Hellberg Michael E
Department of Zoology and Center for Population Biology, University of California, Davis, California, 95616.
Evolution. 1996 Jun;50(3):1167-1175. doi: 10.1111/j.1558-5646.1996.tb02357.x.
When the level of gene flow among populations depends upon the geographic distance separating them, genetic differentiation is relatively enhanced. Although the larval dispersal capabilities of marine organisms generally correlate with inferred levels of average gene flow, the effect of different modes of larval development on the association between gene flow and geographic distance remains unknown. In this paper, I examined the relationship between gene flow and distance in two co-occurring solitary corals. Balanophyllia elegans broods large, nonfeeding planulae that generally crawl only short distances from their place of birth before settling. In contrast, Paracyathus stearnsii free-spawns and produces small planktonic larvae presumably capable of broad dispersal by oceanic currents. I calculated F-statistics using genetic variation at six (P. stearnsii) or seven (B. elegans) polymorphic allozyme loci revealed by starch gel electrophoresis, and used these F-statistics to infer levels of gene flow. Average levels of gene flow among twelve Californian localities agreed with previous studies: the species with planktonic, feeding larvae was less genetically subdivided than the brooding species. In addition, geographic isolation between populations appeared to affect gene flow between populations in very different ways in the two species. In the brooding B. elegans, gene flow declined with increasing separation, and distance explained 31% of the variation in gene flow. In the planktonically dispersed P. stearnsii distance of separation between populations at the scale studied (10-1000 km) explained only 1% of the variation in gene flow between populations. The mechanisms generating geographic genetic differentiation in species with different modes of larval development should vary fundamentally as a result of these qualitative differences in the dependence of gene flow on distance.
当种群间基因流水平取决于分隔它们的地理距离时，遗传分化会相对增强。尽管海洋生物幼体的扩散能力通常与推断的平均基因流水平相关，但不同幼体发育模式对基因流与地理距离之间关联的影响仍不明确。在本文中，我研究了两种共生的独居珊瑚的基因流与距离之间的关系。秀丽柱星珊瑚产出大型、不摄食的浮浪幼虫，这些幼虫通常在定居前仅从出生地短距离爬行。相比之下，斯特恩氏拟杯珊瑚自由产卵并产生小型浮游幼虫，推测这些幼虫能够通过洋流进行广泛扩散。我利用淀粉凝胶电泳揭示的六个（斯特恩氏拟杯珊瑚）或七个（秀丽柱星珊瑚）多态性等位酶位点的遗传变异计算了F统计量，并使用这些F统计量来推断基因流水平。加利福尼亚州十二个地点之间的平均基因流水平与先前的研究一致：具有浮游、摄食幼虫的物种在遗传上的细分程度低于育幼物种。此外，种群间的地理隔离似乎以非常不同的方式影响了这两个物种种群间的基因流。在育幼的秀丽柱星珊瑚中，基因流随着隔离距离的增加而下降，距离解释了基因流变异的31%。在所研究的尺度（10 - 1000千米）下，在浮游扩散的斯特恩氏拟杯珊瑚中，种群间的隔离距离仅解释了种群间基因流变异的1%。由于基因流对距离的依赖性存在这些质的差异，不同幼体发育模式的物种产生地理遗传分化的机制应该有根本的不同。
