Lisa Cicchetti, MSc Candidate Grogan Lab Evolved tolerance to road salt among wild populations of Daphnia Snowmelt and rain carry road salt from paved surfaces through the watershed via runoff and groundwater and increase the salinity of lakes, often measured as chloride concentration (Cl- mg/L). Salinization negatively impacts freshwater organisms, including Daphnia pulicaria, a ubiquitous crustacean zooplankton grazer that is integral to healthy ecosystems. Daphnia are sensitive to environmental changes, but studies have shown they are capable of rapid evolution. We investigated intraspecific variation in salt sensitivity among D. pulicaria collected from 10 lakes in southeastern Ontario to understand how wild Daphnia respond to salt pollution. Acclimation can also influence tolerance, so we tested the effect of acclimation on acute 48-hour salt tolerance for Daphnia grown at low (18 mg Cl-/L) and high (218 mg Cl-/L) Cl-. Our results indicate that acclimation to salt does not significantly impact tolerance. Our common garden experiments testing acute toxicity of salt on Daphnia from lakes ranging from <1 mg Cl-/L to 271 mg Cl-/L show a wide range of salt tolerances for wild Daphnia. Daphnia from Presqu’ile Bay, Lake Ontario (26.2 mg Cl-/L) and Lake Wilcox (194 mg Cl-/L) have higher salt tolerances of 2222 mg Cl-/L and 2344 mg Cl-/L, respectively, compared to Daphnia from unimpacted lakes (1277 – 1617 mg Cl-/L). This indicates that D. pulicaria may have adapted to localized road salt pollution. Understanding the factors contributing to robust tolerance to road salt will help inform decisions regarding freshwater ecosystem conservation.
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