THE EFFECT OF TEMPERATURE ON THE SURVIVAL AND REPRODUCTION OF Daphnia magna FOLLOWING EXPOSURE TO ULTRAVIOLET-B RADIATION

In recent years there has been increasing concern regarding the damaging effects of ultraviolet radiation (UVR) on aquatic organisms. Daphnia, a well-studied genus of freshwater zooplankton, employs two mechanisms of deoxyribonucleic acid (DNA) repair that are temperature-dependent: photoenzymatic repair (PER, light-dependent repair), and nucleotide excision repair (NER, light-independent repair). In the presence of photorecovery radiation (PRR), Daphnia have the ability to undergo PER. This research focused on the effect of acute UV-B exposure, temperature and variable PRR on the survival and reproduction of Daphnia magna. Three day-old D. magna were exposed to a single six-hour dose of UV-B radiation followed by varying periods of PRR. Animals were maintained within several degrees of 32oC throughout the experiment, and survival and reproduction of the parental and first filial (F1) generations were followed until the animals were twelve days old. It has been previously demonstrated at 26 ̊C that mortality of the parental generation following UV-B exposure is partially mitigated by PRR and absence of PRR results in 100 % mortality. Between 30 ̊C and 32oC, it appears that in the absence of PRR, some survival occurred possibly as a result of temperaturerelated increased enzymatic repair. The UV treatment history of the parental generation had no effect on F1 survival; however, survival and reproduction of the F1 generation were compromised at 32 oC.