Accuracy of taxis response to water waves in the clawed toad (Xenopus laevis Daudin) with intact or with lesioned lateral line system

Abstract

1. The accuracy of taxis response in blinded adult clawed toads (Xenopus laevis Daudin) to water surface waves was measured in animals with an intact lateral line system and in animals with either total or one of 12 different partial lesions of the system. 2. Animals with an intact lateral line system are able to locate wave directions at least to within ±5 ° (Fig. 2A). 3. In response to stimuli coming from behind,Xenopus tend to turn through less than the stimulus angle. This tendency varies substantially even in the same animal and apparently reflects the frog's motivational state rather than sensory inaccuracy of the system (Fig. 2). It can be affected by the type of food the animals are given (Table 1). 4. Shallow water (3–4 cm) decreases the angle through which the animals turn by 5–15% irrespective of the stimulus direction (Table 1). 5. Xenopus with all of their lateral line organs destroyed are still able to respond to surface waves in an oriented fashion. Compared to animals with an intact system they respond somewhat less accurately to anterior stimuli and much less accurately to stimuli from behind (Fig. 3). 6. Elimination of fewer than half of the receptors has no effect on response accuracy. In some lesions even after destruction of 70–95% of the receptors response accuracy does not differ from that of animals with an intact system (Fig. 3). 7. After certain lesions involving unilateral destruction of the head receptors differences in the responses to right- and left-side stimulation are found (Fig. 3). 8. Several lesions resulted in an increased tendency to turn contralateral to the stimulus. The average size of these contralateral rotations increases with increasing stimulus angle (Table 2). 9. The following conclusions can be drawn about spatial analysis by the lateral line system: Wave directions are not located by evaluating their intensity gradient along the animal. The animal does not orient according to the direction of maximum sensitivity of its activated receptors. Temporal comparison of receptor activation seems to be involved in the location of wave directions. Multiple representation with full accuracy of all stimulus angles is present in several subsets of the lateral line receptors. Decisions about the size and the side of the response are, at least in part, made independently.