Department of Bioscience, Plant Biology, Aarhus University, Ole Worms Allé 1, 8000 Aarhus C, Denmark.
Am J Bot. 2012 Mar;99(3):538-51. doi: 10.3732/ajb.1100396. Epub 2012 Feb 14.
Long-distance dispersal can affect speciation processes in two opposing ways. Dispersal can promote geographic isolation or it can bring together geographically distant and distantly related genotypes, thus counteracting local differentiation. We used the Gulf Coast of North America (GC), a "hot spot" of reed diversity and evolutionary dynamics, as a model system to study the diversification processes within the invasive, cosmopolitan, polyploid grass Phragmites.
Genetic diversity was studied using collections representing all species of the genus and from all continents (except Antarctica). A range of molecular markers, including chloroplast and nuclear sequences, microsatellites, and AFLPs, was analyzed to detect DNA variation from the population to the species level and to infer phylogenetic relationships across continents.
An interspecific hybrid, Phragmites mauritianus × P. australis, and four P. australis cp-DNA haplotypes from Africa, Europe, and North America have been dispersed to the GC and interbreed with each other.
Long-distance dispersal and weak breeding barriers appear to be recurring phenomena, not only in the GC, but worldwide. We present data strongly suggesting that interspecific hybridization and introgression among different Phragmites species take place and appear to have contributed significantly to the diversification processes within the genus. Hence, the application of traditional species concepts within Phragmites might be inappropriate.
长距离扩散可以通过两种相反的方式影响物种形成过程。扩散可以促进地理隔离，也可以将地理上遥远且远缘的基因型聚集在一起，从而抵消局部分化。我们使用北美海湾地区（GC）作为模型系统，该地区是芦苇多样性和进化动态的“热点”，研究入侵、世界性、多倍体草属芦苇属内的多样化过程。
使用代表该属所有物种并来自所有大陆（南极洲除外）的采集物来研究遗传多样性。分析了一系列分子标记，包括质体和核序列、微卫星和 AFLP，以检测从种群到物种水平的 DNA 变异，并推断跨大陆的系统发育关系。
种间杂种 Phragmites mauritianus × P. australis 和来自非洲、欧洲和北美的四个 P. australis cp-DNA 单倍型已被传播到 GC 并相互杂交。
长距离扩散和较弱的繁殖障碍似乎是反复出现的现象，不仅在 GC 地区，而且在全球范围内都是如此。我们提供的证据强烈表明，不同芦苇种间的种间杂交和基因渗入确实发生了，并似乎对属内的多样化过程做出了重大贡献。因此，在芦苇属内应用传统的物种概念可能不恰当。
