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.
Keywords: Conservatism, Disparity, Fish, Geometric morphometrics, Morphological evolution, Phylogeny