Genetic variation, but no evidence of evolved tolerance, for Daphnia in road salt polluted lakes in Ontario
Bibliographic record
Abstract
Snowmelt and rain carry road salt from paved surfaces through the watershed via runoff and groundwater. When road salt reaches lakes, it increases the salinity, often measured as chloride concentration (Cl- mg/L). Salinization negatively impacts freshwater organisms, including Daphnia pulicaria, a common crustacean zooplankton grazer that is integral to healthy ecosystems and maintenance of ecosystem services. 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. Lakes were distributed along a Cl- gradient from <1 mg Cl-/L (unimpacted by road salt) to 271 mg Cl-/L, which is above the Canadian Water Quality Guidelines for chronic exposure (120 mg Cl-/L) but below the guideline for acute exposure (640 mg Cl-/L). Acclimation can 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 higher salt concentrations does not improve salt tolerance. Our acute toxicity tests conducted under common garden conditions show a range of salt tolerances for Daphnia originating from different lakes. Daphnia from Presqu’ile Bay (26.2 mg Cl-/L Lake Ontario, Brighton, ON, CA) and Lake Wilcox (194 mg Cl-/L, Richmond Hill, ON, CA) had the highest salt tolerances in this study, with lethal concentrations for 50% (LC50) of the test individuals of 2251 mg Cl-/L and 2328 mg Cl-/L, respectively. Verona Lake had the lowest LC50, at 1809 mg Cl-/L. However, there was no impact of lake chloride on the salt tolerance of Daphnia, providing no evidence of evolved salt tolerance in southeastern Ontario. This suggests that either the current salinities are not predominant selection forces in these lakes, or evolved tolerance is coupled with an evolutionary trade-off. Further research is needed to understand the standing variation of salt tolerance within local populations, and variation across different regions, to inform decisions regarding freshwater ecosystem conservation and roadway management.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".