Abstract
Tropical reef fishes are widely regarded as being perhaps the most morphologically diverse vertebrate assemblage on earth, yet much remains to be discovered about the scope and patterns of this diversity. We created a morphospace of 2,939 species spanning 56 families of tropical Indo-Pacific reef fishes and established the primary axes of body shape variation, the phylogenetic consistency of these patterns, and whether dominant patterns of shape change can be accomplished by diverse underlying changes. Principal component analysis showed a major axis of shape variation that contrasts deep-bodied species with slender, elongate forms. Furthermore, using custom methods to compare the elongation vector (axis that maximizes elongation deformation) and the main vector of shape variation (first principal component) for each family in the morphospace, we showed that two thirds of the families diversify along an axis of body elongation. Finally, a comparative analysis using a principal coordinate analysis based on the angles among first principal component vectors of each family shape showed that families accomplish changes in elongation with a wide range of underlying modifications. Some groups such as Pomacentridae and Lethrinidae undergo decreases in body depth with proportional increases in all body regions, while other families show disproportionate changes in the length of the head (e.g., Labridae), the trunk or caudal region in all combinations (e.g., Pempheridae and Pinguipedidae). In conclusion, we found that evolutionary changes in body shape along an axis of elongation dominates diversification in reef fishes. Changes in shape on this axis are thought to have immediate implications for swimming performance, defense from gape limited predators, suction feeding performance and access to some highly specialized habitats. The morphological modifications that underlie changes in elongation are highly diverse, suggesting a role for a range of developmental processes and functional consequences.
Highlights
Repeated patterns of trait variation across species, such as wing analogies, can be of major interest for evolutionary biologists since they may reflect shared underlying evolutionary processes, such as flight mechanical constraints
We created a morphospace of 2,939 species spanning 56 families of tropical Indo-Pacific reef fishes and established the primary axes of body shape variation, the phylogenetic consistency of these patterns, and whether dominant patterns of shape change can be accomplished by diverse underlying changes
Principal component analysis showed a major axis of shape variation that contrasts deepbodied species with slender, elongate forms
Summary
Repeated patterns of trait variation across species, such as wing analogies, can be of major interest for evolutionary biologists since they may reflect shared underlying evolutionary processes, such as flight mechanical constraints. One such repeated pattern appears to be body elongation in vertebrates [1,2,3,4,5]. Teleosts are a speciesrich clade of vertebrates with more than 32 000 species among little more than 60 000 vertebrate species [6] As such, this major group is of prime interest to study occurrences and processes of elongation in vertebrates
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