Moullec Héloïse, Berger Vérane, Santos Diogo J, Ukonaho Susanna, Yon Lisa, Briga Michael, Nyein U Kyaw, Lummaa Virpi, Reichert Sophie
Department of Biology, University of Turku, Vesilinnantie, 5, Turku 20014, Finland.
School of Veterinary Medicine & Science, University of Nottingham, Sutton Bonington Campus, Leicestershire, LE12 5RD, United Kingdom.
Conserv Physiol. 2024 Nov 22;12(1):coae076. doi: 10.1093/conphys/coae076. eCollection 2024.
Hormones are known to be involved in life-history trade-offs as systemic signals that establish functional links among traits and regulate key behavioural and physiological transitions between states in organisms. Although major functions of many steroid hormones such as testosterone are conserved among vertebrates, circulating concentrations vary widely both within and across species, and the degree to which observed hormone concentrations mediate life-history responses to environmental variation is less understood. In this study, we investigated how faecal testosterone metabolite (FTM) concentrations varied with extrinsic and intrinsic factors. To do so, we took advantage of a 6-year period of longitudinal sampling of FTM, indicators of stress and oxidative status in a semi-captive population of Asian elephants ( = 3163 samples from 173 individuals) in Myanmar. We determined how the variation in FTM is associated with age, sex, origin (captive-born or wild-caught), seasonality of the environment, individual stress level [measured by faecal glucocorticoid metabolite (FGM) and heterophil to lymphocyte ratio (H/L)] and oxidative status (reactive oxygen metabolite concentrations and superoxide dismutase activity). We reported that FTM increased with age from juvenile to adulthood for both sexes, with higher FTM concentrations in males than females. Moreover, elephants showed significantly higher FTM concentrations during the hot season and monsoon than in the cold season. However, for the physiological indicators, we found contrasting results. While FTM concentrations were strongly positively correlated with FGM concentrations, FTM concentrations were not related to H/L ratios. Finally, we found no relationship between FTM and the oxidative status of individuals. Our study provides new insights on the factors associated with variation in testosterone concentrations-a key hormone for reproduction and fitness of individuals-in Asian elephants living in their natural environment, which has relevance for effective conservation measures of this endangered species.
激素作为系统信号参与生命史权衡，在生物体的性状之间建立功能联系，并调节不同状态之间关键的行为和生理转变。尽管睾酮等许多类固醇激素的主要功能在脊椎动物中是保守的，但不同物种内部和之间的循环浓度差异很大，而观察到的激素浓度介导生命史对环境变化反应的程度尚不清楚。在本研究中，我们调查了粪便睾酮代谢物（FTM）浓度如何随外在和内在因素而变化。为此，我们利用了对缅甸亚洲象半圈养种群（来自173头个体的3163个样本）进行的为期6年的FTM、应激指标和氧化状态的纵向采样。我们确定了FTM的变化如何与年龄、性别、来源（圈养出生或野生捕获）、环境季节性、个体应激水平[通过粪便糖皮质激素代谢物（FGM）和嗜异性粒细胞与淋巴细胞比率（H/L）测量]以及氧化状态（活性氧代谢物浓度和超氧化物歧化酶活性）相关。我们报告说，两性从幼年到成年FTM均随年龄增加而升高，雄性FTM浓度高于雌性。此外，大象在炎热季节和季风期间的FTM浓度明显高于寒冷季节。然而，对于生理指标，我们发现了相反的结果。虽然FTM浓度与FGM浓度呈强正相关，但FTM浓度与H/L比率无关。最后，我们发现FTM与个体氧化状态之间没有关系。我们的研究为生活在自然环境中的亚洲象体内睾酮浓度变化的相关因素提供了新见解，睾酮是个体繁殖和健康的关键激素，这对该濒危物种的有效保护措施具有重要意义。
