Department of Biology, University of Konstanz, Konstanz, Germany.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA.
Mol Biol Evol. 2020 Oct 1;37(10):2825-2837. doi: 10.1093/molbev/msaa118.
Chromosomal evolution is widely considered to be an important driver of speciation, as karyotypic reorganization can bring about the establishment of reproductive barriers between incipient species. One textbook example for genetic mechanisms of speciation are large-scale chromosomal rearrangements such as Robertsonian (Rb) fusions, a common class of structural variants that can drastically change the recombination landscape by suppressing crossing-over and influence gene expression by altering regulatory networks. Here, we explore the population structure and demographic patterns of a well-known house mouse Rb system in the Aeolian archipelago in Southern Italy using genome-wide data. By analyzing chromosomal regions characterized by different levels of recombination, we trace the evolutionary history of a set of Rb chromosomes occurring in different geographical locations and test whether chromosomal fusions have a single shared origin or occurred multiple times. Using a combination of phylogenetic and population genetic approaches, we find support for multiple, independent origins of three focal Rb chromosomes. The elucidation of the demographic patterns of the mouse populations within the Aeolian archipelago shows that an interplay between fixation of newly formed Rb chromosomes and hybridization events has contributed to shaping their current karyotypic distribution. Overall, our results illustrate that chromosome structure is much more dynamic than anticipated and emphasize the importance of large-scale chromosomal translocations in speciation.
染色体进化被广泛认为是物种形成的重要驱动因素，因为染色体组的重新组织可以在初期物种之间建立生殖隔离。大规模染色体重排，如罗伯逊易位（Rb）融合，是物种形成的遗传机制的一个典型例子，它可以通过抑制交叉互换极大地改变重组景观，并通过改变调控网络影响基因表达。在这里，我们利用全基因组数据研究了意大利南部爱奥尼亚群岛上一个著名的家鼠 Rb 系统的种群结构和人口动态模式。通过分析具有不同重组水平的染色体区域，我们追踪了一组发生在不同地理位置的 Rb 染色体的进化历史，并检验了染色体融合是否具有单一的共同起源或多次发生。我们采用系统发育和种群遗传相结合的方法，为三个焦点 Rb 染色体的多次独立起源提供了支持。对爱奥尼亚群岛内的鼠群的人口动态模式的阐明表明，新形成的 Rb 染色体的固定和杂交事件之间的相互作用有助于塑造它们当前的染色体组分布。总的来说，我们的结果表明染色体结构比预期的更加动态，并强调了大规模染色体易位在物种形成中的重要性。
