Multiple stressor effects of predation by rotifers and herbicide pollution on different Chlamydomonas strains and potential impacts on population dynamics

Abstract

Environmental factors can interact with the effects of chemical pollutants on natural systems by inducing multiple stressor effects in individual organisms as well as by altering selection pressure on tolerant strains in heterogeneous populations. Predation is a stressful environmental factor relevant for many species. Therefore, the impact of predation by the rotifer Brachionus calyciflorus on tolerance of eight genetically different strains of the green alga Chlamydomonas reinhardtii to simultaneous exposure to each of the three herbicides (diuron, paraquat, and S-metolachlor) was tested. Interactions of combined stressors were analyzed based on the independent action model; additive, synergistic, and antagonistic effects of the combined exposure could be detected depending on the herbicide and strain tested. If cultures were acclimated (pre-exposed) to one stressor, tolerance to the second stressor could be increased. This indicates that physiological changes can induce cotolerance of predation-exposed algae to herbicides and of herbicide-treated algae to predation depending on the combination of stressors. The strain-specific differences in multiple stressor effects also changed the correlation of strains' tolerances to individual stressors determined during combined and single-stressor exposure. Changes in cotolerance to stressors affect selection pressure and population dynamics during long-term exposure. This shows that predation stress can have adverse effects on the toxicity of chemical pollutants to microalgae on the organism and population levels.

Phenotypic plasticity influences the eco‐evolutionary dynamics of a predator–prey system

“…However, there is also some evidence for the induction of Chlamydomonas defenses in response to rotifer predation (Lurling and Beekman 2006), as is common in other algal species (Van der Stap et al 2006, Van der Stap al. 2009), and strain specificity in the phenotypic response of Chlamydomonas to multiple environmental stressors, including rotifer predation (Fischer et al 2012). Taken together, such previous work suggests that a rotifer-Chlamydomonas model system is useful for experimentally testing how intrapopulation variation in the reaction norms of prey defense traits might affect eco-evolutionary dynamics between predators and their prey.…”

“…Strains and growth conditions.-In a previous study, we documented differences between eight genetically distinct strains of Chlamydomonas reinhardtii in terms of their growth rate and protection against rotifer predation (Fischer et al 2012). For the current study, we selected two unpalatable strains (CC2343, CC2344) and two palatable strains (CC125, CC2342), based on previous feeding experiments (Fischer et al 2012), and quantified variation in three ecologically relevant traits, including growth rate, standing protection (fraction of cells clumped in palmella), and induced defense (induction of the palmelloid phenotype in the presence of rotifers; Table 1). The four strains (CC125, CC2342, CC2343, and CC2344 from the Chlamydomonas Resource Center, St. Paul, Minnesota, USA) and a clonal population of the rotifer Brachionus calyciflorus Pallas (Florida Aqua Farms, Dade City, Florida, USA) were cultured in Talaquil media as described in Fischer et al (2012).…”

“…For the current study, we selected two unpalatable strains (CC2343, CC2344) and two palatable strains (CC125, CC2342), based on previous feeding experiments (Fischer et al 2012), and quantified variation in three ecologically relevant traits, including growth rate, standing protection (fraction of cells clumped in palmella), and induced defense (induction of the palmelloid phenotype in the presence of rotifers; Table 1). The four strains (CC125, CC2342, CC2343, and CC2344 from the Chlamydomonas Resource Center, St. Paul, Minnesota, USA) and a clonal population of the rotifer Brachionus calyciflorus Pallas (Florida Aqua Farms, Dade City, Florida, USA) were cultured in Talaquil media as described in Fischer et al (2012). To measure growth rates of the individual algal strains we incubated them in 100 mL of fresh Talaquil media at a concentration of 2 3 10 5 cells/mL.…”

Peer Review #1 of "An affordable and automated imaging approach to acquire highly resolved individual data—an example of copepod growth in response to multiple stressors (v0.1)"

“…Most studies on mixture toxicity and multiple stressors focus either on interactive effects of two toxicants, or one pollutant in interaction with changes in the physical environment (Gunderson, Armstrong, and Stillman 2016). The effects of combined stressor exposures range from synergistic to antagonistic when compared to single stressor exposure (Rose et al 2001, Fischer et al 2012Holmstrup et al 2010), and the scales and timing of response differ widely, rendering it challenging to predict the outcome of additional stressors (e.g. Segner et al 2014).…”

Brief communication: The ecosystem perspective in ecotoxicology as a way forward for the ecological risk assessment of chemicals

“…Effects of predation and chemicals are not by definition additive or synergistic but can also be antagonistic, and acclimation to one of both stressors increases the tolerance against the other stressor, as shown for herbicides (Fischer et al ). Also, nonspecific predation (“culling”) can help to maintain genetic diversity in metal‐exposed Daphnia longispina (Lopes et al ).…”