School of Aquatic and Fishery Sciences, University of Washington Box 355020, Seattle, Washington, 98195.
Conservation Genetics Laboratory, U.S. Fish and Wildlife Service 1011 East Tudor Road, Anchorage, Alaska, 99503.
Ecol Evol. 2014 Jun;4(12):2515-32. doi: 10.1002/ece3.1113. Epub 2014 May 22.
Numerous studies of population genetics in salmonids and other anadromous fishes have revealed that population structure is generally organized into geographic hierarchies (isolation by distance), but significant structure can exist in proximate populations due to varying selective pressures (isolation by adaptation). In Chignik Lakes, Alaska, anadromous Dolly Varden char (Salvelinus malma) spawn in nearly all accessible streams throughout the watershed, including those draining directly to an estuary, Chignik Lagoon, into larger rivers, and into lakes. Collections of Dolly Varden fry from 13 streams throughout the system revealed low levels of population structure among streams emptying into freshwater. However, much stronger genetic differentiation was detected between streams emptying into freshwater and streams flowing directly into estuarine environments. This fine-scale reproductive isolation without any physical barriers to migration is likely driven by differences in selection pressures across freshwater and estuarine environments. Estuary tributaries had fewer larger, older juveniles, suggesting an alternative life history of smolting and migration to the marine environment at a much smaller size than occurs in the other populations. Therefore, genetic data were consistent with a scenario where isolation by adaptation occurs between populations of Dolly Varden in the study system, and ecological data suggest that this isolation may partially be a result of a novel Dolly Varden life history of seawater tolerance at a smaller size than previously recognized.
许多鲑鱼和其他溯河洄游鱼类的群体遗传学研究表明，种群结构通常组织成地理层次结构（距离隔离），但由于不同的选择压力（适应隔离），近缘种群中可能存在显著的结构。在阿拉斯加的奇尼克湖，溯河洄游的多利瓦登鲑（Salvelinus malma）在整个流域的几乎所有可进入的溪流中产卵，包括那些直接排入河口、奇尼克泻湖、入海口河流和湖泊的溪流。从系统中 13 条溪流中收集的多利瓦登鲑幼鱼表明，流入淡水的溪流之间的种群结构水平较低。然而，在流入淡水的溪流和直接流入河口环境的溪流之间，检测到更强的遗传分化。这种没有任何迁移物理障碍的精细繁殖隔离可能是由淡水和河口环境之间选择压力的差异驱动的。河口支流中较小、较老的幼鱼较少，这表明与其他种群相比，在较小的体型下，有替代的洄游和向海洋环境发育的生活史。因此，遗传数据与适应隔离发生在研究系统中的多利瓦登鲑种群之间的情况一致，而生态数据表明，这种隔离可能部分是由于一种新的多利瓦登鲑的生活史，即对海水的耐受性在以前未被认识到的较小体型。
