1. Anthropogenic stream impoundments often result in altered flow regimes and reservoir formations. Functional fish characteristics may change in response to altered flow conditions, and understanding the underlying mechanisms at work (e.g. natural selection and phenotypic plasticity) is of great importance in both evolutionary and conservation contexts. Cyprinella lutrensis is a widely distributed minnow native to stream systems in Missouri, U.S.A. Following impoundment of the Osage River, C. lutrensis currently occurs in the resultant Truman Reservoir and surrounding tributaries. To examine the impacts of this habitat alteration on functional fish characteristics, we hypothesised that C. lutrensis populations in altered systems with no‐flow would show an overall less streamlined body shape as compared to those in flowing systems, assuming body streamlining is beneficial for locomotion in flowing environments.
2. We conducted field and laboratory studies to test effects of flow and no‐flow on C. lutrensis body shape. Geometric morphometric techniques were used to quantify body shape in field and laboratory individuals, and non‐structural lipid extractions were conducted to assess whether fat storage contributes to body shape under flow and no‐flow treatments.
3. Morphological comparisons between C. lutrensis from Truman Reservoir and surrounding streams yielded significant differences in body shape, with greater body streamlining in stream populations. A laboratory experiment using artificial stream units revealed similar significant differences in body streamlining between flow and no‐flow treatments within a single generation. In addition, individuals under no‐flow treatment had significantly higher levels of non‐structural lipids compared to flow treatment individuals.
4. Our results indicate that changes in flow regime can alter the evolutionary trajectories (i.e. related to morphology) of fish populations. We suggest that body shape alterations are likely to occur within and across generations in a cumulative manner, therefore, it is plausible that both natural selection and plastic response mechanisms play roles in defining minnow body shape following flow alteration.

中文翻译：

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符合状态流：栖息地改变对鱼体形特征的影响

1. 人为的水库蓄水经常导致流态和储层形成改变。鱼类的功能特性可能会因水流条件的变化而发生变化，因此，了解进化中的潜在机制（例如自然选择和表型可塑性）在进化和保护方面都至关重要。Cytrinella lutrensis是分布于美国密苏里州河流系统中的广泛分布的min鱼，在奥塞奇河（Osage River）蓄水后，目前在杜鲁门水库和周边支流中出现了C. lutrensis。为了检查这种生境变化对功能性鱼类特征的影响，我们假设C. lutrensis 假设身体精简对流动环境中的运动有益，那么与没有流动的系统相比，在没有流动的变化系统中，总体上流线型的人体形状会更少。
2. 我们进行了野外和实验室研究，以测试流动和不流动对C. lutrensis体形的影响。几何形态计量学技术用于量化田间和实验室个体的身体形状，并进行了非结构性脂质提取，以评估在流动和不流动的处理条件下，脂肪储存是否有助于身体形状。
3. 杜鲁门水库和周围河流的卢氏梭菌的形态学比较显示出明显的体形差异，溪流种群的体形更大。使用人工流单位的实验室实验表明，在同一代中，流处理和不流处理之间的人体流线化具有相似的显着差异。此外，与不进行流处理的个体相比，不进行流处理的个体的非结构性脂质水平要高得多。
4. 我们的结果表明，流态的变化可以改变鱼类种群的进化轨迹（即与形态有关）。我们建议，体型的改变很可能以累积的方式发生在代内和世代之间，因此，自然选择和塑性响应机制都可能在流量改变后在定义min鱼体型中起作用。