Research Department for Limnology, University of Innsbruck, Mondsee, Austria.
J Eukaryot Microbiol. 2023 Jul-Aug;70(4):e12969. doi: 10.1111/jeu.12969. Epub 2023 Mar 14.
Population dynamics of aquatic ciliates are controlled "bottom-up" via food supply and "top-down" by grazing and parasitism. While intrinsic growth rates of ciliates under saturating food conditions have been studied in some detail, mortality rates induced by starvation have received little attention thus far. To this end, we examined the response of three algivorous freshwater ciliate species to starvation using three different optical methods. Two of these methods, i.e. ciliate mortality rates (δ) estimated from (i) numerical response experiments and (ii) the rate of decline (ROD) in cell numbers, investigated the response of the ciliate population using conventional light microscopy. The third method, imaging cytometry using a FlowCAM instrument, monitored single cells during the starvation experiment. Like light microscopy, the FlowCAM approach estimated δ based on ROD in the experimental containers. However, imaging cytometry also measured the relative cellular chlorophyll a content in the ciliates' food vacuoles as a proxy for the nutritional status of the cells. The linear decline of the cellular chl. a yielded an independent estimate of δ that was similar to δ calculated from ROD. Additionally, the FlowCAM measurements revealed a high degree of phenotypic plasticity of the ciliates when exposed to starvation.
浮游纤毛虫的种群动态受食物供应的“自上而下”控制，也受摄食和寄生的“自下而上”控制。虽然已经对在饱和食物条件下纤毛虫的内在增长率进行了一些详细的研究，但迄今为止，对饥饿引起的死亡率关注甚少。为此，我们使用三种不同的光学方法研究了三种食藻性淡水纤毛虫对饥饿的反应。其中两种方法，即（i）通过数值响应实验和（ii）细胞数量的下降率（ROD）估算的纤毛虫死亡率（δ），使用传统的光学显微镜研究了纤毛虫种群的反应。第三种方法，使用 FlowCAM 仪器的图像细胞计数法，在饥饿实验期间监测单个细胞。与光学显微镜一样，FlowCAM 方法基于实验容器中的 ROD 估算 δ。然而，图像细胞计数法还测量了纤毛虫食物泡中的相对细胞叶绿素 a 含量，作为细胞营养状况的替代指标。细胞 chl. a 的线性下降提供了 δ 的独立估计值，与从 ROD 计算出的 δ 相似。此外，FlowCAM 测量结果表明，纤毛虫在暴露于饥饿时表现出高度的表型可塑性。
