An emerging issue in environmental toxicology is in understanding how climate change will alter responses of organisms to chemical contaminants. The objective of the present study was to characterize the interactive effects of cadmium and elevated temperature on life-stage-specific responses in the freshwater snail Physa pomilia. We exposed developing eggs, juveniles, and adults to Cd (5 µg/L, 15 µg/L, and 25 µg/L for eggs, and 250 µg/L for juveniles and adults) and 2 temperatures of 25 °C (control) and 35 °C (upper range of tolerance). In the absence of Cd, time to hatch was shorter at 35 °C compared with 25 °C, demonstrating a stimulatory effect of the higher temperature. However, when egg masses were reared at 35 °C and exposed to Cd, hatching success was significantly lower, and time-to-hatching was significantly longer. The effects of the higher temperature and Cd on newly hatched neonate survival were additive, except at the highest Cd concentration, at which effects of the 2 stressors were greater than additive. Overall, within the combined stressor treatments, adult snails generally survived significantly longer than did juvenile snails, and both were more tolerant than developing snails. Many climate projection models predict future increases in global temperatures. The present study shows that combined stressors may produce greater-than-additive effects, challenging predictive power. More studies are needed to better characterize the interactive effects of chemical contaminants and stressors related to climate change.

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The Intergovernmental Panel on Climate Change projects that global climate change will have significant impacts on environmental conditions including potential effects on sensitivity of organisms to environmental contaminants. The objective of this study was to test the climate-induced toxicant sensitivity (CITS) hypothesis in which acclimation to altered climate parameters increases toxicant sensitivity. Adult Physa pomilia snails were acclimated to a near optimal 22 °C or a high-normal 28 °C for 28 days. After 28 days, snails from each temperature group were challenged with either low (150 μg/L) or high (300 μg/L) cadmium at each temperature (28 or 22 °C). In contrast to the CITS hypothesis, we found that acclimation temperature did not have a strong influence on cadmium sensitivity except at the high cadmium test concentration where snails acclimated to 28 °C were more cadmium tolerant. However, snails that experienced a switch in temperature for the cadmium challenge, regardless of the switch direction, were the most sensitive to cadmium. Within the snails that were switched between temperatures, snails acclimated at 28 °C and then exposed to high cadmium at 22 °C exhibited significantly greater mortality than those snails acclimated to 22 °C and then exposed to cadmium at 28 °C. Our results point to the importance of temperature variability in increasing toxicant sensitivity but also suggest a potentially complex cost of temperature acclimation. Broadly, the type of temporal stressor exposures we simulated may reduce overall plasticity in responses to stress ultimately rendering populations more vulnerable to adverse effects.

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