Effects of predictability in food conditions on individual growth in Daphnia magna

Abstract

Daphnia magna is known for living in environments were temperature and food conditions may vary a lot. Food can be a determining factor for growth and reproduction. In the presence of rapid environmental changes, ecosystems become more unpredictable, which concerns the availability of food. How increased unpredictability in food conditions affects species is not fully understood. In this study Daphnia magna is used to look at possible life history responses to unpredictable environments with focus on food availability. Two clones of Daphnia magna, with 30 individuals from each, were exposed to three different food treatments: constant food level, predictable variation, and unpredictable variation in food level. There were 10 individuals in each treatment. The constant treatment involved the same intermediate food ration given each day, while the two variation treatments involved daily variations between high and low food rations, where one treatment had predictable variations and the other unpredictable variations. Due to a general lack of reproduction and the majority of the Daphnia in one of the clones being males, this study is focused on how unpredictability in food affects individual growth in female and male Daphnia magna. ANOVA-analyses and post-hoc tests were used to indicate significance between the treatments. Individuals given the constant treatment grew significantly bigger than individuals exposed to the two variation-treatments. There was no significant size difference between Daphnia in the predictable variation and unpredictable variation treatments. Increased unpredictability in food variation did not seem to affect growth.