Short-Term Memory of the Amplitude of Body Rotation in Orienting Behavior of African Clawed Frog (Xenopus laevis)

African clawed frog (Xenopus laevis) can orient its body toward the prey by analyzing the direction of approaching water waves. Xenopus accurately orients toward the source of the stimulus when the stimulus is generated several cm away from its body. However, although Xenopus orientation behavior fluctuates when the stimulus is generated very near or above its body, the amplitude of the body rotation in the orienting behavior was affected by the preceding orienting behavior that had been performed several seconds before. In particular, the amplitude of the rotation in response to the stimulus applied above the body was positively correlated with that of the preceding rotation behavior in response to a stimulus generated several cm away from the body, indicating that Xenopus tends to repeat the preceding behavior if the direction of the stimulus is ambiguous. The results presented show the evidence that Xenopus can retain the amplitude of the rotation of the preceding orienting behavior for several seconds. 1. Introduction African clawed frogs (Xenopus laevis) capture living insects on the water surface by analyzing the directions of water waves produced by the movement of the prey [1]. During this orienting behavior, water waves are predominantly detected by lateral lines that are dispersed over the frog’s body. Lateral lines consist of 160–300 stitches, each of which contains hair cells (mechanoreceptors) [2, 3]. When the frog detects water waves produced by the prey using lateral lines, it rapidly orients its body toward the source of the waves. Characteristics of this orienting behavior by African clawed frogs have been analyzed in many previous studies [4–9]. Elepfandt [4] first analyzed the accuracy of African clawed frog’s orienting behavior and showed that African clawed frogs could accurately orient their bodies toward the direction of the wave source. In this study, the distance between the wave source and the frog’s body was nearly constant (10–12？cm). Subsequent studies have shown that African clawed frogs performed the orienting behavior accurately even if the distance between the frog’s body and the wave source was altered [8, 9]. Although African clawed frogs performed the orienting behavior very accurately when the stimulus was presented several cm away from its body, it is unknown (1) how African clawed frog orients its body when the direction of the wave source is difficult to determine, such that the stimulus is generated very near or directly above its body, and (2) what parameters of the stimulus or frog’s behavior affect frog’s