All multicellular organisms are genetic mosaics owing to somatic mutations. The accumulation of somatic genetic variation in clonal species undergoing asexual (or clonal) reproduction may lead to phenotypic heterogeneity among autonomous modules (termed ramets). However, the abundance and dynamics of somatic genetic variation under clonal reproduction remain poorly understood. Here we show that branching events in a seagrass (Zostera marina) clone or genet lead to population bottlenecks of tissue that result in the evolution of genetically differentiated ramets in a process of somatic genetic drift. By studying inter-ramet somatic genetic variation, we uncovered thousands of single nucleotide polymorphisms that segregated among ramets. Ultra-deep resequencing of single ramets revealed that the strength of purifying selection on mosaic genetic variation was greater within than among ramets. Our study provides evidence for multiple levels of selection during the evolution of seagrass genets. Somatic genetic drift during clonal propagation leads to the emergence of genetically unique modules that constitute an elementary level of selection and individuality in long-lived clonal species.

中文翻译：

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克隆海草中的体细胞遗传漂移和多级选择。

由于体细胞突变，所有多细胞生物都是遗传镶嵌。在经历无性（或克隆）繁殖的克隆物种中，体细胞遗传变异的积累可能导致自主模块（称为分株）之间的表型异质性。然而，克隆繁殖下体细胞遗传变异的丰富性和动态性仍然知之甚少。在这里，我们表明海草（Zostera滨海）克隆或种系中的分支事件导致组织的种群瓶颈，从而导致体细胞遗传漂移过程中基因分化的分株的进化。通过研究分株间的体细胞遗传变异，我们发现了分株之间成千上万的单核苷酸多态性。单个分株的超深度重测序表明，在镶嵌遗传变异上纯化选择的强度比在分株中高。我们的研究为海草种系进化过程中多种选择水平提供了证据。克隆繁殖过程中的体细胞遗传漂移导致遗传上独特的模块的出现，这些模块构成了长寿命克隆物种中选择和个体化的基本水平。