Data from: Habitat-based polymorphism is common in stream fishes

1. Morphological differences (size and shape) across habitats are common in lake fish where differences relate to two dominant contrasting habitats: the pelagic and littoral habitat. Repeated occurrence of littoral and pelagic morphs across multiple populations of several lake fish species has been considered as important evidence that polymorphism is adaptive in these systems. It has been suggested that these habitat-based polymorphic differences are due to the temporal stability of the differences between littoral and pelagic habitats. 2. Although streams are spatially heterogeneous, they are also more temporally dynamic than lakes and it is still an open question whether streams provide the environmental conditions that promote habitat-based polymorphism. We tested whether fish from riffle, run and pool habitats, respectively, differed consistently in their morphology. 3. Our test compared patterns of morphological variation (size and shape) in 10 fish species from the three stream habitat types in 36 separate streams distributed across three watersheds. 4. For most species, body size and shape (after controlling for body size) differed across riffle, run and pool habitats. Unlike many lake species, the nature of these differences was not consistent across species, possibly because these species use these habitat types in different ways. 5. Our results suggest that habitat-based polymorphism is an important feature also in stream-fishes despite the fact that streams are temporally variable in contrast to lake systems. Future research is required to assess whether the patterns of habitat-polymorphism encountered in streams have a genetic basis or they are simply the result of within generation phenotypic plasticity.

1. 不同生境下的形态差异（涵盖体型大小与体形）在湖泊鱼类中极为常见，这类差异主要与两种典型的对立生境相关：远洋带（pelagic）与沿岸带（littoral）。多个湖泊鱼类类群的多个种群中反复出现沿岸型与远洋型形态，这被视为这类系统中多态现象具有适应性的重要佐证。有研究提出，这类基于生境的多态差异，源于沿岸带与远洋带之间环境差异的时间稳定性。
2. 尽管溪流生境在空间上存在异质性，但相较于湖泊，其时间动态性更强。目前仍不清楚溪流是否具备催生基于生境多态现象的环境条件。本研究旨在验证：分别取自急流（riffle）、缓流（run）与静水区（pool）生境的鱼类，其形态特征是否存在稳定差异。
3. 本研究比对了分布于3个流域的36条独立溪流中，10种鱼类在三种溪流生境下的形态变异（体型大小与体形）模式。
4. 多数鱼类的体型大小与经体型校正后的体形，在急流、缓流与静水区生境间均存在显著差异。与多数湖泊鱼类类群不同的是，这类差异的具体模式在不同物种间并不统一，这可能源于不同物种对三类生境的利用策略存在差异。
5. 本研究结果表明，尽管溪流环境的时间变异性与湖泊系统存在显著差异，但基于生境的多态现象同样是溪流鱼类的重要特征之一。未来仍需开展相关研究，以明确溪流中观测到的生境多态模式，究竟具备遗传基础，抑或仅仅是当代个体内表型可塑性（phenotypic plasticity）的产物。