Independent effects of the pineal and a bacterial pyrogen in behavioural thermoregulation in lizards.

The pineal complex of lizards is comprised of an extracranial photoreceptive structure known as the parietal eye, and an intracranial pineal organ which is homologous to the pineal gland of birds and mammals. Studies have shown that removing the parietal eye or severing the parietal nerve causes lizards to select higher temperatures when allowed to thermoregulate behaviourally in thermal or photothermal laboratory gradients. Although comparable studies involving removal of the lizard pineal organ have not previously been attempted, field data indicate that pinealectomy may have an antagonistic effect to parietalectomy. We present evidence here which shows that (1) following pinealectomy, collared lizards (Crotaphytus collaris) behaviourally select or prefer lower temperatures than their controls in thermal laboratory gradients, and (2) the effect of surgical treatment is independent of the effects of a behavioural fever-inducing substance which elevates by a fixed amount the environmental temperatures selected.