Combined cadmium and temperature acclimation in Daphnia magna: Physiological and sub-cellular effects

Effects of temperature and Cd acclimation (≥6 generations) on life history and tolerance responses to stress in three clones of Daphnia magna was examined using a 2×2 design (20 and 24 °C, 0 and 5 μg L−1 Cd). Endpoints include acute Cd and heat tolerance, individual traits such as ingestion rates, growth and reproduction responses and physiological attributes such as acute Cd and heat tolerance, energy reserves, electron transport system activity, haemoglobin and oxidative stress enzymes. Cd (20 °C+Cd) did reduce reproduction, but acclimation to 24 °C+Cd did not decrease reproductive output additionally. For energy reserves, on which Cd and temperature acted similarly, no synergistic effect could be demonstrated. Generally, the effect of 24 °C+Cd was comparable to that of the 24 °C acclimation. Cd acclimation at 20 °C resulted in organisms, which were more tolerant to acute Cd and heat shock challenge, while the contrary was observed at 24 °C. A relationship between tolerance to Cd and heat shock and superoxide dismutase (SOD) activity was observed. Significant interclonal variation and genotype×environmental interactions in the measured traits evidenced that clones responded differently. As natural populations are invariably exposed to multiple stressors and genetic variability may change accordingly, it is essential to improve our knowledge on the effects of such scenarios in order to allow a correct incorporation in ecological risk assessment methodologies.