Canadian Genomics and Conservation Genetics Institute, Faculty of Forestry and Environmental Management, University of New Brunswick, 28 Dineen Drive, Fredericton, NB E3B 5A3, Canada.
BMC Evol Biol. 2012 Apr 5;12:48. doi: 10.1186/1471-2148-12-48.
Fine-scale or spatial genetic structure (SGS) is one of the key genetic characteristics of plant populations. Several evolutionary and ecological processes and population characteristics influence the level of SGS within plant populations. Higher fine-scale genetic structure may be expected in peripheral than core populations of long-lived forest trees, owing to the differences in the magnitude of operating evolutionary and ecological forces such as gene flow, genetic drift, effective population size and founder effects. We addressed this question using eastern white cedar (Thuja occidentalis) as a model species for declining to endangered long-lived tree species with mixed-mating system.
We determined the SGS in two core and two peripheral populations of eastern white cedar from its Maritime Canadian eastern range using six nuclear microsatellite DNA markers. Significant SGS ranging from 15 m to 75 m distance classes was observed in the four studied populations. An analysis of combined four populations revealed significant positive SGS up to the 45 m distance class. The mean positive significant SGS observed in the peripheral populations was up to six times (up to 90 m) of that observed in the core populations (15 m). Spatial autocorrelation coefficients and correlograms of single and sub-sets of populations were statistically significant. The extent of within-population SGS was significantly negatively correlated with all genetic diversity parameters. Significant heterogeneity of within-population SGS was observed for 0-15 m and 61-90 m between core and peripheral populations. Average Sp, and gene flow distances were higher in peripheral (Sp = 0.023, σg = 135 m) than in core (Sp = 0.014, σg = 109 m) populations. However, the mean neighborhood size was higher in the core (Nb = 82) than in the peripheral (Nb = 48) populations.
Eastern white cedar populations have significant fine-scale genetic structure at short distances. Peripheral populations have several-folds higher within-population fine-scale genetic structure than core populations. Anthropogenic disturbances and population fragmentation presumably have significant effects on fine-scale genetic structure in eastern white cedar. Core populations have higher neighborhood size than peripheral populations, whereas gene flow distances are higher in peripheral than in core populations. The results of our study contribute to the knowledge of poorly-understood spatial genetic structure of core versus peripheral populations in plants. As well, the information is of significance for conservation of genetic resources of eastern white cedar and perhaps of other long-lived forest trees with mixed-mating system.
细微或空间遗传结构（SGS）是植物种群的关键遗传特征之一。几个进化和生态过程以及种群特征影响植物种群内 SGS 的水平。由于基因流动、遗传漂变、有效种群大小和奠基者效应等作用进化力量的大小不同，预期在长寿森林树木的边缘种群中会出现更高的细微遗传结构。我们使用东方白杉（Thuja occidentalis）作为具有混合交配系统的衰退濒危长寿树种的模型物种来解决这个问题。
我们使用六个核微卫星 DNA 标记从其加拿大东部沿海地区的两个核心和两个边缘种群中确定了东方白杉的 SGS。在四个研究种群中观察到了 15 米至 75 米距离类别的显著 SGS。对四个种群的综合分析表明，在 45 米的距离类中存在显著的正 SGS。在边缘种群中观察到的平均正显著 SGS 是核心种群的六倍（高达 90 米）。种群内的 SGS 程度与所有遗传多样性参数呈显著负相关。在核心和边缘种群之间，观察到 0-15 米和 61-90 米的种群内 SGS 显著异质性。在边缘（Sp = 0.023，σg = 135 m）种群中，平均 Sp 和基因流距离高于核心（Sp = 0.014，σg = 109 m）种群。然而，核心种群的平均邻域大小（Nb = 82）高于边缘种群（Nb = 48）。
东方白杉种群在短距离内具有显著的细微遗传结构。边缘种群的种群内细微遗传结构比核心种群高出数倍。人为干扰和种群破碎化可能对东方白杉的细微遗传结构产生重大影响。核心种群的邻域大小大于边缘种群，而基因流距离在边缘种群中高于核心种群。我们的研究结果有助于了解植物核心种群与边缘种群中细微遗传结构的知识。此外，这些信息对于保护东方白杉和其他具有混合交配系统的长寿森林树木的遗传资源具有重要意义。
