Why do some salamanders remain in a larval form throughout life?

Some salamanders remain in a larval form throughout their lives due to a phenomenon known as paedomorphosis, where an organism retains juvenile or larval traits into its adult, sexually mature phase. This condition is a result of heterochrony, which refers to changes in the timing and rate of developmental events.12

For many species, such as the axolotl and the mud puppy, this permanent larval state is determined by heredity. In these cases, the animals are biologically programmed to reach sexual maturity while maintaining larval structures like gills.12

In other instances, the failure to metamorphose can be induced by environmental factors, such as cold temperatures or drought, which may make the terrestrial environment unfavorable for the adult form. While metamorphosis is typically mediated by hormones from the thyroid and pituitary glands, some populations or species may experience delayed or incomplete development, allowing them to successfully breed while remaining in an essentially larval state.123