De novo origins of multicellularity in response to predation

The transition from unicellular to multicellular life was one of a few major events in the history of life that created new opportunities for more complex biological systems to evolve. Predation is hypothesized as one selective pressure that may have driven the evolution of multicellularity. Here we show that de novo origins of simple multicellularity can evolve in response to predation. We subjected outcrossed populations of the unicellular green alga Chlamydomonas reinhardtii to selection by the filter-feeding predator Paramecium tetraurelia. Two of five experimental populations evolved multicellular structures not observed in unselected control populations within ~750 asexual generations. Considerable variation exists in the evolved multicellular life cycles, with both cell number and propagule size varying among isolates. Survival assays show that evolved multicellular traits provide effective protection against predation. These results support the hypothesis that selection imposed by predators may have played a role in some origins of multicellularity.

从单细胞生命向多细胞生命的演化过渡，是生命演化史上为数不多的重大事件之一，为更复杂的生物系统的演化创造了全新机遇。捕食作用被假说为驱动多细胞性演化的选择性压力之一。本研究表明，简单多细胞性的从头起源（de novo）可响应捕食压力而演化产生。我们将单细胞绿藻莱茵衣藻（Chlamydomonas reinhardtii）的异交种群，置于滤食性捕食者草履虫（Paramecium tetraurelia）的选择压力之下。在约750个无性世代内，5个实验种群中的2个演化出了未在未选择的对照种群中出现的多细胞结构。演化得到的多细胞生活史存在显著变异，不同分离株的细胞数量与繁殖体大小均存在差异。存活实验表明，演化出的多细胞性状可有效抵御捕食压力。本研究结果支持这一假说：捕食者施加的选择压力可能在部分多细胞生物的起源过程中发挥了作用。