Energetics of metamorphic climax in the southern toad (Bufo terrestris)

During metamorphic climax, anuran larvae must rely on stored energy because changes in oral and digestive morphology prevent foraging and efficient assimilation. Thus, the time required to store adequate energy for metamorphic climax may set a lower limit on age at which it can occur. Therefore, the amount and type of energy used during metamorphic climax must be determined. To quantify the energetic costs of metamorphic climax in Bufo terrestris, oxygen consumption during climax was measured. Wet mass, dry mass, and lipid mass for a group of individuals at the initiation of climax (forelimb emergence, FL) and for another group at the end of climax (complete tail resorption, TR) were also measured to determine whether lipids were used to fuel metamorphic climax. The total amount of energy used, maintenance costs, and development costs during metamorphic climax varied considerably among individuals. Variation in energy metabolism during climax was not related to differences in energy metabolism during larval development or body mass at initiation of climax. TR individuals were significantly lighter in terms of wet mass and had less body water than FL individuals. However, the two groups did not differ in dry mass or lipid mass. Therefore, lipid catabolism is not a major source of energy during metamorphic climax in B. terrestris. As a result, decreases in age at metamorphosis may not be constrained by the need to store energy in the form of lipids.