Effect of hypoxia and body size on the energy metabolism of lungless tadpoles, Bufo woodhousei, and air‐breathing anuran larvae

Abstract

AbstractUnlike most anuran larvae, tadpoles of Bufo woodhousei (toads) lack lungs. To investigate the consequences of lunglessness and its interaction with the body size of larvae, resting and active tadpoles were exposed to hypoxia. In resting larvae, rates of O2 consumption (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} {\rm o}_{\rm 2} $\end{document}) were proportional to aquatic PO2, even though larvae increased buccopharyngeal ventilation considerably in hypoxia. Whole body lactate concentrations increased only in severe hypoxia. Hypoxia also depressed the \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} {\rm o}_{\rm 2} $\end{document} of active larvae, which accumulated lactate even in normoxic water. Air‐ and water‐breathing tadpoles (Rana berlandieri and Xenopus laevis) can maintain greater routine \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} {\rm o}_{\rm 2} $\end{document} in hypoxia than can Bufo tadpoles. However, Bufo tadpoles can extract more O2 from hypoxic water than can Rana and Xenopus tadpoles, when all are breathing only water.The critical Po2 of active larvae and the gill ventilatory frequency of resting larvae were proportional to body size. By contrast, large and small Bufo tadpoles were similar in routine \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} {\rm o}_{\rm 2} $\end{document} in hypoxia, the ration \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} {\rm o}_{\rm 2} $\end{document} max:\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} {\rm o}_{\rm 2} $\end{document} routine, and tolerance of hypoxia. Also, small tadpoles accumulated more lactate than large tadpoles when swimming at similar absolute velocities for the same times. Thus, lunglessness apparently does not limit the size of Bufo tadpoles by forcing reliance upon cutaneous gas exchange.