Energy budget in Daphnia magna exposed to natural stressors

Background, aim, and scope: Climate changes are nowadays an important issue of concern, and it is expected that in the near future it will be intensified, leading to extreme environmental conditions. These changes are expected to originate additional sources of stress; therefore, the exposure of organisms to natural stressors is receiving an increased importance in risk assessment. Organisms tend to avoid extremely environmental conditions looking for optimum conditions. This work aimed to evaluate the effects of natural stressors on the energetic reserves of Daphnia magna using the quantification of lipids, proteins, and sugars. Materials and methods: Daphnids were exposed to different temperature regimes (16, 18, 22, 24, and 26°C), food levels (2, 1.5, 1, 0.5, and 0 and 4, 4.5, 5, 5.5, and 6 × 10 cells/ml Pseudokirchneriella subcapitata) and oxygen depletion (2 to 6 mg DO/L) and their energy reserves quantified. Protein, lipid, and sugar contents where compared between daphnids exposed to control conditions and ones exposed to considered stress situations. Results and discussion: Significant changes in energy reserves content after a 96-h exposure were observed in temperatures 16, 22, 24, and 26°C. In the exposure to different food levels, daphnids showed significant differences on their energetic reserves when exposed to higher or lower levels of algae when compared with the control. Oxygen depletion did not affect significantly their energy budget. Conclusions: The results from this work demonstrate that the environmental alterations related mainly to temperatures variations and food availability produced changes in D. magna energetic reserves. These changes can be transposed to the population levels as they are a result of changes in the metabolic rate and physiological processes that are related to growth and maturation. © 2010 Springer-Verlag.