Abstract

All organisms experience fundamental conflicts between divergent metabolic processes. In plants, a crucial conflict occurs between allocation to growth, which accelerates the acquisition of resources, and defense, which protects existing tissues against herbivory. Trade-offs between growth and defense traits are not universally observed, and a central prediction of evolutionary plant ecology is that context dependence of these compromises contributes to the maintenance of intraspecific variation in defense. [Züst and Agrawal, Annu. Rev. Plant Biol., 68, 513–534 (2017)]. However, this prediction has rarely been tested and the evolutionary consequences of growth-defense trade-offs in different environments are poorly understood, particularly in long-lived species. [Cipollini et al., Annual Plant Reviews (Wiley, 2014), pp. 263–307]. Here, we show that intraspecific trait compromises, even when fixed in divergent environments, interact with competition to lead to the natural selection of tree genotypes corresponding to their growth-defense phenotypes. Our results show that a compromise of functional traits, when associated with environmental variation, causes real-time divergence in the genetic architecture of tree populations in an experimental setting. Specifically, competitive selection for faster growth resulted in the dominance of fast growing tree genotypes that were poorly defended against natural enemies. This result is an emblematic example of eco-evolutionary dynamics: competitive interactions have affected micro-evolutionary trajectories on a time scale relevant for subsequent ecological interactions. [Brunner et al., Funct. Ecol. 33, 7–12 (2019)]. Eco-evolutionary drivers of tree growth and defense are therefore central to the variation in stand-level traits, which structures communities and ecosystems over vast spatiotemporal scales.