Predation is a major selective force structuring natural biological communities and causing the evolution of many defence or avoidance mechanisms in prey organisms. Major predators in riverine ecosystems are primarily fish but also several macroinvertebrate taxa. Beside the direct predation effect, indirect interactions between predator and prey (e.g., drift or hiding behaviour) are often mediated by chemical cues (kairomones) released by predators. However, single, and multiple stressors might significantly interfere with this evolved interspecific interaction as anthropogenic stressors may modify or inhibit the signal transfer and thereby alter, or even suppress the defensive responses. Therefore, the effects of predation in stream ecosystems affected by stressors might differ substantially from near-natural conditions with consequences for the structure of biological communities. With this project we aim to elucidate the mechanisms underlying predator perception and how this is affected in anthropogenically stressed environments (i.e. salt and temperature increase) and a natural stressor (i.e. parasitism) also reflecting the local history of representative populations. It has been shown that rapid evolution within short ecological periods can occur. Predation pressure in multiply stressed habitats might favour those genotypes that can still sense the predators. In Phase I of RESIST, our ExStream mesocosm project results revealed that several macroinvertebrate species from the Boye community responded to fish kairomone exposure by entering the drift (avoidance behaviour). When exposed to anthropogenic stressors, this reaction to fish predators was suppressed. Building on these key results, project A10 will use small indoor mesocosms and beaker-sized microcosms equipped with a selfdeveloped digital tracking system to study modifying stressors and anti-predator-responses in detail with different populations of the two focal taxa Gammarus fossarum (crustacean model) and the ephemeropteran Baetis rhodani (as an insect model). We will test the effects of fish cues and stressors on populations from the Emscher tributary area which differ in fish and stressor history. This will provide information about i.) the generality of the response, ii.) local adaptations to fish cues and iii.) differing tolerance to stressors. We will do this by applying fish and stressor gradients to find reaction norms and response thresholds between these communities which is also essential for further mesocosm experiments. Based on this information we will target mechanisms of chemical information transfer disruption focussing on neurophysiological assays of one focal genus i.e. G. fossarum. Here we intend to identify genes and pathways underlying anti-predator responses, and how these are altered when exposed to sublethal stressor levels, by analysing differential gene expressions and by comparing differential gene expression patterns. To study if predator-induced effects are manipulated through parasitism, we will also focus on G. fossarum and monitor drift and hiding behaviour of parasitized individuals in response to predation. In line with MH 1 and MH 2, this project will focus on biotic interactions (defences against predation) and their modification by multiple stressors. Recovery from moderate degradation is mainly influenced by biotic interactions (MH 1.3). It may lead to local adaptations and will provide insight into the eco-evolutionary processes in populations with different stressor histories.

Anna-Maria Vermiert (Ruhr University Bochum)

Predator-mediated shifts in benthic invertebrate community composition in multiply-stressed riverine ecosystems

A major selective force in the structuring of natural biological communities are predators. Predator-prey interactions can have serious effects on population size and prey behaviour and may even cause cascading effects on the ecosystem. In stream ecosystems, predators are primarily fish and secondarily various macroinvertebrate taxa. They can directly or indirectly cause defence and avoidance behaviour in their prey through their presence or their kairomones. In many aquatic ecosystems, kairomones play a relevant role not only in food web dynamics but also in ecosystem functions. Significant changes can threaten not only biodiversity, but also the ecological functions of the ecosystems.

Anthropogenic stressors such as increased salinity, reduced flow velocity and increased temperature can not only affect the macrozoobenthos, but can also influence chemical information transfer, e.g., predator recognition. It is hypothesized that stressors such as increased salinity and temperature, which directly affect the physiology or sensory system, may result in the inability of prey to respond appropriately to predator signals. Reduced flow velocity, in turn, can cause stressful hydromorphological changes such as higher sedimentation, leading to higher rates of emigration. In ecosystems suffering from multiple stressors, higher mortality and low recovery rates of the macroinvertebrates are to be expected.

In order to ensure the good status of all streams, it is crucial to investigate existing anthropogenic stressors, to determine their effects on aquatic ecosystems and to provide approaches for possible renaturation.

Several mesocosm experiments (ExStream System) will be used to investigate how macrozoobenthos communities change under single and multiple stressors, as well as direct and indirect predator effects, and how these stressors may affect the chemical information transfer networks of predator-prey interactions along with the classical food webs.

Contact: Anna-Maria.Vermiert@hhu.de

First Supervisor: Prof. Dr. Ralph Tollrian (Ruhr University Bochum, Animal Ecology, Evolution and Biodiversity)
Second Supervisor: Prof. Dr. Florian Leese (University of Duisburg-Essen, Aquatic Ecosystem Research)
Mentor: Dr. Jens Arle (Umweltbundesamt)