CAREER: Adapting to life with a dash of salt: Eco-evolutionary consequences of freshwater salinization

Lakes provide important services to communities across the United States, including recreation, drinking water, and habitat for fish and wildlife. Yet many lakes are becoming saltier, mainly due to road runoff and sea level rise. While too much salt can be toxic, very low levels of salt can also stress aquatic life. In places like coastal Maine, lakes span a wide range of salinity due to natural factors and human influence. This project studies how changing salt levels affect lake food webs, focusing on Daphnia–a tiny freshwater grazer that helps keep algal blooms in check and serves as food for fish. Daphnia can evolve quickly—within just a few generations—making them a powerful model for studying how rapid adaptation to environmental change can ripple through ecosystems. Understanding how Daphnia cope with salt stress could help explain and predict changes in water clarity and fish populations. In addition to advancing scientific knowledge, this research will create hands-on research opportunities for undergraduate students, integrate local fieldwork and lab experiments into college courses, and partner with state agencies and citizen scientists to support lake stewardship. The project investigates how ecological and evolutionary responses to salinity shape freshwater lake ecosystems. The research integrates field surveys of zooplankton and phytoplankton communities across a natural salinity gradient in coastal Maine lakes, laboratory common garden experiments quantifying local adaptation in Daphnia ambigua populations, and population genomic analyses to characterize spatial and temporal patterns of salt tolerance. Complementary mesocosm experiments manipulate salinity and resource availability to test how salt-driven evolutionary changes in Daphnia influence consumer-resource dynamics, potentially intensifying herbivory with consequent evolutionary feedbacks. By linking phenotypic and genetic variation in a keystone herbivore to community- and ecosystem-level outcomes, this project will contribute to a mechanistic understanding of eco-evolutionary dynamics in nature. Findings will inform both theory in evolutionary ecology and the management of freshwater systems experiencing salinization due to land-use change and rising sea levels. 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.