Effects of macrocyclic lactone anthelmintics on seed germination and seedling establishment of grassland species

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Endo- and ectoparasites are a major cause of ill health and poor productivity in domestic animals, such as sheep and cattle. In order to control these parasites a broad spectrum of anthelmintics, e.g. macrocyclic lactones (MLs), is administered to domestic species worldwide. After application, the main path into the environment is via faeces excretion. Subsequently, many non-target organisms may be adversely affected. Well-studied are the negative effects of MLs on decomposers, especially arthropods but the assessment of anthelmintics on seedling emergence has been almost completely neglected.Rare and endangered plant species in grazed vegetation might profit from endozoochorous dispersal of seeds by ungulates, which is a common and well-documented phenomenon. Especially sheep have been proven to be effective seed dispersal vectors resulting in a successful establishment of plant individuals at new sites. Thus, it can be expected that any negative effect on the effectiveness of seed dispersal by livestock will be of significant general ecological relevance; especially in nature conservation and ecological restoration. Survival and persistence of plant populations strongly depend on reproduction, thus seed germination and seedling establishment are the most critical stages in the life of plant individuals. Without successful germination and establishment, populations are threatened by extinction. Germination processes are affected by the biotic environment, and by abiotic environmental conditions. When the environment of seeds changes, effects on seedling emergence are very likely to occur. In this context, possible direct negative effects of MLs, administered to livestock as anthelmintic formulations, on seed viability, seed germination and seedling establishment threaten effective seed dispersal, germination and seedling establishment. To our knowledge the first study that directly addressed the effect of an anthelmintic on seed germination was conducted by the project group of this proposal (Eichberg et al., 2016). In this study, we found clear negative effects of the anthelmintic Cydectin and its active ingredient on seed germination (Eichberg et al., 2016). This situation of very limited knowledge about the effects of MLs on germination, seedling emergence and seedling establishment calls for further research. To this end, we want to assess i) whether the response patterns found in the study of Eichberg et al. (2016) can be confirmed for a wider spectrum of plant species and ii) to which degree different MLs show similar effects on seed germination, seedling emergence and establishment.