Laboratory of Aquatic Ecology, Evolution and Conservation, University of Leuven, Charles Deberiotstraat 32, 3000 Leuven, Belgium.
Laboratory of Aquatic Ecology, Evolution and Conservation, University of Leuven, Charles Deberiotstraat 32, 3000 Leuven, Belgium.
Aquat Toxicol. 2015 Feb;159:176-83. doi: 10.1016/j.aquatox.2014.12.016. Epub 2014 Dec 19.
Although Daphnia magna is a key species in many lentic freshwater ecosystems and is commonly used as model organism in ecology and ecotoxicology, very little is known about the effects of chemicals on their dormant life stages. Dormant eggs (ephippia) are produced when environmental conditions deteriorate, and Daphnia switch from clonal to sexual reproduction. Ephippia produced over different growing seasons can accumulate in the sediment of ponds and lakes, where they can be exposed to pesticides and other (anthropogenic) stressors. In the present study, we have investigated the effects of pesticide exposure on dormant eggs at different embryonic developmental stages and evaluated the degree of protection against pollution provided by the ephippial case. We therefore conducted a hatching experiment in which decapsulated and encapsulated dormant eggs were exposed to an insect growth regulator (fenoxycarb) at different stages during their development, both before and after activation of the eggs. In addition, we developed an analytical method to measure fenoxycarb concentrations in the dormant eggs. Fenoxycarb negatively affected development and hatching success and changed the timing of hatching in activated and in dormant eggs. Hatching characteristics as well as fenoxycarb concentrations inside the eggs differed significantly between exposure treatments. Final stages of embryonic development were most sensitive to pesticide exposure and had the highest tissue concentrations of fenoxycarb. Tissue concentrations did not differ significantly between decapsulated and encapsulated eggs, suggesting that the ephippial case offers limited or no direct protection against pesticide exposure. With this study we provide new evidence showing that pesticides can bioconcentrate in and affect D. magna dormant eggs. The severity of the effects on developing embryos depends on the timing of pesticide exposure. Our results stress the importance of considering the full life-cycle of model organisms used in ecotoxicological studies, since these are ultimately aimed at assessing risks of chemical exposure on natural aquatic ecosystems.
尽管大型溞是许多淡水湖泊生态系统中的关键物种，并且通常被用作生态学和生态毒理学的模式生物，但对于化学物质对其休眠生命阶段的影响知之甚少。当环境条件恶化时，大型溞会从无性繁殖转变为有性繁殖，并产生休眠卵（休眠卵）。在不同的生长季节产生的休眠卵会在池塘和湖泊的沉积物中积累，在那里它们可能会暴露于农药和其他（人为）胁迫源中。在本研究中，我们研究了农药暴露对不同胚胎发育阶段休眠卵的影响，并评估了休眠卵壳提供的防污染程度。因此，我们进行了孵化实验，其中在休眠卵发育的不同阶段，在卵激活之前和之后，对去壳和包裹的休眠卵暴露于昆虫生长调节剂（fenoxycarb）。此外，我们开发了一种分析方法来测量休眠卵中的 fenoxycarb 浓度。fenoxycarb 对发育和孵化成功率产生负面影响，并改变了激活和休眠卵的孵化时间。孵化特征以及休眠卵内的 fenoxycarb 浓度在暴露处理之间存在显著差异。胚胎发育的最后阶段对农药暴露最敏感，组织中的 fenoxycarb 浓度最高。去壳和包裹的卵之间的组织浓度没有显著差异，这表明休眠卵壳提供的直接保护作用有限或没有。通过这项研究，我们提供了新的证据，表明农药可以在大型溞休眠卵内浓缩并影响其发育。对发育中胚胎的影响的严重程度取决于农药暴露的时间。我们的研究结果强调了在生态毒理学研究中考虑模型生物的整个生命周期的重要性，因为这些研究最终旨在评估化学物质暴露对自然水生生态系统的风险。
