Data from: Study of morphological variation of northern Neotropical Ariidae reveals conservatism despite macrohabitat transitions

Background: Morphological convergence triggered by trophic adaptations is a common pattern in adaptive radiations. The study of shape variation in an evolutionary context is usually restricted to well-studied fish models. We take advantage of the recently revised systematics of New World Ariidae and investigate skull shape evolution in six genera of northern Neotropical Ariidae. They constitute a lineage that diversified in the marine habitat but repeatedly adapted to freshwater habitats. 3D geometric morphometrics was applied for the first time in catfish skulls and phylogenetically informed statistical analyses were performed to test for the impact of habitat on skull diversification after habitat transition in this lineage. Results: We found that skull shape is conserved throughout phylogeny. A morphospace analysis revealed that freshwater and marine species occupy extreme ends of the first principal component axis and that they exhibit similar Procrustes variances. Yet freshwater species occupy the smallest shape space compared to marine and brackish species (based on partial disparity), and marine and freshwater species have the largest Procrustes distance to each other. We observed a single case of shape convergence as derived from 'C-metrics', which cannot be explained by the occupation of the same habitat. Conclusions: Although Ariidae occupy such a broad spectrum of different habitats from sea to freshwater, the morphospace analysis and analyses of shape and co-variation with habitat in a phylogenetic context shows that conservatism dominates skull shape evolution among ariid genera.

背景：由营养适应引发的形态趋同，是适应性辐射中常见的演化模式。当前演化框架下的形态变异研究，通常局限于研究较为充分的鱼类模式类群。本研究借助新近修订的新世界海鲶科（Ariidae）分类系统，对新热带区北部6个海鲶科属类群的头骨形态演化展开探究。该类群起源于海洋生境并发生分化，随后多次独立适应淡水生境。本研究首次针对鲶形目鱼类头骨采用3D几何形态测量法（3D geometric morphometrics），并开展系统发育校正的统计分析，以检验该类群在生境转型后，生境对头骨形态分化的影响。
结果：研究发现，头骨形态在系统发育框架下整体呈现保守性。形态空间分析结果显示，淡水与海洋物种分别占据第一主成分轴的两端，且二者的普氏方差（Procrustes variances）水平相近。但相较于海洋与咸淡水物种，淡水物种的形态空间占据范围最小（基于半差异值计算），且海洋与淡水物种间的普氏距离（Procrustes distance）最大。基于“C-指标（C-metrics）”的分析仅发现一例形态趋同事件，且该趋同无法通过相同生境的占据情况加以解释。
结论：尽管海鲶科（Ariidae）类群占据了从海洋到淡水的广泛生境谱系，但形态空间分析以及系统发育框架下的形态与生境共变异分析均表明，海鲶科各属的头骨形态演化整体以保守性为主导。