Data from: Sharp genetic discontinuity across a unimodal Heliconius hybrid zone

Hybrid zones are powerful natural systems to study evolutionary processes to gain an understanding of adaptation and speciation. In the Cauca Valley (Colombia), two butterfly races, Heliconius cydno cydnides and Heliconius cydno weymeri, meet and hybridize. We characterized this hybrid zone using a combination of mitochondrial DNA (mtDNA) sequences, Amplified Fragment Length Polymorphisms (AFLPs), microsatellites, and sequences for nuclear loci within and outside of the genomic regions that cause differences in wing color pattern. The hybrid zone is largely composed of individuals of mixed ancestry. However, there is strong genetic discontinuity between the hybridizing races in mtDNA and, to a lesser extent, in all nuclear markers surveyed. The mtDNA clustering of H. c. cydnides with the H. cydno race from the Magdalena Valley and H. c. weymeri with the H. cydno race from the pacific coast suggests that H. c. cydnides colonized the Cauca Valley from the north, whereas H. c. weymeri did so by crossing the Andes in the southern part, implying a secondary contact origin. Colonization of the valley by H. cydno was accompanied by mimicry shift. Strong ecological isolation, driven by locally adaptive differences in mimetic wing patterns, is playing an important role in maintaining the hybrid zone. However, selection on wing pattern alone is not sufficient to explain the genetic discontinuity observed. There is evidence for differences in male mating preference, but the contribution of additional barriers need further investigation. Overall our results support the idea that speciation is a cumulative process, where the combination of multiple isolation barriers, combined with major phenotypic differences, facilitate population divergence in face of gene flow.杂交带(Hybrid zones)是研究进化过程、解析适应与物种形成机制的强大天然研究系统。在哥伦比亚考卡山谷(Cauca Valley)，西多诺袖蝶(Heliconius cydno)的两个地理宗——西多诺袖蝶考卡地理宗(Heliconius cydno cydnides)与西多诺袖蝶韦默里地理宗(Heliconius cydno weymeri)——相遇并发生杂交。本研究结合线粒体DNA(mitochondrial DNA, mtDNA)序列、扩增片段长度多态性(Amplified Fragment Length Polymorphisms, AFLPs)、微卫星(microsatellites)标记，以及调控翅色模式差异的基因组区域内外的核基因座(nuclear loci)序列，对该杂交带开展了系统表征。该杂交带主体由遗传背景混杂的个体构成，但杂交宗间在线粒体DNA中存在显著的遗传不连续性，在所有检测的核标记中也存在一定程度的遗传不连续性。研究发现，H. c. cydnides的线粒体DNA聚类结果与来自马格达莱纳山谷(Magdalena Valley)的西多诺袖蝶地理宗聚为一支，而H. c. weymeri则与太平洋沿岸的西多诺袖蝶地理宗聚为一支，这表明H. c. cydnides从北部迁入考卡山谷，而H. c. weymeri则通过安第斯山脉南部区域完成迁入，暗示二者为次生接触起源。西多诺袖蝶对该山谷的定殖伴随拟态模式的转变。由拟态翅色模式的局部适应性差异驱动的强烈生态隔离，在维持该杂交带的过程中发挥了重要作用。然而仅靠翅色模式相关的选择不足以解释观测到的遗传不连续性。现有证据表明雄性交配偏好存在差异，但其他生殖隔离屏障的贡献仍需进一步研究。总体而言，本研究结果支持物种形成是一个累积过程的观点：在基因流存在的情况下，多重生殖隔离屏障与显著的表型差异共同推动了种群分化。