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Interacting species exert ecological and evolutionary pressures on one another, forming reciprocal relationships that are sensitive to abiotic and biotic perturbations. Understanding how systems will respond to anthropogenic climate change is imperative for predicting broad, ecosystem-level consequences. In my dissertation, I investigated the effects of extreme temperature events and the introduction of a novel plant species on the evolutionary ecology of a tritrophic terrestrial system. I focused on the herbivorous caterpillar Manduca sexta, the specialist parasitoid wasp Cotesia congregata, and the common hostplant Nicotiana tabacum, introducing heat waves and the novel, non-native hostplant Proboscidea louisanica as system perturbations. I used laboratory and field experiments to measure ecologically and evolutionarily relevant traits (such as development rate, survival, and fitness) for each species, and separately parsed the bottom-up effects of differential plant quality and the top-down effects of parasitization and heat stress on the system. I first investigated how M. sexta feeding behavior changed based on diet type. I discovered that caterpillars fed P. louisianica more frequently switched between states of feeding and non-feeding, when compared to N. tabacum or artificial diet. Next, I identified how hostplant identity influences wasp development, and how the introduction of heat shocks disrupts this dynamic. While caterpillar developmental outcomes were consistent across hostplants, wasp success differed. More wasps survived on hosts fed P. louisianica when reared at normal temperatures; however, that trend was reversed when exposed to thermal stress early in development. I also uncovered that parasitization and heat stress interact to change the amount of leaf material consumed by M. sexta. Finally, I used this differential consumption to assess how tolerance to herbivory differed between the two hostplants, directly measuring hostplant fitness from a combination of seed set and germination success. In the greenhouse, P. louisianica exhibited lower tolerance than N. tabacum, although this result was not observed in the field. Due to the ubiquity of such parasitoid-herbivore-plant interactions in both wild and agricultural settings, this work has important implications for management and conservation in a warming world: it predicts lessened biological control ofinsect herbivores by parasitoids, with cascading negative consequences for novel hostplants. |
