Abstract
Snakes are a highly successful group of vertebrates, within great diversity in habitat, diet, and morphology. The unique adaptations for the snake skull for ingesting large prey in more primitive macrostomatan snakes have been well documented. However, subsequent diversification in snake cranial shape in relation to dietary specializations has rarely been studied (e.g. piscivory in natricine snakes). Here we examine a large clade of snakes with a broad spectrum of diet preferences to test if diet preferences are correlated to shape variation in snake skulls. Specifically, we studied the Xenodontinae snakes, a speciose clade of South American snakes, which show a broad range of diets including invertebrates, amphibians, snakes, lizards, and small mammals. We characterized the skull morphology of 19 species of xenodontine snakes using geometric morphometric techniques, and used phylogenetic comparative methods to test the association between diet and skull morphology. Using phylogenetic partial least squares analysis (PPLS) we show that skull morphology is highly associated with diet preferences in xenodontine snakes.
Highlights
The origin and diversification of morphology are topics of great interest with the field of evolutionary biology, and the adaptation of organismal form to ecological conditions has been attributed as a primary driving force of morphological diversification [1]
The principal components (PC) analysis of the skull shapes reveals that most of the shape variation is contained in few dimensions; in the dorsal view the first four principal axes (PCs) explained 91.5%, while in the lateral view the first four PCs explained 88.3% of the total shape variation
PC1 explained 56.4% of the variation, and the species with negative values show an increase of skull length, especially of the parietal bone, and a relative decrease in orbit size; while positive values indicate a wider and shorter skull (Fig 3)
Summary
The origin and diversification of morphology are topics of great interest with the field of evolutionary biology, and the adaptation of organismal form to ecological conditions has been attributed as a primary driving force of morphological diversification [1]. Classic support for the hypothesis of adaptation by natural selection is evolutionary convergence. Evolutionary convergence occurs when similar phenotypes evolve in phylogenetically independent taxa as a response to similar ecological conditions [2, 3]. Due to the importance of the skull, and its direct link to an animal’s fitness, it is presumed that skull morphology is under considerably strong selection pressure [4]. Many studies within vertebrates have corroborated this idea, showing strong correlations between diet and skull morphology [6, 7, 8]. Stayton [9] studied lizard skulls shape evolution across 17 families, using geometric morphometric tools. He showed morphological convergent evolution among lizards
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