Escaping the flow: boundary layer use by the darter Etheostoma tetrazonum (Percidae) during benthic station holding
Escaping the flow: boundary layer use by the darter Etheostoma tetrazonum (Percidae) during benthic station holding
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DOI：
10.1242/jeb.051938
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发表时间：
2011-04-01
影响因子：
2.8
通讯作者：
Lauder, George V.
中科院分区：
文献类型：
--
作者：
Carlson, Rose L.;Lauder, George V.
以定向水流为特征的水生生境(热带环境)给其居民带来了许多挑战，包括不断被赶走和向下游运输的威胁。因此，许多生物表现出形态和/或行为适应，有利于在这些环境中保持中水或底栖站，例如装甲叉尾鱼的腹吸盘。然而，少数种群，包括物种丰富的小种群(7-8个。长1-2厘米。北美洲的流水鱼，称为飞镖，对热带生境的生活没有明显的形态适应能力。因此，我们问，小尺寸本身是否有利于底栖站容纳这些鱼。我们首次使用数字粒子图像测速仪来量化在各种基质上流动的流体动力学。然后，我们可视化了在底栖站举行期间，流经四带飞镖的流动模式。与几种岩石基质有关的水流减速区域(即边界层)的厚度足够大(在某些情况下接近2厘米高)，足以让四带棘藻和许多其他较暗的物种逃脱迎面而来的水流。我们还发现，尽管它的胸鳍很大，但它的鳍只能产生非常弱的负升力。这些底物导向的力很可能与尾翼、肛门和腹鳍与底板之间的上游导向摩擦力共同作用，以促进站位保持。因此，我们假设，在飞镖类中，体型较小是对热带环境底栖边界层生活的一种适应。
Aquatic habitats characterized by directional water flow (lotic environments) pose numerous challenges to their inhabitants, including the constant threat of dislodgement and downstream transport. As a result, many organisms exhibit morphological and/or behavioral adaptations that facilitate midwater or benthic station holding in these environments, such as the ventral sucker disc of armored catfishes. However, a few groups, including the species-rich group of small (7-8. cm long and 1-2. cm high) North American stream fishes called darters, exhibit no obvious morphological adaptations to life in lotic habitats. We therefore asked whether small size itself facilitates benthic station holding in these fish. We first used digital particle image velocimetry to quantify the fluid dynamics of flow over a variety of substrates. We then visualized the patterns of flow over the darter Etheostoma tetrazonum during benthic station holding. The thickness of the region of decreased water velocity (i.e. the boundary layer) associated with several types of rocky substrate was large enough (similar to 2. cm high in some cases) for E. tetrazonum and many other darter species to escape the oncoming flow. We also found that, despite the large size of its pectoral fins, E. tetrazonum is capable of producing only very weak negative lift forces with fins. These substrate-directed forces likely act in conjunction with upstream-directed frictional forces between the tail, anal and pelvic fins and the substrate to facilitate station holding. Thus, we hypothesize that, in darters, small size is an adaptation to life in the benthic boundary layer of lotic environments.