Abstract
We experimentally tested the hypothesis that individuals from a single species but genetically different exposed to the same chemical stress factor are able to realize opposite life history strategies-they can invest more resources in current reproduction and release neonates well-prepared to harmful condition or they can invest in their own safety as well as future reproductions and release neonates of poor quality condition. In order to do this, we used the Daphnia-salinity model: we exposed Daphnia magna females originating from various ponds to two concentrations of sodium chloride, and then observed the key life histories parameters of their offspring exposed or not exposed to salinity stress. Our results confirmed the hypothesis. In a clone from one pond, Daphnia exposed to salinity stress produced neonates which were worse-prepared to the local conditions than those released by non-stressed females. In clones from the two other ponds, Daphnia released newborns similarly or better-prepared to cope with the salinity stress, depending on the concentration of salt and the duration of their exposure to salinity. Our results suggest that both longer (two-generational) and stronger (higher salt concentration) impacts of selective factors may be perceived by individuals as information indicating reduced chances of successful reproduction in the future and, thus, they may drive mothers to produce better-prepared descendants.