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: 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: Most animals show strong 24-h patterns of activity, usually being diurnal or nocturnal. An Australian desert skink, Ctenotus pantherinus, is unusual in being active day and night when all other Ctenotus species are diurnal, making it an excellent model to explore factors that promote night-time activity. We tested whether C. pantherinus 1) selects cooler temperatures than diurnal skinks, 2) shows no difference in mean selected temperature between day and night, 3) has the same metabolic rate during the day and night, 4) selects termites over other prey types, 5) can detect prey using only auditory or olfactory senses, and 6) experiences lower predation risk at night than during the day. C.pantherinus shows many features of diurnal skink species, with a high mean selected temperature (36.1+/-1.6 degrees C) that is the same night and day, and a 32% lower metabolic rate at night than during the day. C.pantherinus selects termite prey over other insects and can detect prey using only auditory and olfactory senses; models of C. pantherinus experienced less predation at night than during the day. Preference for termites and reduced predation risk at night favour opportunistic nocturnal activity in this predominantly diurnal lizard and may contribute to its wide geographic distribution in arid Australia.Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 02/2010; 156(2):255-61. · 2.20 Impact Factor
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ABSTRACT: Australian sleepy lizards (Tiliqua rugosa) exhibit marked locomotor activity rhythms in the field and laboratory. Light-dark (LD) and temperature cycles (TCs) are considered important for the entrainment of circadian locomotor activity rhythms and for mediating seasonal adjustments in aspects of these rhythms, such as phase, amplitude, and activity pattern. The relative importance of 24 h LD and TCs in entraining the circadian locomotor activity rhythm in T. rugosa was examined in three experiments. In the first experiment, lizards were held under LD 12:12 and subjected to either a TC of 33:15 degrees C in phase with the LD cycle or a reversed TC positioned in antiphase to the LD cycle. Following LD 12:12, lizards were maintained under the same TCs but were subjected to DD. Activity was restricted to the thermophase in LD, irrespective of the lighting regime and during the period of DD that followed, suggesting entrainment by the TC. The amplitude of the TC was lowered by 8 degrees C to reduce the intensity and possible masking effect of the TC zeitgeber in subsequent experiments. In the second experiment, lizards were held under LD 12.5:11.5 and subjected to one of three treatments: constant 30 degrees C, normal TC (30:20 degrees C) in phase with the LD cycle, or reversed TC. Following LD, all lizards were subjected to DD and constant 30 degrees C. Post-entrainment free-run records revealed that LD cycles and TCs could both entrain the locomotor rhythms of T. rugosa. In LD, mean activity duration (alpha) of lizards in the normal TC group was considerably less than that in the constant 30 degrees C group. Mean alpha also increased between LD and DD in lizards in the normal TC group. Although there was large variation in the phasing of the rhythm in relation to the LD cycle in reversed TC lizards, TCs presented in phase with the LD cycle most accurately synchronized the rhythm to the photocycle. In the third experiment, lizards were held in DD at constant 30 degrees C before being subjected to a further period of DD and one of four treatments: normal TC (06:00 to 18:00 h thermophase), delayed TC (12:00 to 00:00 h thermophase), advanced TC (00:00 to 12:00 h thermophase), or control (no TC, constant 30 degrees C). While control lizards continued to free-run in DD at constant temperature, the locomotor activity rhythms of lizards subjected to TCs rapidly entrained to TCs, whether or not the TC was phase advanced or delayed by 6 h. There was no difference in the phase relationships of lizard activity rhythms to the onset of the thermophase among the normal, delayed, and advanced TC groups, suggesting equally strong entrainment to the TC in each group. The results of this experiment excluded the possibility that masking effects were responsible for the locomotor activity responses of lizards to TCs. The three experiments demonstrated that TCs are important for entraining circadian locomotor activity rhythms of T. rugosa, even when photic cues are conflicting or absent, and that an interaction between LD cycles and TCs most accurately synchronizes this rhythm.Chronobiology International 10/2009; 26(7):1369-88. · 4.35 Impact Factor