title: Herbicides interfere with antigrazer defenses in Scenedesmus obliquus.
abstract: The extensive application of herbicides has led to a serious threat of herbicide contamination to aquatic ecosystem. Herbicide exposure affects aquatic communities not only by exerting toxicity on single species but also by changing interspecific interactions. This study investigated the antigrazer defenses of the common green alga Scenedesmus obliquus against different herbicides [glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D), and atrazine] at various concentrations (0-2.0 mg L(-1)). In the presence of grazer (Daphnia)-derived cues, S. obliquus populations without herbicides formed high proportions of multicelled (e.g., four- and eight-celled) colonies. This result confirms that S. obliquus exhibits a morphological defense against grazing risk. At the low concentration range of 0.002-0.02 mg L(-1), the three herbicides exerted no influence on the growth and photosynthetic efficiency of S. obliquus, and multicelled colonies showed constant proportions. At the high concentration range of 0.20-2.0 mg L(-1), atrazine significantly inhibited the algal growth and photosynthesis whereas glyphosate or 2,4-D did not. Nonetheless, these levels of glyphosate or 2,4-D remarkably decreased the proportion of multicelled colonies, with reduced numbers of cells per particle in Daphnia filtrate-treated population. No eight-celled colony was formed after treatment with atrazine at 0.20-2.0 mg L(-1) despite the addition of Daphnia filtrate. These results suggest that herbicide exposure impairs antigrazer colonial morphs in phytoplankton although it is not sufficient to hamper algal growth. This phenomenon can increase the risk of predation by herbivores, thereby disrupting the inducible phytoplankton community. Furthermore, the predator-prey interactions between herbivores and phytoplankton can be potentially changed more seriously than previously considered.
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors: Xuexia
authors: X
authors: Zhu
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors: Yunfei
authors: Y
authors: Sun
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors: Xingxing
authors: X
authors: Zhang
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors: Hailu
authors: H
authors: Heng
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors: Haihong
authors: H
authors: Nan
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China.
authors: Lu
authors: L
authors: Zhang
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China. Electronic address: huangyuan@njnu.edu.cn.
authors: Yuan
authors: Y
authors: Huang
authors: Jiangsu Key Laboratory for Biodiversity and Biotechnology, School of Biological Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023, China. Electronic address: yangzhou@njnu.edu.cn.
authors: Zhou
authors: Z
authors: Yang
mesh_terms: D000818:Animals; D001673:Biodegradation, Environmental; D003621:Daphnia / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D017753:Ecosystem; D006540:Herbicides / Q000302:isolation & purification / Q000378:metabolism / Q000633:toxicity*; D010788:Photosynthesis / Q000187:drug effects; D044444:Scenedesmus / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification / Q000378:metabolism / Q000633:toxicity*
chemical_list: D006540:Herbicides; D014874:Water Pollutants, Chemical
keywords: Colony formation; Herbicide; Morphological defense; Photosynthetic efficiency; Scenedesmus obliquus