Format: ORAL

Martin Volf????1,2, Jing Vir Leong?1,2, Paola de Lima Ferreira1,3, Ezgi Ogutcen1, Natascha D. Wagner4, Gibson Aubona??????1,2, Simon T. Segar5, Juha-Pekka Salminen6, Vojtech Novotny1,2, Brian E. Sedio7,8

1 Biology Centre of the Czech Academy of Sciences, Branisovska 31, Ceske Budejovice, CZ 2 Faculty of Science, University of South Bohemia, Branisovska 31, Ceske Budejovice, CZ 3 Department of Biology, Aarhus University, Aarhus, DK 4 Department of Systematics, Biodiversity and Evolution of Plants (with Herbarium), University of Goettingen, Göttingen, Germany 5 Agriculture and Environment Department, Harper Adams University, Newport, UK 6 Natural Chemistry Research Group, Department of Chemistry, University of Turku, Turku, FI 7 Department of Integrative Biology, University of Texas at Austin, Austin, TX, US 8 Smithsonian Tropical Research Institute, Ancón, PA

Plants produce hundreds of thousands of specialized metabolites and many more probably remain to be discovered. There are currently multiple competing explanations for the origins and roles of chemical diversity in plants. We propose that to understand the origins and functions of chemical diversity, we need to decompose it into its various dimensions and link these to prevailing types of environmental stress. From this perspective, the willow family (Salicaceae) represents an ideal model system as the family is diverse from lowlands to highlands and from warm to cold climates. Our results from elevational gradients suggest that changes in the relative importance of stress by specialized insect herbivores and abiotic conditions drive differential phylogenetic trends in willow chemistry that, in turn, support increase in different dimensions of chemical diversity. Abiotic stress promotes directional phylogenetic increase in the concentration of metabolites such as flavonoids that protect plants from abiotic conditions. Abiotic pressures also act as a filter that selects for similar responses, which results in convergent chemical traits in plants growing under similar conditions. Contrastingly, divergent chemistry can improve plant fitness under strong pressure by specialized insect herbivores. Under prevailing pressure by specialized enemies, plants can thus be selected to switch to a completely different form of defence rather than invest in high concentration or richness of their current metabolites. The resulting divergence should allow for a 'chemical niche partitioning and promote chemical variation among plant species. We suggest that similar gradients in the relative importance of various types of stress can underlay global trends in the diversity of metabolites. Specifically, we propose that the elevational clines may be analogous to latitudinal patterns of herbivory, host specialization, and quantitative investment in chemical defence, due to similar underlying gradients in the relative importance of abiotic stress and biotic interactions.