The influence of fluctuating temperature on the effect of copper toxicity in Caenorhabditis elegans

Climatic variables like humidity and temperature have been shown to affect the toxic effect of some chemicals. Temperature especially has a direct effect on the toxicity of metals and pesticides, generally causing toxicity to rise with increasing temperature, in particular when approaching the temperature tolerance limit of the test organism. Studies on the effect of temperature differences on toxicity have so far been done at static temperature regimes, which ignore any additional stress which may be caused by fluctuating temperature. Since daily temperature changes in the terrestrial environment can fluctuate with more than 10 degrees, it is questionable whether information from static conditions can be extrapolated to describing the effect of temperature on toxicity in the field. We hypothesize that fluctuating temperatures will prove to be a stress factor in itself, which may increase the effect of a toxicant, as compared to the equivalent static scenario at the average temperature. In the present study we expose the nematode Caenorhabditis elegans to a range of copper concentrations at three static temperatures (12, 16 and 20°C), as well as in a non-static temperature scenario with a daily temperature fluctuation from 12 to 20°C and an average daily temperature of 16°C. The temperature exposures were chosen to be within the approximate optimal temperature range of C. elegans. The study use full life cycle exposures, with daily measurements of reproduction and survival during the entire lifespan. To our knowledge this is the first study to compare the effect of static and fluctuating temperature on toxicity of copper.