Xia Yun, Yuan Xiuyun, Luo Wei, Yuan Siqi, Zeng Xiaomao
Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China.
College of Computer Science, Sichuan University, Chengdu, China.
Front Genet. 2020 Jan 21;10:1364. doi: 10.3389/fgene.2019.01364. eCollection 2019.
Chromosomal rearrangements have long fascinated evolutionary biologists for being widely implicated in causing genetic differentiation. Suppressed recombination has been demonstrated in various species with inversion; however, there is controversy over whether such recombination suppression would facilitate divergence in reciprocal translocation with reduced fitness. In this study, we used the spiny frog, , whose western Sichuan Basin populations exhibit translocation polymorphisms, to test whether the genetic markers on translocated (rearranged) or normal chromosomes have driven this genetic differentiation. We also investigated its overall genetic structure and the possibility of chromosomal fixation. Whole-chromosome painting and genetic structure clustering suggested a single origin of the translocation polymorphisms, and high-throughput sequencing of rearranged chromosomes isolated many markers with known localizations on chromosomes. Using these markers, distinct patterns of gene flow were found between rearranged and normal chromosomes. Genetic differentiation was only found in the translocated chromosomes, not in normal chromosomes or the mitochondrial genome. Hybrid unfitness cannot explain the genetic differentiation, as then the differentiation would be observed throughout the whole genome. Our results suggest that suppressed recombination drives genetic differentiation into a balanced chromosomal polymorphism. Mapping to a reference genome, we found that the region of genetic differentiation covered a wide range of translocated chromosomes, not only in the vicinity of chromosomal breakpoints. Our results imply that the suppressed recombination region could be extended by accumulation of repetitive sequences or capture of alleles that are adapted to the local environment, following the spread and/or fixation of chromosomal rearrangement.
染色体重排长期以来一直吸引着进化生物学家，因为它被广泛认为与导致遗传分化有关。在各种具有倒位的物种中都已证明存在重组抑制现象；然而，对于这种重组抑制是否会促进适应性降低的相互易位中的分化，存在争议。在本研究中，我们使用了棘蛙，其四川盆地西部种群表现出易位多态性，以测试易位（重排）染色体或正常染色体上的遗传标记是否驱动了这种遗传分化。我们还研究了其整体遗传结构以及染色体固定的可能性。全染色体涂染和遗传结构聚类表明易位多态性有单一起源，并且对重排染色体的高通量测序分离出了许多在染色体上具有已知定位的标记。使用这些标记，在重排染色体和正常染色体之间发现了不同的基因流模式。遗传分化仅在易位染色体中发现，而在正常染色体或线粒体基因组中未发现。杂种不适应性无法解释这种遗传分化，因为那样的话在整个基因组中都会观察到分化。我们的结果表明，重组抑制将遗传分化驱动为一种平衡的染色体重多态性。通过与参考基因组比对，我们发现遗传分化区域覆盖了广泛的易位染色体，而不仅仅是在染色体断点附近。我们的结果意味着，随着染色体重排的传播和/或固定，抑制重组区域可能会因重复序列的积累或适应当地环境的等位基因的捕获而扩展。
