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<p>Waterfalls are natural in-stream barriers that can limit fish movement and gene flow, resulting in isolated populations and divergent environmental conditions upstream and downstream. We investigated morphological variation in four common stream fish species – Creek Chub <i>Semotilus atromaculatus</i>, Highland Stoneroller <i>Campostoma spadiceum</i>, Redfin Darter <i>Etheostoma whipplei,</i> and Plains Orangethroat Darter <i>Etheostoma</i> sp. <i>cf pulchellum I/II</i> – located above and below a waterfall in an intermittent stream in the southeastern United States to assess how natural barriers influence phenotypic variation. Using geometric morphometric analyses, we compared body shape between upstream and downstream populations. Redfin Darter and Plains Orangethroat Darter had significantly larger centroid sizes upstream. After accounting for allometry, shape differences between reaches were significant in Creek Chub, Highland Stoneroller, and Plains Orangethroat Darter, whereas reach did not significantly affect Redfin Darter shape. All species except Creek Chub showed, on average, deeper bodies upstream. These findings suggest that waterfalls can promote intraspecific morphological divergence, potentially reflecting local adaptation to distinct environmental conditions, and provide a useful baseline for assessing the impacts of anthropogenic barriers such as dams and culverts. Understanding how natural fragmentation shapes phenotypic diversity is critical for the conservation and management of freshwater ecosystems increasingly threatened by habitat alteration.</p>

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Morphological variation in four common stream fish across an intermittent waterfall in Arkansas, USA

  • 期刊论文

  • 发表日期：

    2025年10月28日

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  • Risa McCollough,
  • Kyler Hecke

摘要

Waterfalls are natural in-stream barriers that can limit fish movement and gene flow, resulting in isolated populations and divergent environmental conditions upstream and downstream. We investigated morphological variation in four common stream fish species – Creek Chub Semotilus atromaculatus, Highland Stoneroller Campostoma spadiceum, Redfin Darter Etheostoma whipplei, and Plains Orangethroat Darter Etheostoma sp. cf pulchellum I/II – located above and below a waterfall in an intermittent stream in the southeastern United States to assess how natural barriers influence phenotypic variation. Using geometric morphometric analyses, we compared body shape between upstream and downstream populations. Redfin Darter and Plains Orangethroat Darter had significantly larger centroid sizes upstream. After accounting for allometry, shape differences between reaches were significant in Creek Chub, Highland Stoneroller, and Plains Orangethroat Darter, whereas reach did not significantly affect Redfin Darter shape. All species except Creek Chub showed, on average, deeper bodies upstream. These findings suggest that waterfalls can promote intraspecific morphological divergence, potentially reflecting local adaptation to distinct environmental conditions, and provide a useful baseline for assessing the impacts of anthropogenic barriers such as dams and culverts. Understanding how natural fragmentation shapes phenotypic diversity is critical for the conservation and management of freshwater ecosystems increasingly threatened by habitat alteration.