ORCID ID
https://orcid.org/0000-0003-0747-3890
Date Awarded
2023
Document Type
Thesis
Degree Name
Master of Science (M.Sc.)
Department
Biology
Advisor
Harmony J Dalgleish
Committee Member
James Skelton
Committee Member
M. Drew LaMar
Abstract
Plants, insects, and microorganisms engage in dynamic interactions that can significantly influence the fitness of the organisms involved, carrying important implications for conservation and agriculture. However, the underlying reasons for species declines resulting from global land use change often remain obscure, hidden within subtle associations among species. This study focused on common milkweed (Asclepias syriaca) as a model system to explore the impacts of insect-plant interactions on microbial communities and plant fitness, specifically examining herbivory and pollination dynamics. In response to herbivory, many plants produce defensive chemical compounds to deter herbivores. This growth-defense trade-off framework suggests a resource reallocation from growth to defense upon induction. When subjected to insect damage, common milkweed produces toxic cardenolides that are unpalatable to most herbivores. These compounds have been shown to suppress fungal and bacterial growth. We hypothesized that the induction of cardenolides would reduce plant growth and fecundity and influence the composition of microbial communities in both the leaves and rhizosphere soil due to their antimicrobial activity. To test our hypothesis, we mechanically damaged milkweed plants, assessed vital rates, and sequenced the soil and leaf microbiomes. Our findings revealed a decline in growth and flowering with increasing levels of herbivory, but we did not observe significant differences in microbial community composition between the herbivory treatments. Next, we investigated the direct impact of the nectar microbiome, introduced to flowers by pollinators, on plant fitness. Common milkweed hosts specialized nectar microbes which can modulate conditions for the germination of its pollinia (masses of pollen) within the nectar. These microbes alter the sugar compositions within the nectar, which subsequently affect germination success. We found that optimal concentrations of pure sugars exist that allow for good quality germination. In a pollinator-exclusion experiment, we observed distinct bacterial nectar communities in flowers visited by pollinators, along with consistent alterations in sugar compositions toward the identified optimal conditions. Remarkably, when placed in nectar samples that had been visited by pollinators, pollinia exhibited diminished germination rates and often even burst, indicating potential microbial inhibition or exploitation. These findings establish a novel and direct link between nectar microbes and plant reproductive success. Overall, this research sheds light on the intricate dynamics between plants, insects, and microorganisms. Our findings underscore the need to consider the complex nature of species associations in the face of global change. Further research in this area will deepen our understanding of the intricate relationships within ecological networks and foster more effective conservation and management strategies.
DOI
https://dx.doi.org/10.21220/s2-tg2w-f597
Rights
© The Author
Recommended Citation
Munkres, Ivan, "Microbes Mediate Plant-Insect Interactions In Asclepias Syriaca" (2023). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1697552506.
https://dx.doi.org/10.21220/s2-tg2w-f597
