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.杂交带是研究演化过程、解析适应与物种形成机制的优质天然实验体系。在哥伦比亚考卡山谷（Cauca Valley）中，西多诺袖蝶考卡亚种（Heliconius cydno cydnides）与西多诺袖蝶韦氏亚种（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序列，对该杂交带开展了系统表征分析。 该杂交带的主体为遗传背景混杂的个体，但线粒体DNA在两个杂交亚种间呈现显著的遗传不连续性，而在所有检测的核标记中，该现象的程度相对较弱。西多诺袖蝶考卡亚种的线粒体DNA聚类结果与马格达莱纳山谷的西多诺袖蝶种群一致，而西多诺袖蝶韦氏亚种则与太平洋沿岸的西多诺袖蝶种群聚类，这表明考卡亚种从北部拓殖考卡山谷，而韦氏亚种则通过南部安第斯山脉完成拓殖，暗示该杂交带起源于二次接触。 西多诺袖蝶拓殖考卡山谷的过程伴随了拟态模式的转变。由拟态翅型的本地适应性差异驱动的强生态隔离，在维持该杂交带的过程中发挥了关键作用。但仅依靠翅型相关的选择，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，但其他额外生殖隔离屏障的贡献仍需进一步探究。 综上，本研究结果支持物种形成是一个累积过程的观点：在基因流存在的前提下，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。