Divergent antiherbivore syndromes in tarweed: Play it safe and hide or roll the dice and call for help

Background/Question/Methods

Specialist herbivores of plants can overcome even extreme direct hostplant defenses, to which plants have adapted means of tolerating their damage, luring predators to kill them, and/or hiding from them in time and space. Using divergent populations of a species of tarweed (Asteraceae: Madia elegans) and its arthropod community as a model system, we investigated a variety of functional herbivore resistance traits (i.e., apparency, tolerance, indirect defense) and plant reproductive output. We use these data to characterize the life-history syndromes of the populations and develop a broad framework to interpret their evolutionary ecology.

Results/Conclusions

M. elegans, like many California tarweed species, is comprised of spring-flowering non-sticky populations and fall-flowering sticky populations. Spring-flowering plants avoid specialist herbivores (Lepidoptera: Noctuiidae: Heliothodes diminutiva) by flowering, setting seed and senescing before they emerge, but the plants are very small; most plants produce just a few fruits and there is very little variation in fruitset. Fall-flowering plants are larger and entrap insect carrion on their sticky hairs to lure scavenging predators for indirect defense, and they can tolerate more herbivore damage than spring-flowering plants. Fruitset for fall-flowering plants is quite variable but sometimes very high. We interpret these divergent life history strategies into a framework of a low-risk low-reward syndrome for spring-flowering plants versus a high-risk high-reward syndrome for fall-flowering plants, with herbivores being a key selective driver of the divergent syndromes.