Department of Biological Sciences, Purdue University, West Lafayette, Indiana.
Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana.
Mol Ecol. 2018 Oct;27(20):4041-4051. doi: 10.1111/mec.14726. Epub 2018 Jun 10.
Introduced species often colonize regions that have vastly different ecological and environmental conditions than those found in their native range. As such, species introductions can provide a deeper understanding into the process of adaptive evolution. In the 1880s, steelhead trout (Oncorhynchus mykiss) from California were introduced into Lake Michigan (Laurentian Great Lakes, North America) where they established naturally reproducing populations. In their native range, steelhead hatch in rivers, migrate to the ocean and return to freshwater to spawn. Steelhead in Lake Michigan continue to swim up rivers to spawn, but now treat the freshwater environment of the Great Lakes as a surrogate ocean. To examine the effects of this introduction, we sequenced the genomes of 264 fish. By comparing steelhead from Lake Michigan to steelhead from their ancestral range, we determined that the introduction led to consistent reductions in genetic diversity across all 29 chromosomes. Despite this reduction in genetic diversity, three chromosomal regions were associated with rapid genetic adaptation to the novel environment. The first region contained functional changes to ceramide kinase, which likely altered metabolic and wound-healing rates in Lake Michigan steelhead. The second and third regions encoded carbonic anhydrases and a solute carrier protein, both of which are critical for osmoregulation, and demonstrate how steelhead physiologically adapted to freshwater. Furthermore, the contemporary release of diverse hatchery strains into the lake increased genetic diversity but reduced the signature of genetic adaptation. This study illustrates that species can rapidly adapt to novel environments despite genome-wide reductions in genetic diversity.
引入物种常常在生态和环境条件与原产地大不相同的地区定居。因此，物种引入可以更深入地了解适应进化的过程。19 世纪 80 年代，来自加利福尼亚的虹鳟鱼（Oncorhynchus mykiss）被引入密歇根湖（北美大湖地区），在那里它们建立了自然繁殖的种群。在它们的原生栖息地，虹鳟鱼在河流中孵化，迁移到海洋，然后返回淡水产卵。密歇根湖的虹鳟鱼仍然会游回河流产卵，但现在将大湖的淡水环境视为替代海洋。为了研究这种引入的影响，我们对 264 条鱼的基因组进行了测序。通过比较密歇根湖的虹鳟鱼和它们的祖先种群的虹鳟鱼，我们发现引入导致了所有 29 条染色体的遗传多样性持续减少。尽管遗传多样性减少，但有三个染色体区域与对新环境的快速遗传适应有关。第一个区域包含神经酰胺激酶的功能变化，这可能改变了密歇根湖虹鳟鱼的代谢和伤口愈合速度。第二个和第三个区域分别编码碳酸酐酶和溶质载体蛋白，这两种蛋白对渗透调节都很关键，并且表明虹鳟鱼如何在生理上适应淡水。此外，当代不同的养殖场品系在湖中释放增加了遗传多样性，但减少了遗传适应的特征。这项研究表明，尽管遗传多样性在全基因组范围内减少，物种仍然可以快速适应新环境。
