Responses to pulsed light stimuli in a pulmonate slug (Limax pseudoflavus)

Abstract

The phase changes in the activity rhythm of the pulmonate slug Limax pseudoflavus caused by light pulses (30 min, 10,000 lux) in otherwise dark conditions were recorded using time lapse cinematography and tipping aktographs. From the timing of the pulse relative to an individual activity cycle a phase response curve was constructed. Phase delays occurred when the pulse was administered in the early subjective night and subjective day, phase advances were recorded during the mid and late subjective night.The effects of two pulses (30 min, 10,000 lux) forming symmetric and asymmetric skeleton photoperiods were also recorded and related to the phase response curve. Both stable and unstable entrained states were found, the condition being dependent upon the relative timing of the two pulses and the previous activity onset. It was also shown that there was a time lag between the light pulse and its expressed phase setting effect. Thus phase setting is not instantaneous as with some insects.