Department of Evolution and Ecology, University of California, Davis, California 95616 USA.
Am J Bot. 2008 Jun;95(6):713-9. doi: 10.3732/ajb.2007358.
Rapid evolution in contemporary time can result when related species, brought together through human-aided introduction, hybridize. The significant evolutionary consequences of post-introduction hybridization range from allopolyploid speciation to extinction of species through genetic amalgamation. Both processes are known to occur in the perennial cordgrass genus, Spartina. Here we report the existence of a third recent Spartina hybridization, discovered in 2002, between introduced S. densiflora and native S. foliosa in San Francisco Bay, California, USA. We used nuclear and chloroplast DNA analysis and nuclear DNA content with chromosome counts to examine plants of morphology intermediate between S. densiflora and S. foliosa in a restored marsh in Marin County, California. We found 32 F(1) diploid hybrids and two triploid plants, all having S. densiflora and S. foliosa as parents; there is also evidence of a genetic contribution of S. alterniflora in some hybrids. None of these hybrids set germinable seed. In 2007 we found a hybrid over 30 miles away in a marsh where both parental species occurred, suggesting hybridization may not be a localized phenomenon. The presence of diploid and triploid hybrids is important because they indicate that several avenues existed that may have given rise to a new allopolyploid species. However, such an event is now unlikely because all hybrids are targets of eradication efforts.
当相关物种因人类介导的引入而聚集在一起时，就会发生当代的快速进化。引种后杂交的重要进化后果范围从异源多倍体物种形成到通过遗传融合导致物种灭绝。这两个过程都已知发生在多年生绳草属（Spartina）中。在这里，我们报告了第三种最近的 Spartina 杂交种的存在，该杂交种于 2002 年在美国加利福尼亚州旧金山湾的引入种 Spartina densiflora 和本地种 Spartina foliosa 之间发现。我们使用核和叶绿体 DNA 分析以及核 DNA 含量和染色体计数来检查加利福尼亚州马林县一个恢复的沼泽中形态介于 Spartina densiflora 和 Spartina foliosa 之间的植物。我们发现了 32 个 F1 二倍体杂种和两个三倍体植物，它们的亲本均为 Spartina densiflora 和 Spartina foliosa；还有证据表明一些杂种中存在 Spartina alterniflora 的遗传贡献。这些杂种都没有产生可发芽的种子。2007 年，我们在一个有两种亲本物种的沼泽中发现了一个距离超过 30 英里的杂种，这表明杂交可能不是局部现象。二倍体和三倍体杂种的存在很重要，因为它们表明可能存在多种途径导致新的异源多倍体物种的产生。然而，由于所有杂种都是根除努力的目标，因此这种情况现在不太可能发生。
