ABSTRACT Swimming is of vital importance for aquatic organisms because it determines several aspects of fitness, such as encounter rates with food, predators, and mates. Generally, rotifer swimming speed is measured by manual tracking of the swimming paths filmed in videos. Recently, an open-source package has been developed that integrates different open-source software and allows direct processing and analysis of the swimming paths of moving organisms. Here, we filmed groups of females and males of Keratella cochlearis separately and in a mixed experimental setup. We extracted movement trajectories and swimming speeds and applied the classification method random forest to assign sex to individuals of the mixed setup. Finally, we used advanced statistical methods of movement ecology, namely a hidden Markov model, to investigate swimming states of females and males. When not discriminating swimming states, females swam faster than males, while when discriminating states males swam faster. Specifically, females and males showed two main states of movement with many individuals switching between states resulting in four modes of swimming. We suggest that switching between states is related to predator avoidance. Males of K. cochlearis especially exhibited switching between turning in a restricted area and swimming over longer distances. No mating or other male–female interactions were observed. Our study elucidates the steps necessary for automatic analysis of rotifer trajectories with open-source software. Application of sophisticated software and analytical models will broaden our understanding of zooplankton ecology from the individual to the population level.

中文翻译：

---

在轮虫的游泳状态之间切换——案例研究 Keratella cochlearis

摘要 游泳对水生生物至关重要，因为它决定了健康的几个方面，例如与食物、捕食者和配偶的相遇率。通常，轮虫游泳速度是通过手动跟踪视频中拍摄的游泳路径来测量的。最近，开发了一个开源包，它集成了不同的开源软件，可以直接处理和分析移动生物的游动路径。在这里，我们分别在混合实验设置中拍摄了 Keratella cochlearis 的雌性和雄性组。我们提取了运动轨迹和游泳速度，并应用分类方法随机森林为混合设置的个体分配性别。最后，我们使用了运动生态学的先进统计方法，即隐马尔可夫模型，调查女性和男性的游泳状态。在不区分游泳状态时，雌性比雄性游得更快，而在区分状态时，雄性游得更快。具体来说，女性和男性表现出两种主要的运动状态，许多人在状态之间切换，从而形成四种游泳模式。我们建议状态之间的切换与避免捕食者有关。K. cochlearis 的雄性尤其表现出在限制区域内转弯和长距离游泳之间的转换。没有观察到交配或其他雄性-雌性相互作用。我们的研究阐明了使用开源软件自动分析轮虫轨迹所需的步骤。