Dorken M E, Barrett S C H
Department of Botany, University of Toronto, 25 Willcocks Street, ON, M5S 3B2, Canada.
Mol Ecol. 2004 Sep;13(9):2699-707. doi: 10.1111/j.1365-294X.2004.02246.x.
Aquatic plants commonly have extensive geographical distributions, implying few restrictions to dispersal. Here we investigate the postglacial history of an aquatic plant with contrasting sexual systems (monoecy and dioecy), which are predicted to affect dispersal ability. We examined the distribution of cpDNA haplotypes using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) among 76 populations (32 monoecious, 38 dioecious, two mixed and four undetermined populations) of Sagittaria latifolia sampled throughout eastern North America. We also use these data to investigate the polarity of the evolutionary transition between monoecy and dioecy. Using PCR-RFLP, we identified eight cpDNA haplotypes. All haplotypes were found in unglaciated areas of the species' range, clustered primarily in the southeastern United States, providing evidence that glacial refugia probably occurred in this area. Genetic diversity (hT) was more than six times greater among monoecious compared to dioecious populations. All seven of the haplotypes for which the sexual system could be determined were represented among monoecious populations. In contrast, only four haplotypes were detected in dioecious populations and 94% of individuals from dioecious populations possessed a single haplotype. Monoecious populations possessing this widespread haplotype were restricted to the southern portion of the range, indicating that dioecy probably originated in this region and then spread northwards. The distribution of cpDNA haplotypes in dioecious populations represents a subset of the variation found in monoecious populations, a pattern expected if dioecy has evolved from monoecy in S. latifolia.
水生植物通常具有广泛的地理分布，这意味着其扩散几乎没有限制。在此，我们研究了一种具有不同性系统（雌雄同株和雌雄异株）的水生植物的冰期后历史，预计这两种性系统会影响扩散能力。我们使用聚合酶链反应-限制性片段长度多态性（PCR-RFLP）技术，检测了北美东部各地采集的76个宽叶慈姑种群（32个雌雄同株、38个雌雄异株、2个混合和4个未确定种群）中cpDNA单倍型的分布。我们还利用这些数据来研究雌雄同株和雌雄异株之间进化转变的极性。通过PCR-RFLP，我们鉴定出了8种cpDNA单倍型。所有单倍型都在该物种分布范围的未受冰川影响区域被发现，主要集中在美国东南部，这表明该地区可能是冰期避难所。与雌雄异株种群相比，雌雄同株种群的遗传多样性（hT）高出六倍多。在雌雄同株种群中，所有可确定性系统的7种单倍型都有代表。相比之下，在雌雄异株种群中仅检测到4种单倍型，且94%的雌雄异株个体拥有单一单倍型。拥有这种广泛分布单倍型的雌雄同株种群仅限于该分布范围的南部，这表明雌雄异株可能起源于该地区，然后向北扩散。雌雄异株种群中cpDNA单倍型的分布代表了雌雄同株种群中发现的变异的一个子集，如果宽叶慈姑的雌雄异株是从雌雄同株进化而来，那么这种模式是可以预期的。
