植物物种形成的模式与机制

The modes and mechanisms of plant speciation

物种形成是指由已有的物种通过各种进化机制进化出新物种的过程。持续不断的物种形成产生了地球上灿烂的生物物种多样性。然而,研究人员对物种形成的模式与机制的了解却非常有限。一直以来,谱系分裂被认为是最重要的物种形成模式,但在植物中,谱系融合,即通过杂交形成新物种的过程,也是一个非常重要的物种形成模式。经过几十年的研究才逐渐认识到,生殖隔离是差异适应和遗传漂变的副产品,而不是物种形成的前提。相比合子形成后隔离,合子形成前的隔离在物种形成过程中更早地发挥作用。合子形成前的隔离,尤其是生态地理的隔离是植物中最重要的隔离机制。一些基于QTLs分析的研究发现,基因组中的少数主效位点在物种形成中起了关键作用,并且这些位点往往受到自然选择的作用。适应性辐射往往发生在隆起的山脉和新形成的岛屿上,很可能与这些地方能够提供很多可利用的生态位有关。最新的物种形成理论认为,基因是物种形成的基本单位,不同的物种可以在非控制物种差异适应性状的位点上存在基因流。这一观点为植物物种形成的研究提供了新的思路。随着植物物种形成研究的深入,越来越多植物物种形成基因被分离,包括花色素苷合成通路和S-基因座上的一些关键基因,揭示了植物物种形成的分子机制。前期的研究主要集中在模式植物和农作物上,许多生态上非常有趣的非模式植物还未得到广泛的研究。在未来的研究中,还需要更多来自非模式植物的例子以全面理解植物物种形成的多样化机制。

Speciation is the process of the formation of new species through various evolutionary mechanisms. Repeated speciation processes result in the numerous species on Earth. However, our understanding on the modes and mechanisms of speciation process is still very limited to date. [t is generally accepted that lineage split is the most important speciation mode. However, lineage fusion, i.e. speciation through hybridization, also plays a very important role, especially in plants. Researches in the past several decades make it clear that reproductive isolation is just a by-product of genetic drift and differential adaptation rather than the prerequisite for speciation. Compared with postzygotic barriers, prezygotic barriers, especially ecogeographical isolation, is viewed as the earlier-acting reproductive barriers and contribute more to reproductive isolation. Studies based on QTLs have shown that a very few loci with major effect in the genome are critical in the speciation process, and these loci usually undergo natural selection. Adaptive radiation can be frequently seen on some uplifted mountains and oceanic islands, which could be attributable to the available ecological niches provided by these places. The latest theory considered genes or gene complexes as the units of speciation. Genomic regions would remain shared and undifferentiated except the loci underlying differential adaptation between different species. The theory provides new insights into the plant speciation process. In the past two decades, quite a few speciation genes have been cloned in plants. These genes, including those in the anthocyanin biosynthesis pathway and S-locus, provide clue to the mechanisms of plant speciation. However, previous studies were mainly focused on the model plants and crops rather than non-model plants of ecological interest. In future, examples from ecologically interesting non-model plants should he studied for comprehensive understanding of the speciation mechanisms.