Hybridisation can lead to homoploid hybrid speciation, i.e., the origin of new species without change in chromosome number between parents and offspring. Central to homoploid hybrid speciation is the role of hybridisation in the establishment of reproductive isolation between the hybrid and the parental species in the early stages of speciation, when typically all species occur at least partly in sympatry. In this work we analyse genome‐wide polymorphism data obtained by transcriptome sequencing of the British hybrid species Oxford ragwort (Senecio squalidus, Asteraceae), its two Italian parental species (S. aethnensis and S. chrysanthemifolius) and their naturally occurring hybrids on Mt Etna (Italy). We show that Oxford ragwort most likely originated from de novo hybridisation between its two Italian parental species whilst they were in cultivation in British gardens at the turn of the 18th century. Reproductive isolation between the new hybrid species and its parental species probably resulted from inheritance of genetic incompatibilities between the two parental species and subsequent ecological segregation – both of which have been shown in previous studies. Our results imply that S. squalidus meets the most stringent criteria set forth to identify homoploid hybrid speciation, and call attention to the creative role of hybridisation in responding to novel environmental conditions.

中文翻译：

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英国花园中的快速单倍体杂种形成：牛津草（Senecio squalidus）的起源。

杂交可以导致同倍体杂交物种形成，即新物种的起源，而父母和后代之间的染色体数目没有变化。单倍体杂交物种形成的核心是杂交，在物种形成的早期阶段，杂种与亲本物种之间建立生殖隔离时，通常所有物种至少部分出现在共生体中。在这项工作中，我们分析了通过英国杂交种牛津布氏植物（Senecio squalidus，菊科），其两个意大利亲本物种（S. aethnensis和S. chrysanthemifolius）的转录组测序获得的全基因组多态性数据。及其在埃特纳火山（意大利）上的自然杂交种。我们显示，牛津狗舌草很可能起源于18世纪初在英国花园中种植时，两个意大利亲本物种之间的从头杂交。新的杂交种与其亲本之间的生殖隔离可能是由于两个亲本之间遗传不相容的遗传以及随后的生态隔离所引起的，这两者都在先前的研究中得到了证明。我们的结果表明，S。squalidus符合提出的最严格标准，以鉴定同倍体杂交物种，并引起人们注意杂交在应对新环境条件方面的创新作用。