Genome structural variations within species are rare. How selective constraints preserve gene order and chromosome structure is a central question in evolutionary biology that remains unsolved. Our sequencing of several genomes of the appendicularian tunicate Oikopleura dioica around the globe reveals extreme genome scrambling caused by thousands of chromosomal rearrangements, although showing no obvious morphological differences between these animals. The breakpoint accumulation rate is an order of magnitude higher than in ascidian tunicates, nematodes, Drosophila, or mammals. Chromosome arms and sex-specific regions appear to be the primary unit of macrosynteny conservation. At the microsyntenic level, scrambling did not preserve operon structures, suggesting an absence of selective pressure to maintain them. The uncoupling of the genome scrambling with morphological conservation in O. dioica suggests the presence of previously unnoticed cryptic species and provides a new biological system that challenges our previous vision of speciation in which similar animals always share similar genome structures.

中文翻译：

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海洋浮游 Oikopleura dioica 隐秘物种的极端基因组扰乱

物种内的基因组结构变异很少见。选择性约束如何保持基因顺序和染色体结构是进化生物学中尚未解决的一个核心问题。我们对全球范围内的被囊动物Oikopleura dioica的几个基因组进行测序，揭示了由数千次染色体重排引起的极端基因组混乱，尽管这些动物之间没有明显的形态差异。断点积累率比海鞘类被囊动物、线虫、果蝇或哺乳动物高一个数量级。染色体臂和性别特异性区域似乎是大同线性保守的主要单位。在微同线水平上，扰乱并没有保留操纵子结构，表明不存在维持它们的选择压力。O. dioica基因组混乱与形态保守的解耦表明存在以前未被注意到的神秘物种，并提供了一个新的生物系统，挑战了我们之前对物种形成的看法，即相似的动物总是共享相似的基因组结构。