Pesticide effects at the edge? Implications of downstream agrochemical pollution for organisms in refugia

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Based on several studies in the last two decades, it is relatively well established that pesticides shape invertebrate assemblages in streams, with an increase in the relative abundance of tolerant taxa. Our understanding of the response and long-term consequences of toxicant effects is still deficient with respect to spatial dynamics and adaptation processes. Genetic adaptations to pesticides in terms of tolerance may propagate to non-polluted patches as shown in modelling studies. However, empirical studies on the potential of downstream effects of pesticide pollution to propagate to organisms in non-polluted upstream sections are scarce. In this project, we will examine for different invertebrates to which extent pesticide effects can propagate to organisms in refugia. The project profits from a nationwide pesticide monitoring programme (Implementation of the national monitoring of small water bodies for pesticides) that provides high quality pesticide data, high resolution physicochemical data as well as assemblage data on invertebrates and diatoms without extra costs. We will sample three invertebrate species, including a gammarid, a trichopteran and an ephemeropteran, in agricultural sites with high pesticide toxicity and in refugia at two distances (edge of refugia and further upstream). Using rapid tests, we will determine the tolerance of the invertebrates, which will enable us to evaluate potential adaptations. Moreover, we will determine the genetic diversity and energy reserves in gammarids. We hypothesise that the adaptation reduces genetic diversity and that this propagates to non-polluted patches at the edge of the refugium. Moreover, following the concept of resource allocation, we assume that a higher tolerance is associated with higher allocation of energy to defence mechanisms, resulting in lower energy reserves compared to less tolerant organisms. Overall, this research project will add considerably to the understanding of the mechanisms underlying a higher tolerance observed in polluted habitat patches in a previous study (Shahid et al. 2018) and it will advance our assessment of the costs of pollution for organisms and populations in non-polluted areas.