We manipulated diet quality, food availability, and ambient temperature to investigate the role of these variables in fat deposition by growing prairie voles (Microtus ochrogaster) and fat use by adult voles. Exposure to either 5 degrees C or a high-fiber diet reduced fat deposition by growing voles and also reduced growth as measured by body length. Adult voles on the high-fiber diet reduced fat content, but exposure to 5 degrees C had no effect on body composition. Both the high-fiber diet and exposure to 5 degrees C caused increased food intake and reduced diet digestibility for adult voles. Restricting access to food resulted in reduced lipid mass of all adult voles and reduced fat-free mass of those held at 5 degrees C. When faced with poor food quality or cold ambient temperature, voles will increase food intake rather than catabolize lipid tissue. When food availability is limited, however, voles will use fat stores to meet the balance of their energy requirements.
Abstract-Energy budgets have provided physiological ecologists with a vital link between environmental variables and individual performance and should also prove useful to ecotoxicologists in understanding the effects of sublethal exposure in the field. Exposure to toxic compounds is likely to be metabolically expensive and may result in a trade-off between energy spent to detoxify and excrete contaminants and energy allocated to growth or reproduction. To quantify the energetic cost of polychlorinated biphenyl (PCB) exposure, we fed captive white-footed mice (Peromyscus leucopus) diets containing PCBs (2:1 Aroclor 1242:1254) at levels of 0, 0.1, 10, and 25 ppm (mg PCBs/kg food). After six weeks on the diets, there were no differences in food intake (g/d), diet digestibility (%), or body mass related to the level of dietary PCBs. This indicated that short-term exposure to PCBs did not cause a detectable increase in energy need as measured by voluntary food intake. We continued to feed mice the PCB-containing diets for one year, at which time we repeated the food intake trial, and also measured oxygen consumption at 20 and 30ЊC. After one year, all mice had gained mass, but mice on the 25-ppm diet tended to be heavier than mice in the other groups. Compared to the control group, mice on the 25-ppm diet had higher food intake (4.1 vs 3.7 g/d; p ϭ 0.06) and higher oxygen consumption at 30ЊC (40.1 vs 36.6 ml O 2 /h; p ϭ 0.01). These results suggest that there is an energetic cost to long-term contaminant exposure that, when combined with other environmental stresses, may influence patterns of energy acquisition and allocation.
Prairie voles (Microtus ochroguster) were trapped during different seasons in order to examine simultaneous variation in body composition and gut capacity. Voles in reproductive condition were trapped
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