Amphibian Ontogeny: Evolutionary Shift in the Primary Mechanisms of Regulation

Amphibian skull development is a traditional model system for evo-devo study. Based on morphological and experimental data, tissue and hormonal inductions were revealed as main regulatory mechanisms involved in craniogeny. In salamander “nasal complex” (cartilaginous nasal capsule and associated dermal bones), the earliest developmental events are regulated by tissue interactions, while later events become hormonally induced. Similar increase of hormonal induction is displayed in urodelan evolution from basal to advanced taxa. This evolutionary shift in dominating regulatory mechanisms results in progressive divergence of larval and adult morphologies, thus providing grounds for diversification of ontogenetic strategies and life history evolution.