Estimating body composition of lizards from total body electrical conductivity and total body water

Nondestructive methods of estimating body composition are crucial for measu ring energy budgets of free-ranging animals. However, most methods have pro ved to be either difficult or inaccurate for estimating lipid mass, particu larly in small animals. I validated the use of total body electrical conduc tivity (TOBEC) and total body water (TBW) to estimate lean mass and nonpola r lipid mass in the lizard Sceloporus undulatus. Regression models based on either TOBEC or TBW were able to predict dry lean mass and wet lean mass w ithin 5% of actual values. Estimates of nonpolar lipid mass, derived by sub tracting predicted wet lean mass from total body mass, were highly correlat ed with actual nonpolar lipid mass. When total nonpolar lipid mass was grea ter than 0.1 g; the average percent error in predicted nonpolar lipid was 3 0% and 15% for the TOBEC and TBW methods, respectively. A sensitivity analy sis suggests that, in most cases, TBW can be used to estimate nonpolar lipi d mass within 15% of actual lipid mass. Both TOBEC and TBW:measurements are relatively easy methods of tracking qualitative changes in body compositio n within individuals, but TBW should be used when quantitative estimates of nonpolar lipid mass are desired.