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：产间间隔（Interbirth Intervals, IBIs）是衡量雌性繁殖成功率的核心指标；解析其受环境、社会及人口统计因素调控的机制，可揭示雌性繁殖适合度变异的来源。 材料与方法：本研究依托针对160只野生雌性狒狒的490次产间间隔的36年繁殖数据集，解析了产间间隔及其各组成阶段——产后闭经（postpartum amenorrhea, PPA）、性周期阶段与妊娠阶段——时长的变异来源。同时分析了雌性狒狒在产间间隔期间体脂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，产间间隔通常更短（即繁殖周期加快），但该效应在产间间隔的不同组成阶段存在特异性差异。本研究同时发现，雌性狒狒在产后闭经阶段会出现显著体脂丢失，表明该阶段随进程推进将累积能量消耗。在性周期恢复前，雌性狒狒开始恢复体脂；性周期阶段体脂保持稳定，而妊娠的大部分阶段体脂持续上升。然而，体脂评分本身与各组成阶段的时长均无关联。最后，本研究观测到粪便糖皮质激素（fecal glucocorticoid）浓度随产后闭经阶段的推进逐渐降低，提示该阶段的能量应激水平有所下降。性周期阶段中，粪便孕激素（progestogen）与雌激素（estrogen）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、晚期的差异）。 讨论：本研究揭示了雌性灵长类动物繁殖所受的能量限制，阐明了雌性生存环境、体脂变化与类固醇激素浓度如何影响产间间隔时长与繁殖准备状态。