Metamorphosis is one of the most fascinating phenomena in animals, implying an abrupt change in morphology and ecology during the lifetime of an individual, transforming it from a larva into an adult (tadpoles to frogs or caterpillars to butterflies, for example). From insects to sea urchins, fishes, and frogs, most animals on our planet undergo metamorphosis. Life cycle complexity is consequently a widespread phenomenon and may be an important driver of biodiversity. Yet, the origin and evolution of different life-history stages and their impact on species diversification remain poorly understood. As species with complex life cycles have the genetic and developmental programs to change their morphology and allowing them to use different ecological niches during their lifetime, understanding whether and how life cycle complexity is a driver of biodiversity is critical. Consequently, it is of prime importance to understand how and why complex developmental strategies appeared and were maintained during evolution. The aim of my project is to understand why metamorphosis is so common in animals and whether it is an advantage for them to be able to produce different morphologies in comparison to animals that do not show metamorphosis (including mammals like us, for example). To do so, I use salamanders and newts as a model system as they display a tremendous diversity of species and ecologies, and show the largest variation in life cycle types among tetrapods.
The variety of developmental strategies and thus the differences in lifestyle and feeding modes should be reflected by changes in morphology during ontogeny in salamanders. In this project, I focused on different parts of the head as their morphology is impacted by changes in feeding strategy during ontogeny. I used interdisciplinary approaches combining functional morphology, developmental biology, and statistical modelling to disentangle the factors driving diversity at different ontogenetic stages in deep-time. More specifically, I addressed the following research objectives: 1) How do developmental strategies foster the patterns of morphological and functional variation among species throughout ontogeny? Here, I tested whether larval stages overlap in morphology and function with adults, and how this translates into morphological and functional variation. 2) Does the fossil record shed light on the origin and evolution of complex life cycles? For this part I aimed to explore morphofunctional variation in deep time and to assess if extinct species can be used in reconstructing the evolution of metamorphosis evolution in salamanders. 3) Does metamorphosis drive morpho-functional diversity and its impact on biodiversity? Here I aimed to test whether there is a decoupling within and/or between the different structures of the head and their function depending on life cycle.
