The pineal and circadian rhythms of temperature selection and locomotion in lizards.
ABSTRACT The existence of a circadian rhythm of behavioral temperature selection has been demonstrated in lizards (Podarcis sicula) held on a thermal gradient in constant darkness. This rhythm becomes temporarily abolished during 1 week following parietalectomy and 2-3 weeks following pinealectomy. Parietalectomy does not affect the locomotor rhythm, while pinealectomy invariably lengthens the freerunning period of this rhythm. These results support the contention of separate control systems for the temperature selection rhythm and the locomotor rhythm. As neither rhythm is definitively abolished by parietalectomy and pinealectomy, other pacemaking components exist elsewhere in the circadian system of Podarcis sicula which can control both rhythms.
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ABSTRACT: The pineal complex of reptiles is a morphologically and functionally con-nected set of organs that originates as an evagination of the roof of the dien-cephalon. It is formed by two structures: the pineal organ and the parietal eye. The pineal gland is present in Chelonia, Squamata and Rhynchocephalia, but not in Crocodilia. The parietal eye is present in some species of lizards (Squama-ta) and in the tuatara (Rhynchocephalia). Both the pineal gland and the parietal eye are photosensitive. In particular, the parietal eye is an highly organized pho-toreceptive structure, with a well-defined lens, cornea and retina. The most important (and studied) secretory product of this complex is the hormone melat-onin which is synthesized by both organs (pineal and parietal eye). The pineal organ is believed to be the neuroendocrine transducer of changes in photoperiod and environmental temperature and it has been demonstrated to have a func-tional role in many aspects of reptilian biology. Melatonin has an influence on the mechanisms controlling thermoregulation (behavioral and physiological), because its manipulation or removal may produce significant alterations of behavioral and physiological thermoregulatory parameters. The reptilian pineal complex may also possess self-sustained circadian oscillators which are involved in the circadian organization of these animals and in their reproduction. It is believed that many of the roles played by the pineal complex are mediated by the hormone melatonin, since exogenous administration of melatonin may affect the animal's physiology and/or behavior. The present paper will review the cur-rent knowledge about the neuroendocrinology and functional roles of the reptil-ian pineal complex.Ethology Ecology & Evolution - ETHOL ECOL EVOL. 01/1997; 9(4).
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ABSTRACT: Thermal trait variation is of fundamental importance to forecasting the impacts of environmental change on lizard diversity. Here, we review the literature for patterns of variation in traits of upper and lower sub-lethal temperature limits, temperature preference and active body temperature in the field, in relation to space, time and phylogeny. Through time, we focus on the direction and magnitude of trait change within days, among seasons and as a consequence of acclimation. Across space, we examine altitudinal and latitudinal patterns, incorporating inter-specific analyses at regional and global scales. This synthesis highlights the consistency or lack thereof, of thermal trait responses, the relative magnitude of change among traits and several knowledge gaps identified in the relationships examined. We suggest that physiological information is becoming essential for forecasting environmental change sensitivity of lizards by providing estimates of plasticity and evolutionary scope.Journal of Comparative Physiology B 08/2013; · 2.02 Impact Factor
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ABSTRACT: The conquest of land has endowed air-breathers with the capability to utilize ventilation not only to acquire oxygen but also to control blood and intracellular acid-base state. Hypercapnic acidosis (resulting from ventilatory control and/or behavioral choice), thus, has become a universal component of hypometabolic states in air-breathers, with inhibitory and/or protective roles. Here, special emphasis is placed on the understanding of alterations of acid-base state associated with changes in temperature. Hypercapnic acidosis in connection with hypometabolism has been found in a variety of air-breathing clades, from snails to mammals through lungfish, amphibians, and reptiles. The discovery of the plesiomorphic character of mammalian hibernation has made the transfer to hibernation biology of the experience gained in the application of hypercapnic acidosis (the so-called "pH-stat" procedure) relevant to acid-base control in clinical artificial hypothermia. This paves the way for mutual benefits from such reciprocal exchange of information between hibernation biology and clinical applications.Integrative and Comparative Biology 02/2014; · 3.02 Impact Factor