The Evolution of the Motor Control of Feeding in Amphibians1

Abstract

Based on studies of a few model taxa, amphibians have been considered stereotyped in their feeding movements relative to other vertebrates. However, recent studies on a wide variety of amphibian species have revealed great diversity in feeding mechanics and kinematics, and illustrate that stereotypy is the exception rather than the rule in amphibian feeding. Apparent stereotypy in some taxa may be an artifact of unnatural laboratory conditions. The common ancestor of lissamphibians was probably capable of some modulation of feeding movements, and descendants have evolved along two trajectories with regard to motor control: (1) an increase in modulation via feedback or feed-forward mechanisms, as exemplified by ballistic-tongued plethodontid salamanders and hydrostatic-tongued frogs, and (2) a decrease in variation dictated by biomechanics that require tight coordination between different body parts, such as the tongue and jaws in toads and other frogs with ballistic tongue projection. Multi-joint coordination of rapid movements may hamper accurate tongue placement in ballistic-tongued frogs as compared to both short-tongued frogs and ballistic tongued-salamanders that face simpler motor control tasks. Decoupling of tongue and jaw movements is associated with increased accuracy in both hydrostatic-tongued frogs and ballistic-tongued salamanders.