Hellberg Michael E
Department of Zoology and Center for Population Biology, University of California, Davis, California, 95616.
Evolution. 1994 Dec;48(6):1829-1854. doi: 10.1111/j.1558-5646.1994.tb02218.x.
When the dispersal capability of a species is considerably less than its geographic range, genetic differences between populations should increase with the distance separating those populations. This pattern should be most evident in linearly distributed species. The sessile solitary cup coral Balanophyllia elegans lives along nearly the entire Pacific coast of North America, yet its crawling larvae usually settle within 40 cm of their birthplace. In this paper, I document geographic patterns of allozyme differentiation within and among populations of B. elegans and estimate the proportion of observed geographic pattern attributable to gene flow between adjacent populations. Genetic subdivision among localities separated by up to 3000 km was high (F = 0.283, SE = 0.038). Inferred gene flow between pairs of localities (M∘, individuals per generation) correlated inversely with the geographic distance between those localities, consistent with the pattern expected for a species at equilibrium in which gene flow occurred exclusively between adjacent localities. Within localities, patches separated by 4 to 30 m were also significantly subdivided, but genetic differentiation between patches did not vary significantly with the distance separating them. Simulations revealed that the power to detect genetic pattern expected from gene flow between adjacent populations increased with both the number of loci used to infer gene flow and the heterozygosity of those loci. Simulations also verified that when geographic distance poorly approximated the number of steps between populations, reduced major-axis regression more accurately portrayed the structural relationship between gene flow and separation than did ordinary least-squares regression. Attenuation of gene flow with distance explained 15% of the between-locality pattern of genetic differentiation in B. elegans. The remaining variation appeared to be due to neither natural selection nor a recent rangewide recolonization. Loci from the northern sampled localities, however, had fewer alleles than those from the remainder of the range, suggesting these localities had been recolonized recently following Pleistocene cooling.
当一个物种的扩散能力远小于其地理分布范围时，种群之间的遗传差异应随着种群间距离的增加而增大。这种模式在呈线性分布的物种中应最为明显。固着的独居杯形珊瑚优雅柱星珊瑚几乎生活在北美洲太平洋沿岸的整个区域，但其爬行幼虫通常在出生地40厘米范围内定居。在本文中，我记录了优雅柱星珊瑚种群内部和种群之间等位酶分化的地理模式，并估计了观察到的地理模式中可归因于相邻种群间基因流动的比例。相隔达3000公里的不同地点之间的遗传细分程度很高（F = 0.283，标准误 = 0.038）。推断的成对地点之间的基因流动（M∘，每代个体数）与这些地点之间的地理距离呈负相关，这与处于平衡状态的物种的预期模式一致，即基因流动仅发生在相邻地点之间。在各个地点内，相隔4至30米的斑块也有显著的细分，但斑块之间的遗传分化并未随它们之间的距离而显著变化。模拟结果表明，检测相邻种群间基因流动预期的遗传模式的能力随着用于推断基因流动的基因座数量以及这些基因座的杂合度的增加而增强。模拟还证实，当地理距离不能很好地近似种群之间的步数时，与普通最小二乘法回归相比，简化主轴回归能更准确地描绘基因流动与隔离之间的结构关系。基因流动随距离的衰减解释了优雅柱星珊瑚地点间遗传分化模式的15%。其余的变异似乎既不是由于自然选择，也不是由于近期的全范围重新定殖。然而，来自北部采样地点的基因座的等位基因比该分布范围其余部分的要少，这表明这些地点在更新世变冷后最近才重新定殖。
