| Popis: |
Calculating body water through isotope dilution has become a useful way to nondestructively estimate body composition in many species. The most accurate estimates using this method require calibration against proximate chemical analysis of body composition for individual species, but no studies to our knowledge have calibrated this method on a hibernating mammal that seasonally undergoes dramatic changes in body composition. We use deuterium oxide to estimate total body water in captive arctic ground squirrels, Urocitellus parryii, and compare two approaches of calculating lean mass from total body water, both calibrated against lean mass based on proximate analysis. The first method uses a single tissue hydration constant to calculate lean mass from total body water; the second method uses a predictive equation to calculate lean mass from total body water and body mass. We found that the predictive equation performs better over the large range of body composition common to this species. Distillation of blood samples did not affect lean mass estimates from either calculation method. These findings indicate that isotope dilution using a predictive equation should work well as an alternative to destructive methods in other small mammals that undergo radical changes in body composition across their annual cycle. Copyright © 2011 John Wiley & Sons, Ltd. Body composition of birds and mammals is a key metric in many physiological and ecological studies. The most accurate method for measuring body composition, proximate analysis, directly determines the mass of body water, fat, and lean dry mass by chemical extraction; [1] however, this method is destructive and precludes repeated sampling. Many methods have been developed to estimate body composition nonlethally and even noninvasively, including dual energy X-ray absorptiometry (DXA), which directly estimates fat and lean mass content. [2] In contrast to DXA, several of these methods depend on the difference in water content (hereafter, 'hydration') between lipid and lean tissue, including bioelectrical impedance analysis (BIA), total body electrical conductivity (TOBEC), and isotope dilution. Of these, stable isotope dilution is particularly attractive because, unlike other methods, it is insensitive to the position of the animal during measurements and does not require technical equipment in the field. Here we present a brief description of the method and some outstanding issues underlying its current application across different taxa. Estimation of body composition through isotope dilution involves injecting a known quantity of water labeled with eitherdeuterium ( 2 H)or 18 O into thebodywater pool and mea |
Plný text