Eco-evolutionary effects of heatwaves on bacterium-yeast competition in nectar and consequences for plant-pollinator mutualism

In this project, investigators will conduct experiments at Jasper Ridge Biological Preserve in California to study ecological relationships between flowering plants, the hummingbirds that pollinate them and the microorganisms that live in the floral nectar and are transmitted by the birds from flower to flower. The experiments will examine the effects of heatwaves, or the periods of excessive heat, on how bacteria and yeasts interact with each other in nectar and how their interactions alter nectar chemistry, hummingbird preference, and seed production by the plants. It is widely appreciated that plants, animals, and microorganisms influence one another in many ecosystems, but how these relationships are altered by environmental changes such as heatwaves is difficult to understand because of the complexities of biological relationships. This project will seek to disentangle these relationships and will use genetic analysis of nectar-specialist microorganisms to understand their adaptation to rapid nutrient uptake. The microbial studies will provide advances in biotechnology, a national priority area. The project will also contribute to student training, and advance community engagement through collaboration with a local nonprofit with ties to the local community. The objective of this research is to investigate how microorganisms that inhabit floral nectar will respond to heatwaves and how this microbial response will affect a plant–pollinator mutualism. To achieve this goal, investigators will use monkeyflower, a hummingbird-pollinated shrub native to California, as a well-characterized system to test four hypotheses. Testing these hypotheses will reveal (1) heatwave-induced changes in nectar chemistry, (2) genetic mechanisms by which heatwave-induced changes to nectar chemistry and temperature affect the growth of nectar-inhabiting yeasts and bacteria, (3) combined eco-evolutionary effects of nectar chemistry, nectar temperature, and yeast–bacteria competition on the microbes’ growth rate and other traits that influence microbial community assembly in nectar, and (4) consequences of these eco-evolutionary changes for pollinator preference and plant reproduction. Findings from this research will have broad significance in biology. The same unique set of nectar-associated yeast and bacterial species to be studied in these experiments are found in many plant species around the world, engaging in the same type of competitive interactions with one another, with similar effects on mutualisms between plants and their pollinators. This work also involves (1) synergistic feedback between research and education through continued teaching of an established inquiry-based course, (2) broadening participation through mentoring of students via the Stanford Biology Summer Undergraduate Research Program, Building Up Developing Scientists program, and Community College Outreach Program, focusing on first-generation, low-income, or otherwise non-traditional students, and (3) outreach and community engagement through collaboration with the Stanford Haas Center of Public Service. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.