Wittemyer George, Ganswindt André, Hodges Keith
Save the Elephants, P.O. Box 54667, Nairobi, Kenya.
Horm Behav. 2007 Mar;51(3):346-54. doi: 10.1016/j.yhbeh.2006.12.013. Epub 2007 Jan 10.
Non-invasive endocrine methods enable investigation of the relationship between ecological variation and ovarian activity and how this impacts on demographic processes. The underlying physiological factors driving high variation in inter-calving intervals among multi-parous African elephants offer an interesting system for such an investigation. This study investigates the relationship between Normalized Differential Vegetation Index (NDVI), an ecosystem surrogate measure of primary productivity, and fecal progestin concentrations among wild female elephants. Matched fecal samples and behavioral data on reproductive activity were collected from 37 focal individuals during the two-year study. Linear mixed models were used to explore the relationship between fecal 5alpha-pregnane-3-ol-20-one concentrations and the independent variables of NDVI, calf sex, female age, gestation day, and time since last parturition. Among both non-pregnant and pregnant females, fecal 5alpha-pregnane-3-ol-20-one concentrations were significantly correlated with time-specific NDVI indicating a strong relationship between ecological conditions and endocrine activity regulating reproduction. In addition, the age of a female and time since her last parturition impacted hormone concentrations. These results indicate that the identification of an individual's reproductive status from a single hormone sample is possible, but difficult to achieve in practice since numerous independent factors, particularly season, impact fecal hormone concentrations. Regardless of season, however, fecal 5alpha-pregnane-3-ol-20-one concentrations below 1 microg/g were exclusively collected from non-pregnant females, which could be used as a threshold value to identify non-pregnant individuals. Collectively the information generated contributes to a better understanding of environmental regulation of reproductive endocrinology in wild elephant populations, information salient to the management and manipulation of population dynamics in this species.
非侵入性内分泌方法能够研究生态变化与卵巢活动之间的关系，以及这如何影响种群动态过程。在多产非洲象中，产犊间隔差异很大，其背后的生理因素为这类研究提供了一个有趣的系统。本研究调查了归一化植被指数（NDVI）（一种衡量初级生产力的生态系统替代指标）与野生雌性大象粪便中孕激素浓度之间的关系。在为期两年的研究中，从37个重点个体收集了匹配的粪便样本和生殖活动行为数据。使用线性混合模型来探究粪便中5α-孕烷-3-醇-20-酮浓度与NDVI、幼崽性别、雌性年龄、妊娠天数以及上次分娩后的时间等自变量之间的关系。在未怀孕和怀孕的雌性大象中，粪便中5α-孕烷-3-醇-20-酮浓度均与特定时间的NDVI显著相关，这表明生态条件与调节生殖的内分泌活动之间存在密切关系。此外，雌性大象的年龄和上次分娩后的时间会影响激素浓度。这些结果表明，从单一激素样本识别个体的生殖状态是可能的，但在实际操作中很难实现，因为众多独立因素，尤其是季节，会影响粪便激素浓度。然而，无论季节如何，粪便中5α-孕烷-3-醇-20-酮浓度低于1微克/克的样本均仅来自未怀孕的雌性大象，这一浓度可作为识别未怀孕个体的阈值。总体而言，所产生的信息有助于更好地理解野生大象种群生殖内分泌的环境调节，这对于该物种种群动态的管理和调控具有重要意义。
