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

B. T. Firth, M. B. Thompson, D. J. Kennaway, I. Belan

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27 Citations (Scopus)


Daily rhythms in plasma melatonin levels were compared in two ecologically diverse reptilian species under natural environmental conditions in autumn. The nocturnal, cold temperate-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 (~750 pmol/l), the threshold temperature at which a significant daily rhythm occurs is ~15°C in S. punctatus compared with ~25°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°C and T. rugosa, 32.5°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.

Original languageEnglish
Pages (from-to)25/5
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number5
Publication statusPublished - May 1989
Externally publishedYes


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