The influence of light on locomotion in the gastropod melibe leonina

In this study, we investigated the effects of light on both the locomotion of intact animals and the swim motor program expressed by isolated brains in the gastropod Melibe leonina. Spontaneous locomotion (crawling and swimming) was examined during a period of natural lighting (L:D) to establish normal behavior, and then under two different light regimes: constant darkness (D:D) and constant light (L:L). In L:D, there was significantly more locomotor activity at night than during the day and this pattern continued in D:D. However, in L:L, activity was substantially reduced at all times. Using isolated brain preparations, we further demonstrated that the swim motor program was rapidly inhibited by light, and that this inhibition was mediated by the eyes. These results indicate that M. leonina displays a nocturnal activity pattern, and that light has a strong inhibitory effect on locomotion in the intact animal and on the swim motor program expressed by the isolated brain.