Schnabel Andrew, Hamrick J L
Department of Botany, Iowa State University, Ames, Iowa, 50011.
Departments of Botany and Genetics, University of Georgia, Athens, Georgia, 30602.
Evolution. 1995 Oct;49(5):921-931. doi: 10.1111/j.1558-5646.1995.tb02327.x.
Spatial and temporal patterns of gene flow determine the extent to which populations can differentiate from one another as a result of natural selection or genetic drift. In this study, we investigated pollen-mediated gene flow in two eastern Kansas populations of the subdioecious tree species, Gleditsia triacanthos L. (Leguminosae), or honeylocust. In 2 yr at each site, we used paternity-exclusion analysis to estimate the proportion of seeds sired by immigrant pollen. We also used a single-parent and parent-pair exclusion analysis on naturally established seedlings and saplings to estimate gene flow into one site over a 12-yr period and into the second site over a 22-yr period. Results of both analyses showed high minimum estimates of pollen gene flow into each site (17%-30%). In each population, we found significantly less gene flow in years of high fruit production than in years of low fruit production, but in one population, we observed little variation in gene-flow rates among age classes of seedlings and saplings. The level of pollen gene flow showed weak negative dependence on the relative isolation distances of the maternal trees sampled (140-240 m at one site vs. 85-120 m at the second site), and gene-flow estimates from naturally established juveniles were very similar at the two sites. Within populations, a multiple regression model showed that maximum-likelihood estimates of male fertility were negatively associated with distances between mates and positively associated with male size as measured by stem diameter. In neither population, however, did the regression explain more than 16% of the total variation in male fertilities.
基因流的时空模式决定了种群由于自然选择或遗传漂变而彼此分化的程度。在本研究中，我们调查了堪萨斯州东部两个雌雄异株树种刺槐（豆科）种群中花粉介导的基因流情况。在每个地点的两年时间里，我们采用父系排除分析来估计由外来花粉授精的种子比例。我们还对自然生长的幼苗和幼树进行单亲及双亲排除分析，以估计12年间流入一个地点以及22年间流入另一个地点的基因流情况。两种分析结果均显示，流入每个地点的花粉基因流最低估计值较高（17%-30%）。在每个种群中，我们发现果实高产年份的基因流显著低于低产年份，但在一个种群中，我们观察到不同年龄级别的幼苗和幼树之间基因流速率的变化很小。花粉基因流水平对所采样母树的相对隔离距离呈弱负相关（一个地点为140-240米，另一个地点为85-120米），并且两个地点自然生长的幼树的基因流估计值非常相似。在种群内部，一个多元回归模型显示，雄性育性的最大似然估计值与配偶之间的距离呈负相关，与以茎直径衡量的雄性大小呈正相关。然而，在两个种群中，该回归模型均未解释雄性育性总变异的16%以上。
