The effects of temperature and light on the circadian activity of the pulmonate slug, Limax pseudoflavus Evans

The activity of a natural population of the slug Limax pseudoflavus was monitored and related to variations in light intensity and temperature. The activity pattern was unimodal in conditions of both rising and falling temperatures and was similar in artificial conditions under constant temperature and a light: dark (LD) 12:12 cycle. Both crawling and feeding rhythms were entrained by LD cycles of 24 h, temperature cycles of 23 h and a combined temperature and light cycle of 23 h. A light cycle of 19 h weakly entrained the crawling rhythm but failed to entrain the feeding rhythm. Under continuous light, weak rhythmicity was shown with a period less than 24 h. Stronger crawling and feeding rhythms with periods of greater than 24 h were shown under constant darkness. A temperature reduction to 4°C was followed by bursts of crawling and the previously expressed rhythm was disrupted. A reduction to 1°C caused a short burst of crawling followed by inactivity.