Collaborative Research: Bridging plant drought and herbivory stress adaptation through comparative multi-domain trait networks

Plants face multiple environmental challenges simultaneously, yet most scientific research has examined how plants respond to individual stressors in isolation. This project investigates how plants coordinate their traits—physical structures, physiological processes, and chemical defenses—as integrated systems shaped by the joint pressures of drought and herbivory. Understanding this coordination is essential for predicting how plants survive and function under realistic environmental conditions and has direct relevance to improving crop resilience under water stress and pest pressure. Using milkweeds (Asclepias) as a study system, this research will reveal how trait integration shapes plant performance across 30 closely related species adapted to disparate environments ranging from deserts to wetlands. The work will be conducted by a collaborative team and will train staff and graduate and undergraduate students across all three participating institutions. In addition, a broader impacts initiative will be integrated directly with the research: in partnership with the Orange County (California) Department of Education's Inside the Outdoors program, cohorts of undergraduate interns at UC Irvine will translate their research experiences to the classroom by co-developing K–12 curriculum and fieldwork focused on plant function and environmental change to reach over 300 K–12 students annually. All research data, outputs, and educational tools will be made openly available. This project takes a comparative, multi-domain trait network approach to understanding how plants integrate functional traits across the domains of drought adaptation and herbivore resistance. The research examines 30 species of Asclepias that share a conserved defense repertoire—including latex and cardenolide toxins—yet span a wide range of climatic niches, providing a phylogenetically controlled system to disentangle evolutionary and dynamic responses to stress. Three coordinated aims address: (1) how evolutionary adaptation to arid environments shapes multi-domain trait network architecture and trait investment across species; (2) how dynamic plant responses to pulsed versus sustained drought stress alter trait networks and drive downstream effects on two herbivore feeding guilds—leaf-chewing monarch caterpillars (Danaus plexippus) and sap-feeding oleander aphids (Aphis nerii); and (3) how plants tolerate individual and combined drought and herbivory stress, and which traits underlie that tolerance. Plant traits spanning ecophysiology, biomass allocation, water relations, defense chemistry, and nutritional quality will be measured alongside herbivore condition and performance traits including body composition, cardenolide sequestration, survival, growth, and fecundity. Trait networks will be constructed and compared using graph-theoretic metrics—including edge density, modularity, clustering coefficients, and centrality measures—and causal pathways will be evaluated using structural equation modeling with phylogenetic correction. By linking multi-domain trait network structure to organismal performance across species, environments, and stress contexts, this work advances a systems-level framework for organismal biology that captures the pleiotropy and multifunctionality inherent in biological traits, with implications for understanding plant resilience under the intensifying and co-occurring stresses associated with variable environments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.