Lateral Line Scene Analysis in the Purely Aquatic Frog Xenopus laevis Daudin (Pipidae)

The ability to locate and discriminate water surface waves that impinge simultaneously from multiple directions was studied in the clawed frog, Xenopus laevis. Monofrequency waves of 5-30 Hz were presented from point sources at a distance of 10 cm from the frog, unless stated otherwise, and the animal's response turn towards the wave origin examined. Two-choice conditioning with two simultaneous frontal waves at a 90-degree inter-wave angle revealed discrimination thresholds lower than 1 Hz for 10- to 20-Hz source wave frequencies. Smaller inter-wave angles resulted in larger thresholds, and no discrimination was found below 40°. If a third wave was added from behind, the frequency discrimination of the two frontal waves deteriorated, with 18 Hz being discriminated from waves differing by at least 2.75 Hz. Subjects also discriminated between two simultaneous waves of equal frequency presented from differing distances. At a distance of 10 cm, the discrimination threshold was 0.95 cm. Thus, X. laevis is capable of discriminating source distances in an overlap on the basis of wave curvatures. The detection of source directions among four, six or eight waves of equal frequency and distance was investigated by measuring the angular distribution of the response turns. Turns were significantly more closely oriented towards sources than to intermediate directions. The orientation accuracy did not degrade with the number of waves.