團(tuán)藻屬綠藻植物是研究從單細(xì)胞到多細(xì)胞生命形式轉(zhuǎn)變的一種模型,。科學(xué)家報(bào)告說,，它從祖先那里分化的年代遠(yuǎn)遠(yuǎn)早于此前所認(rèn)為的,。團(tuán)藻屬及其親緣物種組成的“團(tuán)藻”顯示出了一大批合作性質(zhì)的結(jié)合——從嵌入到一個(gè)粘性基質(zhì)上的4個(gè)細(xì)胞到由5萬個(gè)細(xì)胞組成的球形的、由鞭毛推動(dòng)的團(tuán)藻,。此前的研究確定了團(tuán)藻的分化時(shí)間是在大約5000萬年到7500萬年前,，但是這個(gè)結(jié)果是根據(jù)單個(gè)基因以及單個(gè)化石的校正。
Matthew Herron及其同事對(duì)團(tuán)藻的演化進(jìn)行了廣泛的研究,，利用幾種化石校正點(diǎn)和一組葉綠體基因測(cè)繪了團(tuán)藻物種如何分化,。根據(jù)一項(xiàng)系統(tǒng)發(fā)育的計(jì)算機(jī)分析，這組科學(xué)家發(fā)現(xiàn)團(tuán)藻很可能是在2.34億年前從其他藻類分化出來,。到了約2億年前,，這種藻進(jìn)化出了我們今天看到的大多數(shù)主要的適應(yīng)性。這組作者提出,，他們的結(jié)果凸顯了包括動(dòng)物的祖先在內(nèi)的所有多細(xì)胞生物起源——從個(gè)體細(xì)胞變成了復(fù)雜的生物體——必須出現(xiàn)的遺傳變化的類型,。相關(guān)論文發(fā)表在美國(guó)《國(guó)家科學(xué)院院刊》（PNAS）上。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
