Melatonin and thermoregulation in ectothermic vertebrates: a review

Abstract

Precise behavioral thermoregulation is well documented in many ectothermic vertebrates. However, many complexities involving the influence of the pineal gland and melatonin (MEL) on thermoregulatory behavior, and thus body temperature (Tb), remain unresolved. Although MEL is commonly considered to decrease Tb in both endotherms and ectotherms, several ectothermic species do not modulate Tb in response to MEL. Furthermore, it is not yet clear how MEL integrates thermoregulatory behavior with environmental stimuli or how it modulates Tb. Some inferences about MEL action in endotherms are not applicable to ectotherms. Changes in ectothermic Tb are mediated primarily through behavioral modulation (not physiological modulation as in endotherms). Thus, the most likely mechanism underlying MEL's actions on ectothermic Tb is adjustment of the temperature set point in the hypothalamus. We provide a review of the literature addressing the effects of MEL on thermoregulatory behavior in ectothermic vertebrates. We also discuss mechanisms underlying MEL's influence on physiological and behavioral processes in ectotherms and hypotheses regarding interspecific differences in pineal complex and MEL function.