Seasonal Variations of Pineal Involvement in the Circadian Organization of the Ruin Lizard Podarcis Sicula

To establish whether the effects of pinealectomy on circadian locomotor rhythmicity vary with season, we examined, in constant temperature and darkness, the locomotor behaviour of ruin lizards Podarcis sicula collected and subjected to pinealectomy at different times of the year. Changes in the freerunning period in response to pinealectomy were found to be significantly greater in summer than in winter, spring and autumn. Circadian activity time changed significantly in response to pinealectomy only in spring and summer. Furthermore, while pinealectomy was effective in altering the locomotor rhythms of all individual lizards tested in summer, the same surgery was found to leave locomotor rhythmicity of many lizards tested in autumn and winter completely undisturbed. These results demonstrate for the first time in a non-mammalian vertebrate that the pineal gland is centrally involved in determining circadian organization in some seasons and is only marginally involved in others.