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Am J Physiol Regul Integr Comp Physiol 256: R1160-R1163, 1989;
0363-6119/89 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 5 1160-R1163, Copyright © 1989 by American Physiological Society

ARTICLES

Thermal sensitivity of reptilian melatonin rhythms: "cold" tuatara vs. "warm" skink

B. T. Firth, M. B. Thompson, D. J. Kennaway and I. Belan
Department of Anatomy, University of Adelaide, Australia.

Daily rhythms in plasma melatonin levels were compared in two ecologically diverse reptilian species under natural environmental conditions in autumn. The nocturnal, cold temperature-adapted tuatara (Sphenodon punctatus) had a melatonin rhythm of much lower amplitude than did the diurnal desert-adapted sleepy lizard (Tiliqua rugosa). Experiments in controlled laboratory environments showed that, although both species are capable of attaining a comparable melatonin peak (approximately 750 pmol/l), the threshold temperature at which a significant daily rhythm occurs is approximately 15 degrees C in S. punctatus compared with approximately 25 degrees C in T. rugosa. This difference probably reflects the disparate thermoregulatory adaptations of the two species, S. punctatus favoring mean activity temperatures of 11.5 degrees C and T. rugosa, 32.5 degrees C. In ectotherms such as reptiles, therefore, species-typical thermoregulatory behavior may provide thermal cues that interact with photoperiod to provide the appropriate melatonin signal for the regulation of annual physiological cycles.


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B. T. Firth, I. Belan, D. J. Kennaway, and R. W. Moyer
Thermocyclic entrainment of lizard blood plasma melatonin rhythms in constant and cyclic photic environments
Am J Physiol Regulatory Integrative Comp Physiol, December 1, 1999; 277(6): R1620 - R1626.
[Abstract] [Full Text] [PDF]


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