Energy acquisition and allocation in an ectothermic predator exposed to a common environmental stressor

Stressors are commonly encountered by organisms and often prove to be energetically costly. Certain stressors can simultaneously affect multiple components of an animal's energy budget and can either exacerbate energetic costs to the individual or offset one another. Here we used a commonly encountered stressor, the pesticide carbaryl, to examine the complex effects that acute environmental disturbances can have on energy expenditure, allocation, and acquisition, important processes that influence growth and reproduction. After exposing lizards (Sceloporus occidentalis) to carbaryl, we measured their metabolism over a 48 h period and assessed their food consumption over 96 h. We found no difference in total energy expenditure among treatment groups, but lizards exposed to the highest dose of carbaryl allocated energy differently than other groups. Compared to controls, these lizards exhibited a 16–30% increase in standard metabolic rate (SMR), which was offset by a 45–58% decrease in additional energy expenditures. Lizards in the highest dose group also exhibited a 30–34% decrease in energy acquisition compared to controls. The net result was a 1.83 kJ decrease in energy assimilation, equivalent to 5 times their daily SMR requirements. Our results indicate that energetic consequences of stressors may result in complex energetic trade-offs, and emphasize the need to simultaneously examine the effect of stressors on multiple portions of an animal's energy budget.