Toxicological and thermoregulatory effects of feather contamination with artificially weathered MC 252 oil in western sandpipers (Calidris mauri).

The external contamination of bird feathers with crude oil might have effects on feather structure and thus on thermoregulation. We tested the thermoregulatory ability of western sandpipers (Calidris mauri) in a respirometry chamber with oil applied either immediately prior, or three days before the experiment. The birds were then exposed to a sliding cold temperature challenge between 27°C and -3°C to calculate thermal conductance. After the experiment, a large blood sample was taken and the liver extracted to measure a range of parameters linked to toxicology and oxidative stress. No differences in thermal conductance were observed among groups, but birds exposed to oil for three days had reduced body temperatures and lost more body mass during that period. At necropsy, oiled birds showed a decrease in plasma albumin and sodium, and an increase in urea. This is reflective of dysfunction in the kidney at the loop of Henle. Birds, especially when exposed to the oil for three days, showed signs of oxidative stress and oxidative damage. These results show that the ingestion of externally applied oil through preening or drinking can cause toxic effects even in low doses, while we did not detect a direct effect of the external oil on thermoregulation over the temperature range tested.

Mitochondrial metabolism during daily torpor in the dwarf Siberian hamster: role of active regulated changes and passive thermal effects.

During daily torpor in the dwarf Siberian hamster, Phodopus sungorus, metabolic rate is reduced by 65% compared with the basal rate, but the mechanisms involved are contentious. We examined liver mitochondrial respiration to determine the possible role of active regulated changes and passive thermal effects in the reduction of metabolic rate. When assayed at 37 degrees C, state 3 (phosphorylating) respiration, but not state 4 (nonphosphorylating) respiration, was significantly lower during torpor compared with normothermia, suggesting that active regulated changes occur during daily torpor. Using top-down elasticity analysis, we determined that these active changes in torpor included a reduced substrate oxidation capacity and an increased proton conductance of the inner mitochondrial membrane. At 15 degrees C, mitochondrial respiration was at least 75% lower than at 37 degrees C, but there was no difference between normothermia and torpor. This implies that the active regulated changes are likely more important for reducing respiration at high temperatures (i.e., during entrance) and/or have effects other than reducing respiration at low temperatures. The decrease in respiration from 37 degrees C to 15 degrees C resulted predominantly from a considerable reduction of substrate oxidation capacity in both torpid and normothermic animals. Temperature-dependent changes in proton leak and phosphorylation kinetics depended on metabolic state; proton leakiness increased in torpid animals but decreased in normothermic animals, whereas phosphorylation activity decreased in torpid animals but increased in normothermic animals. Overall, we have shown that both active and passive changes to oxidative phosphorylation occur during daily torpor in this species, contributing to reduced metabolic rate.