Nutrient allocation into Daphnia resting eggs seems to be a hardly affected by temporal changes

Jana Isanta Navarro, doctoral researcher in the team of Dominik Martin-Creuzburg, found in collaboration with other researchers that the nutrient allocation into Daphnia resting eggs was mostly resilient to changes in lake trophic state.

During past decades, many lakes underwent drastic human‐caused changes in trophic state with strong implications for population dynamics and food web processes. We investigated the influence of trophic state on nutrient allocation into Daphnia resting eggs. The production of resting eggs is an important survival strategy, allowing Daphnia to cope with unfavorable environmental conditions. Allocation of essential nutrients into resting eggs may crucially influence embryonic development and offspring survival and thus is of great ecological and evolutionary interest. The capacity of Daphnia to adjust the allocation of nutrients into resting eggs may depend on the dietary nutrient supply, which may vary with trophic state‐related changes in the phytoplankton community composition. Resting eggs were isolated from sediment cores taken from Lake Constance, and analyzed for elemental (carbon, nitrogen, and phosphorus) and biochemical (sterols and fatty acids) nutrients. Nutrient allocation into Daphnia resting eggs seems to be a hardly affected by temporal changes in trophic state and the associated changes in food quantity (i.e., phytoplankton biovolume) and quality (i.e., relative proportions of phytoplankton taxonomic groups). This suggests some sort of homeostatic nutrient regulation within the eggs to ensure offspring survival and that the essential nutrient supply was always sufficient to maintain this homeostasis. In the few cases where we found significant changes in nutrient concentrations over time (C and N), changes could not be linked to eutrophication. The allocation of phosphorus, sterols and long‐chain polyunsaturated fatty acids, such as eicosapentaenoic acid, into Daphnia resting eggs did not change significantly over time. Changes in trophic state strikingly influenced all trophic levels in Lake Constance. However, nutrient allocation into Daphnia resting eggs was mostly resilient to changes in lake trophic state.