Williamson P S, Werth C R
Department of Biology, Southwest Texas State University, San Marcos, Texas 78666; and.
Am J Bot. 1999 Feb;86(2):293-301.
Genetic variation was evaluated in the federally endangered species Abronia macrocarpa (large-fruited sand-verbena), an herbaceous perennial restricted to deep sandy soils and endemic to three counties of east-central Texas. Seven of the ten known populations were sampled and analyzed using starch gel electrophoresis of eight enzymes coded by 18 interpretable loci. Duplicate gene expression was observed for four loci, suggesting polyploid ancestry for the lineage that includes A. macrocarpa. Values for estimators of genetic polymorphism within populations (ranges: P = 38.9%-61.1%, A = 1.7-2.1, H = 0.122-0.279) exceeded average values for seed plants (P = 34.2%, A = 1.53, H = 0.113). Genotype proportions at most loci in most populations were in Hardy-Weinberg equilibrium, consistent with obligate outcrossing previously documented for this species; exceptions could be attributed to population substructure. Values of F(ST) tended to be high, ranging from 0.021 to 0.481 for individual loci (mean F(ST) = 0.272), indicating substantial divergence and limited gene flow among populations, despite their close geographic proximity. Pairwise values of Nei's genetic identity between populations ranged from 0.799 to 0.975 and tended to be influenced by geographic proximity of population pairs. Collectively, these data suggest a long history of isolation among populations that have not been subjected to bottlenecks. Isolation of A. macrocarpa populations apparently results from the disjunct occurrence of suitable habitat and perhaps has been accentuated by human disturbance.
对联邦濒危物种大果砂马鞭草（Abronia macrocarpa）的遗传变异进行了评估。大果砂马鞭草是一种多年生草本植物，仅生长于深厚的沙质土壤中，且仅分布于德克萨斯州中东部的三个县。对已知的10个种群中的7个进行了采样，并使用淀粉凝胶电泳对由18个可解释位点编码的8种酶进行了分析。在4个位点观察到了重复基因表达，这表明包括大果砂马鞭草在内的谱系具有多倍体祖先。种群内遗传多态性估计值（范围：P = 38.9%-61.1%，A = 1.7-2.1，H = 0.122-0.279）超过了种子植物的平均值（P = 34.2%，A = 1.53，H = 0.113）。大多数种群中大多数位点的基因型比例处于哈迪-温伯格平衡，这与该物种先前记录的专性异交一致；例外情况可能归因于种群亚结构。F(ST)值往往较高，单个位点的F(ST)值范围为0.021至0.481（平均F(ST) = 0.272），这表明尽管种群在地理上距离较近，但种群间存在显著分化且基因流有限。种群间的奈氏遗传同一性成对值范围为0.799至0.975，并且往往受到种群对地理距离的影响。总体而言，这些数据表明种群之间存在长期的隔离历史，且未经历瓶颈效应。大果砂马鞭草种群的隔离显然是由于适宜栖息地的间断出现所致，或许还因人类干扰而加剧。
