Does previous disease exposure influence the temperature-dependent disease response of a marine foundation species, Zostera marina?

Seagrasses are marine flowering plants that provide important benefits, including protection from shoreline erosion and creating habitats that support ecologically and commercially important marine species. They are often infected with a slime-mold pathogen that creates dark brown lesions on the plants, called eelgrass wasting disease. The effects of this disease range from the die-off of entire meadows to smaller declines in plant growth, with the reasons for this variation generally unknown. The disease typically peaks during the summer when temperatures are warmer, highlighting the relationship between temperature and disease. However, plants from different populations vary in how they grow and survive at different temperatures, suggesting that plants that are adapted to cold versus warmer water may show different temperature-dependent responses to the disease. Furthermore, when plants survive the infection, it is unknown if previous exposure to disease influences future plant response to disease in beneficial or harmful ways. In this project, the investigators are testing how plants adapted to different temperatures respond to disease, and how the effects of disease on eelgrass change depending on temperature and the plant’s history of disease. Results will be useful to local, state, and federal agencies, as well as non-profit organizations that manage and restore critical eelgrass habitat. The study is helping identify characteristics of populations that may make them more or less resistant to the combined effects of disease and other stressors, allowing prioritization of intervention efforts. It is providing support for graduate students and a post-doctoral scientist, engaging undergraduate students in research through immersive classes, and expanding and supporting research opportunities and mentorship of students from a local two-year college. Infectious diseases are increasing globally, causing significant declines in the abundance of ecologically and commercially important species. Disease is often associated with warmer temperatures, suggesting that diseases are often thermally dependent. However, disease dynamics are difficult to predict because host populations vary in their response and recovery to infection. Theory suggests that thermal mismatch between hosts and broadly-tolerant pathogens can drive disease dynamics: warm-adapted hosts are more likely to be diseased in colder conditions, and cold-adapted hosts are more likely to show disease in warm conditions. How prior disease exposure modifies a host’s thermal critical limits and disease response is important to consider when repeated pathogen exposures exist in species without adaptive immunity. Ultimately, an understanding of how previous disease exposure influences future disease response across populations is needed to predict which populations will be susceptible to outbreaks. To that end, the investigators are using the eelgrass Zostera marina as a model species to test how locally-adapted hosts respond to wasting disease across the range of currently-observed temperatures and whether previous exposure influences host response. Project aims are to: 1) compare disease severity and plant productivity across a gradient of temperatures in the field through both field surveys and reciprocal transplants; 2) determine the thermal performance of host-pathogen interactions of warm and cold-adapted populations in the lab; and 3) determine how carry-over effects associated with disease modify plant responses to future disease attack across temperatures. 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.