Data from: Social and ecological drivers of reproductive seasonality in geladas

Many non-seasonally breeding mammals demonstrate some degree of synchrony in births, which is generally associated with ecological factors that mediate fecundity. However, disruptive social events, such as alpha male replacements, also have the potential to affect the timing of female reproduction. Here, we examined reproductive seasonality in a wild population of geladas (Theropithecus gelada) living at high altitudes in an afro-alpine ecosystem in Ethiopia. Using 9 years of demographic data (2006-2014) we determined that, while females gave birth year-round, a seasonal peak in births coincided with peak green grass availability (their staple food source). This post-rainy season “ecological peak” in births meant that estimated conceptions for these births occurred when temperatures were at their highest and mean female fecal glucocorticoid concentrations were at their lowest. In addition to this ecological birth peak, we also found a separate birth peak that occurred only for females in groups that had experienced a recent replacement of the dominant male (i.e., a takeover). Because new dominant males cause abortions in pregnant females and kill the infants of lactating females, takeovers effectively “reset” the reproductive cycles of females in the group. This “social birth peak” was distinct from the ecological peak and was associated with higher rates of cycling and conceptions overall and higher glucocorticoid levels immediately following a takeover as compared to females that did not experience a takeover. These data demonstrate that social factors (in this case, male takeovers) can contribute to population-level reproductive seasonality above and beyond group-level reproductive synchrony.

许多非季节性繁殖的哺乳动物均存在一定程度的分娩同步性，这类现象通常与调控繁殖力的生态因素密切相关。然而，具有破坏性的社会事件（如雄性首领更替）同样可能影响雌性的繁殖时序。本研究以栖息于埃塞俄比亚非洲高山型（afro-alpine）生态系统高海拔区域的野生狮尾狒（*Theropithecus gelada*）种群为研究对象，探究其繁殖季节性特征。我们利用2006至2014年共计9年的种群统计数据发现：尽管雌性狮尾狒全年均可分娩，但分娩的季节性高峰与青绿草类——其主食——的丰度峰值恰好重合。这种雨季过后的分娩“生态高峰”意味着，对应这批分娩的预估受孕事件发生于气温最高、雌性粪便糖皮质激素平均浓度最低的时段。除上述生态性分娩高峰外，本研究还发现另一独立的分娩高峰：该高峰仅见于近期经历过雄性首领更替（即群体接管）的种群中的雌性个体。由于新任雄性首领会导致怀孕雌性流产，并杀害哺乳期雌性的幼崽，群体接管行为实质上会“重置”种群内雌性的繁殖周期。这一“社会性分娩高峰”与生态性高峰截然不同：与未经历群体接管的雌性相比，经历接管后的雌性整体的发情周期与受孕率更高，且接管后即刻的糖皮质激素水平也更高。本研究数据表明，社会因素（本案例中为雄性群体接管）可在群体繁殖同步性之外，进一步推动种群层面的繁殖季节性形成。