A comparative study of the buccal pumping mechanism of tadpoles

Abstract

To understand the ecological significance of diversity in the buccal pump morphology of anuran larvae we have developed a descriptive geometric model of the tadpole buccal pump. The model allows comparison of the buccal puinping mechanism of different species. The reliability of the model was established by comparing buccal volumes predicted by the model with buccal volumes reported in the literature for Rana sylvatica and Rana catesbeiana as well as those obtained from our own feeding experiments with Xenopus laevis larvae. The model was used to examine the following features for the larvae of 40 species from 11 anuran families: (1) the amount of deflection in the buccal floor with each stroke of the buccal pump (angle of rotation of the ceratohyal); (2) the mechanical advantage of the pump (the relative length of the lever arm on the ceratohyal); and (3) buccal volume. We identify patterns in diese three features that correlate with the feeding ecology of a variety of tadpoles. Macrophagous larvae tend to have a long lateral lever arm on the ceratohyal (high mechanical advantage), and produce a large buccal volume by deflecting a large buccal floor area through a shallow arc (i.e. a large bore, short stroke system). Midwater, microphagous larvae tend to have poor mechanical advantage, but nevertheless achieve a large buccal volume; in these forms the large buccal volume is obtained by deflecting a smaller buccal floor area through a larger arc (i.e. a small bore, long stroke system). Benthic larvae, such as stream tbrms with suctorial mouths, tend to have high mechanical advantage, but only modest buccal volume. Larvae can regulate their feeding rate by varying either the p umping rate (frequency modulation) or the buccal floor displacement (amplitude modulation). The anatomy of the buccal pump may determine not only the feeding ecology of a larva, but the predominant behavioral pattern it uses to regulate its feeding rate. Buccal volume has a negative allometric relationship to body length both intraspecifically and interspecihcally.