Adult axolotls are typically aquatic, with gills and underdeveloped limbs, as shown in the image. Under certain conditions, an axolotl can undergo metamorphosis to its terrestrial form, which has completely developed limbs and lungs instead of gills. When an aquatic axolotl is either given food containing the element iodine or is injected with iodine, the axolotl rapidly undergoes metamorphosis to the terrestrial form. Based on this information, what is most likely true about the effect of iodine on axolotls?