Biodiversity and Development Institute, 4 Gunner's Park, Grenville Avenue, Epping 1, Cape Town, 7460, South Africa.
Mammal Research Institute, Department of Zoology and Entomology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa.
BMC Ecol. 2020 Feb 18;20(1):12. doi: 10.1186/s12898-020-00280-z.
Glucocorticoids mediate responses to perceived stressors, thereby restoring homeostasis. However, prolonged glucocorticoid elevation may cause homeostatic overload. Using extensive field investigations of banded mongoose (Mungos mungo) groups in northern Botswana, we assessed the influence of reproduction, predation risk, and food limitation on apparent homeostatic overload (n=13 groups, 1542 samples from 268 animals). We experimentally manipulated reproduction and regulated food supply in captive mongooses, and compared their glucocorticoid responses to those obtained from free-living groups.
At the population level, variation in glucocorticoid levels in free-living mongooses was explained by food limitation: fecal organic matter, recent rainfall, and access to concentrated anthropogenic food resources. Soil macrofauna density and reproductive events explained less and predation risk very little variation in glucocorticoid levels. Reproduction and its associated challenges alone (under regulated feeding conditions) increased glucocorticoid levels 19-fold in a captive group. Among free-living groups, glucocorticoid elevation was seasonal (occurring in late dry season or early wet season when natural food resources were less available), but the timing of peak glucocorticoid production was moderated by access to anthropogenic resources (groups with fewer anthropogenic food sources had peaks earlier in dry seasons). Peak months represented 12- and 16-fold increases in glucocorticoids relative to nadir months with some animals exhibiting 100-fold increases. Relative to the captive group nadir, some free-living groups exhibited 60-fold increases in peak glucocorticoid levels with some animals exhibiting up to 800-fold increases. Most of these animals exhibited 1- to 10-fold increases relative to the captive animal peak.
Banded mongooses exhibit seasonal chronic glucocorticoid elevation, associated primarily with food limitation and secondarily with reproduction. Magnitude and duration of this elevation suggests that this may be maladaptive for some animals, with possible fitness consequences. In late dry season, this population may face a convergence of stressors (food limitation, agonistic encounters at concentrated food resources, evictions, estrus, mate competition, parturition, and predation pressure on pups), which may induce homeostatic overload.
糖皮质激素介导对感知到的应激源的反应，从而恢复体内平衡。然而，长期的糖皮质激素升高可能导致体内平衡过载。本研究通过对博茨瓦纳北部带状獴（Mungos mungo）群体的广泛实地调查，评估了繁殖、捕食风险和食物限制对表观体内平衡过载的影响（n=13 个群体，来自 268 只动物的 1542 个样本）。我们在圈养獴中实验性地操纵繁殖并调节食物供应，并将它们的糖皮质激素反应与从自由生活群体中获得的反应进行比较。
在种群水平上，自由生活的獴的糖皮质激素水平的变化可以用食物限制来解释：粪便有机物、最近的降雨量以及获得集中的人为食物资源。土壤大型动物密度和繁殖事件解释了糖皮质激素水平变化的较少部分，而捕食风险则很少。仅繁殖及其相关挑战（在受监管的喂养条件下）就使圈养组的糖皮质激素水平增加了 19 倍。在自由生活的群体中，糖皮质激素升高是季节性的（发生在旱季后期或雨季早期，此时天然食物资源较少），但峰值糖皮质激素产生的时间由获得人为资源的情况调节（获得人为食物来源较少的群体在旱季早期达到峰值）。与低谷月份相比，峰值月份的糖皮质激素水平增加了 12-16 倍，一些动物的水平增加了 100 倍。与圈养组的低谷相比，一些自由生活的群体的峰值糖皮质激素水平增加了 60 倍，一些动物的水平增加了 800 倍。大多数动物的峰值水平相对于圈养动物的峰值水平增加了 1-10 倍。
带状獴表现出季节性慢性糖皮质激素升高，主要与食物限制有关，其次与繁殖有关。这种升高的幅度和持续时间表明，这可能对一些动物不利，可能会产生适应不良的后果。在旱季后期，这个种群可能面临压力源的趋同（食物限制、在集中的食物资源处发生的争斗、驱逐、发情、配偶竞争、分娩以及对幼崽的捕食压力），这可能会导致体内平衡过载。
