University of North Carolina Wilmington, Department of Biology and Marine Biology, Wilmington, NC, 28403, USA.
University of Washington, School of Oceanography, Seattle, WA, 98195, USA.
Sci Rep. 2018 Jul 12;8(1):10492. doi: 10.1038/s41598-018-28630-4.
Sexual reproduction roots the eukaryotic tree of life, although its loss occurs across diverse taxa. Asexual reproduction and clonal lineages persist in these taxa despite theoretical arguments suggesting that individual clones should be evolutionarily short-lived due to limited phenotypic diversity. Here, we present quantitative evidence that an obligate asexual lineage emerged from a sexual population of the marine diatom Thalassiosira pseudonana and rapidly expanded throughout the world's oceans. Whole genome comparisons identified two lineages with characteristics expected of sexually reproducing strains in Hardy-Weinberg equilibrium. A third lineage displays genomic signatures for the functional loss of sexual reproduction followed by a recent global colonization by a single ancestral genotype. Extant members of this lineage are genetically differentiated and phenotypically plastic, potentially allowing for rapid adaptation when they are challenged by natural selection. Such mechanisms may be expected to generate new clones within marginal populations of additional unicellular species, facilitating the exploration and colonization of novel environments, aided by exponential growth and ease of dispersal.
有性生殖为真核生物树扎根生命之根，尽管它的丧失发生在不同的类群中。有性生殖和无性系在这些类群中仍然存在，尽管理论上认为，由于表型多样性有限，单个无性系应该在进化上是短暂的。在这里，我们提供了定量证据，证明一种强制性的无性谱系是从海洋硅藻拟菱形藻的有性种群中产生的，并迅速扩展到世界海洋中。全基因组比较确定了两个具有处于哈迪-温伯格平衡中的有性繁殖菌株特征的谱系。第三个谱系显示出性功能丧失的基因组特征，随后是单一祖先基因型的最近全球殖民化。该谱系的现存成员在遗传上存在分化，表型上具有可塑性，当它们受到自然选择的挑战时，可能会允许快速适应。这种机制可能会在其他单细胞物种的边缘种群中产生新的无性系，有助于在指数增长和易于传播的帮助下探索和殖民新环境。
