Limnetica 35

Information on the physiological tolerance of species is essential when forecasting their responses to climatic change, especially for those with restricted distributions, as well as those inhabiting extreme environments, such as inland saline waters. Temperature and salinity are expected to increase in these ecosystems under climate change, and both factors are known to affect the thermal tolerances of aquatic insects. The objective of this study was to determine, in the laboratory, the thermal limits and their plasticity to changes under the environmental conditions of the aquatic beetle Enochrus politus, a typical species of saline streams from the southeast of Spain. Supercooling temperature (point before the freezing temperature) and Heat coma (point of paralysis prior to death) were used as the lower and upper thermal limits, respectively. They were determined by a dynamic method combined with infrared thermography in groups of individuals previously acclimated at different conditions of temperature and salinity. E. politus showed a wide range of thermal tolerance (–10.38 ± 0.32 °C-57.37 ± 0.19 °C) and was higher in specimens acclimated at 20 °C and 12 g/L, coinciding with the mean environmental conditions of the habitats where the species often lives. At lower temperatures and salinities, its thermal tolerance range decreased. The temperature and salinity of acclimation both had significant effects on the thermal limits. Elevated salinity decreased the heat tolerance and increased the freezing tolerance. The lower thermal limit of the species showed more plasticity than the upper limit. The species would potentially be able to tolerate temperature increase according to its wide thermal range, when compared to other insects; however, the salinization of its habitat might reduce its heat tolerance.