Taylor Eric B, Foote Chris J, Wood C C
Canadian Department of Fisheries and Oceans, Biological Sciences Branch, Pacific Biological Station, Nanaimo, British Columbia, V9R 5K6, Canada.
School of Fisheries, WH-10, University of Washington, Seattle, Washington, 98195.
Evolution. 1996 Feb;50(1):401-416. doi: 10.1111/j.1558-5646.1996.tb04502.x.
The Pacific salmon Oncorhynchus nerka typically occurs as a sea-run form (sockeye salmon) or may reside permanently in lakes (kokanee) thoughout its native North Pacific. We tested whether such geographically extensive ecotypic variation resulted from parallel evolutionary divergence thoughout the North Pacific or whether the two forms are monophyletic groups by examining allelic variation between sockeye salmon and kokanee at two minisatellite DNA repeat loci and in mitochondrial DNA (mtDNA) Bgl II restriction sites. Our examination of over 750 fish from 24 populations, ranging from Kamchatka to the Columbia River, identified two major genetic groups of North Pacific O. nerka: a "northwestern" group consisting of fish from Kamchatka, western Alaska, and northwestern British Columbia, and a "southern" group consisting of sockeye salmon and kokanee populations from the Fraser and Columbia River systems. Maximum-likelihood analysis accompanied by bootstrapping provided strong support for these two genetic groups of O. nerka; the populations did not cluster by migratory form, but genetic affinities were organized more strongly by geographic proximity. The two major genetic groups resolved in our study probably stem from historical isolation and dispersal of O. nerka from two major Wisconsinan glacial refugia in the North Pacific. There were significant minisatellite DNA allele frequency differences between sockeye salmon and kokanee populations from different parts of the same watershed, between populations spawning in different tributaries of the same lake, and also between sympatric populations spawning in the same stream at the same time. MtDNA Bgl II restriction site variation was significant between sockeye salmon and kokanee spawning in different parts of the same major watershed but not between forms spawning in closer degrees of reproductive sympatry. Patterns of genetic affinity and allele sharing suggested that kokanee have arisen from sea-run sockeye salmon several times independently in the North Pacific. We conclude that sockeye salmon and kokanee are para- and polyphyletic, respectively, and that the present geographic distribution of the ecotypes results from parallel evolutionary origins of kokanee from sockeye (divergences between them) thoughout the North Pacific.
太平洋鲑鱼红大麻哈鱼（Oncorhynchus nerka）通常以溯河洄游型（红大马哈鱼）的形态出现，或者可能会永久栖息在其原产的北太平洋地区的湖泊中（银大麻哈鱼）。我们通过检测红大马哈鱼和银大麻哈鱼在两个小卫星DNA重复位点以及线粒体DNA（mtDNA）Bgl II限制性酶切位点的等位基因变异，来探究这种在地理上广泛存在的生态型变异是源于整个北太平洋地区平行的进化分歧，还是这两种形态属于单系类群。我们对来自从堪察加半岛到哥伦比亚河的24个种群的750多条鱼进行了检测，确定了北太平洋红大麻哈鱼的两个主要遗传类群：一个“西北”类群，由来自堪察加半岛、阿拉斯加西部和不列颠哥伦比亚省西北部的鱼组成；另一个“南部”类群，由来自弗雷泽河和哥伦比亚河水系的红大马哈鱼和银大麻哈鱼种群组成。伴随自展法的最大似然分析为红大麻哈鱼的这两个遗传类群提供了有力支持；这些种群并非按洄游形态聚类，而是遗传亲缘关系更强烈地按地理距离组织起来。我们研究中解析出的这两个主要遗传类群可能源于北太平洋地区红大麻哈鱼从两个主要的威斯康星冰川避难所的历史隔离和扩散。在同一流域不同区域的红大马哈鱼和银大麻哈鱼种群之间、在同一湖泊不同支流产卵的种群之间，以及同时在同一条溪流中产卵的同域种群之间，小卫星DNA等位基因频率存在显著差异。在同一主要流域不同区域产卵的红大马哈鱼和银大麻哈鱼之间，mtDNA Bgl II限制性酶切位点变异显著，但在生殖共生程度较近的形态之间则不显著。遗传亲缘关系和等位基因共享模式表明，在北太平洋地区，银大麻哈鱼曾多次独立地从溯河洄游的红大马哈鱼演化而来。我们得出结论，红大马哈鱼和银大麻哈鱼分别为并系和多系类群，并且目前这些生态型的地理分布是由于整个北太平洋地区银大麻哈鱼从红大马哈鱼平行的进化起源（它们之间的分歧）所致。
