Response of Daphnia magna from Natural Populations to Ultraviolet Radiation

Sammanfattning: Diel vertical migration (DVM) is performed by various zooplankton taxa. The general movement pattern of DVM has been well studied while the possible clonal differences of this movement largely remain unknown. My master thesis focus on investigating the effects of environmental stressors on Daphnia magna strains isolated from natural populations. Here I maintained 11 strains of Daphnia magna originating from natural populations from lakes and ponds in southern Sweden. Their response under three consecutive treatments of UV radiation (UV turned off; UV turned on; UV turned off) was observed and the swimming speed and depth were analyzed. Results showed that D. magna from natural populations may respond to UV radiation with increasing swimming speed and depth. After UV exposure the swimming behavior remained similar to the phase when UV radiation exists. Difference in swimming behavior among strains under neutral environmental conditions was found. Furthermore, this difference disappeared under UV threat and all strains then performed a similar pattern of movement.