Dam constructions cause fundamental changes in the natural landscape, creating new ecological and evolutionary challenges for aquatic organisms. In some cases, such water impoundments have been related with morphological changes in organisms. Understanding how populations respond to rapid environmental changes imposed by dams is the first step to elucidate the consequences that disturbed habitats may have on species evolution. In this work, we analyzed shape and size variation in Bryconamericus iheringii Boulenger 1887 from the Chasqueiro stream basin, south of Brazil, which was recently dammed. We used linear measurements and geometric morphometrics to identify morphological differences among specimens from the reservoir (lentic habitat) compared to the habitat upstream and downstream of the dam (lotic habitats). We also tested for size- and shape-related sexual dimorphism to determine whether variations observed were the same for both sexes. We found that B. iheringii from the artificial reservoir were distinct in shape and size to those from their natural habitat in the stream. The size variation between environments was the same for both sexes, but the shape variation differed between males and females. Regarding the linear measurements, lotic populations were larger (greater body length, width, pectoral fin base length and caudal peduncle length), probably in response to increased swimming activity. Regarding body shape, we found that both sexes have a more fusiform body in lotic habitats than in the reservoir. In addition, females showed an altered mouth position that was distinct between these environments. This work indicates that the water reservoir seems to be an important factor influencing morphological variation in B. iheringii, a species with sexual shape dimorphism.

中文翻译：

---

一种characid物种中人工lentic和相邻lotic环境之间的形态差异

大坝建设导致自然景观发生根本性变化，为水生生物带来新的生态和进化挑战。在某些情况下，这种蓄水与生物体的形态变化有关。了解种群如何应对水坝造成的快速环境变化是阐明栖息地受到干扰可能对物种进化产生的后果的第一步。在这项工作中，我们分析了来自巴西南部 Chasqueiro 河流盆地的 Bryconamericus iheringii Boulenger 1887 的形状和大小变化，该盆地最近被筑坝。我们使用线性测量和几何形态计量学来识别水库（静水栖息地）标本与大坝上游和下游栖息地（水洼栖息地）之间的形态差异。我们还测试了与大小和形状相关的性别二态性，以确定观察到的变化是否对两性都相同。我们发现人工水库中的 B. iheringii 在形状和大小上与其在溪流中的自然栖息地不同。两性环境之间的大小变化相同，但男性和女性之间的形状变化不同。关于线性测量，激流种群更大（更大的体长、宽度、胸鳍基部长度和尾柄长度），可能是对游泳活动增加的反应。关于体型，我们发现在激流栖息地中，两性的身体比在水库中更呈梭形。此外，女性表现出不同的嘴部位置，这在这些环境中是不同的。