Ruckelshaus Mary H
Department of Botany, KB-15, University of Washington, Seattle, Washington, 98195.
Evolution. 1996 Apr;50(2):856-864. doi: 10.1111/j.1558-5646.1996.tb03894.x.
The relative importance of random genetic drift and local adaptation in causing population substructuring in plant species remains an important empirical question. Here I estimate the effective size of the genetic neighborhood, N , as a means of evaluating the likely role of genetic drift in creating genetic differentiation within a population of a marine plant, Zostera marina L. (eelgrass). Calculations of effective neighborhood size are based on field estimates of pollen and seed-dispersal distributions, an electrophoretic estimate of the mating system using open-pollinated progeny arrays, and determination of the effective density of reproductive individuals in the population. Neighborhood area calculated from the parent-offspring dispersal variances was equal to N = 524 m ; variance in the seed-dispersal distribution contributes more than twice as much as variance in pollen dispersal to N . Including an outcrossing rate slightly different from random, estimated neighborhood size for Z. marina is N = 6255. This estimate is one of the largest reported for plants or animals and indicates that genetic drift in small neighborhoods is highly unlikely to cause genetic substructuring in the study population. High gene-flow levels provided by the marine environment appear to prevent genetic isolation by distance among eelgrass patches, but the importance of drift through founder events in this population characterized by high patch turnover cannot be discounted and is the subject of ongoing study.
随机遗传漂变和局部适应性在导致植物物种种群亚结构形成过程中的相对重要性仍是一个重要的实证问题。在此，我估算了遗传邻域的有效大小(N)，以此来评估遗传漂变在造成一种海洋植物——大叶藻（Zostera marina L.）种群内遗传分化方面可能发挥的作用。有效邻域大小的计算基于对花粉和种子传播分布的实地估计、利用开放授粉子代阵列对交配系统的电泳估计，以及对种群中繁殖个体有效密度的测定。根据亲代 - 子代传播方差计算出的邻域面积为(N = 524 m²)；种子传播分布的方差对(N)的贡献是花粉传播方差的两倍多。若纳入一个与随机情况略有不同的异交率，大叶藻的估计邻域大小为(N = 6255)。这一估计是动植物中报道的最大估计值之一，表明在小邻域内的遗传漂变极不可能在研究种群中导致遗传亚结构的形成。海洋环境提供的高基因流水平似乎能防止大叶藻斑块间因距离产生遗传隔离，但在这个斑块更替率高的种群中，由奠基者事件导致的漂变的重要性不能被忽视，这也是正在进行的研究课题。
