Thermal tolerance of a freshwater amphipod Gammarus lacustris can be enhanced by acclimation to higher mineralization

Temperature and mineralization are among the most important environmental factors affecting all processes of aquatic ecosystems, including geographical distribution of water animals. Previously we showed that a brackish water population of Gammarus lacustris, a widespread amphipod, demonstrates substantially higher thermotolerance than a freshwater population. A possible reason for this difference is the fact that brackish water conditions are closer to internal media mineralization. Here we aimed to test this hypothesis and relate the observed effects in animal survival under the heat shock to the status of cellular defence systems. We acclimated four groups of amphipods from the same freshwater population to 0.5 %o and 15 %o at the temperatures of 6 degrees C or 15 degrees C. Acclimation at 6 degrees C, but not at 15 degrees C, to 15 %o significantly increased resistance of the amphipods to heat shock at 30 degrees C. At 6 degrees C activities of antioxidant enzymes and levels of the lipid peroxidation products in G. lacustris did not react to the increase in mineralization and the heat shock, while the level of HSP70 elevated two-fold in amphipods acclimated to mineralization of 15 %o compared to animals acclimated to 0.5 %o. Thus, the observed increase in thermotolerance could be explained by the higher initial level of HSP70 and potentially other heat shock proteins caused by a less energy-demanding, more isotonic level.