Resilience to changes in lake trophic state: Nutrient allocation into Daphnia resting eggs

Abstract

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, a large prealpine lake with a distinct eutrophication and reoligotrophication history, and analyzed for elemental (carbon, nitrogen, and phosphorus) and biochemical (sterols and fatty acids) nutrients. Carbon allocation into Daphnia resting eggs continuously decreased over time, irrespective of changes in trophic state. The allocation of nitrogen into Daphnia resting eggs followed the changes in trophic state, that is, nitrogen concentrations in resting eggs increased with eutrophication and decreased again with reoligotrophication. 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.

A sterol-mediated gleaner–opportunist trade-off underlies the evolution of grazer resistance to cyanobacteria

“…The exact mode of invasion, as well as the origin of the species, remain unknown; possible explanations can be found in the literature [21,23,36]. Daphnia galeata was the dominant species in routine zooplankton samples during the eutrophic period [23,53], and also in the resting egg bank [21]. To minimize any effects of hybridization with the native D. longispina on our study results we used only those genotypes for our experiments that could be clearly assigned to the species D. galeata .…”

Reversed evolution of grazer resistance to cyanobacteria

“…Total phosphorus concentrations during winter mixing (TP mix ) increased more than tenfold from about 7 μg P L −1 in the 1950s to more than 80 μg P L −1 in the early 1980s 41 . These changes in trophic state also led to shifts in the phytoplankton community composition, with a marked increase in the relative abundance of cyanobacteria (up to 25% of total phytoplankton biomass in summer) 14 , 42 . Since then, due to a substantial reduction in external phosphorus inputs, total phosphorus concentrations decreased again to levels that are currently similar to those measured in the 1950s 14 , 43 .…”

Interactions between two functionally distinct aquatic invertebrate herbivores complicate ecosystem- and population-level resilience

“…However, D. magna densities were much higher in perturbed treatments so this likely contributed to switching reproductive tactics, though Booksmythe et al (2018) did not find increased density leading clearly to increased ephippia production. It is possible D. magna switch to ephippia production in new trophic states ( i.e., change in available nutrients) because the ephippia are resilient to changes in trophic state ( Isanta Navarro et al, 2019 ). If true, ephippia may signal a transition to a different state of the system.…”