摘要:
长久以来,杂交和基因渗入在进化上的重要性都在争论之中。杂种通常十分稀有并且适应性不强,但即使是罕见的杂种也可以通过在种间传递有益的特征来帮助物种适应。这里,我们使用了基因组分析工具来研究釉蛱蝶属的行为、拟态和物种形成。釉蛱蝶是一个快速扩张的新热带地区属,在生态学研究中的应用十分广泛。我们对诗神袖蝶进行了全基因组测序,并与其它分类群比较,以此来研究鳞翅目的染色体进化和釉蛱蝶属内不同种和小种之间的基因流。在12669个预测基因中,化学感受器基因和Hox基因家族的扩张格外值得注意,因为它们有重要的生物学价值。从白垩纪,蝴蝶由蚕属中分化出来之后,它们的染色体组成一直保持着广泛的保守性。通过基因组重排测序,我们展示了共拟态的三个杂种之间的基因交流,尤其是在控制拟态模式的基因区域间的交流,它们分别是湿神袖蝶、白毒蝶和艳丽袖蝶。我们推测,在釉蛱蝶属下有较近亲缘关系的种间,与保护色样式有关的基因的交流是十分杂乱的,这暗示了杂交在适应辐射中有非常重要的作用。
The evolutionary importance of hybridization and introgression has long been debated1. Hybrids are usually rare and unfit, but even infrequent hybridization can aid adaptation by transferring beneficial traits between species. Here we use genomic tools to investigate introgression in Heliconius, a rapidly radiating genus of neotropical butterflies widely used in studies of ecology, behaviour, mimicry and speciation2–5. We sequenced the genome of Heliconius melpomene and compared it with other taxa to investigate chromosomal evolution in Lepidoptera and gene flow among multiple Heliconius species and races. Among 12,669 predicted genes, biologically important expansions of families of chemosensory and Hox genes are particularly noteworthy. Chromosomal organization has remained broadly conserved since the Cretaceous period, when butterflies split from the Bombyx (silkmoth) lineage. Using genomic resequencing, we show hybrid exchange of genes between three co-mimics, Heliconius melpomene, Heliconius timareta and Heliconius elevatus, especially at two genomic regions that control mimicry pattern. We infer that closely related Heliconius species exchange protective colour-pattern genes promiscuously, implying that hybridization has an important role in adaptive radiation.
正文:
釉蛱蝶属(蛱蝶科:釉蛱蝶亚科)与一些列派生的生活史和生态特征有关,这些特征包括摄食花粉、较长寿命、较强的紫外视觉、“陷阱路线”觅食行为、群居栖息和复杂的交配行为。釉蛱蝶属为有关适应辐射和物种形成的基因组研究提供了优越的机会。这个属十分有名,其下的43个种内包括了数百个拥有不同颜色图案的小种,它们提供了远源种间的趋同进化和相近分类群间趋异进化的种种例证。许多有着颜色图案的种,例如诗神袖蝶,的地理镶嵌(图1)与其它种中相似的小镶嵌汇聚到一起,导向了拟态假说。脊椎类的捕食者并不喜欢以釉蛱蝶属为食,而利用缪勒拟态形成警告色也让它们可以共同抵御天敌。因为翅膀图案在拟态和择偶中都有作用,它的分化还与物种形成和适应辐射有关。最近的一次是诗神袖蝶–羽衣袖蝶的辐射,从它看来,拟态的模式似乎是多元的。在这一进化支中的大多数种都曾在野外与其它进化支的成员杂交。基于较少位点数的基因谱显示,不同种间存在基因渗入,且无拟态现象的富丽秀蝶是混合起源的。因此,拟态位点的适应性基因渗入为诗神袖蝶–羽衣袖蝶分支间不同拟态模式的平行进化提供了合理解释。
The butterfly genus Heliconius (Nymphalidae: Heliconiinae) is associated with a suite of derived life-history and ecological traits, including pollen feeding, extended lifespan, augmented ultraviolet colour vision, ‘trap-lining′ foraging behaviour, gregarious roosting and complexmating behaviours, and provides outstanding opportunities for genomic studies of adaptive radiation and speciation4,6.The genus is best known for the hundreds of races with different colour patterns seen among its 43 species, with repeated examples of both convergent evolution among distantly related species and divergent evolution between closely related taxa3. Geographic mosaics of multiple colour-pattern races, such as in Heliconius melpomene (Fig. 1), converge to similar mosaics in other species, and this led to the hypothesis of mimicry2. Heliconius are unpalatable to vertebrate predators and Müllerian mimicry of warning colour patterns enables species to share the cost of educating predators3. As a result of its dual role in mimicry and mate selection, divergence in wing pattern is also associated with speciation and adaptive radiation3,5. A particularly recent radiation is the melpomene–silvaniform clade, in which mimetic patterns often seem to be polyphyletic (Fig. 1a). Most species in this clade occasionally hybridize in the wild with other clade members7. Gene genealogies at a small number of loci indicate introgression between species8, and one non-mimetic species, Heliconius heurippa, has a hybrid origin9. Adaptive introgression of mimicry loci is therefore a plausible explanation for parallel evolution of multiple mimetic patterns in the melpomene–silvaniform clade.
一个来自巴拿马达连湾的诗神袖蝶群体与五个同胞交配的世代进行了近亲杂交。我们使用结合454和Illumina公司(补充信息,第1-8节)的技术对一个雄性进行测序,覆盖了338个位点(经过质量过滤)。269兆的完整基因组草图装包括了3800个支架和一个277kb的N50,草图中有12669个预测蛋白质编码基因。我们用限制性位点相关DNA(RAD)的连锁图谱将83%的已测序基因组定位到21条染色体(补充信息,第4节)上。这些数据使得与家蚕进行大幅优化的全基因组染色体共线性比对成为可能。
A Heliconius melpomene melpomene stock from Darie´n, Panama (Fig. 1), was inbred through five generations of sib mating. We sequenced a single male to 338 coverage (after quality filtering) using combined 454 and Illumina technologies (Supplementary Information, sections 1–8). The complete draft genome assembly, which is 269 megabases (Mb) in size, consists of 3,800 scaffolds with an N50 of 277 kb and contains 12,669 predicted protein-coding genes. Restriction-site-associated DNA (RAD) linkage mapping was used to assign and order 83% of the sequenced genome onto the 21 chromosomes (Supplementary Information, section 4). These data permit a considerably improved genome-wide chromosomal synteny comparison with the silkmoth Bombyx mori10,11.
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