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First published online April 18, 2006
Journal of Experimental Biology 209, 1651-1661 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02195
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Metabolic scaling associated with unusual size changes during larval development of the frog, Pseudis paradoxus

Silvia Cristina R. de Souza* and Claudia M. Kuribara

Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, Travessa 14, no 321, Cidade Universitária, CEP 05508-900, São Paulo, SP, Brazil

* Author for correspondence (e-mail: scrsouza{at}ib.usp.br)

Accepted 2 March 2006

The early larvae of P. paradoxus grow large but metamorphose into relatively small frogs, the diminished post-metamorphic growth producing a marked contrast between maximum larval size and adult. Thus, O2 uptake does not appear to limit the energy expenditure on growth processes, and unlike in other anuran larvae, may not be a surface area-related function in P. paradoxus larvae. The resting rates of metabolism (MO2) and partitioning between aquatic (MwO2) and aerial O2 uptake (MaO2) were measured on tadpoles and froglets by closed system respirometry, using water of PO2 ranging from 145 to 40 mmHg. Correlative changes in body glycogen and lactate were examined by standard enzyme assays. Scaling patterns in the growth and degrowth stages were analysed on whole-body, log-transformed data using linear regressions. In normoxia, MO2 was 2.1–2.5 µmol g–1 h–1 in the early larvae, increasing more than twofold on forelimb emergence and decreasing sharply in the froglets; MO2 varies in strict proportion to body mass (Mb), both in the growth (b=1.02) and degrowth (b=0.97) phases, according to the equation MO2=aMbb, where b is the scaling coefficient. MwO2 constitutes >90% of total uptake in the growth stages, increasing with b=1.02 while MaO2 increases with b=1.13; during degrowth there is a change in the pattern related to intensification of metamorphosis. Hypoxic water did not affect MO2; however, in all larval stages MwO2 and MaO2 changed with a decrease in PO2. At 60 mmHg, rates are more severely affected in the largest tadpoles, causing the b values for MwO2 and MaO2 to change to 0.11 and 1.44, respectively, in the growth phase. Glycogen and lactate levels increase out of proportion with body mass increase (b=2.05 and 1.47, respectively) in the growth stages, and increase anaerobic capacity in late metamorphosis. In hypoxic water, glycogen levels decrease in the growth stages and the largest tadpoles accumulate surplus lactate, possibly related to surfacing activity. Our results may reveal the consequences of size on energy demand at the tissue level in P. paradoxus larvae, indicating that air breathing must subsidise energy expenditure during larval development.

Key words: metabolic rate, oxygen uptake, metamorphosis, scaling, hypoxia, glycogen, lactate, Amphibia, anuran, Pseudis paradoxus






© The Company of Biologists Ltd 2006