Directionality of antennal sweeps elicited by water jet stimulation of the tailfan in the crayfish Procambarus clarkii

Directionality and intensity dependence of antennal sweeps elicited by water jet stimulation of the tailfan in tethered, reversibly blinded adult and juvenile crayfish (Procambarus clarkii) were analyzed. Resting crayfish keep their antennae at about 50° symmetrically to the longitudinal body axis (Figs. 2 bottom, and 3). In adults, tailfan stimulation elicits synchronous backward sweeps of both antennae, which increase for more caudal stimulus directions (Figs. 2-4 and 5A). Directions differing by 30°-60° are significantly distinguished (Fig. 4). The mean sweep of the ipsilateral antenna significantly overrides that of the contralateral antenna for rostrolateral stimulation at 40-200 mm/s stimulus velocity and lateral to caudolateral stimulation at 40 mm/s and thus lateralization of the stimulus is revealed (Figs. 2 top, 4 and 5A). Mean antennal sweeps at a given stimulus direction and distance increase with increasing stimulus velocity (40-250 mm/s, Fig. 5A). In juveniles, the directional dependence of antennal sweeps is reduced compared to that of adults, while a similar intensity dependence is found (Fig. 5B). The pronounced directionality of the antennal response in adult crayfish vanishes and response latencies increase after reversibly covering the tailfan with a small bag or the telson with waterproof paste (Figs. 6 and 7). Thus, tailfan and especially telson mechanoreceptors play an important role in the localization of water movements elicited by predators or prey behind the crayfish.