Kelly Clint D, Tawes Brittany R, Worthington Amy M
Département des Sciences Biologiques, Université du Québec à Montréal CP-8888 Succursale Centre-ville, Montréal, Quebec, Canada, H3C 3P8.
Department of Ecology, Evolution & Organismal Biology, Iowa State Univeristy Ames, Iowa, 50011.
Ecol Evol. 2014 Dec;4(23):4476-87. doi: 10.1002/ece3.1257. Epub 2014 Nov 11.
Body mass components (dry mass, lean dry mass, water mass, fat mass) in each sex correlate strongly with body mass and pronotum length in Gryllus texensis and Acheta domesticus. Ordinary least squares (OLS) regression underestimates the scaling relationship between body mass and structural size (i.e., pronotum length) in both cricket species compared with standard major axis (SMA) regression. Standardized mass components correlate more strongly with scaled mass index ([Formula: see text]) than with residual body mass (R i). R i represents the residuals from an OLS regression of log body mass against log pronotum length. Neither condition index predicts energy stores (i.e., fat content) in G. texensis. R i is not correlated with energy stores in A. domesticus whereas [Formula: see text] is negatively correlated. A comparison of condition index methods using published data showed that neither sex nor diet quality affected body condition at adulthood in G. texensis when using the scaled mass index. However, the residual index suggested that sex had a significant effect on body condition. Further, analysis of covariance (ANCOVA) suggested that diet quality significantly affects body mass while statistically controlling for body size (i.e., body condition). We conclude that the statistical assumptions of condition index methods must be met prior to use and urge caution when using methods that are based on least squares in the y -plane (i.e., residual index ANCOVA).
在德州沙螽和家蟋蟀中，各性别间的身体质量组成部分（干质量、瘦干质量、水质量、脂肪质量）与体重及前胸背板长度密切相关。与标准主轴（SMA）回归相比，普通最小二乘法（OLS）回归低估了这两种蟋蟀体重与结构大小（即前胸背板长度）之间的比例关系。标准化质量组成部分与标度质量指数（[公式：见正文]）的相关性比与残差体重（Ri）的相关性更强。Ri表示对数体重对对数前胸背板长度进行OLS回归得到的残差。两种条件指数均无法预测德州沙螽的能量储备（即脂肪含量）。Ri与家蟋蟀的能量储备不相关，而[公式：见正文]呈负相关。使用已发表数据对条件指数方法进行比较表明，在使用标度质量指数时，性别和饮食质量均不会影响德州沙螽成年后的身体状况。然而，残差指数表明性别对身体状况有显著影响。此外，协方差分析（ANCOVA）表明，在对体型（即身体状况）进行统计控制时，饮食质量会显著影响体重。我们得出结论，在使用条件指数方法之前必须满足其统计假设，并敦促在使用基于y平面最小二乘法的方法（即残差指数ANCOVA）时要谨慎。
