Preface

Although chemical interactions between plants and other organisms had been documented many years previously (e.g. Stahl, 1888; Verschaffelt, 1910), it was the seminal work of Fraenkel published in 1959 that placed the ecological function of plant secondary metabolites (PSMs) onto the agenda of modern ecology. He recognised that PSMs are not merely a repository for plants’ waste products, but rather they had a primary function: they could act as defences against enemies such as phytophagous insects. Crucially, he also realised that these enemies exert a selection pressure on the plants to defend themselves. Since then, numerous ecological roles of PSMs have been elucidated, notably as defences against a broad range of herbivores and pathogens, as mediators of interactions with competitors and mutualists, and as defence against abiotic stress. Recently, emerging developments have taken us well beyond consideration of PSMs in the context of simple interactions between pairs of species. Our view of plant secondary metabolites has shifted significantly in the past 50 years and we now understand the subtlety and scale of their effects, which cross trophic levels, spread throughout ecosystems, and even affect global processes. At the same time, methodological developments, particularly in the ‘-omics’ technologies, have led to a greater understanding of the synthesis and regulation of PSMs. These methodological developments now also facilitate unique tools for the targeted manipulation of both the synthesis of PSMs and their ecological function independently of other phenotypic effects. Consequently, we are now in a position to assess the extent to which PSMs and their effects traverse natural systems from genes upwards, and, in the spirit of Fraenkel, the reciprocal effects of the biotic and abiotic environment on those genes. This is, therefore, the ideal time to take stock of our current understanding of the function, ecology and evolution of PSMs, in order to focus our future efforts to use this knowledge to best effect in science and its application.