ABSTRACT
Most animals develop through a succession of ontogenetic niches. For example, adult tunicates are sessile, living attached to a substrate in the sea floor, but larval tunicates are free-swimming animals (see Figure 4.10). Similarly, most amphibians, including frogs and salamanders, live under water as larvae (the tadpole stage) but develop into terrestrial animals as adults, and fully terrestrial caterpillars develop into free-flying butterflies. These transitions involve substantial changes given the disparate nature of the environments in which these animals live at different stages of their development. Development goes through a process of metamorphosis, that is, a morphological and functional reorganization during which adaptations appropriate for the early environment are eliminated (e.g., the tadpole’s gills), while traits needed for the next ontogenetic niche are induced (e.g., the frog’s legs).
