Heidelberg University, Heidelberg Institute of Plant Sciences, Biodiversity and Plant Systematics, Im Neuenheimer Feld 345, D-69120 Heidelberg, Germany.
BMC Evol Biol. 2010 Apr 8;10:98. doi: 10.1186/1471-2148-10-98.
The genomes of higher plants are, on the majority, polyploid, and hybridisation is more frequent in plants than in animals. Both polyploidisation and hybridisation contribute to increased variability within species, and may transfer adaptations between species in a changing environment. Studying these aspects of evolution within a diversified species complex could help to clarify overall spatial and temporal patterns of plant speciation. The Arabidopsis lyrata complex, which is closely related to the model plant Arabidopsis thaliana, is a perennial, outcrossing, herbaceous species complex with a circumpolar distribution in the Northern Hemisphere as well as a disjunct Central European distribution in relictual habitats. This species complex comprises three species and four subspecies, mainly diploids but also several tetraploids, including one natural hybrid. The complex is ecologically, but not fully geographically, separated from members of the closely related species complex of Arabidopsis halleri, and the evolutionary histories of both species compexes have largely been influenced by Pleistocene climate oscillations.
Using DNA sequence data from the nuclear encoded cytosolic phosphoglucoisomerase and Internal Transcribed Spacers 1 and 2 of the ribosomal DNA, as well as the trnL/F region from the chloroplast genome, we unravelled the phylogeography of the various taxonomic units of the A. lyrata complex. We demonstrate the existence of two major gene pools in Central Europe and Northern America. These two major gene pools are constructed from different taxonomic units. We also confirmed that A. kamchatica is the allotetraploid hybrid between A. lyrata and A. halleri, occupying the amphi-Beringian area in Eastern Asia and Northern America. This species closes the large distribution gap of the various other A. lyrata segregates. Furthermore, we revealed a threefold independent allopolyploid origin of this hybrid species in Japan, China, and Kamchatka.
Unglaciated parts of the Eastern Austrian Alps and arctic Eurasia, including Beringia, served as major glacial refugia of the Eurasian A. lyrata lineage, whereas A. halleri and its various subspecies probably survived in refuges in Central Europe and Eastern Asia with a large distribution gap in between. The North American A. lyrata lineage probably survived the glaciation in the southeast of North America. The dramatic climatic changes during glaciation and deglaciation cycles promoted not only secondary contact and formation of the allopolyploid hybrid A. kamchatica, but also provided the environment that allowed this species to fill a large geographic gap separating the two genetically different A. lyrata lineages from Eurasia and North America. With our example focusing on the evolutionary history of the A. lyrata species complex, we add substantial information to a broad evolutionary framework for future investigations within this emerging model system in molecular and evolutionary biology.
高等植物的基因组大多数是多倍体，而且植物中的杂交比动物中更为频繁。多倍化和杂交都会增加物种内的变异性，并可能在不断变化的环境中在物种之间转移适应性。在一个多样化的物种复合体中研究这些进化方面，可以帮助澄清植物物种形成的整体时空模式。拟南芥 lyrata 复合体与模式植物拟南芥密切相关，是一种多年生、异交、草本物种复合体，在北半球呈环极分布，在中欧的残余栖息地呈间断分布。该物种复合体由三个物种和四个亚种组成，主要是二倍体，但也有几个四倍体，包括一个天然杂种。该复合体在生态上但不完全在地理上与密切相关的拟南芥 halleri 物种复合体的成员分开，两个物种复合体的进化历史在很大程度上受到更新世气候波动的影响。
我们使用来自核编码胞质磷酸葡萄糖异构酶和核糖体 DNA 的内部转录间隔区 1 和 2 以及叶绿体基因组的 trnL/F 区的 DNA 序列数据，揭示了 A. lyrata 复合体的各种分类单元的系统地理学。我们证明了中欧和北美存在两个主要的基因库。这两个主要的基因库是由不同的分类单元构成的。我们还证实 A. kamchatica 是 A. lyrata 和 A. halleri 之间的异源四倍体杂种，占据东亚和北美的环北极地区。该物种填补了其他各种 A. lyrata 分离物的大分布缺口。此外，我们揭示了该杂种物种在日本、中国和堪察加的三倍独立的异源多倍体起源。
未受冰川影响的奥地利东部阿尔卑斯山和欧亚大陆的北极地区，包括白令地区，是欧亚 A. lyrata 谱系的主要冰川避难所，而 A. halleri 及其各种亚种可能在中欧和东亚的避难所中幸存下来，两者之间存在很大的分布缺口。北美 A. lyrata 谱系可能在北美东南部的冰期中幸存下来。冰川作用和去冰川作用循环中的剧烈气候变化不仅促进了异源多倍体杂种 A. kamchatica 的再次接触和形成，还为该物种提供了环境，使其能够填补欧亚大陆和北美的两个遗传上不同的 A. lyrata 谱系之间的大地理差距。通过我们的例子聚焦于 A. lyrata 物种复合体的进化历史，我们为未来在这个新兴的分子和进化生物学模型系统中进行的广泛进化框架内的研究提供了实质性的信息。
