡早期或晚期）。 讨论：本研究揭示了雌性灵长类繁殖所受的能量约束，阐明了雌性所处环境、体脂变化与类固醇激素浓度如何与产间期时长及繁殖准备状态相关联。