Department of Fisheries Biology, Cal Poly Humboldt, Arcata, CA, United States.
Fisheries Ecology Division, NOAA Southwest Fisheries Science Center and University of California, Santa Cruz, CA, United States.
J Hered. 2023 May 25;114(3):219-230. doi: 10.1093/jhered/esad022.
Hybridization between coastal cutthroat trout (Oncorhynchus clarkii clarkii) and steelhead (O. mykiss) was assessed in the Smith River, California. Individuals were categorized as pure or as 1 of 10 hybrid classes using 30 "diagnostic" single-nucleotide polymorphisms positioned on 26 separate chromosomes. Most of the individuals examined (n = 876), were pure coastal cutthroat trout (n = 634) or pure steelhead (n = 213), and 29 individuals were identified as having hybrid ancestry. Among hybrids, first generation hybrids (n = 15) and coastal cutthroat trout backcrosses (n = 12) were the most common. No individuals were identified as backcrosses to SH, suggesting the presence of genetic or behavioral mechanisms constraining such backcrosses, or the growth and survival of their progeny. Mitochondrial DNA of 14 of 15 F1 hybrids was of steelhead origin, suggesting that hybridization was driven primarily by sneak-mating of male coastal cutthroat trout with female steelhead. Evaluation of classical phenotypic characters for coastal cutthroat trout and steelhead (i.e. jaw slash, maxillary length, and hyoid teeth) were not reliable by themselves for identification of either pure parental fish or hybrids. In contrast, analysis with geometric morphometrics revealed distinctive body shapes for pure coastal cutthroat trout and steelhead, and the combination of classical traits and geometric morphology was mostly accurate in distinguishing them. However, first generation hybrids and backcrosses overlapped completely with parental types, highlighting challenges in hybrid identification using phenotypic traits.
在加利福尼亚州的史密斯河评估了沿海斑鳟（Oncorhynchus clarkii clarkii）和虹鳟（O. mykiss）之间的杂交情况。个体通过 30 个位于 26 个独立染色体上的“诊断”单核苷酸多态性被归类为纯系或 10 个杂交类中的 1 个。大多数检查的个体（n = 876）为纯沿海斑鳟（n = 634）或纯虹鳟（n = 213），有 29 个个体被鉴定为具有杂交血统。在杂种中，第一代杂种（n = 15）和沿海斑鳟回交（n = 12）最为常见。没有个体被鉴定为回交到 SH，这表明存在遗传或行为机制限制了这种回交，或限制了它们后代的生长和存活。15 个 F1 杂种中的 14 个的线粒体 DNA 来自虹鳟，这表明杂交主要是由雄性沿海斑鳟与雌性虹鳟的偷偷交配驱动的。对沿海斑鳟和虹鳟的经典表型特征（即下颌裂缝、上颌骨长度和下咽齿）的评估本身并不可靠，无法识别纯亲鱼或杂种。相比之下，对经典特征和几何形态的分析显示，纯系沿海斑鳟和虹鳟具有独特的体型，并且组合使用经典特征和几何形态学在区分它们方面大多是准确的。然而，第一代杂种和回交与亲本类型完全重叠，这突出了使用表型特征识别杂种的挑战。
