Multiple Stressor Differential Tolerances: Possible Implications at the Population Level

Abstract

The probability of the most sensitive genotypes being eliminated from a population due to a contaminant pulse–genetic erosion–is negatively associated to the within-genotype variation. A sensitive genotype with a small phenotypic variation would be more prone to be lost–a critically sensitive genotype. Furthermore, natural populations inhabiting contaminated sites are usually exposed to several pollutants. Such co- or sequential exposure can have severe effects if at least some tolerant clonal lineages surviving one contaminant are sensitive to the others. Such an inverse relationship coupled with a low within-genotype variation potentially enhances genetic erosion. Accordingly, this study evaluated co-tolerance and the occurrence of clonal lineages critically sensitive to 48-hours lethal exposures of copper, zinc, cobalt, and chromium among eight clonal lineages of the cladocerans Daphnia longispina. Median lethal concentrations (LC50) of each metal were found to have the potential to provoke genetic erosion. Pairwise comparisons of LC50, from the eight clonal lineages, revealed neither negative nor positive correlations (r ≤ |0.56|; p ≥ 0.18), but inversely sensitive clonal lineages were found for all pairs of metals. Therefore, besides having the potential to eliminate critically sensitive clonal lineages in a first intermediately lethal pulse, all tested metals may provoke further losses of clonal lineages in an already genetically eroded population.

Predictability of the impact of multiple stressors on the keystone species Daphnia

“…Mitigation strategies to reduce the impact of environmental change are limited because the effect of multiple stressors can be synergistic (greater than the sum of individual effects), antagonistic (resulting from the contrasting action of two or more stressors) or additive (sum of the individual effects) 7 , making predictions of the impact of multiple stressors compared to a single stressor challenging 8 , 9 . Furthermore, population level responses can vary dramatically because of differences in environmental sensitivity 10 , tolerance among individuals 11 , ecological trade-offs and patterns of local adaptation 12 , 13 . Modelling efforts have demonstrated that some of the main drivers of global change (e.g.…”

Recovery Responses of Freshwater Phytoplankton Assemblage After the Disappearance of Metal Toxicity in Semi-Continuous Cultures

“…Greater metal tolerance of these two species together with elimination of competing species, that were probably metal sensitive, had possibly led to a very large increase in their populations. Concurrent tolerance of S. opolinensis and C. bioculatum to Cu and Zn may have resulted through multiple tolerance or co-tolerance (Venâncio et al 2016), but which one of the two was operating in these two organisms is di cult to pin point. Laboratory experiments in future can only throw light on the mode of concurrent tolerance to test metals in the present study.…”