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arXiv 1604.06299q-bio.PE
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小型和大型数字生物种群复杂性的不同进化路径

Different evolutionary paths to complexity for small and large populations of digital organisms

Thomas LaBar, Christoph Adami

摘要:

进化生物学的一个主要目的是解释适应性变化和非适应性变化在复杂性进化中各自的作用。虽然选择当然是复杂表型的传播和维持的原因,但这并不意味着强选择增加了新性状出现的机会,也就是说,复杂性的起源。种群规模是改变适应性和非适应性过程相对重要性的一个参数:随着种群规模的减小,选择减弱,遗传漂变的重要性增加。由于这种关系,许多理论援引人口规模在复杂性进化中的作用。由于生物种群复杂性的进化需要时间,这些理论很难进行经验检验。在这里,我们使用数字实验进化来测试大型或小型无性种群是否倾向于进化出更大的复杂性。我们发现,无论是小的和大的-但不是中等大小-人口有利于进化更大的基因组,这为随后增加表型复杂性提供了机会。然而,小型和大型种群遵循不同的进化路径,以这些新的特征。小种群通过固定稍微有害的插入进化出更大的基因组,而大种群固定罕见的有益插入,增加基因组大小。这些结果表明,遗传漂变可以导致小种群的复杂性进化,而纯化选择不足以阻止大种群复杂性的进化。

英文摘要:

A major aim of evolutionary biology is to explain the respective roles of adaptive versus non-adaptive changes in the evolution of complexity. While selection is certainly responsible for the spread and maintenance of complex phenotypes, this does not automatically imply that strong selection enhances the chance for the emergence of novel traits, that is, the origination of complexity. Population size is one parameter that alters the relative importance of adaptive and non-adaptive processes: as population size decreases, selection weakens and genetic drift grows in importance. Because of this relationship, many theories invoke a role for population size in the evolution of complexity. Such theories are difficult to test empirically because of the time required for the evolution of complexity in biological populations. Here, we used digital experimental evolution to test whether large or small asexual populations tend to evolve greater complexity. We find that both small and large---but not intermediate-sized---populations are favored to evolve larger genomes, which provides the opportunity for subsequent increases in phenotypic complexity. However, small and large populations followed different evolutionary paths towards these novel traits. Small populations evolved larger genomes by fixing slightly deleterious insertions, while large populations fixed rare beneficial insertions that increased genome size. These results demonstrate that genetic drift can lead to the evolution of complexity in small populations and that purifying selection is not powerful enough to prevent the evolution of complexity in large populations.

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