NATURAL XENOBIOTICS CHANGE MAJOR LIFE HISTORY TRAITS IN A CLONE OF Daphnia galeata

摘要

It recently emerged that dissolved organic carbon (DOC) with humic substances (HSs) as its major fraction, in concert with increasing temperatures, may reduce zoo-plankton diversity in freshwater lakes. The mechanisms of this reduction include indirect ones, such as release of reactive oxygen species and their interactions with organisms, as well as direct ones, such as internal xenobiotic action. The latter may lead to changes in the energy allocation and thereby impact population maintenance. In this contribution, we tested a laboratory clone of Daphnia galeata with respect to energy allocation under the challenge by dissolved HSs. The exposure to HSs increased lifespans, but reduced offspring numbers in an almost linear concentration dependency. The most likely mechanism for lifespan extension is mitohormesis, which implies that a certain increase of internal reactive oxygen production leads to improved health and longevity. Direct or indirect nutrition by the exposed HSs is very unlikely to apply. In the protected environment of the applied experimental set-up, the observed energy re-allocation may pose the population at risk, and this clone of D. galeata appears to be a candidate who could suffer from the seasonal variability of DOC in lakes.