The Unexpected Absence of Nickel Effects on A Daphnia Population at Three Temperatures Is Correctly Predicted by A Dynamic Energy Budget Individual‐based Model (DEB‐IBM)

Recent studies have shown that toxicity of metals to Daphnia magna depends on the temperature. In a population experiment, we investigated if the effect of temperature on nickel (Ni) sensitivity observed on the apical level can be extrapolated to the population level. However, we observed no consistent population-level effects of Ni at concentrations that significantly affected reproduction. An individual-based model (IBM) with the dynamic energy budget (DEB) theory for Daphnia magna was calibrated based on Ni toxicity data at three temperatures (15, 20 and 25°C). Using the model, we confirmed the unexpected absence of Ni effects at the population level. Furthermore, population-level EC50 values of Ni, predicted with the DEB-IBM, were higher than the concentrations imposed in the experiment. In addition, predicted population-level EC50 values showed less variation between temperature treatments (1.9-fold variation) compared to at the individual level (6.5-fold variation). Our results show the potential of DEB-IBM models as mechanistic tools for effect extrapolation, optimal test design, and population-level risk assessment of chemicals.

Scientific abstract

Recent studies have shown that temperature affects chronic Ni toxicity to Daphnia magnaat the individual (apical) level. However, the effect of temperature on Ni toxicity to D. magna at population‐level is unknown. The present study investigated whether the effect of temperature on chronic Ni toxicity to D. magna assessed on apical endpoints can be extrapolated to the population‐level. The results of the performed population experiment showed no consistent Ni effects on total D. magna population abundance at 15, 20 and 25ºC although the Ni concentrations tested were previously reported to significantly reduce reproduction in D. magna individuals. This result supports the idea that ecological risk assessment should not extrapolate as such from apical endpoints to the population‐level. A Dynamic Energy Budget Individual‐Based Model (DEB‐IBM) was calibrated using apical Ni toxicity data at 15, 20 and 25°C. The goal was to investigate whether the calibrated DEB‐IBM would be able to predict the unexpected absence of effects at population‐level and to further investigate the effect of temperature on Ni toxicity to a D. magna population. At the population level, the calibrated DEB‐IBM correctly predicted the unexpected absence of Ni effect to a D. magna population. Detailed analysis of simulation output suggests that the predicted lower Ni sensitivity at population level occurs because Ni‐induced mortality is compensated by reduced starvation (less intra‐specific competition). Extrapolated EC50 values for population density predicted that the effect of temperature on Ni toxicity to D. magna populations was smaller (1.9‐fold higher at 25°C than at 15°C) than on Ni toxicity to D. magna apical reproduction (the EC50 is 6.5‐fold higher at 25°C than at 15°C, previous study). These results show that the DEB‐IBM can help to replace population experiments by in silicosimulations and to optimize the experimental design of population studies.

Full reference (link):

Pereira, C. M. S., Vlaeminck, K., Viaene, K., & De Schamphelaere, K. (2019). The Unexpected Absence of Nickel Effects on A Daphnia Population at Three Temperatures Is Correctly Predicted by A Dynamic Energy Budget Individual‐based Model (DEB‐IBM). Environmental Toxicology and Chemistry.