Multiple stressor effects on sculpins (Cottus sp.) and related top-down effects on riverine food-webs
In stream ecosystems, fish are highly mobile top predators that significantly shape food-web interactions. They are also highly affected by multiple stressors and immediately respond to stressors such as salinization and elevated water temperatures. The project will investigate stressor response patterns in two model species (Cottus rhenanus and C. gobio). We are planning a detailed analysis of dispersal and recolonisation patterns (WP1) as well as adaptation to stressors and stressor combinations (WP2). In addition, the influence of Cottus sp. on prey invertebrates and the food web in general will be investigated (WP3). The survival of small populations in isolated locations of the Emscher catchment as well as large populations in the Kinzig and the Rhine makes Cottus sp. an ideal candidate to test local adaptation.
The first part of the project will focus on the distribution and genetic diversity of Cottus sp. in the partly degraded and partly restored Emcher/Boye catchment and in the moderately stressed Kinzig catchment under single and multiple stressor conditions. Since the restoration projects in the Emscher catchment started, C. rhenanus was re-introduced but also dispersed naturally into the rehabilitated tributaries despite high water temperatures in summer.
A higher tolerance for warm temperature and higher salinity might explain the fast recolonisation of habitats, where environmental conditions have improved just enough for tolerant genotypes. We will combine field data with molecular methods. Individuals of Cottus sp. will be caught, marked and monitored in the field. A wide range of environmental variables (including temperature and salinity) will be correlated with fish presence and individual relatedness.
Population genetic diversity will be analysed using neutral genetic markers (WP1). In addition, we will use transcriptome data as well as detailed candidate gene analyses and qPCR to analyse candidate genes of the respiratory chain (oxygen stress response), osmoregulation (salinity stress response) and the immune system (pathogen response) for evidence of adaptation to environmental stressors (WP2).
In addition, the project will characterise the influence of Cottus sp. on food web interactions by comparing small water bodies with and without predatory fish. In cooperation with other projects, we will investigate resource abundance, feeding types and parasite diversity. The synthesis of this integrative approach will provide a deeper understanding of the ecological and evolutionary consequences of stressor impact on vertebrate and invertebrate populations.