一項研究報告說,，從單細胞到多細胞的轉變的最初關鍵步驟的進化速度可能比此前認為得更快。
William C. Ratcliff及其同事讓單細胞酵母釀酒酵母（Saccharomyces cerevisiae）生活在一種環(huán)境中，在這種環(huán)境中,，多細胞被認為是一種適應性的性狀,，這是建立在一個事實的基礎上，即酵母細胞集群比單個細胞在液體中的定居速度更快,。在60天的快速定居選擇中,，全部實驗酵母種群都以多個附著細胞的雪花樣集群為主，這是由在細胞分裂之后仍然相互粘著的細胞形成的,。
這種集群顯示出了幾種多細胞性狀,，包括通過產生雪花樣子代集群的多細胞“生殖芽”進行繁殖以及一個幼年階段的出現(xiàn)。當定居選擇的強度發(fā)生變化的時候,，雪花酵母通過在多細胞層次而非單細胞層次上對變化進行了適應,，這表明整個細胞集群作為一個整體進行進化。
這組科研人員還觀察到了集群內部的勞動分工的進化：大多數(shù)細胞仍然活著并能進行繁殖,，但是少部分細胞進行了程序細胞死亡,，或者說細胞凋亡。凋亡的細胞起到了多細胞集群中的斷裂點的作用,，讓雪花酵母調控它們產生的后代的數(shù)量和尺寸,。
這些發(fā)現(xiàn)提示多細胞復雜性的關鍵特性可以在一種單細胞真核細胞中容易地進化出來。(生物谷Bioon.com)
doi: 10.1073/pnas.1115323109
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Experimental evolution of multicellularity
William C. Ratcliffa,1, R. Ford Denisona, Mark Borrelloa, and Michael Travisanoa,b
Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes.
