1. Water impoundment is among the most prevalent and potent forms of anthropogenic environmental modification worldwide. Flow modification can drive morphological changes in riverine species that persist after dam closure, but little is known about the tempo and trajectory of phenotypic responses to impoundment.
2. Through geometric morphometric analysis of natural history collections from behind Claiborne Lock and Dam (i.e. in Claiborne Lake reservoir) and nearby Chilatchee Creek (Alabama River Basin, Alabama, U.S.A.), we reconstructed multidecadal chronosequences of morphological change in a stream fish (Cyprinella venusta Girard) to characterise phenotypic responses to impoundment and unrestricted flow. We then conducted cross-correlation analysis of hydrological and morphological time series to determine whether morphological responses to impoundment are consistent with expected outcomes of evolution, phenotypic plasticity, or some combination thereof.
3. We found evidence of marked phenotypic change shortly after impoundment. Within a year of dam closure, individuals from Claiborne Lake exhibited a reduction in head size, an increase in body depth, and a decline in the length of the dorsal fin base, with further responses becoming apparent c. 6 years thereafter. The morphology of individuals from the nearby stream consistently differed from individuals in the reservoir. We found that fish from Chilatchee Creek exhibited gradual directional shifts and morphological fluctuations over time, which differed from patterns of change observed in C. venusta from Claiborne Lake. There also were indications of multidecadal lags at both sites, probably reflecting common responses to periodic climatic variation that were mitigated by site-specific differences in physiography and ecology.
4. Our findings are consistent with the hypothesis that impoundment can elicit punctuated responses attributable to within-generational phenotypic change and rapid evolution over as few as two generations. Our findings also indicate that hydrological variation in unrestricted streams can elicit pronounced shifts in body shape, suggesting that space-for-time substitutions may not effectively capture the nature of responses to flow modification. Additional investigations based on more extensive and complete chronosequences would further illustrate the value of natural history collections and offer more insight into the mechanistic basis of biotic responses to environmental change.

中文翻译：

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河流鱼类蓄水后形态变化的时间序列

1. 蓄水是世界范围内最普遍和最有效的人为环境改变形式之一。流量改变可以驱动大坝关闭后持续存在的河流物种的形态变化，但对蓄水表型反应的节奏和轨迹知之甚少。
2. 通过对 Claiborne Lock and Dam 后面（即 Claiborne Lake 水库）和附近 Chilatchee Creek（美国阿拉巴马州阿拉巴马河流域）的自然历史收藏进行几何形态计量分析，我们重建了溪流鱼类（Cyprinella venusta Girard）形态变化的数十年时间序列) 来表征对蓄水和无限制流动的表型反应。然后，我们对水文和形态时间序列进行了互相关分析，以确定对蓄水的形态响应是否与进化、表型可塑性或其某种组合的预期结果一致。
3. 我们在蓄水后不久发现了显着表型变化的证据。在大坝关闭的一年内，来自克莱伯恩湖的个体表现出头部尺寸减小，身体深度增加，背鳍基部长度减少，进一步的反应变得明显c。6年后。来自附近河流的个体的形态与水库中的个体始终不同。我们发现 Chilatchee Creek 的鱼随着时间的推移表现出逐渐的方向变化和形态波动，这与C 中观察到的变化模式不同。维努斯塔来自克莱本湖。两个地点也有多年滞后的迹象，这可能反映了对周期性气候变化的共同反应，这些反应因地点特定的地貌和生态差异而减轻。
4. 我们的研究结果与以下假设一致，即蓄水可以引起由于代内表型变化和短短两代的快速进化而引起的间断反应。我们的研究结果还表明，不受限制的河流中的水文变化会引起身体形状的显着变化，这表明时空替代可能无法有效地捕捉对流量改变的反应的性质。基于更广泛和完整的时间序列的其他调查将进一步说明自然历史收藏的价值，并提供对生物对环境变化反应的机制基础的更多见解。