Recent hybrid origin and invasion of the British Isles by a self-incompatible species, Oxford ragwort (Senecio squalidus L., Asteraceae)
Recent hybrid origin and invasion of the British Isles by a self-incompatible species, Oxford ragwort (Senecio squalidus L., Asteraceae)
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DOI：
10.1007/s10530-008-9382-3
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发表时间：
2009-05-01
影响因子：
2.9
通讯作者：
Hiscock, Simon J.
中科院分区：
文献类型：
--
作者：
Abbott, Richard J.;Brennan, Adrian C.;Hiscock, Simon J.
Senecio squalidus是一种二倍体杂交物种，大约300年前从西西里岛埃特纳火山的杂交区收集的材料引入后，起源于不列颠群岛。引进的杂交材料在牛津植物园种植，并产生了稳定的二倍体杂交物种，后来扩散到英国的大部分地区和爱尔兰的一些地区。不同于入侵物种的是，角鲨具有很强的孢子体自交不亲和（SSI）系统，该系统可能由于其最近的杂交起源和传播而被修改。首先，与其他具有SSI的物种（估计平均每个种群有17个S等位基因）相比，S等位基因相对较少（单个英国种群中有2到6个S等位基因）。这很可能反映了引入杂交材料所经历的种群瓶颈。其次，与其他SSI物种相比，S等位基因间的显性关系更为广泛。第三，尽管伪自交亲和性偶有发生，但并不普遍，这表明尽管S等位基因数量少限制了潜在的配偶可用性，但SSI在该物种中仍保持着。对其他遗传多样性形式的调查表明，同工酶变异相对于祖先物种有所减少，但随机扩增多态性DNA变异相对较高。这两种类型的遗传变异都很少或没有显示出种群之间的距离隔离模式，这与物种最近的范围扩张保持一致。在不列颠群岛的传播过程中，S. squalidus与当地的自相容（SC）四倍体物种S. vulgaris杂交，从而产生了三个新的SC杂交类群：S. vulgaris （var. hibernicus）的辐射型、S. eboracensis的四倍体杂交种和S. cambrensis的异源六倍体。
Senecio squalidus is a diploid hybrid species which originated in the British Isles following the introduction of material collected from a hybrid zone on Mount Etna, Sicily, approximately 300 years ago. Introduced hybrid material was cultivated in the Oxford Botanic Garden and gave rise to the stabilized diploid hybrid species, which later spread throughout much of the UK and into some parts of Ireland. Unusually for an invasive species, S. squalidus has a strong system of sporophytic self-incompatibility (SSI) that may have become modified as a result of its recent hybrid origin and spread. First, S. squalidus contains relatively few S alleles (between 2 and 6 S alleles within individual UK populations) compared to other species with SSI (estimates average similar to 17 S alleles per population). This most probably reflects the population bottleneck experienced by introduced hybrid material. Second, dominance relationships among S. squalidus S alleles are more extensive than those reported in other species with SSI. Third, although pseudo-self-compatibility occurs sporadically in S. squalidus, it is not widespread, indicating that SSI is maintained in the species despite potential mate availability restrictions imposed by low numbers of S alleles. Surveys of other forms of genetic diversity in S. squalidus show that allozyme variation is reduced relative to that within the progenitor species, but Randomly Amplified Polymorphic DNA variation is relatively high. Both types of genetic variation show little or no pattern of isolation-by-distance between populations in keeping with the recent range expansion of the species. During its spread in the British Isles, S. squalidus has hybridized with the native self-compatible (SC) tetraploid species, S. vulgaris, which has led to the origin of three new SC hybrid taxa: a radiate form of S. vulgaris (var. hibernicus), a tetrapoid hybrid species (S. eboracensis) and an allohexaploid (S. cambrensis).