Data from: Tracking changes in chromosomal arrangements and their genetic content during adaptation

There is considerable evidence for an adaptive role of inversions, but how their genetic content evolves and affects the subsequent evolution of chromosomal polymorphism remains controversial. Here, we track how life-history traits, chromosomal arrangements and 22 microsatellites, within and outside inversions, change in three replicated populations of Drosophila subobscura for 30 generations of laboratory evolution since founding from the wild. The dynamics of fitness-related traits indicated adaptation to the new environment concomitant with directional evolution of chromosomal polymorphism. Evidence of selective changes in frequency of inversions was obtained for seven of 23 chromosomal arrangements, corroborating a role for inversions in adaptation. The evolution of linkage disequilibrium between some microsatellites and chromosomes suggested that adaptive changes in arrangements involved changes in their genetic content. Several microsatellite alleles increased in frequency more than expected by drift in targeted inversions in all replicate populations. In particular, there were signs of selection in the O3+4 arrangement favouring a combination of alleles in two loci linked to the inversion and changing along with it, although the lack of linkage disequilibrium between these loci precludes epistatic selection. Seven other alleles increased in frequency within inversions more than expected by drift, but were not in linkage disequilibrium with them. Possibly these alleles were hitchhiking along with alleles under selection that were not specific to those inversions. Overall, the selection detected on the genetic content of inversions, despite limited coverage of the genome, suggests that genetic changes within inversions play an important role in adaptation.

已有大量证据表明染色体倒位（inversion）具有适应性功能，但其携带的遗传物质如何演化，以及如何影响后续的染色体多态性演化，这一问题仍存在争议。本研究对3个由野生个体建立起始种群的重复亚暗果蝇（Drosophila subobscura）实验种群开展了30代实验室演化追踪，测定了倒位内部与倒位外部的生活史性状、染色体构型以及22个微卫星标记（microsatellite）的频率变化。与适合度相关的性状动态显示，种群在适应新环境的同时，染色体多态性也发生了定向演化。在23个染色体构型中，有7个出现了倒位频率的选择性变化，这证实了倒位在适应性演化中发挥的作用。部分微卫星标记与染色体之间的连锁不平衡（linkage disequilibrium）演化结果表明，染色体构型的适应性变化与其携带的遗传物质改变密切相关。在所有重复种群的目标倒位中，多个微卫星等位基因的频率增幅超出了遗传漂变的预期水平。具体而言，O3+4染色体构型中存在选择信号，倾向于保留与该倒位连锁的两个位点的等位基因组合，并随倒位一同发生频率变化；不过这两个位点之间未检测到连锁不平衡，因此排除了上位性选择的可能性。另有7个等位基因在倒位内的频率增幅同样超出漂变预期，但未与倒位表现出连锁不平衡。这类等位基因可能通过搭乘未针对特定倒位的受选择等位基因而实现频率上升，即遗传搭车效应（hitchhiking effect）。总体而言，尽管本研究对基因组的覆盖范围有限，但在倒位的遗传物质中检测到的选择作用表明，倒位内部的遗传改变在适应性演化中扮演了重要角色。