Density influences selection; selection influences genetic make-up; and in turn, genetic make-up influences density.
The traditional view is that evolution is so slow that it has no direct influence on ecological changes, such as the increase and decrease of plankton biomass in a lake within a year. However, there are more and more examples showing that evolutionary processes are rapid and therefore on the same time scale as ecological processes. Thus, ecological and evolutionary processes can influence each other continuously (so-called eco-evolutionary dynamics). Since the diversification and maintenance of diversity within populations and species communities is determined by ecological and evolutionary mechanisms, research approaches are needed that take into account the mutual interactions of ecological and evolutionary processes. We study the often complex interactions of evolutionary and ecological processes in aquatic systems and their impact on phenotypic and genetic diversity within populations and species communities in order to gain a mechanistic and basic understanding of important evolutionary changes such as the evolution of symbiotic interactions and sexual reproduction, as well as for the stability and long-term persistence of populations and communities and the conservation of biodiversity. The study of these mechanisms is the core interest in ecology and evolutionary biology and is indispensable for making predictions and developing strategies to cope with the consequences of global change.
Eco-Evolutionary Dynamics
In order to be able to predict the reactions and consequences of changes in environmental conditions such as biodiversity loss, climate change or antibiotic residues in water bodies, a better understanding of the interaction between trait and population dynamics is necessary. The interaction between population and trait dynamics can enable ecosystems and species communities to buffer external disturbances. However, the underlying mechanisms are not well understood. For example, it is unclear whether and how the variation of traits within populations determines the potential and degree of buffering. Furthermore, the role of trait variation in buffering different types of disturbances, such as an increase in mortality, a change in the health status of individuals or a change in the strength of species interactions, is unknown. We combine experiments with plankton organisms with mathematical modelling to gain a general understanding of the relationship between the potential of systems to cushion disturbances and trait variability
Why sex?
Why sexual reproduction occurs so much more frequently than asexual reproduction is an unsolved question in biology. Although numerous mechanisms have been proposed to explain the evolution of sexual reproduction, there are still no conclusive explanations under which conditions sexual reproduction is adventageous. Sexual reproduction has several disadvantages compared to asexual reproduction, which often limits the predicted conditions under which the advantages of sexual reproduction outweigh the disadvantages. Despite extensive studies, there is little empirical data to test existing theories. We test and further develop existing hypotheses on the evolution of sexual reproduction using facultatively reproducing organisms such as the rotifer Brachionus calyciflorus and the green alga Chlamydomonas reinhardtii.
Aquatic Viruses
Aquatic viruses infecting bacteria, algal species or protists are considered to be key players in structuring microbial communities and biogeochemical cycles due to their abundance and diversity within aquatic systems. Their high reproduction rates and short generation times can make them extremely successful, often with immediate and strong effects for their hosts and thus on their biological and abiotic environments. There is, however, very little known about the relative role of aquatic viruses in lake systems. To better understand the ecology and evolution of viruses in aquatic systems, we study viruses that infect algal cells, protists or bacteria by combining laboratory experiments with high-throughput methods. In this way, we aim to identify traits that control the interaction between viruses and hosts (e.g., host cell resistance) and to show how these traits evolve over time, for example, during the course of an experiment or a season in a lake.
Symbiosis
The evolution of symbiosis constitutes a major transition in the organization of life. A major challenge in this transition is that two autonomous species must lose their individuality, reproduce as a unit and form a new unit of selection. We still know little about the evolutionary processes that lead to symbiotic relationships and the ecological conditions that favour them. It is possible that at the beginning of the symbiotic interaction both partners experience an immediate benefit (cooperation). However, it is more likely that at least initially one partner will exploit the other. We use experimental evolution with ciliates and algae to uncover evolutionary pathways that lead to a facultative or obligatory symbiosis under different ecological conditions. Our goal is to investigate how likely it is that a symbiosis evolves from direct cooperation or initial exploitation. Furthermore, we investigate which ecological conditions are crucial and the evolutionary steps (phenotypic and genomic changes) that lead to symbioses in which both partners live in complete dependence on each other.
Anthropogenic stressors
Over the last decades, anthropogenic stressors have increased in frequency and diversity. These stressors have both direct and indirect effects on aquatic ecosystems. Direct stressors are contaminants from agriculture and pharmaceuticals, but also light and noise pollution. Especially light pollution will play an important role in future, because a yearly increase can already be observed, and the switch to LEDs with a high proportion of blue light will especially affect the circadian clock of organisms. Indirect effects on lakes are due to the combined action of eutrophication of freshwater systems and the increase in temperature because of climate change. This often results in cyanobacterial mass developments, that frequently produce different toxins that have been shown to also harm humans. An aquatic model organism for the investigation of anthropogenic stressors are daphnids. Daphnia has a well-known ecology and also genetic information is available. Furthermore, daphnids are keystone organisms in aquatic food webs. If daphnids are affected by a stressor this will influence all connected organisms within a lake. We investigate the impact of single and combined stressors, especially toxins and light pollution, on the physiology, genetics and ecology of Daphnia. For this we use both classic laboratory experiments and up-to-date genetic methods.