Chew on this: Oral jaw shape is not correlated with diet type in loricariid catfishes.

The correlation between form and function is influenced by biomechanical constraints, natural selection, and ecological interactions. In many species of suction-feeding fishes, jaw shape has shown to be closely associated with diet. However, these correlations have not been tested in fishes that have more complex jaw functions. For example, the neotropical loricariid catfishes possess a ventrally facing oral disk, which allows for the oral jaws to adhere to surfaces to conduct feeding. To determine if jaw shape is correlated to diet type, we assessed oral jaw shape across 36 species using CT scans. Shape was quantified with traditional and automated landmarking in 3DSlicer, and diet type correlation was calculated using the phylogenetic generalized least squares (PGLS) method. We found that traditional and automated processes captured shape effectively when all jaw components were combined. PGLS found that diet type did not correlate to jaw shape; however, there was a correlation between clades with diverse diets and fast evolutionary rates of shape. These results suggest that shape is not constrained to diet type, and that similarly shaped jaws coupled with different types of teeth could allow the fishes to feed on a wide range of materials.

Evolutionary integration and modularity in the diversity of the suckermouth armoured catfishes.

The evolution of morphological diversity has held a long-standing fascination among scientists. In particular, do bodies evolve as single, integrated units or do different body parts evolve semi-independently (modules)? Suckermouth armoured catfishes (Loricariidae) have a morphology that lends nicely to evolutionary modularity and integration studies. In addition to a ventrally facing oral jaw that directly contacts surfaces, the neurocranium and pectoral girdle are fused, which limits movement of the anterior part of the body. Functional constraints suggest it is likely the head and post-cranial body act as separate modules that can evolve independently. If true, one would expect to see a two- or three-module system where the head and post-cranial body are morphologically distinct. To test this hypothesis, we quantified shape using geometric morphometric analysis and assessed the degree of modularity across functionally important regions. We found the armoured catfish body is highly modularized, with varying degrees of integration between each module. Within subfamilies, there are different patterns of evolutionary modularity and integration, suggesting that the various patterns may have driven diversification along a single trajectory in each subfamily. This study suggests the evolution of armoured catfish diversification is complex, with morphological evolution influenced by interactions within and between modules.

Morphological diversity within the Ozark minnow (Notropis nubilus: Leuciscidae).

The Ozark minnow, Notropis nubilus, is a small stream fish that has a disjunct distribution in the Ozark Plateau and upper Mississippi River basin. Three reciprocally monophyletic and deeply divergent lineages have been hypothesized within the species based on molecular data. These lineages are allopatric and isolated from each other. The objective of this study was to test the hypothesis that these lineages and the disjunct population in the upper Mississippi River basin are morphologically distinct. Meristic and geometric morphometric data were used to identify and quantify morphological diversity within the Ozark minnow. Analyses of the meristic data and a principal component analysis of the morphometric data were unable to find any noticeable differences in morphology among groups. However, canonical variates analyses of the morphometric data and linear models were able to define statistically significant differences in shape. Analyses of all-individuals were able to identify shape differences between all groups. Males-only analyses were less conclusive, but there was some indication that males may be diverging more quickly than all-individuals. The detection of subtle variation in shape implies selection is not a strong factor in morphological divergence and observed differences are most likely due to morphological drift. This indicates that the lineages within the Ozark minnow are likely on the trajectory for speciation. The allopatric nature of these clades makes the Ozark minnow an interesting model for the study of morphological drift and speciation.

Shared ecological traits influence shape of the skeleton in flatfishes (Pleuronectiformes).

In the age of phylogenetic comparative methods, evolutionary biologists have been able to explore evolutionary trends in form in unique and extraordinarily diverse groups of animals. Pleuronectiformes, commonly known as flatfishes, is a diverse and specialized order of fishes that have remarkable asymmetry induced by ocular migration and a benthic life style. Although flatfishes are unique from other fishes, species within the group are morphologically diverse. The origin of ocular migration has been a primary focus of research; however, little is known about overall shape diversification among the flatfishes. In this study, we use integrative methods to examine how body shape evolved within the flatfishes. Shape was quantified from X-rays using geometric morphometrics for 389 individuals across 145 species. The most recent and robust phylogeny was overlaid onto the morphospace and phylogenetic signal was calculated to ascertain convergence in the morphospace. In addition, phylogenetic linear models were employed to determine if ecological traits were correlated with shape and if size had an effect on overall body shape. Results revealed that the majority of variation evolved recently, within the past 15-10-million-years in the middle Miocene, and is highly variable within the flatfishes. These changes are best summarized by body depth, jaw length and medial fin length. Dorsal and anal fin length are correlated, which may be due to the unique mode of locomotion used by flatfishes. A phylogenetic linear model and phylomorphospace analysis suggested that several ecological traits are correlated with shape, which indicates an ecological role in the diversification of flatfishes.