Predicting if and how quickly organisms can adapt to anthropogenic change is one of the greatest challenges of our times. Unfortunately, prediction is notoriously challenging in practice because the rate and direction of adaptive evolutionary change depends on the phenotypic variation that is available to selection. This, in turn, depends on the relationship between genetic and phenotypic variation (GP map), something that is very difficult and laborious to quantify. As a result, biologists have generally been rather pessimistic about the possibility to predict evolution over more than a few generations, even when selective pressures are known. Recent theory suggests a way out of this dilemma. The basic idea is that the responses to genetic (e.g., mutation) and environmental perturbation are linked through development. Here we set out to answer the question: Why are organisms so good at adapting, and can they get even better? Utilizing environmental perturbations as selective pressures, we are studying the relationship between plasticity and evolvability in green algae. Stay tuned for the first results.

Salinization of freshwater ecosystems is a growing hazard for organisms and ecosystem functioning worldwide. In northern latitudes, road salt that is being transported into water bodies can cause year-round increases in lake salinity levels. Exploring the environmental factors driving the susceptibility of freshwater zooplankton to road salt is crucial for assessing the impact of salinization on food web processes. We found that the susceptibility of freshwater zooplankton to salinization strongly depends on the dietary lipid supply and thus the phytoplankton community composition. Hence, trophic state related differences in the phytoplankton community composition need to be considered when assessing the consequences of salinization for freshwater ecosystem functioning. However, in nature it is seldom only a single stressor but rather a variety of stressors affecting eco- system functioning and organismal interactions. We could show that road salt and the tire rubber antiozonant, 6PPD, have synergistic negative effects on the population growth on rotifers, common freshwater herbivores.

We were involved in a global study, assessing how salt tolerance of Daphnia is related to the prevailing environmental conditions of site of origin. During the summer of 2023, we also participated in an Aquacosm experiment, investigating different modes of salinization on plankton communities. Stay tuned for the first results on both projects.

A key component of the theory of ecological stoichiometry is the Growth Rate Hypothesis (GRH). The GRH states that variation in organismal stoichiometry (in particular, C:P and N:P ratios) is driven by growth-dependent allocation to P-rich ribosomal RNA that leads to differential increases in biomass P content. The GRH was originally formulated to help explain observed differences in C:N:P ratios of different species of zooplankton and has since been applied across a wide range of organisms. The GRH has found broad but not uniform support in studies across diverse biota and habitats. In this project we investigated if there are fundamental rules that link the biochemical properties of cells to dynamical processes in eco- systems. We evaluated the GRH with intensive physiological, evolutionary, and ecological work on three model organisms that represent key ecological functional groups: Pseudomonas putida (chemoheterotrophic decomposer), the green alga Chlamydomonas reinhardtii (photoautotroph), and the crustacean Daphnia pulex (primary consumer / herbivore).

In a first publication we show that in Chlamydomonas reinhardtii, the different components of the GRH differed in their robustness. The most reliable component is that %P of organismal biomass increases with faster growth. Furthermore, we could show that the GRH is most robust under high N:P environmental conditions and performs worst under low light conditions, helping to clarify the domain of conditions under which the GRH holds or fails to hold. More publications on the empirical work have been submitted- stay tuned.

Lake ecosystems around the globe are suffering from nutrient pollution and the associated proliferation of harmful cyanobacteria. In past decades, eutrophication has been reversed in many lake ecosystems through extensive restoration measures. Making use of resurrection ecology, we showed how trophic state-related changes in the relative abundance of cyanobacteria resulted in the evolution and the subsequent loss of grazer resistance to cyanobacteria. We demonstrated that this evolution of grazer resistance involved changes in dietary sterol requirements, challenging the common assumption that changes in the ability to cope with cyanobacteria are exclusively mediated through an adaptation to cyanobacterial toxins.