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Contributed Talk

Session: : Herbivory: Plant Defenses

COS 85-3 - Effects of herbivory and drought on the ecology and evolution of fruit defenses in a native California wildflower

Tuesday, August 8, 2023
10:30 AM – 10:45 AM PDT
Location: B115
Abstract: Changes in plant-environment interactions are already occurring due to climate change, and have the potential to impact species interactions, fitness, and adaptation to habitats. Increased drought is expected under climate change, which often lowers defensive glucosinolate compounds. Decreased levels of glucosinolates may leave plants more vulnerable to attack from their herbivores, which has implications for plant fitness and persistence under climate change. Herbivores also respond to climate change, and herbivory may shift temporally in response to increased temperatures and drought. The timing of herbivory events may have crucial implications for a plant's ability to respond, especially under increased drought stress and resource limitation.



Here, we examine how variation in herbivory timing and water availability affects intraspecific defense responses. We conducted a common garden experiment using the native California wildflower Streptanthus tortuosus, which experiences variation in water availability and herbivory, and displays variable life history strategies across its range. We exposed eight populations to factorial combinations of simulated herbivory clipping timing and watering treatments representing range-wide field conditions. At the end of the season, fruit tissues were removed to assess the effects of the herbivory and drought treatments on fruit glucosinolate profile and investment.



Results show that herbivory and drought regimes impact population-level variation in fitness and life history traits. Drought and herbivory timing affects fitness; specifically, later herbivory timing reduced fecundity across populations. Plants that were clipped during fruiting tended to have a near-zero fitness, while plants that were clipped during flowering were able to replace reproductive tissue, but had lower fitness compared to control plants. Populations tend to vary in herbivory intensity in their native habitats. Cooler, high elevation sites tended to have less herbivory than warmer, low elevation sites, which could drive differences in the evolution of defensive chemistry and investment in these environments. Preliminary results suggest that fruit glucosinolate profile and investment responses to drought and herbivory vary across populations. Understanding how abiotic and biotic factors such as drought and herbivory impact defense investment and fitness across populations is essential for accurately predicting the potential for adaptation to future climate-induced environmental change.