Honors Theses and Capstones

Date of Award

Spring 2024

Project Type

Senior Honors Thesis

College or School




Program or Major


Degree Name

Bachelor of Science

First Advisor

Anna O'Brien


Organisms in their home environment sometimes outperform transplanted individuals native to other areas, in a phenomenon termed local adaptation. While local adaptation is traditionally considered to be driven by the abiotic factors of an environment, scientists have recently increased consideration of biotic factors. Specifically, of interest to many is host-associated microbiomes, which can alter host trait expression. As the desire to commercialize microbiome treatments for agriculture and medicine grows, it is important to analyze the potential value of local microbiomes, which may be adapted to their hosts, or to which local hosts may have adapted. Using Lemna minor (duckweed) as a model organism, we examined differences in host fitness when grown in local and foreign microbiomes and in local and foreign water. We hypothesized that duckweeds grown with their local microbiome and water would display higher fitness than those grown in different contexts. For the study, we collected duckweeds, microbes, and water from 4 different sites in Durham, New Hampshire. Water, duckweeds, and microbes were crossed and assembled as microcosms in 96-well plates. After 2 weeks, we measured frond area as a proxy of duckweed fitness and optical density, as a measure of microbial cell growth across the microbiome. We found that duckweeds grown in their local water and microbiome had higher fitness. We also found that microbe fitness was not dependent on their local water or plant. Therefore, local adaptation to a host’s microbiome conveys benefits to the host, and inocula with similar compositions as the local microbiome may be more beneficial than generic compositions.