Background: Salamander morphology changes substantially during metamorphosis, prompting the hypothesis that larvae need a different processing mechanism than post-metamorphic adults. Salamandrid newts with facultative metamorphosis are suitable for testing this hypothesis, because paedomorphic and metamorphic adults often coexist in the same population. Facultative paedomorphic newts provide a direct comparison of form-function relationships with specimens of the same species sharing similar body size and feeding on overlapping prey spectra, whilst having divergent food-processing morphologies.
Methods: We use high-speed videography to quantify the in vivo movements of key anatomical elements during food processing in paedomorphic and metamorphic Alpine newts ( Ichthyosaura alpestris ). Additionally, we use micro-computed tomography (μCT) to analyze morphological differences in the feeding apparatus of paedomorphic and metamorphic Alpine newts and sort them into late-larval, mid-metamorphic and post-metamorphic morphotypes.
Results: Paedomorphic and metamorphic individuals exhibited clear morphological differences of their feeding apparatus. Regardless of the paedomorphic state being externally evident, different paedomorphic specimens can conceal different morphotypes (i.e., late-larval and mid-metamorphic morphotypes). Though feeding on the same prey under the same (aquatic) condition, food processing kinematics differed between late-larval, mid-metamorphic and post-metamorphic morphotypes.
Conclusions: While the Alpine Newt still lives in water, food processing mechanism changes along with morphology of the feeding apparatus during ontogeny, from a mandible-based to a tongue-based processing mechanism as the mandible’s changing morphology prevents chewing and the tongue allows enhanced protraction. These results could indicate that early tetrapods, in analogy to salamanders, may have developed new feeding mechanisms in their aquatic environment and that these functional innovations may have later paved the way for terrestrial feeding mechanisms.