Eckert Christopher G, Lui Keiko, Bronson Kelly, Corradini Pierre, Bruneau Anne
Department of Biology, Queen's University, Kingston, Ontario K7L 3N6 Canada.
Mol Ecol. 2003 Feb;12(2):331-44. doi: 10.1046/j.1365-294x.2003.01737.x.
Most plants combine sexual reproduction with asexual clonal reproduction in varying degrees, yet the genetic consequences of reproductive variation remain poorly understood. The aquatic plant Butomus umbellatus exhibits striking reproductive variation related to ploidy. Diploids produce abundant viable seed whereas triploids are sexually sterile. Diploids also produce hundreds of tiny clonal bulbils, whereas triploids exhibit only limited clonal multiplication through rhizome fragmentation. We investigated whether this marked difference in reproductive strategy influences the diversity of genotypes within populations and their movement between populations by performing two large-scale population surveys (n = 58 populations) and assaying genotypic variation using random amplified polymorphic DNA (RAPDs). Contrary to expectations, sexually fertile populations did not exhibit higher genotypic diversity than sterile populations. For each cytotype, we detected one very common and widespread genotype. This would only occur with a very low probability (< 10-7) under regular sexual recombination. Compatibility analysis also indicated that the pattern of genotypic variation largely conformed to that expected with predominant clonal reproduction. The potential for recombination in diploids is not realized, possibly because seeds are outcompeted by bulbils for safe sites during establishment. We also failed to find evidence for more extensive movement of fertile than sterile genotypes. Aside from the few widespread genotypes, most were restricted to single populations. Genotypes in fertile populations were very strongly differentiated from those in sterile populations, suggesting that new triploids have not arisen during the colonization of North America. The colonization of North America involves two distinct forms of B. umbellatus that, despite striking reproductive differences, exhibit largely clonal population genetic structures.
大多数植物在不同程度上结合了有性繁殖和无性克隆繁殖，但生殖变异的遗传后果仍知之甚少。水生植物花蔺表现出与倍性相关的显著生殖变异。二倍体产生大量可育种子，而三倍体则是有性不育的。二倍体还产生数百个微小的克隆珠芽，而三倍体仅通过根茎断裂表现出有限的克隆繁殖。我们通过进行两项大规模种群调查（n = 58个种群）并使用随机扩增多态性DNA（RAPD）分析基因型变异，来研究这种生殖策略上的显著差异是否会影响种群内基因型的多样性及其在种群间的移动。与预期相反，有性可育种群的基因型多样性并不比不育种群高。对于每种细胞类型，我们都检测到一种非常常见且分布广泛的基因型。在正常的有性重组情况下，这种情况发生的概率非常低（< 10-7）。相容性分析还表明，基因型变异模式在很大程度上符合主要为克隆繁殖时预期的模式。二倍体中重组的潜力未得到实现，可能是因为在定植过程中种子在安全位点上被珠芽竞争淘汰。我们也没有找到证据表明可育基因型比不育基因型有更广泛的移动。除了少数广泛分布的基因型外，大多数都局限于单个种群。可育种群中的基因型与不育种群中的基因型差异非常大，这表明在北美殖民化过程中没有出现新的三倍体。北美殖民化涉及花蔺的两种不同形式，尽管它们在生殖上有显著差异，但种群遗传结构在很大程度上表现为克隆性。
