Respiratory quotient during metamorphosis of Hyla regilla tadpoles

Metamorphosis may be defined as postembryonic developmental changes in non-reproductive structures of an organism. Such changes anticipate changes in the organism\u27s environment (Frieden, 1961). Metamorphosis of amphibian larvae is dependent on the thyroid hormone in the circulating body fluid, and the normal sequence of metamorphosis has been correlated with a progressive increase in the concentration of thyroxine in the blood (Barch, 1953; Moore, 1964). While the rate of oxygen uptake in developing tadpoles has been well studied and documented, only a single reference on carbon dioxide release could be found. Belehradek and Huxley (1927) noted that carbon dioxide output increased immediately after the feeding of thyroid to frog tadpoles, but that during the ensuing induced metamorphosis, the carbon dioxide production diminished, finally reaching 60% of the original larval value. No references on carbon dioxide release during spontaneous metamorphosis could be found. In normal, aerobic respiration, the relative amounts of oxygen consumed and carbon dioxide released changed characteristically with the chemical nature of the metabolized substrate. An RQ of 1.0, 0.8, and 0.7 indicate metabolism of pure carbohydrate, lipid, and protein, respectively. Thus, the RQ provides some information about the nature of the transformations in progress (Witschi, 1956; Brown, 1964). The dietary change from herbivore to carnivore which occurs toward the end of anuran metamorphosis would be expected to result in a change in the ratio of oxygen consumed to CO2 produced. This study was undertaken with the intention of gaining an insight into the nature of the metabolic reactions in metamorphosing Hyla regilla tadpoles by determining the RQ at various stages of development