title: Thermal sensitivity of reptilian melatonin rhythms: "cold" tuatara vs. "warm" skink.
abstract: 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.
authors.affiliation: Department of Anatomy, University of Adelaide, Australia.
authors.forename: B T
authors.initials: BT
authors.lastname: Firth
authors.forename: M B
authors.initials: MB
authors.lastname: Thompson
authors.forename: D J
authors.initials: DJ
authors.lastname: Kennaway
authors.forename: I
authors.initials: I
authors.lastname: Belan
mesh_terms: D000818:Animals; D004056:Differential Threshold; D006358:Hot Temperature; D008116:Lizards / Q000502:physiology*; D008297:Male; D008550:Melatonin / Q000097:blood*; D010507:Periodicity; D013045:Species Specificity
chemical_list: D008550:Melatonin