团藻属绿藻植物是研究从单细胞到多细胞生命形式转变的一种模型。科学家报告说，它从祖先那里分化的年代远远早于此前所认为的。团藻属及其亲缘物种组成的“团藻”显示出了一大批合作性质的结合——从嵌入到一个粘性基质上的4个细胞到由5万个细胞组成的球形的、由鞭毛推动的团藻。此前的研究确定了团藻的分化时间是在大约5000万年到7500万年前，但是这个结果是根据单个基因以及单个化石的校正。
Matthew Herron及其同事对团藻的演化进行了广泛的研究，利用几种化石校正点和一组叶绿体基因测绘了团藻物种如何分化。根据一项系统发育的计算机分析，这组科学家发现团藻很可能是在2.34亿年前从其他藻类分化出来。到了约2亿年前，这种藻进化出了我们今天看到的大多数主要的适应性。这组作者提出，他们的结果凸显了包括动物的祖先在内的所有多细胞生物起源——从个体细胞变成了复杂的生物体——必须出现的遗传变化的类型。相关论文发表在美国《国家科学院院刊》（PNAS）上。（生物谷Bioon.com）
生物谷推荐原始出处：
PNAS，doi: 10.1073/pnas.0811205106，Matthew D. Herron，Richard E. Michod
Triassic origin and early radiation of multicellular volvocine algae
Matthew D. Herron1, Jeremiah D. Hackett, Frank O. Aylward2 and Richard E. Michod
Department of Ecology and Evolutionary Biology, University of Arizona, 1041 East Lowell Street, Tucson, AZ 85721
Abstract
Evolutionary transitions in individuality (ETIs) underlie the watershed events in the history of life on Earth, including the origins of cells, eukaryotes, plants, animals, and fungi. Each of these events constitutes an increase in the level of complexity, as groups of individuals become individuals in their own right. Among the best-studied ETIs is the origin of multicellularity in the green alga Volvox, a model system for the evolution of multicellularity and cellular differentiation. Since its divergence from unicellular ancestors, Volvox has evolved into a highly integrated multicellular organism with cellular specialization, a complex developmental program, and a high degree of coordination among cells. Remarkably, all of these changes were previously thought to have occurred in the last 50–75 million years. Here we estimate divergence times using a multigene data set with multiple fossil calibrations and use these estimates to infer the times of developmental changes relevant to the evolution of multicellularity. Our results show that Volvox diverged from unicellular ancestors at least 200 million years ago. Two key innovations resulting from an early cycle of cooperation, conflict and conflict mediation led to a rapid integration and radiation of multicellular forms in this group. This is the only ETI for which a detailed timeline has been established, but multilevel selection theory predicts that similar changes must have occurred during other ETIs.
