COMBINED EFFECTS OF TEMPERATURE AND HEAVY METALS ON THE PERFORMANCE OF THE GIANT SALMONFLY.

In many freshwater ecosystems, communities of aquatic insects are facing the combined stresses of warmer waters due to climate change and increased exposure to heavy metal toxicants. Although each stressor may threaten aquatic insects independently, they also likely interact in important ways to affect insect physiology and performance. Here we investigate this potential interaction using two populations of aquatic nymphs of the giant salmonfly, Pteronarcys californica, collected from adjacent rivers in Montana: naïve individuals from Rock Creek, a relatively pristine stream, and individuals from the Upper Clark Fork River, which has a history of heavy metal pollution and higher temperatures. We used a factorial design that exposed nymphs from the two rivers to one of two varying concentrations of metals (copper or lead) in combination with one of two temperatures (12 or 18 °C). We measured survival, growth, and upper critical temperature (CTMAX), as well as individual heavy metal concentration. Nymphs from both rivers exposed to the highest amounts of copper showed reduced survival and growth rates, and their CTMAX were reduced by up to 10 °C. By contrast, lead had little effect on survival, growth, or CTMAX of either population. These results suggest that acute exposure to heavy metals may reduce the ability of aquatic insects to withstand exposure to climate-induced warming