Why is there such high diversity of chemical defences? The role of insect herbivory in promoting chemical diversity in willows
Chemical diversity of plant defences is a major driver of insect-plant interactions. Answering the question “Why is there such high diversity of chemical defences?” is thus crucial for understanding key ecological processes that shape composition and diversity of insect-plant assemblages. Our aim is to unravel the mechanisms by which chemical diversity evolves. To achieve this, we use ecologically dominant and diverse willows as a model genus. We contrast chemical defences and herbivore communities of allopatric and sympatric willow species. This will help us to show how the exposure to local pools of herbivores promotes the diversity of willow defences and leads to their divergent evolution (Figure 1). Furthermore, we use greenhouse experiments to dissect how the overall diversity of chemical defences arises from individual insect-plant interactions and their specificity. Only such an integrative approach using field surveys, manipulative experiments, and cutting-edge analytical methods can demonstrate how the diversity of defensive secondary metabolites is generated.
Figure 1. Evolution of defences along the phylogeny of Ficus (A), Salix (B), and Macaranga (C) based on the data from Segar et al. (2017); Volf et al. (2015); Volf et al. (2018) and our preliminary results. Left-oriented columns suggest divergence.
We combine field sampling with manipulative greenhouse experiments to achieve our goals (Figure 2). 
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Figure 2.  Photos from field and greenhouse experiment 2020.
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