Complete metamorphosis promotes morphological and functional diversity in Caudata

Metamorphosis, a common and spectacular developmental process, involves major phenotypic changes often linked to environmental transitions. Understanding how these changes affect morphological evolution is crucial for examining metamorphosis's evolutionary impacts. In this study, we analysed the role of metamorphosis and life cycle variation on the morphological evolution of the mandible in Caudata (salamanders and newts), a clade that exhibits a great diversity of life cycles and ecologies. We focused on the mandible, a key component of the masticatory apparatus, to investigate how life cycle variation may influence the diversification of feeding modes. Using 3D geometric morphometrics on 317 extant species of Caudata, we found that both life cycle and size influence mandible shape, with complex interactions between these factors. The morphology of the mandibular bones evolved more independently in species undergoing complete metamorphosis compared to those with partial metamorphosis, likely facilitating feeding diversification in terrestrial adults. On the other hand, high morphological integration in species undergoing partial metamorphosis could promote the rapid evolution of traits, resulting in the differentiation of more disparate morphologies, potentially aiding paedomorphic species in adapting to challenging environments. This study highlights the interplay between metamorphosis and the environment in shaping morphological evolution among species and provides new insights into the role of heterochrony in the morphological diversification of organisms. Read the free Plain Language Summary for this article on the Journal blog.