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Normalized difference vegetation index, temperature and age affect faecal thyroid hormone concentrations in free-ranging African elephants.
Conservation Physiology ( IF 2.7 ) Pub Date : 2020-04-04 , DOI: 10.1093/conphys/coaa010
Isabelle D Szott 1 , Yolanda Pretorius 2, 3 , Andre Ganswindt 2, 4 , Nicola F Koyama 1
Affiliation  

Conservation biologists can use hormone measurements to assess animals’ welfare, reproductive state, susceptibility to stressors, as well as energy expenditure. Quantifying hormone concentrations from faecal samples is particularly advantageous as samples can be collected without disturbing animals’ behaviour. In order for an endocrine marker to be useful for wildlife managers, we need to understand how extrinsic and intrinsic factors affect hormone concentrations in free-ranging animal populations. Thyroid hormones are linked to basal metabolic rate and energy expenditure. Previous research demonstrated that triiodothyronine (T3) can be measured successfully in faecal matter of African elephants, Loxodonta africana. However, to our knowledge, research into factors affecting changes in elephant T3 levels has only been carried out in captive elephants so far. Thus, we present the first study of faecal T3 metabolite (mT3) concentrations of a large population of free-ranging African elephants. Over 15 months, we collected faecal samples from identified (n = 43 samples) and unidentified (n = 145 samples) individuals in Madikwe Game Reserve, South Africa. We investigated whether vegetative productivity [normalized difference vegetation index (NDVI)] in interaction with mean monthly temperature, age and sex affected mT3 concentrations. We found a significant negative interaction effect of NDVI and temperature. Increasing NDVI was related to higher concentrations of mT3, but increasing temperature was related to a decrease in mT3 concentrations in individually identified and unidentified elephants. In unidentified individuals, juvenile elephants had significantly higher mT3 concentrations compared to adult elephants. Faecal T3 can successfully be quantified in samples from free-ranging elephant populations and thus provides insight into energy expenditure in large herbivores.

中文翻译:

归一化的植被指数,温度和年龄影响自由放养的非洲象的粪便甲状腺激素浓度。

保护生物学家可以使用激素测量来评估动物的福利,生殖状态,对压力源的敏感性以及能量消耗。从粪便样品中定量激素浓度特别有利,因为可以采集样品而不会干扰动物的行为。为了使内分泌标记物对野生动植物管理者有用,我们需要了解外在因素和内在因素如何影响自由放养动物种群中的激素浓度。甲状腺激素与基础代谢率和能量消耗有关。此前的研究表明,碘甲状腺原氨酸(T3)可以成功的非洲象的粪便来衡量,非洲象。但是,据我们所知,迄今为止,仅在圈养大象中进行了影响大象T3水平变化的因素的研究。因此,我们目前对大量自由放养的非洲象的粪便T3代谢物(mT3)浓度进行了首次研究。在15个月的时间里,我们从已识别(n  = 43个样本)和未识别(n = 145个样本)在南非Madikwe Game Reserve的个人。我们调查了平均月温度,年龄和性别与植被生产力[归一化植被指数(NDVI)]的相互作用是否会影响mT3浓度。我们发现NDVI和温度之间存在显着的负面相互作用。NDVI的增加与mT3的较高浓度有关,但温度的升高与个体识别和未识别的大象的mT3浓度降低有关。在未确认身份的个体中,与成年大象相比,幼年大象的mT3浓度明显更高。粪便T3可以成功地从自由放养的大象种群的样品中定量,从而可以洞察大型食草动物的能量消耗。
更新日期:2020-04-17
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