Sion Guy, Watson Maggie J, Bouskila Amos
Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, 8410501, Beer Sheva, Israel.
Present address: School of Zoology, Faculty of Life Sciences, Tel Aviv University, 69978, Tel Aviv, Israel.
Front Zool. 2021 Jan 5;18(1):1. doi: 10.1186/s12983-020-00382-w.
Condition indices (CIs) are used in ecological studies as a way of measuring an individual animal's health and fitness. Noninvasive CIs are estimations of a relative score of fat content or rely on a ratio of body mass compared to some measure of size, usually a linear dimension such as tarsus or snout-vent length. CIs are generally validated invasively by lethal fat extraction as in a seasonal sample of individuals in a population. Many alternatives to lethal fat extraction are costly or time consuming. As an alternative, dual-energy X-ray absorptiometry (DXA) allows for non-destructive analysis of body composition and enables multiple measurements during an animal's life time. DXA has never been used for ecological studies in a small, free-ranging lizard before, therefore we calibrated this method against a chemical extraction of fat from a sample of 6 geckos (Israeli fan toed gecko Ptyodactylus guttatus) ranging in body mass between 4.2-11.5 g. We then used this calibrated DXA measurements to determine the best linear measurement calculated CI for this species.
We found that fat mass measured with DXA was significantly correlated with the mass of chemically extracted fat for specimens more than 4.8 g (N = 5, R = 0.995, P < 0.001). Fat percentage regressed with body mass significantly predicted the DXA fat percentage (N = 29, R = 0.862, p < 0.001). Live wet mass was significantly correlated with predicted fat mass (N = 30, R = 0.984, P < 0.001) for specimens more than 4.8 g. Among the five calculated non-invasive CIs that we tested, the best was mass/SVL.
We recommend that in situations where DXA cannot be used, that the most accurate of the body condition estimators for this species is mass/SVL (snout-vent length) for both sexes.
状况指数（CIs）在生态学研究中用于衡量个体动物的健康和适合度。非侵入性状况指数是对脂肪含量相对分数的估计，或依赖于体重与某种大小测量值的比率，通常是线性尺寸，如跗骨或吻肛长度。状况指数通常通过对种群中个体的季节性样本进行致死性脂肪提取来进行侵入性验证。许多替代致死性脂肪提取的方法成本高昂或耗时。作为一种替代方法，双能X射线吸收法（DXA）允许对身体成分进行非破坏性分析，并能在动物的生命周期内进行多次测量。此前，DXA从未用于小型自由放养蜥蜴的生态学研究，因此我们针对从6只体重在4.2 - 11.5克之间的壁虎（以色列扇趾壁虎Ptyodactylus guttatus）样本中化学提取的脂肪，对该方法进行了校准。然后，我们使用这些校准后的DXA测量值来确定该物种计算得出的最佳线性测量状况指数。
我们发现，对于体重超过4.8克的标本，用DXA测量的脂肪量与化学提取脂肪的量显著相关（N = 5，R = 0.995，P < 0.001）。脂肪百分比与体重的回归显著预测了DXA脂肪百分比（N = 29，R = 0.862，p < 0.001）。对于体重超过4.8克的标本，活湿重与预测脂肪量显著相关（N = 30，R = 0.984，P < 0.001）。在所测试的五个计算得出的非侵入性状况指数中，最佳的是体重/吻肛长度。
我们建议，在无法使用DXA的情况下，对于该物种，最准确的身体状况估计指标是两性的体重/吻肛长度（吻肛长度）。
