Banerjee Avik, Fahis K T, Joshi Mihir, Raubenheimer David, Thaker Maria
Centre for Ecological Sciences, Indian Institute of Science, Bengaluru, India.
M.E.S Mampad College (Autonomous), Department of Zoology, Centre for Conservation Ecology, Malappuram, India.
J Anim Ecol. 2025 Apr;94(4):627-641. doi: 10.1111/1365-2656.14249. Epub 2025 Jan 30.
Challenging events in the environment that are both predictable (e.g. seasonal patterns in breeding activities) and unpredictable (e.g. predator encounter) are known to induce a glucocorticoid response that facilitates metabolic requirements during the challenge. Given its role in mobilizing energy, glucocorticoid levels can influence the nutritional ecology of an individual by shifting dietary intake or retention patterns, but this relationship has not been tested in free-ranging vertebrates. Using a tropical lizard species (Psammophilus dorsalis) as a model system, we tested whether the elemental composition of dietary intake and excretion (faecal samples) varies with stress-induced corticosterone levels in males and females across different seasons. From free-ranging lizards in the wild, we measured levels of stress-induced corticosterone and glucose in blood and determined diet composition from gut-flushing. Elemental composition of the diet was determined by analysing the carbon and nitrogen content of identified prey Orders caught from the wild. We also collected faecal samples and estimated their elemental composition. We found that stress-induced corticosterone levels varied across seasons, with the lowest levels during the breeding season for both males and females. Despite high variation in corticosterone responsiveness, lizards did not shift the elemental composition of their diets and maintained an intake carbon:nitrogen ratio of 4.56. We did, however, find a negative correlation between stress-induced corticosterone levels and faecal elemental composition, suggesting selective retention of both carbon and nitrogen in individuals that have higher corticosterone responsiveness. This study highlights the interplay between corticosterone responsiveness and nutritional ecology, challenging the existing links in literature and illustrating how free-ranging animals, such as lizards, adjust the elemental composition of excretion and not dietary intakes as a potential strategy to modulate natural physiological and ecological challenges.
环境中具有可预测性（例如繁殖活动的季节性模式）和不可预测性（例如遭遇捕食者）的挑战性事件，已知会引发糖皮质激素反应，从而在挑战期间促进新陈代谢需求。鉴于其在调动能量方面的作用，糖皮质激素水平可通过改变饮食摄入或保留模式来影响个体的营养生态，但这种关系尚未在自由放养的脊椎动物中得到验证。我们以一种热带蜥蜴物种（背纹沙蜥）作为模型系统，测试了不同季节雄性和雌性蜥蜴饮食摄入与排泄（粪便样本）的元素组成是否会随应激诱导的皮质酮水平而变化。我们从野外自由放养的蜥蜴身上测量了血液中应激诱导的皮质酮和葡萄糖水平，并通过肠道冲洗确定了饮食组成。通过分析从野外捕获的已识别猎物目类的碳和氮含量，确定了饮食的元素组成。我们还收集了粪便样本并估计了它们的元素组成。我们发现，应激诱导的皮质酮水平随季节变化，雄性和雌性在繁殖季节的水平最低。尽管皮质酮反应性存在很大差异，但蜥蜴并未改变其饮食的元素组成，维持了4.56的摄入碳氮比。然而，我们确实发现应激诱导的皮质酮水平与粪便元素组成之间存在负相关，这表明皮质酮反应性较高的个体对碳和氮都有选择性保留。这项研究突出了皮质酮反应性与营养生态之间的相互作用，挑战了文献中现有的联系，并说明了像蜥蜴这样的自由放养动物如何调整排泄的元素组成而非饮食摄入，作为调节自然生理和生态挑战的潜在策略。
