Is thermal tolerance in non-biting midges driven by phenotypic plasticity or adaptation?

Effects of seasonal or daily temperature variation on fitness and physiology of ectothermic organisms have been widely studied, but the effect of long term climatic modification is still not well understood and complex to predict. With the current climatic change, it becomes more important to investigate the adaptive potential and underlying mechanisms of organisms in response to temperature changes. The aim of this study is to investigate whether the multi-voltine (multiple generations per year) midge Chironomus riparius Meigen (1803) responds mainly via acclimatization or by long term modification using adaptation mechanism. A mix of larvae from five European populations was raised at three different pre-exposure temperatures (PET): 14, 20, 26°C. After three and five generations in laboratory cultures larvae were exposed to three treatment temperatures (TT) 14, 20, 26°C. Mortality was monitored for the first 48h and after emergence. After three generations a significant mortality rate differences dependent on an interaction between PET and TT could be observed. This finding supports the hypothesis that Chironomid midges respond to climatic variation via adaptive mechanisms. Moreover, these results accordingly show that three generations were sufficient to already adapt to warm temperature, increasing the resilience and decreasing the mortality rate.