The Cisco Coregonus artedi is a planktivorous fish that is widely distributed in lakes across glaciated areas of North America. With retreat of Laurentide ice, Cisco dispersed from refugia into a vast network of meltwater (proglacial) lakes that eventually receded, stranding populations in depressions—today’s lakes. Refugial populations also colonized lakes that fell outside of the footprint of a proglacial lake. These two types of Cisco lakes, those inside the footprint of a proglacial lake and those outside the footprint, though uncounted, number in the high hundreds or more. All 53 lakes reported to contain sympatric forms of Cisco occur in previously inundated lakes; no sympatric forms occur in lakes that were not inundated. We reviewed Laurentide zoogeography to assess whether secondary contacts in the proglacial lakes were extensive enough to account for the distribution of sympatric lakes. We concluded that secondary contacts had been more extensive in the proglacial lakes than detected in genetic studies of Cisco. We inferred that secondary contacts in the proglacial lakes resulted in more plastic, diverse phenotypes than were found in lakes not inundated and that these phenotypes were more capable of divergence than were phenotypes inhabiting lakes not inundated. Secondary contacts in the proglacial lakes appear to have been limited to shallow‐water forms of Cisco. Deepwater forms likely did not evolve until after the proglacial lakes receded, as meltwater appears to have been trophically unsuitable for pelagic fishes like Cisco. Cisco are assumed to have colonized meltwater lakes by “hopscotching” between inlets, thereby avoiding prolonged existence in meltwater. Sympatric populations of Cisco are rare in comparison with the number of allopatric populations, even in inundated lakes, indicating that divergence occurs under specialized conditions. Canalization appears to have diminished the evolvability of contemporary forms as compared to their ancestors. Hybridization within Cisco species pairs appears to be the norm and is aggravated by anthropogenically induced events.

中文翻译：

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思科中的物种，重点是次要联系，可塑性和杂交

思科Coregonus artedi是一种浮游鱼类，广泛分布在北美冰河地区的湖泊中。随着Laurentide冰的撤退，Cisco从避难所分散到一个庞大的融水（冰川湖）湖网中，这些湖最终消退，使人口陷入了萧条-今天的湖泊中。避难人口还殖民了落在冰河湖足迹之外的湖泊。这两种类型的思科湖，虽然位于湖泊湖泊脚印之内，却位于湖泊脚印之外，尽管数量不多，但数量高达数百个甚至更多。据报告，所有53个含有思科同胞型思科的湖泊都发生在以前被淹没的湖泊中。没有被淹没的湖泊中不会发生同胞形态。我们回顾了Laurentide的动物地理学，以评估冰河湖泊中的次生接触是否足够广泛，足以说明同胞湖泊的分布。我们得出的结论是，与Cisco的遗传学研究相比，冰川湖中的次要接触面更为广泛。我们推断，与没有被淹没的湖泊相比，与未淹没的湖泊相比，冰川湖的次生接触导致了更多的可塑性，多样化的表型，并且这些表型具有更大的发散能力。冰川湖的次生接触似乎仅限于思科的浅水形式。深水形式可能直到冰川湖退去后才演化，因为融水似乎在营养上不适合像思科这样的中上鱼类。思科被认为是通过在入口之间“跳网”在殖民地的融水湖中定殖的，从而避免了融水长期存在。与同种异体种群的数量相比，即使在淹没的湖泊中，思科的同伴种群也很少见，这表明在特殊条件下会发生分歧。与他们的祖先相比，运河化似乎削弱了现代形式的可演变性。思科物种对之间的杂交似乎是正常现象，并且由于人为诱发的事件而加剧。与他们的祖先相比，运河化似乎削弱了现代形式的可演变性。思科物种对之间的杂交似乎是正常现象，并且由于人为诱发的事件而加剧。与他们的祖先相比，运河化似乎削弱了现代形式的可演变性。思科物种对之间的杂交似乎是正常现象，并且由于人为诱发的事件而加剧。