Xenopus laevis larvae (Amphibia,Anura) as model suspension feeders

Larvae of the South African clawed frog, Xenopus laevis (Daudin), are efficient, obligate suspension feeders. We examine the relationship between the ambient particle concentration offered these larvae as food and their filtering, ingestion, and buccal pumping rates. We demonstrate that: (i) the larvae can sense and respond to a broad range of particle concentrations, down to 0.2 mg 1^–1 (dry weight); (ii) their metabolic needs theoretically can be met by particle concentrations as low as 5 mg 1^–1; and (iii) their patterns of regulation of filtering and ingestion fit predictions from certain models used to describe zooplankton feeding dynamics. Two such models are discussed: the modified Monod (Michaelis-Menten) model, with a lower threshold below which the tadpoles do not feed, and an energy optimization model. Both the models and the observed behavior of the tadpoles allow for stability of populations of food organisms. Tadpole feeding dynamics apparently are compatible with both the predictions and assumptions of these models, suggesting similar regulation of feeding by tadpoles and zooplankton. However, the size, morphology, and behavior of X. laevis larvae make their feeding regulation uniquely accessible to direct observation.Contribution No. 223, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.Contribution No. 223, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.