Taylor E B, Harvey S, Pollard S, Volpe J
Department of Zoology, University of British Columbia, Vancouver, Canada.
Mol Ecol. 1997 Jun;6(6):503-17. doi: 10.1046/j.1365-294x.1997.00213.x.
Okanagan Lake, south-central interior of BC, contains two reproductive ecotypes of kokanee Oncorhynchus nerka; individuals spawn in tributary streams ('stream-spawners') as well as on shoreline gravel areas ('beach-spawners'). We tested the hypothesis that these sympatric ecotypes comprise a single panmictic population by assaying variation in morphological traits and at allozyme, mitochondrial and minisatellite DNA loci in fish collected from three stream-spawning and two beach-spawning sites. No morphological traits consistently distinguished the reproductive ecotypes with the exception of the number of anal fin rays which was greater in stream-spawning kokanee. Four of 18 allozyme loci screened were polymorphic, but no significant allele frequency differences were detected among populations within ecotypes or between ecotypes. Similarly, allele frequencies at two minisatellite DNA loci were not significantly different among populations or between ecotypes. By contrast, significant differences in the frequencies of mitochondrial DNA restriction fragment length polymorphism (mtDNA RFLP) haplo-types were detected between stream- and beach-spawners, but not among populations within ecotypes. Further, two RFLPs that distinguished stream- and beach-spawning adults were found in juvenile kokanee sampled from the limnetic zone of Okanagan Lake. The two mtDNA RFLPs and a d-loop sequence variant appear to be unique to Okanagan Lake Kokanee because we did not observe these haplotypes in sockeye salmon and kokanee sampled outside of Okanagan Lake. Our data suggest that: (i) there is restricted female-mediated gene flow between stream- and beach-spawning kokanee in Okanagan Lake, (ii) the forms have diverged within the lake basin since the retreat of the Wisconsinian glaciers (< approximately equal to 11 000 years ago), and (iii) distinct reproductive niches may promote divergence in north temperate freshwater fish faunas.
奥卡纳根湖位于不列颠哥伦比亚省中南部内陆地区，湖里有两种繁殖生态型的红大麻哈鱼（Oncorhynchus nerka）；个体在支流中产卵（“溪流产卵型”），也在海岸线砾石区域产卵（“海滩产卵型”）。我们通过分析从三个溪流产卵地点和两个海滩产卵地点采集的鱼类的形态特征、等位酶、线粒体和微卫星DNA位点的变异，来检验这一同域分布的生态型是否构成一个单一的随机交配种群的假设。除了臀鳍鳍条数量在溪流产卵的红大麻哈鱼中更多外，没有形态特征能持续区分这两种繁殖生态型。在筛选的18个等位酶位点中，有4个是多态性的，但在生态型内的种群之间或生态型之间未检测到显著的等位基因频率差异。同样，在两个微卫星DNA位点的等位基因频率在种群之间或生态型之间也没有显著差异。相比之下，在溪流产卵型和海滩产卵型之间检测到线粒体DNA限制性片段长度多态性（mtDNA RFLP）单倍型频率存在显著差异，但在生态型内的种群之间未检测到。此外，在从奥卡纳根湖敞水区采集的幼年红大麻哈鱼中发现了两种区分溪流产卵型和海滩产卵型成鱼的RFLP。这两种mtDNA RFLP和一个d环序列变体似乎是奥卡纳根湖红大麻哈鱼所特有的，因为我们在奥卡纳根湖以外采集的红鲑和红大麻哈鱼中未观察到这些单倍型。我们的数据表明：（i）奥卡纳根湖溪流产卵型和海滩产卵型红大麻哈鱼之间存在有限的雌性介导的基因流动；（ii）自威斯康星冰川消退（<约11000年前）以来，这些形态在湖盆内已经分化；（iii）不同的繁殖生态位可能促进北温带淡水鱼类区系的分化。
