Background/Question/Methods   Climate is an important factor defining organisms' distribution and abundances. As the climate is changing rapidly, organisms are expected to respond. Adaptation to climate change can happen via phenotypic plasticity and microevolution, however, most of the responses described so far have taken place via phenotypic plasticity. In fact, although evolution can occur very rapidly, there are only very few studies that show genetic adaptation to climate change. The question whether microevolution in response to climate change occurs is an important one, as phenotypic plasticity alone might not be able to accommodate the expected changes. We studied whether Stagnicola palustris snails subjected to a 30 year man-made natural selection experiment have genetically adapted to a warmer climate. Our study site receives warmed up cooling water from nuclear power plants, which increases water temperatures by 4 to 10°C. This increase corresponds to some projections of the IPCC for the high northern latitudes. Snail populations affected by cooling water discharge, and control populations from unaffected areas, were sampled and their offspring raised in the laboratory under neutral conditions to control for persistent environmental effects. We conducted a reciprocal transplant experiment in the field with F2 snails and measured their survival and growth performance.

Results/Conclusions   In the reciprocal transplant experiment, all populations - those affected by cooling water discharge and the control populations - grew better in warm conditions. In addition, snails from the control populations grew faster than the warm-origin snails. In the cold environment, no temperature-related differentiation among the populations was found. Our results indicate rapid microevolution in growth strategies of S. palustris and support the countergradient model of temperature adaptation, where individuals from cool conditions grow faster than individuals from warm conditions. Additionally, we are currently conducting a common garden experiment, raising F3 snails from control and warm-origin populations in four temperature treatments. This will allow us to compare population fitness at different temperatures, and give more insight into population differentiation and temperature adaptation.