UV-induced DNA damage in Daphnia magna from ecologically disparate populations

Every day we are exposed to carcinogens, including ultraviolet radiation (UVR). High levels of ultraviolet radiation are known to cause DNA damage. One of the most common forms of UVR-induced damage, the pyrimidine dimer, is repaired by an enzymatic reaction powered by visible light. We wanted to find out if there is variation in the level of UVR-induced DNA damage induced in two different clones of Daphnia magna, a model organism for ecotoxicology. One clone was derived from a mid-latitude deep reservoir, where escape from UVR is possible via vertical migration. The second clone was from a high-latitude shallow rock pool, where D. magna are exposed to high levels of UVR. Pregnant mothers from each clone line were subjected to ecologically relevant levels of UVR in the lab. Immediately afterwards, we extracted the embryos, suspended the cells in agarose, and performed a comet assay, which allows for quantification of DNA damage within individual cells. The slides were viewed under a fluorescent microscope and pictures were obtained for each cell. We then used the image analysis software CometScore to measure the amount of DNA damage. Our results indicated that the reservoir-derived clone had increased damage following UVR light, compared to controls that received no UVR. However, the pool-derived clone showed decreased DNA damage following UVR exposure. This may be due to a combination of DNA protection and efficient, light-powered DNA repair in UVR-adapted populations