Data from: Multicellular group formation in response to predators in the alga Chlorella vulgaris

A key step in the evolution of multicellular organisms is the formation of cooperative multicellular groups. It has been suggested that predation pressure may promote multicellular group formation in some algae and bacteria, with cells forming groups to lower their chance of being eaten. We use the green alga Chlorella vulgaris and the protist Tetrahymena thermophila to test whether predation pressure can initiate the formation of colonies. We found that: (1) either predators or just predator exoproducts promote colony formation; (2) higher predator densities cause more colonies to form and (3) colony formation in this system is facultative, with populations returning to being unicellular when the predation pressure is removed. These results provide empirical support for the hypothesis that predation pressure promotes multicellular group formation. The speed of the reversion of populations to unicellularity suggests that this response is due to phenotypic plasticity and not evolutionary change.多细胞生物演化进程中的核心环节之一是合作型多细胞群体的形成。已有假说提出，捕食压力可推动部分藻类与细菌形成多细胞群体，细胞通过聚集为群体以降低被捕食的风险。本研究以普通小球藻（Chlorella vulgaris）与嗜热四膜虫（Tetrahymena thermophila）为实验对象，旨在验证捕食压力是否能够诱发菌落形成。研究结果表明：（1）无论是捕食者本身，还是仅捕食者的外分泌产物，均可促进菌落形成；（2）捕食者密度越高，菌落形成的数量越多；（3）该实验体系中的菌落形成属于兼性过程——当捕食压力解除后，种群可恢复为单细胞状态。上述结果为"捕食压力推动多细胞群体形成"这一假说提供了实证支持。种群恢复为单细胞状态的速率表明，该响应源于表型可塑性（phenotypic plasticity）而非进化改变。