Abstract. Herbivorous fishes feed on stems, leaves, flowers, seeds, fruits, and nuts of diverse aquatic plants, as well as algae. Pacus are the herbivorous cousins of piranhas and consume a myriad of diets comprised of these plant products, but a few species are phytophages, herbivores that feed almost exclusively on rapids-dwelling (rheophilic) riverweed plants from the family Podostemaceae. The degree to which pacus feed on riverweed varies from obligate year-round consumption to strictly seasonal, facultative feeding. Obligate phytophages feed heavily on riverweed and strictly occur in river rapids, while facultative phytophages only consume riverweed during seasons with low flow. Does ecological specialization (diet) beget morphological specialization in the feeding apparatus and/or body shape of phytophages? Under a phylogenetic framework, we used micro-computed tomography (µCT) scanning to compare functional feeding traits among 26 species of serrasalmids, four of which are obligate phytophages. We also compared body shape between pacus using geometric morphometrics to identify potential locomotor adaptations for rheophily. Obligate phytophages have dentitions and slicing jaws well-suited for shearing fleshy plant material relative to other pacus, which are equipped with fruit and seed crushing morphologies. Unrelated obligate phytophages have also converged on a similar body shape that is distinct from sympatric congeneric herbivores. Phytophagy involves more consistent changes to body shape than to feeding morphology, suggesting that body shape has more important ties to diet.

中文翻译：

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体型比进食形态更好地分离了嗜流性食草动物（Myleinae：Serrasalmidae）的行会

摘要。草食性鱼类以各种水生植物的茎、叶、花、种子、果实和坚果以及藻类为食。Pacus 是食人鱼的食草近亲，食用大量由这些植物产品组成的食物，但有一些物种是植物噬菌体，它们几乎完全以栖息在急流（嗜流性）的河草科植物为食。pacus 以河草为食的程度从全年消费到严格的季节性兼性喂养不等。专性植物噬菌体以河草为食，严格出现在河流急流中，而兼性植物噬菌体仅在低流量季节消耗河草。生态专业化（饮食）是否会导致植物噬菌体的摄食装置和/或体型的形态专业化？在系统发育框架下，我们使用显微计算机断层扫描 (μCT) 扫描来比较 26 种锯齿鲼的功能性摄食性状，其中四种是专性植物噬菌体。我们还使用几何形态测量学比较了 pacus 之间的体型，以确定流变性的潜在运动适应性。专性噬菌体具有齿列和切片颚，非常适合剪切相对于其他具有果实和种子压碎形态的肉质植物材料。不相关的专性噬菌体也聚集在与同域同类食草动物不同的相似体型上。植物吞噬涉及体型的更一致的变化而不是喂养形态，这表明体型与饮食有更重要的联系。