Thermoregulatory spectrum in vertebrates

Thermoregulatory mechanisms and control of homeothermy are quite recent from evolutionary stand point. Animals have either simply recruited or modified other regulatory systems for the purpose of thermoregulation. The degree of such recruitments or modifications vary among different class of vertebrates thus giving rise to a relative diversity in the spectrum of thermoregulatory control and mechanisms. The review briefly summarizes the evidence showing that body temperature control is not an isolated regulated system in vertebrates, rather, a hierarchically integrated multiple system. The available information shows that pineal transduces environmental cues for photoperiodic and seasonal adjustments to the preoptic area of anterior hypothalamus via its primary secretory product, melatonin. The hypothalamus integrates the information and then sets the effector recruitment for each control system consistent with the metabolic rate of the animal taking into considerations the cost and benefit of the action taken. The overwhelming similarity in response to different constituents of the thermoregulatory spectrum contradicts the aphorism that cold-blooded animals are dependent on ambient temperature. It is our collective view that there is no fundamental difference between ectotherms and endotherms since the two vary only in the degree of their ability to maintain thermal homeostasis.