All organisms experience fundamental conflicts between divergent metabolic processes. In plants, a pivotal conflict occurs between allocation to growth, which accelerates resource acquisition, and to defense, which protects existing tissue against herbivory. Trade-offs between growth and defense traits are not universally observed, and a central prediction of plant evolutionary ecology is that context-dependence of these trade-offs contributes to the maintenance of intraspecific variation in defense [Züst and Agrawal, Annu. Rev. Plant Biol., 68, 513–534 (2017)]. This prediction has rarely been tested, however, and the evolutionary consequences of growth–defense trade-offs in different environments are poorly understood, especially in long-lived species [Cipollini et al., Annual Plant Reviews (Wiley, 2014), pp. 263–307]. Here we show that intraspecific trait trade-offs, even when fixed across divergent environments, interact with competition to drive natural selection of tree genotypes corresponding to their growth–defense phenotypes. Our results show that a functional trait trade-off, when coupled 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 dominance by fast-growing tree genotypes that were poorly defended against natural enemies. This outcome is a signature example of eco-evolutionary dynamics: Competitive interactions affected microevolutionary trajectories on a timescale relevant to subsequent ecological interactions [Brunner et al., Funct. Ecol. 33, 7–12 (2019)]. Eco-evolutionary drivers of tree growth and defense are thus critical to stand-level trait variation, which structures communities and ecosystems over expansive spatiotemporal scales. Significance Genetic diversity is critical for ecological resilience and is maintained when different traits are advantageous in different environments. Traits are not entirely independent, however: When trade-offs occur, selection on one trait may indirectly act on another. Here we examine how environmentally mediated selection for growth interacts with a trade-off between growth and herbivore defense in experimental aspen stands. We show that even an environmentally fixed trait trade-off can lead to real-time divergence in population genetic composition between environments. The underlying growth–defense trade-off led to an eco-evolutionary dynamic wherein high-competition environments selected for fast-growing trees and thus ultimately selected against herbivore resistance. This discovery reveals how patterns of genetic covariation, coupled with environmental variation, can link ecological and evolutionary processes.

Leaf-cutter ants are dominant neotropical herbivores capable of deriving energy from a wide range of plant substrates. The success of leaf-cutter ants is largely due to their external gut, composed of key microbial symbionts, specifically, the fungal mutualistL. gongylophorusand a consistent bacterial community. Both symbionts are known to have critical roles in extracting energy from plant material, yet comparatively little is known about their roles in the detoxification of plant secondary compounds. In this study, we assessed if the bacterial communities associated with leaf-cutter ant fungus gardens can degrade harmful plant chemicals. We identify plant secondary compound detoxification in leaf-cutter ant gardens as a process that depends on the degradative potential of both the bacterial community andL. gongylophorus. Our findings suggest that the fungus garden and its associated microbial community influence the generalist foraging abilities of the ants, underscoring the importance of microbial symbionts in plant substrate suitability for herbivores.

The current study aimed to evaluate the presence of chemical variations in essential oils (EOs) extracted from Artemisia scoparia growing at different altitudes and to reveal their antibacterial, mosquito larvicidal, and repellent activity. The gas chromatographic–mass spectrometric analysis of A. scoparia EOs revealed that the major compounds were capillene (9.6–31.8%), methyleugenol (0.2–26.6%), β-myrcene (1.9–21.4%), γ-terpinene (1.5–19.4%), trans-β-caryophyllene (0.8–12.4%), and eugenol (0.1–9.1%). The EO of A. scoparia collected from the city of Attock at low elevation was the most active against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa bacteria (minimum inhibitory concentration of 156–1250 µg/mL) and showed the best mosquito larvicidal activity (LC₅₀, 55.3 mg/L). The EOs of A. scoparia collected from the high-altitude areas of Abbottabad and Swat were the most repellent for females of Ae. aegypti and exhibited repellency for 120 min and 165 min, respectively. The results of the study reveal that different climatic conditions and altitudes have significant effects on the chemical compositions and the biological activity of essential oils extracted from the same species.