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, R2 = 0.995, P < 0.001). Fat percentage regressed with body mass significantly predicted the DXA fat percentage (N = 29, R2adj. = 0.862, p < 0.001). Live wet mass was significantly correlated with predicted fat mass (N = 30, R2 = 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.

中文翻译：

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测量蜥蜴的身体状况：无创双能X射线吸收法，化学脂肪提取法和计算指标之间的比较

在生态学研究中使用条件指数（CI）作为衡量单个动物的健康和适应性的一种方式。非侵入性CI是对脂肪含量的相对得分的估计，或者是与某种尺寸（通常是线性尺寸，例如sus架或口鼻孔长度）的度量相比所依赖的体重比率。通常，通过在人群中季节性采集个体中的致命脂肪来侵入性地验证CI。致命脂肪提取的许多替代方法既昂贵又耗时。作为替代方案，双能X射线吸收仪（DXA）可以对动物的身体成分进行无损分析，并可以在动物的一生中进行多次测量。DXA从未在小型自由放养的蜥蜴中用于生态研究，因此，我们针对从体重在4.2-11.5 g之间的6只壁虎（以色列扇形壁虎Ptyodactylus guttatus）样本中化学提取脂肪的方法对这种方法进行了校准。然后，我们使用此校准的DXA测量值确定该物种的最佳线性测量值计算CI。我们发现，对于大于4.8 g的标本，用DXA测量的脂肪质量与化学提取脂肪的质量显着相关（N = 5，R2 = 0.995，P <0.001）。随着体重下降的脂肪百分比显着预测了DXA脂肪百分比（N = 29，R2adj。= 0.862，p <0.001）。对于大于4.8 g的样本，活湿质量与预测脂肪质量显着相关（N = 30，R2 = 0.984，P <0.001）。在我们测试的五个计算出的非侵入性CI中，最好的是质量/ SVL。