Ecology, Evolution and Behavior and The BioTechnology Institute; University of Minnesota, Minneapolis, MN 55108, USA.
Evolution. 2013 Jun;67(6):1573-81. doi: 10.1111/evo.12101. Epub 2013 Apr 9.
Multicellular complexity is a central topic in biology, but the evolutionary processes underlying its origin are difficult to study and remain poorly understood. Here we use experimental evolution to investigate the tempo and mode of multicellular adaptation during a de novo evolutionary transition to multicellularity. Multicelled "snowflake" yeast evolved from a unicellular ancestor after 7 days of selection for faster settling through liquid media. Over the next 220 days, snowflake yeast evolved to settle 44% more quickly. Throughout the experiment the clusters evolved faster settling by three distinct modes. The number of cells per cluster increased from a mean of 42 cells after 7 days of selection to 114 cells after 227 days. Between days 28 and 65, larger clusters evolved via a twofold increase in the mass of individual cells. By day 227, snowflake yeast evolved to form more hydrodynamic clusters that settle more quickly for their size than ancestral strains. The timing and nature of adaptation in our experiment suggests that costs associated with large cluster size favor novel multicellular adaptations, increasing organismal complexity.
多细胞复杂性是生物学的一个核心课题，但它的起源所涉及的进化过程难以研究，人们对此仍然知之甚少。在这里，我们利用实验进化来研究从头开始向多细胞生物进化过程中多细胞适应性的速度和模式。多细胞的“雪花”酵母是从单细胞祖先进化而来的，经过 7 天的选择，以更快地在液体介质中沉淀。在接下来的 220 天里，雪花酵母的沉淀速度提高了 44%。在整个实验过程中，通过三种不同的模式，集群以更快的速度进化。每个集群的细胞数量从选择后 7 天的平均 42 个细胞增加到 227 天后的 114 个细胞。在第 28 天到第 65 天之间，个体细胞的质量增加了一倍，从而使更大的集群进化。到第 227 天，雪花酵母进化形成了更具流体动力的集群，这些集群相对于原始菌株而言，其大小的沉淀速度更快。我们实验中的适应时间和性质表明，与大集群大小相关的成本有利于新的多细胞适应，从而增加了生物复杂性。
