Charpentier M J E, Givalois L, Faurie C, Soghessa O, Simon F, Kappeler P M
ISEM, Univ. Montpellier, CNRS, IRD, EPHE, Montpellier, France.
MMDN Lab - U1198, INSERM, University of Montpellier, EPHE, Montpellier, France.
Am J Phys Anthropol. 2018 Jan;165(1):20-33. doi: 10.1002/ajpa.23329. Epub 2017 Oct 27.
The activation of the hypothalamic-pituitary-adrenal axis is a neuroendocrine response to external and internal changes that animals face on a predictable or unpredictable basis. Across species, variation in glucocorticoid production has been related to such changes. In this study, we investigated the predictable, seasonal sources of variation in the levels of fecal glucocorticoid metabolites (fGCM) in a large natural population of mandrills (Mandrillus sphinx) in Southern Gabon.
Using five years of regular behavioral monitoring and hormone analyses performed on 1,233 fecal samples collected on 99 individuals of both sexes and all ages and General Linear Mixed Models, we studied the three main seasonal predictors of fGCM concentrations: (i) weather conditions, (ii) number of adult males, and (iii) female reproductive status. These three predictors all vary seasonally in mandrills.
We first showed an increase in fGCM concentrations during the short dry season while controlling for other factors. Pregnant females, which include the large majority of adult females at this time of the year, mainly drove this increase, although a combination of other small-magnitude, season-related effects linked to climatic events and demographic changes also partly explained this seasonal trend. Indeed, fGCM concentrations increased with both low temperatures (and low rainfall) and high numbers of adult males present in the group. These seasonal changes, while correlated, held true throughout the studied years and when restricting our analyses to a given season. Finally, we found that older mandrills showed on average higher fGCM concentrations than younger ones and that medium-ranked females exhibited the highest levels of fGCMs.
The observed patterns suggest that plasticity in mandrills' metabolism in the form of glucocorticoid production allows them to adjust to predictable changes in climatic, demographic and physiological conditions by mobilizing and redirecting energetic resources toward appropriate, calibrated seasonal responses.
下丘脑 - 垂体 - 肾上腺轴的激活是动物对可预测或不可预测的外部和内部变化的一种神经内分泌反应。在不同物种中，糖皮质激素分泌的变化与这些变化有关。在本研究中，我们调查了加蓬南部一个大型自然群体的山魈（Mandrillus sphinx）粪便糖皮质激素代谢物（fGCM）水平变化的可预测季节性来源。
我们对99只不同性别和年龄的个体采集的1233份粪便样本进行了为期五年的定期行为监测和激素分析，并使用广义线性混合模型，研究了fGCM浓度的三个主要季节性预测因素：（i）天气状况，（ii）成年雄性数量，以及（iii）雌性生殖状态。这三个预测因素在山魈中均呈现季节性变化。
我们首先发现，在控制其他因素的情况下，短旱季期间fGCM浓度会升高。怀孕的雌性，在一年中的这个时候包括了绝大多数成年雌性，是导致这种升高的主要原因，尽管与气候事件和人口变化相关的其他小幅度、与季节相关的影响因素组合也部分解释了这种季节性趋势。事实上，fGCM浓度随着低温（和低降雨量）以及群体中成年雄性数量的增加而升高。这些季节性变化虽然相互关联，但在整个研究年份以及将分析限制在特定季节时都成立。最后，我们发现年长的山魈平均fGCM浓度高于年幼的山魈，并且中等地位的雌性表现出最高水平的fGCM。
观察到的模式表明，山魈以糖皮质激素分泌形式存在的代谢可塑性，使它们能够通过调动和重新分配能量资源，以适应气候、人口和生理条件的可预测变化，从而做出适当的、经过校准的季节性反应。
