Data from: Understanding the basis of diminished gene flow between hybridizing chromosome races of the house mouse

Speciation may be promoted in hybrid zones if there is an interruption to gene flow between the hybridizing forms. For hybridizing chromosome races of the house mouse in Valtellina (Italy) distinguished by whole-arm chromosomal rearrangements, previous studies have shown that there is greater interruption to gene flow at the centromeres of chromosomes that differ between the races than at distal regions of the same chromosome or at the centromeres of other chromosomes. Here, by increasing the number of markers along race-specific chromosomes, we reveal a decay in between-race genetic differentiation from the centromere to the distal telomere. For the first time, we use simulation models to investigate the possible role of recombination suppression and hybrid breakdown in generating this pattern. We also consider epistasis and selective sweeps as explanations for isolated chromosomal regions away from the centromere showing differentiation between the races. Hybrid breakdown alone is the simplest explanation for the decay in genetic differentiation with distance from the centromere. Robertsonian fusions/whole-arm reciprocal translocations are common chromosomal rearrangements characterizing both closely related species and races within species, and this fine-scale empirical analysis suggests that the unfitness associated with these rearrangements in the heterozygous state may contribute to the speciation process.

若杂交类群间的基因流（gene flow）受到阻断，杂交带（hybrid zones）内的物种形成（speciation）过程或可得到促进。针对意大利瓦尔泰利纳地区以全臂染色体重排（whole-arm chromosomal rearrangements）相区分的小家鼠（house mouse）杂交染色体宗，既往研究已证实：相较于同染色体的远端区域（distal regions）或其他染色体的着丝粒（centromere），该类群间存在差异的染色体着丝粒处，基因流受到的阻断更为显著。本研究通过提升染色体宗特异性染色体上的标记数量，首次揭示了类群间遗传分化（genetic differentiation）从着丝粒向远端端粒（telomere）逐渐衰减的分布模式。我们首次借助模拟模型（simulation models）探究了重组抑制（recombination suppression）与杂交衰败（hybrid breakdown）在塑造该模式中可能发挥的作用；同时还探讨了上位性（epistasis）与选择性清除（selective sweeps）能否解释着丝粒以外的孤立染色体区域所呈现的类群间分化现象。仅以杂交衰败即可最为简洁地解释遗传分化随距着丝粒距离增加而衰减的规律。罗伯逊融合（Robertsonian fusions）与全臂相互易位（whole-arm reciprocal translocations）是近缘物种及物种内染色体宗共有的常见染色体重排类型，本次精细化的实证分析表明，杂合状态（heterozygous state）下这类重排所引发的适合度降低，或可推动物种形成进程。