*Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
Integr Comp Biol. 2008 Dec;48(6):750-68. doi: 10.1093/icb/icn092. Epub 2008 Nov 16.
Fish inhabit environments greatly varying in intensity of water velocity, and these flow regimes are generally believed to be of major evolutionary significance. To what extent does water flow drive repeatable and predictable phenotypic differentiation? Although many investigators have examined phenotypic variation across flow gradients in fishes, no clear consensus regarding the nature of water velocity's effects on phenotypic diversity has yet emerged. Here, I describe a generalized model that produces testable hypotheses of morphological and locomotor differentiation between flow regimes in fishes. The model combines biomechanical information (describing how fish morphology determines locomotor abilities) with ecological information (describing how locomotor performance influences fitness) to yield predictions of divergent natural selection and phenotypic differentiation between low-flow and high-flow environments. To test the model's predictions of phenotypic differentiation, I synthesized the existing literature and conducted a meta-analysis. Based on results gathered from 80 studies, providing 115 tests of predictions, the model produced some accurate results across both intraspecific and interspecific scales, as differences in body shape, caudal fin shape, and steady-swimming performance strongly matched predictions. These results suggest that water flow drives predictable phenotypic variation in disparate groups of fish based on a common, generalized model, and that microevolutionary processes might often scale up to generate broader, interspecific patterns. However, too few studies have examined differentiation in body stiffness, muscle architecture, or unsteady-swimming performance to draw clear conclusions for those traits. The analysis revealed that, at the intraspecific scale, both genetic divergence and phenotypic plasticity play important roles in phenotypic differentiation across flow regimes, but we do not yet know the relative importance of these two sources of phenotypic variation. Moreover, while major patterns within and between species were predictable, we have little direct evidence regarding the role of water flow in driving speciation or generating broad, macroevolutionary patterns, as too few studies have addressed these topics or conducted analyses within a phylogenetic framework. Thus, flow regime does indeed drive some predictable phenotypic outcomes, but many questions remain unanswered. This study establishes a general model for predicting phenotypic differentiation across flow regimes in fishes, and should help guide future studies in fruitful directions, thereby enhancing our understanding of the predictability of phenotypic variation in nature.
鱼类栖息在水流强度差异很大的环境中，这些水流模式通常被认为具有重要的进化意义。水流在多大程度上驱动可重复和可预测的表型分化？尽管许多研究人员已经研究了鱼类在水流梯度上的表型变化，但对于水流对表型多样性的影响性质尚未达成明确共识。在这里，我描述了一个通用模型，该模型可以产生关于鱼类在不同水流模式之间的形态和运动分化的可测试假设。该模型结合了生物力学信息（描述鱼类形态如何决定运动能力）和生态信息（描述运动表现如何影响适应性），从而产生了在低流速和高流速环境之间存在分歧的自然选择和表型分化的预测。为了测试该模型对表型分化的预测，我综合了现有文献并进行了荟萃分析。基于从 80 项研究中收集的结果，提供了 115 项预测测试，该模型在种内和种间尺度上都产生了一些准确的结果，因为体型、尾鳍形状和稳定游动性能的差异与预测结果非常匹配。这些结果表明，水流基于通用的、通用的模型驱动不同鱼类群体的可预测表型变化，并且微观进化过程可能经常扩展到产生更广泛的、种间模式。然而，太少的研究检验了身体刚度、肌肉结构或非稳定游动性能的分化，无法为这些特征得出明确的结论。分析表明，在种内尺度上，遗传分化和表型可塑性在不同水流模式下的表型分化中都起着重要作用，但我们尚不清楚这两种表型变异来源的相对重要性。此外，虽然物种内和物种间的主要模式是可预测的，但我们几乎没有关于水流在驱动物种形成或产生广泛的宏观进化模式中的作用的直接证据，因为太少的研究涉及这些主题或在系统发育框架内进行分析。因此，水流确实驱动了一些可预测的表型结果，但仍有许多问题尚未得到解答。本研究建立了一个预测鱼类在不同水流模式下的表型分化的通用模型，应有助于指导未来的研究朝着富有成效的方向发展，从而增强我们对自然中表型变异可预测性的理解。
