Heterochrony and limb form variation in crested newts

Abstract

The crested newt superspecies includes four morphotypes, each characterized by a specific body-to-limb conformation associated with their respective ecologies: newts with large, stocky bodies and robust limbs are more terrestrial, whereas newts with small, elongate bodies and small limbs are more aquatic. This study investigated whether heterochronic transformations can account for limb form variation in light of phylogenetic history and ecology. Ossification sequence analyses revealed some synapomorphic heterochronic shifts specific to crested newts, including delay of the ossification in the second finger and accelerations in metacarpal III and metatarsal V. These shifts involve a change from pre-axial to post-axial dominance in a developmental sequence uncommon to caudate salamanders. No adaptive explanation of these shifts is apparent. The allometric trajectories of crested newt species were similar after metamorphosis; however, pre-metamorphic growth showed species differences, potentially reflecting differences among species in ecological or functional demands.