DISSERTATION RESEARCH: Do gut microbiota affect caterpillar herbivory and fitness?

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Recent studies have shown that some animals, including humans, are heavily dependent on trillions of bacteria and other microorganisms that inhabit their gut ("gut microbiota") to digest food and provide nutrients. Although this microbial partnership likely occurs in all animals, it remains unexplored in most. This project assesses the role of gut microbiota in caterpillars, some of which are globally destructive crop pests and thus of major economic interest. Understanding whether caterpillars are reliant on gut microbiota for feeding and growth could help in designing strategies for controlling them more effectively. Researchers will conduct an experiment using the tobacco hornworm caterpillar, a common pest of tomato and tobacco plants. Findings of this project will advance scientific understanding of how much animals and microbes have evolved to depend on each other. This study will also provide research experience for a community college student and will engage the public through an educational workshop and a museum event.Investigators will experimentally test the hypothesis that gut microbiota in the tobacco hornworm, Manduca sexta, affect host feeding behavior and fitness. The experiment will be based in southeastern Arizona, where a large population of wild M. sexta feed on the plant Datura wright-ii. To manipulate gut microbiota, researchers will use antibiotics to selectively remove microbes from D. wrightii without altering leaf chemical or nutritional properties. Feeding rates and development of the caterpillars, as well as fecundity of the resulting adult moths, will be measured and compared between control and antibiotic-treated groups. In addition, the size and composition of gut microbial communities will be characterized using DNA sequencing and fluorescence microscopy. Previous DNA sequencing data indicate that the number of microbes in the M. sexta gut is extremely low relative to other animals. Further, extreme chemical conditions within the caterpillar gut suggest that the gut microbes detected there are unlikely to be metabolically active. Therefore, the researchers anticipate that gut microbiota will not play a large role in host feeding or fitness. This result would challenge the current paradigm that animal growth and reproduction typically depend heavily upon microbial symbiosis.