Nickel response in function of temperature differences: Effects at different levels of biological organization in Daphnia magna

In this study, gene transcription profiling in combination with the assessment of systemic parameters at individual and population levels were applied to study the (toxic) effects induced through temperature stress in the presence or the absence of an additional chemical stressor (nickel) in Daphnia magna. It was illustrated that lower temperatures were mainly characterized by a reduction of growth and lipid content, while higher temperatures caused an increase of both endpoints. Many of the differentially regulated transcripts could be correlated with processes affected at higher hierarchical levels of biological organization. Gene clusters with probable roles in producing offspring (peak expression at 22 °C), enhancing the metabolic rate (temperature related expression) and translational processes (increased expression at 14 °C) were identified. However, it was not possible to pinpoint a specific subset of genes, exclusively responding to temperature or nickel and allowing a retrospective identification of the particular stressor. Overall, extreme temperatures caused a higher level of stress in the organisms in comparison to nickel exposure. Moreover, organisms subjected to the natural stressor appeared to be less capable of dealing with the additional chemical stressor and as a result activate or repress more gene pathways.