Predation and the formation of multicellular groups in algae

Background: The evolution of multicellular organisms must, at some point, have involved the congregating of single-celled organisms. Algal species exist that sometimes live in groups and sometimes live as single cells. Understanding the conditions that lead to algal assemblage in such cases may cast light on the selective forces that favour multicellularity. Hypothesis: Forming groups could defend algae against predation if predators are unable to engulf large-sized entities. Organisms: Three algal prey (Chlorella sorokiniana, Chlorella vulgaris, and Scenedesmus obliquus) and three predators (Ochromonas spp., Tetrahymena thermophila, and Daphnia magna). Methods: We tested the tendency to aggregate in all nine different prey–predator combinations. Results: At least two of the predators, Ochromonas and Daphnia, were significant predators because their presence decreased algal density. In all nine combinations, adding the predator species led to the formation of algal groups. In three ...研究背景：多细胞生物的演化历程必然在某一阶段涉及单细胞生物的聚集行为。现有藻类物种既可营群体生活，亦可独立以单细胞形式存活。阐明此类情境下驱动藻类形成集群的条件，可为揭示青睐多细胞化的选择压力提供关键线索。 研究假说：若捕食者无法吞噬大型个体，则藻类形成群体可使其免受捕食胁迫。 实验生物：共3种藻类猎物（椭圆小球藻（Chlorella sorokiniana）、普通小球藻（Chlorella vulgaris）、斜生栅藻（Scenedesmus obliquus））及3种捕食者（色金藻属（Ochromonas spp.）、嗜热四膜虫（Tetrahymena thermophila）、大型溞（Daphnia magna））。 实验方法：针对全部9种不同的猎物-捕食者组合，我们检测了藻类的聚集倾向。 实验结果：至少有2种捕食者——色金藻属与大型溞——为显著捕食者，其存在会显著降低藻类种群密度。在全部9种组合中，引入捕食者均会诱导藻类形成群体。在3种……