Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, 95616 CA, USA.
Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, 95616 CA, USA; Department of Biology, University of Namur, de Bruxelles 61, B-5000, Namur, Belgium.
Aquat Toxicol. 2020 Nov;228:105611. doi: 10.1016/j.aquatox.2020.105611. Epub 2020 Sep 3.
Bifenthrin is a pyrethroid insecticide commonly used in agricultural and urban sectors, and is found in watersheds worldwide. As a sodium channel blocker, at sublethal concentrations it causes off-target effects, including disruption of calcium signaling and neuronal growth. At the whole organism level, sublethal concentrations of bifenthrin cause behavioral effects in fish species, raising concerns about the neurotoxic properties of the compound on fish populations. Here we describe the application of a high-throughput behavioral system to evaluate contaminant impacts on the sensitive early-life stages of Delta smelt (Hypomesus transpacificus), a critically endangered teleost species endemic to the San Francisco Bay Delta (SFBD), California, USA. Leveraging the natural behavior of early-larval Delta smelt, whereby they increase movement in bright light and decrease movement in the dark, we developed a test using a cycle of light and dark periods in a closed chamber to test hyper- or hypoactivity for this species. We show that early-larval Delta smelt have a significant preference to move toward light, and utilized the behavioral test to evaluate the impact of exposure to bifenthrin at concentrations found in habitats where Delta smelt reportedly spawn, ranging up to concentrations detected in tributaries to these habitats. All tested concentrations of bifenthrin (nominal 2, 10, or 100 ng/L) caused hyperactivity, over a 96 h exposure, with noted significance determined during the light period of the test. To further understand the impact of bifenthrin exposure, expression of a suite of genes relevant to neurodevelopment, the mechanistic target of rapamycin (mTOR) signaling pathway, and biotransformation in exposed larvae were also measured. Following exposure to picomolar concentrations of bifenthrin, expression of genes in the mTOR signaling and neurogenesis pathways were altered alongside behavior. This study demonstrates how light and dark cycle behavioral tests can be used to assess sensitive alterations in swimming activity in Delta smelt at early developmental stages and how gene expression can complement these assays. This approach can be used to assess the impact of multiple compounds that occur within the restricted habitat of Delta smelt, thus having the potential to greatly inform conservation management strategies for this critically sensitive life stage.
联苯菊酯是一种常用于农业和城市领域的拟除虫菊酯杀虫剂，在世界各地的水域中都有发现。作为一种钠离子通道阻断剂，在亚致死浓度下，它会产生非靶标效应，包括破坏钙信号和神经元生长。在整个生物体水平上，亚致死浓度的联苯菊酯会导致鱼类物种的行为效应，引起人们对联苯菊酯化合物对鱼类种群的神经毒性的关注。在这里，我们描述了一种高通量行为系统的应用，该系统用于评估污染物对尖鼻白鲑（Hypomesus transpacificus）早期生命阶段的影响，尖鼻白鲑是一种极度濒危的、原产于美国加利福尼亚州旧金山湾三角洲（SFBD）的硬骨鱼。利用尖鼻白鲑早期幼虫的自然行为，即在明亮的光线下增加运动，在黑暗中减少运动，我们开发了一种在封闭室中使用光暗周期循环的测试方法，以测试该物种的过度或活动不足。我们表明，早期幼虫尖鼻白鲑有向光移动的显著偏好，并利用行为测试来评估在尖鼻白鲑据报道产卵的栖息地中发现的浓度下暴露于联苯菊酯的影响，浓度范围高达这些栖息地支流中检测到的浓度。所有测试浓度的联苯菊酯（名义上为 2、10 或 100ng/L）在 96 小时暴露期间都会导致过度活跃，在测试的光期确定了显著意义。为了进一步了解联苯菊酯暴露的影响，还测量了暴露幼虫中与神经发育、雷帕霉素（mTOR）信号通路的机制靶点和生物转化相关的一套基因的表达。在暴露于皮摩尔浓度的联苯菊酯后，mTOR 信号和神经发生途径中的基因表达与行为一起发生改变。这项研究表明，光暗周期行为测试如何可用于评估早期发育阶段尖鼻白鲑游泳活动的敏感变化，以及基因表达如何补充这些测定。这种方法可用于评估在尖鼻白鲑受限栖息地中存在的多种化合物的影响，从而有可能极大地为这一极度敏感的生命阶段的保护管理策略提供信息。
