Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN 55455, USA.
Proc Natl Acad Sci U S A. 2010 Feb 2;107(5):2082-7. doi: 10.1073/pnas.0912254107. Epub 2010 Jan 19.
Toxins produced by the harmful algal bloom (HAB) forming, mixotrophic dinoflagellate Karlodinium veneficum have long been associated with fish kills. To date, the perceived ecological role for toxins has been relief from grazing pressures. Here, we demonstrate that karlotoxins also serve as a predation instrument. Using high-speed holographic microscopy, we measure the swimming behavior of several toxic and nontoxic strains of K. veneficum and their prey, Storeatula major, within dense suspensions. The selected strains produce toxins with varying potency and dosages, including a nontoxic one. Results clearly show that mixing the prey with the predatory, toxic strains causes prey immobilization at rates that are consistent with the karlotoxins' potency and dosage. Even prey cells that continue swimming slow down after exposure to toxic predators. The swimming characteristics of predators vary substantially in pure suspensions, as quantified by their velocity, radii of helical trajectories, and direction of helical rotation. When mixed with prey, all toxic strains that are involved in predation slow down. Furthermore, they substantially reduced their predominantly vertical migration, presumably to remain in the vicinity of their prey. Conversely, the nontoxic control strain does not alter its swimming and does not affect prey behavior. In separate experiments, we show that exposing prey to exogenous toxins also causes prey immobilization at rates consistent with potency. Clearly, the toxic predatory strains use karlotoxins as a means of stunning their prey, before ingesting it. These findings add a substantiated critical understanding for why some HAB species produce such complex toxin molecules.
产毒有害赤潮（HAB）形成的混合营养型甲藻卡尔多尼氏藻（Karlodinium veneficum）产生的毒素长期以来一直与鱼类死亡有关。迄今为止，人们认为毒素的生态作用是减轻放牧压力。在这里，我们证明卡尔多毒素也可以作为一种捕食工具。我们使用高速全息显微镜，在密集的悬浮液中测量几种有毒和无毒的 K. veneficum 菌株及其猎物 Storetula major 的游泳行为。所选菌株产生具有不同效力和剂量的毒素，包括一种无毒的毒素。结果清楚地表明，将猎物与具有毒性的捕食者混合会导致猎物以与卡尔多毒素的效力和剂量一致的速度被固定。即使是接触有毒捕食者后继续游动的猎物细胞，游动速度也会减慢。在纯悬浮液中，捕食者的游泳特性有很大差异，这可以通过它们的速度、螺旋轨迹的半径和螺旋旋转的方向来量化。当与猎物混合时，所有参与捕食的有毒菌株都会减速。此外，它们大大减少了它们主要的垂直迁移，大概是为了留在猎物附近。相反，无毒的对照菌株不会改变其游动方式，也不会影响猎物的行为。在单独的实验中，我们表明，将猎物暴露于外源性毒素也会导致猎物以与效力一致的速度被固定。显然，有毒的捕食性菌株在摄入猎物之前会用卡尔多毒素使猎物昏迷。这些发现为为什么一些 HAB 物种会产生如此复杂的毒素分子提供了一个合理的关键理解。
