Department of Animal Science, UC Davis, Davis, CA.
Department of Biology, University of Nevada-Reno, MS, Reno, RN.
J Hered. 2020 Dec 7;111(6):548-563. doi: 10.1093/jhered/esaa043.
The preservation of life history and other phenotypic complexity is central to the resilience of Pacific salmon stocks. Steelhead (Oncorhynchus mykiss) express a diversity of life-history strategies such as the propensity to migrate (anadromy/residency) and the timing and state of maturation upon return to freshwater (run-timing), providing an opportunity to study adaptive phenotypic complexity. Historically, the Eel River supported upwards of 1 million salmon and steelhead, but the past century has seen dramatic declines of all salmonids in the watershed. Here we investigate life-history variation in Eel River steelhead by using Rapture sequencing, on thousands of individuals, to genotype the region diagnostic for run-timing (GREB1L) and the region strongly associated with residency/anadromy (OMY5) in the Eel River and other locations, as well as determine patterns of overall genetic differentiation. Our results provide insight into many conservation-related issues. For example, we found that distinct segregation between winter and summer-run steelhead correlated with flow-dependent barriers in major forks of the Eel, that summer-run steelhead inhabited the upper Eel prior to construction of an impassable dam, and that both life history and overall genetic diversity have been maintained in the resident trout population above; and we found no evidence of the summer-run allele in the South Fork Eel, indicating that summer run-timing cannot be expected to arise from standing genetic variation in this and other populations that lack the summer-run phenotype. The results presented in this study provide valuable information for designing future restoration and management strategies for O. mykiss in Northern California and beyond.
生命史和其他表型复杂性的保存是太平洋鲑鱼种群恢复力的核心。虹鳟（Oncorhynchus mykiss）表现出多种生活史策略，例如迁移的倾向（洄游/居留）和返回淡水时的成熟时间和状态（洄游时间），这为研究适应性表型复杂性提供了机会。历史上，鳗鱼河支持着超过 100 万条鲑鱼和虹鳟，但在过去的一个世纪里，该流域的所有鲑鱼都大幅减少。在这里，我们通过使用 Rapture 测序技术，在数千个个体上对用于鉴定洄游时间（GREB1L）的区域和与鳗鱼河及其他地区的居留/洄游（OMY5）强烈相关的区域进行基因分型，研究鳗鱼河虹鳟的生活史变异，并确定整体遗传分化模式。我们的研究结果为许多与保护相关的问题提供了深入的了解。例如，我们发现冬季和夏季洄游虹鳟之间的明显分离与鳗鱼河主要支流中依赖水流的障碍有关，夏季洄游虹鳟在建造一座不可逾越的大坝之前就栖息在上游的鳗鱼河中，并且居留鳟种群中的生活史和整体遗传多样性都得到了维持；我们在南叉鳗鱼河中没有发现夏季洄游等位基因的证据，这表明在缺乏夏季洄游表型的其他种群中，夏季洄游时间不太可能是由遗传变异引起的。本研究的结果为北加州及其他地区虹鳟的未来恢复和管理策略提供了有价值的信息。
