SENSORY INPUTS MEDIATING TWO OPPOSITE BEHAVIOURAL RESPONSES TO LIGHT IN THE CRAYFISH PROCAMBARUS CLARKII

Abstract

Crustaceans are attracted out of their burrows by dim light whereas they withdraw in response to light of high intensity. We have studied attraction and withdrawal responses in freely walking crayfish (Procambarus clarkii) and in animals tethered above a treadmill device. Electrophysiological recordings have been made of retinal and extraretinal visual units to determine their possible inputs Attraction was induced by light of 0.17-1.41x; the crayfish walked forward with the abdomen extended. Withdrawal was observed at intensities above 5.6lx; the crayfish walked backwards with a cyclic pattern of flexion and extension of the tail. A group of sustaining visual neurones of the optic nerve with low thresholds was found to respond to light in the range of intensities that produced attraction. Two groups of neurones responded in the range of intensities that produced withdrawal: sustaining visual neurones with high thresholds and the caudal photoreceptors. In animals in which the visual fields of the high-threshold fibres had been covered with black paint, the attraction response was not affected, while withdrawal was only observed in response to light stronger than 11 lx. When tested on a treadmill, the latency of the responses to light and the direction of walking of crayfish reflected attraction and withdrawal responses. Moreover, under these conditions, illumination of the eye induced forward walking at intensities that produce attraction and backward walking at intensities that produce withdrawal. In contrast, illumination of the tail induced only backward walking