Pollux B J A, Jong M D E, Steegh A, Verbruggen E, van Groenendael J M, Ouborg N J
Section of Molecular Ecology, Department of Aquatic Ecology & Environmental Biology, Institute for Wetland and Water Research, Radboud University Nijmegen, Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands.
Mol Ecol. 2007 Jan;16(2):313-25. doi: 10.1111/j.1365-294X.2006.03146.x.
Many aquatic and riparian plant species are characterized by the ability to reproduce both sexually and asexually. Yet, little is known about how spatial variation in sexual and asexual reproduction affects the genotypic diversity within populations of aquatic and riparian plants. We used six polymorphic microsatellites to examine the genetic diversity within and differentiation among 17 populations (606 individuals) of Sparganium emersum, in two Dutch-German rivers. Our study revealed a striking difference between rivers in the mode of reproduction (sexual vs. asexual) within S. emersum populations. The mode of reproduction was strongly related to locally reigning hydrodynamic conditions. Sexually reproducing populations exhibited a greater number of multilocus genotypes compared to asexual populations. The regional population structure suggested higher levels of gene flow among sexually reproducing populations compared to clonal populations. Gene flow was mainly mediated via hydrochoric dispersal of generative propagules (seeds), impeding genetic differentiation among populations even over river distances up to 50 km. Although evidence for hydrochoric dispersal of vegetative propagules (clonal plant fragments) was found, this mechanism appeared to be relatively less important. Bayesian-based assignment procedures revealed a number of immigrants, originating from outside our study area, suggesting intercatchment plant dispersal, possibly the result of waterfowl-mediated seed dispersal. This study demonstrates how variation in local environmental conditions in river systems, resulting in shifting balances of sexual vs. asexual reproduction within populations, will affect the genotypic diversity within populations. This study furthermore cautions against generalizations about dispersal of riparian plant species in river systems.
许多水生和河岸植物物种的特点是既能进行有性繁殖，也能进行无性繁殖。然而，关于有性和无性繁殖的空间变异如何影响水生和河岸植物种群内的基因型多样性，我们所知甚少。我们使用六个多态性微卫星来检测荷兰和德国两条河流中17个黑三棱种群（606个个体）内的遗传多样性以及种群间的分化情况。我们的研究揭示了黑三棱种群在两条河流中的繁殖方式（有性繁殖与无性繁殖）存在显著差异。繁殖方式与当地主导的水动力条件密切相关。与无性繁殖种群相比，有性繁殖种群表现出更多的多位点基因型。区域种群结构表明，与克隆种群相比，有性繁殖种群间的基因流水平更高。基因流主要通过生殖繁殖体（种子）的水流传播介导，即使在长达50公里的河流距离上，也能阻碍种群间的遗传分化。尽管发现了营养繁殖体（克隆植物片段）水流传播的证据，但这种机制似乎相对不太重要。基于贝叶斯的分配程序揭示了一些来自我们研究区域之外的移民，这表明存在集水区间的植物传播，可能是水鸟介导的种子传播的结果。这项研究表明，河流系统中局部环境条件的变化，导致种群内有性与无性繁殖平衡的改变，将如何影响种群内的基因型多样性。此外，这项研究提醒我们不要对河岸植物物种在河流系统中的传播进行一概而论。
