Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium.
Aquat Toxicol. 2013 Sep 15;140-141:425-31. doi: 10.1016/j.aquatox.2013.07.005. Epub 2013 Jul 18.
Interactive effects between chemical and natural stressors as well as genetically determined variation in stress tolerance among individuals may complicate risk assessment and management of chemical pollutants in natural ecosystems. Although genetic variation in tolerance to single stressors has been described extensively, genetic variation in interactive effects between two stressors has only rarely been investigated. Here, we examined the interactive effects between a chemical stressor (Cd) and a natural stressor (the cyanobacteria Microcystis aeruginosa) on the reproduction of Daphnia magna in 20 genetically different clones using a full-factorial experimental design and with the independent action model of joint stressor action as the reference theoretical framework. Across all clones, the reduction of 21-day reproduction compared to the control treatment (no Cd, no M. aeruginosa) ranged from -10% to 98% following Cd exposure alone, from 44% to 89% for Microcystis exposure alone, and from 61% to 98% after exposure to Cd+Microcystis combined. Three-way ANOVA on log-transformed reproduction data of all clones together did not detect a statistically significant Cd×Microcystis interaction term (F-test, p=0.11), meaning that on average both stressors do not interact in inhibiting reproductive performance of D. magna. This finding contrasted expectations based on some known shared mechanisms of toxicity of Cd and Microcystis and therefore cautions against making predictions of interactive chemical+natural stressor effects from incomplete knowledge on affected biological processes and pathways. Further, still based on three-way ANOVA, we did not find statistically significant clone×Cd×Microcystis interaction when data for all clones were analyzed together (F-test, p=0.07), suggesting no inter-clonal variation of the interactive effect between Cd and Microcystis. However, when the same data were quantitatively analyzed on a clone-by-clone scale, we found a relatively wide range of deviations between observed and IA-model-predicted reproduction in combined Cd+Microcystis treatments (both in direction and magnitude), suggesting some biological significance of inter-clonal variation of interactive effects. In one of the twenty clones this deviation was statistically significant (two-way ANOVA, F-test, p=0.005), indicating an interactive Cd×Microcystis effect in this clone. Together, these two observations caution against the extrapolation of conclusions about mixed stressor data obtained with single clones to the level of the entire species and to the level of natural, genetically diverse populations.
化学和自然胁迫之间的相互作用以及个体对胁迫耐受的遗传决定差异可能会使化学污染物在自然生态系统中的风险评估和管理复杂化。尽管已经广泛描述了单个胁迫因素耐受能力的遗传变异，但两个胁迫因素之间相互作用的遗传变异却很少被研究。在这里，我们使用完全因子实验设计和联合胁迫作用的独立作用模型作为参考理论框架，在 20 个遗传上不同的克隆中，研究了化学胁迫（Cd）和自然胁迫（蓝藻铜绿微囊藻）之间的相互作用对大型溞繁殖的影响。在所有克隆中，与对照处理（无 Cd、无铜绿微囊藻）相比，单独暴露于 Cd 后的 21 天繁殖减少范围为-10%至 98%，单独暴露于铜绿微囊藻时为 44%至 89%，暴露于 Cd+铜绿微囊藻联合时为 61%至 98%。对所有克隆的对数转换繁殖数据进行的三因素方差分析没有检测到统计学上显著的 Cd×铜绿微囊藻相互作用项（F 检验，p=0.11），这意味着这两个胁迫因素平均不会相互作用抑制大型溞的繁殖性能。这一发现与 Cd 和铜绿微囊藻毒性的一些已知共同机制相矛盾，因此警告不要根据对受影响的生物过程和途径的不完全了解来预测化学+自然胁迫因素的相互作用。此外，基于三因素方差分析，当一起分析所有克隆的数据时，我们没有发现统计学上显著的克隆×Cd×铜绿微囊藻相互作用（F 检验，p=0.07），这表明 Cd 和铜绿微囊藻之间的相互作用没有种间变异。然而，当在克隆水平上对相同数据进行定量分析时，我们发现 Cd+铜绿微囊藻联合处理中观察到的繁殖与 IA 模型预测的繁殖之间存在相当大的偏差（无论是在方向还是在幅度上），这表明相互作用的种间变异具有一定的生物学意义。在 20 个克隆中的一个克隆中，这种偏差具有统计学意义（双向方差分析，F 检验，p=0.005），表明该克隆存在 Cd×铜绿微囊藻的相互作用效应。综上所述，这两个观察结果告诫人们不要将从单个克隆获得的混合胁迫数据的结论推断到整个物种的水平以及自然的、遗传多样的种群的水平。
