Rhythms of plasma melatonin levels were determined in lizards (Tiliqua rugosa) subjected to a 12 h photocycle (12 h light:12 h dark) at constant 33°C, and at 7 different thermoperiods (33°C thermophase and 15°C cryophase) whose thermophase duration ranged from 1.5 to 21 h. The melatonin secretion rate, as measured by the amplitude and duration of elevated melatonin levels and the area under the curve, was maximal at thermoperiods whose thermophase was between 9 and 18 h in duration. The results indicate that in ectothermic vertebrates the prevailing thermoperiod as well as the photoperiod may influence melatonin rhythms and hence the timing of annual physiological cycles.
Bibliographical noteFunding Information:
This study was funded by the Australian Research Council, a Universityo f AdelaideR esearchG rant, and the National Health and Medical ResearchC ouncil of Australia. We are gratefult o the South Australian National Parks and Wildlife Servicef or a permit to collect lizards and G. Hermannis,R . Murphy, S. Rich and H. Webb for technicaal ssistance.
- Pineal organ
- Tiliqua rugosa