Palaeontological Institute and Museum, University of Zurich, Karl-Schmid-Strasse 4, 8006, Zurich, Switzerland.
Zoological Institute, University of Basel, Vesalgasse 1, 4051, Basel, Switzerland.
BMC Evol Biol. 2018 Mar 27;18(1):38. doi: 10.1186/s12862-018-1152-y.
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.
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.
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.
营养适应引发的形态趋同是适应性辐射中的常见模式。在进化背景下研究形状变化通常仅限于研究充分的鱼类模型。我们利用最近修订的新世界 Ariidae 系统分类学，并研究了六个北方新热带 Ariidae 属的头骨形状进化。它们构成了一个在海洋生境中多样化但多次适应淡水生境的谱系。首次在鲶鱼头骨中应用了 3D 几何形态测量学，并进行了基于系统发育的统计分析，以检验该谱系中在生境转变后，生境对头骨多样化的影响。
我们发现头骨形状在整个系统发育中是保守的。形态空间分析表明，淡水和海洋物种占据第一主成分轴的极端，并且它们表现出相似的 Procrustes 方差。然而，与海洋和半咸水物种相比，淡水物种占据的形状空间最小（基于部分差异），而海洋和淡水物种彼此之间的 Procrustes 距离最大。我们观察到一个单一的形态趋同案例，来自“C-metrics”，这不能用相同的栖息地来解释。
尽管 Ariidae 从海洋到淡水占据了如此广泛的不同生境，但形态空间分析以及在系统发育背景下对形状和与生境的协变关系的分析表明，保守性主导了 ariid 属之间的头骨形状进化。
