A major question in stream ecology is how invertebrates cope with flow. In aquatic gastropods, typically, larger and more globular shells with larger apertures are found in lotic (flowing water) versus lentic (stagnant water) habitats. This has been hypothetically linked to a larger foot, and thus attachment area, which has been suggested to be an adaptation against risk of dislodgement by current. Empirical evidence for this is scarce. Furthermore, these previous studies did not discuss the unavoidable increase in drag forces experienced by the snails as a consequence of the increased cross sectional area. Here, using Potamopyrgus antipodarum as a study model, we integrated computational fluid dynamics simulations and a flow tank experiment with living snails to test whether 1) globular shell morphs are an adaptation against dislodgement through lift rather than drag forces, and 2) dislocation velocity is positively linked to foot size, and that the latter can be predicted by shell morphology. The drag forces experienced by the shells were always stronger compared to the lift and lateral forces. Drag and lift forces increased with shell height but not with globularity. Rotating the shells out of the flow direction increased the drag forces, but decreased lift. Our hypothesis that the controversial presence of globular shells in lotic environments could be explained by an adaptation against lift rather than drag forces was rejected. The foot size was only predicted by the size of the shell, not by shell shape or aperture size, showing that the assumed aperture/foot area correlation should be used with caution and cannot be generalized for all aquatic gastropod species. Finally, shell morphology and foot size were not related to the dislodgement speed in our flow tank experiment. We conclude that other traits must play a major role in decreasing dislodgement risk in stream gastropods, e.g., specific behaviours or pedal mucus stickiness. Although we did not find globular shells to be adaptations for reducing dislodgement risk, we cannot rule out that they are still flow-related adaptations. For instance, globular shells are more crush-resistant and therefore perhaps adaptive in terms of diminishing damage caused by tumbling after dislodgement or against lotic crush-type predators.

中文翻译：

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测试腹足动物壳形态对流量的自适应值：基于形态计量学，计算流体力学和流量罐实验的多学科方法

河流生态学中的一个主要问题是无脊椎动物如何应对水流。在水生腹足动物中，通常在水生（流动的水）栖息地和水生（停滞的水）栖息地中发现更大，直径更大的球状贝壳。据推测，这与更大的脚和因此的附着区域有关，已经提出该附着区域是针对由于电流而脱落的风险的适应。对此的经验证据很少。此外，这些先前的研究没有讨论蜗牛由于横截面积增加而不可避免地增加的阻力。在这里，以抗草假单胞菌为研究模型，我们将计算流体动力学模拟与活蜗牛进行的水箱实验进行了集成，以测试1）球形壳的形态是否适应通过举升而不是阻力产生的位移，并且2）脱位速度与脚的大小呈正相关，并且后者可以通过壳的形态来预测。与升力和侧向力相比，壳体承受的阻力总是更大。阻力和提升力随壳体高度而增加，但不随球状度而增加。将壳体从流动方向移出会增加阻力，但会降低升力。我们的假设认为，在抽水环境中球状壳的存在争议可以通过对升力而不是阻力的适应来解释。脚的大小只能由外壳的大小来预测，而不是通过壳的形状或孔径大小，这表明应该谨慎使用假定的孔径/英尺面积的相关性，并且不能对所有水生腹足动物物种进行概括。最后，在我们的流量罐实验中，壳的形态和脚的大小与移位速度无关。我们得出结论，其他特征必须在减少腹足类动物脚下动物移位风险中起主要作用，例如特定行为或踏板粘液黏性。尽管我们没有发现球状壳可以降低脱臼风险，但我们不能排除球状壳仍然是与流量相关的适应性。例如，球状壳更具抗压性，因此在减少因移位后翻滚引起的损坏或针对轻压型掠食性动物的损害方面可能具有适应性。表明应该谨慎地使用假定的孔径/脚底面积的相关性，并且不能对所有水生腹足动物物种进行概括。最后，在我们的流量罐实验中，壳的形态和脚的大小与移位速度无关。我们得出结论，其他特征必须在减少腹足类动物脚下动物移位风险中起主要作用，例如特定行为或踏板粘液黏性。尽管我们没有发现球状壳可以降低脱臼风险，但我们不能排除球状壳仍然是与流量相关的适应性。例如，球状壳更具抗压性，因此在减少因移位后翻滚引起的损坏或针对轻压型掠食性动物的损害方面可能具有适应性。表明应该谨慎地使用假定的孔径/脚底面积的相关性，并且不能对所有水生腹足动物物种进行概括。最后，在我们的流量罐实验中，壳的形态和脚的大小与移位速度无关。我们得出结论，其他特征必须在减少腹足类动物脚下动物移位风险中起主要作用，例如特定行为或踏板粘液黏性。尽管我们没有发现球状壳可以降低滑脱风险，但我们不能排除球状壳仍然是与流量相关的适应。例如，球状壳更具抗压性，因此在减少因移位后翻滚引起的损坏或针对轻压型掠食性动物的损害方面可能具有适应性。