Collaborative Research: Linking ion transport, energetics and species distributions in freshwater ecosystems

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The Nation's streams and lakes are growing increasingly salty, as measured by salinity. Some of these changes are associated with local human activities, and some are associated with broader climate changes. Increases in salinity are expected to have important impacts because many aquatic organisms evolved in and require low-salinity environments. Ecologists report that increases in salinity adversely affect some groups of aquatic organisms (e.g., aquatic insects such as mayflies, a focus of this project) that are ecologically important and serve as a primary food source for fishes and birds. Thus, modest increases in salinity could greatly affect both the biodiversity and functioning of freshwater ecosystems. This project is designed to better understand how and why different aquatic insect species vary in their ability to thrive in waters of different salinity. The research will advance understanding of the physiological mechanisms by which salinity affects the metabolism, growth, and survival of aquatic insects, and, ultimately, their distributions and abundance. Project results will help local, tribal, state, and federal water resource agencies and their constituents and stakeholders better interpret monitoring data on aquatic insects, which are widely used as indicators of water quality and ecological conditions. At least three graduate students and several undergraduate researchers will be supported and trained in the project, and the investigators will contribute to K-12 curriculum development related to water quality and ecological physiology.The project will expose a new mayfly model species to short-term and long-term salinity gradients to establish how gene expression patterns, oxygen consumption, hemolymph chemistry, and gill physiology link to measures of fitness. Using comparative methods, the researchers will test the hypothesis that the efficiency of ion uptake in dilute environments and the ability to curtail excessive ion uptake in ion-rich environments are key osmoregulatory characteristics that can shape salinity niches. The investigators further hypothesize that the energetic costs of ion transport interact with temperature to influence growth, fecundity, and mortality to define species-specific salinity niches, the expression of which in nature can be observed from niche analyses of field survey data. The study will significantly advance understanding of how both natural variation in salinity and human-induced changes in salinity contribute to organismal performance and species distributions in an increasingly salty world. By integrating different levels of biological organization (genes to biodiversity patterns) and laboratory and field work, the project should significantly advance the synthesis of physiology and macroecology. The project will also help establish and evaluate a promising and needed model aquatic insect species, and will provide foundational understanding of osmoregulation differences across taxa that will inform the use of aquatic insects as ecological indicators of environmental change. Graduate and undergraduate student trainees will be supported, high-school teachers will conduct summer research and develop relevant curricula, K-12 science curricula that integrate science, management, and policy aspects of water quality will be developed and tested, and public outreach workshops will be held for federal and state agencies.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.