• Daily and annual cycles in thermoregulatory behaviour and cardio‑respiratory physiology of black and white tegu lizards

      Sanders, Colin E; Tattersall, Glenn J; Reichert, Michelle; Andrade, Denis V; Abe, Augusto S; Milsom, William K (2015)
      This study was designed to determine the manner in which metabolism is suppressed during dormancy in black and white tegu lizards (Tupinambis merianae). To this end, heart rate (f H), respiration rate (f R), and deep body temperature (T b) were continuously monitored in outdoor enclosures by radio-telemetry for nine months. There was a continuous decline in nighttime breathing and heart rate, at constant T b, throughout the late summer and fall suggestive of an active metabolic suppression that developed progressively at night preceding the entrance into dormancy. During the day, however, the tegus still emerged to bask. In May, when the tegus made a behavioural commitment to dormancy, T b (day and night) fell to match burrow temperature, accompanied by a further reduction in f H and f R. Tegus, under the conditions of this study, did arouse periodically during dormancy. There was a complex interplay between changes in f H and T b associated with the direct effects of temperature and the indirect effects of thermoregulation, activity, and changes in metabolism. This interplay gave rise to a daily hysteresis in the f H/T b relationship reflective of the physiological changes associated with warming and cooling as preferred T b alternated between daytime and nighttime levels. The shape of the hysteresis curve varied with season along with changes in metabolic state and daytime and nighttime body temperature preferences.
    • The Relationship Between Body Temperature, Heart Rate, Breathing Rate, and Rate of Oxygen Consumption, in the Tegu Lizard (Tupinambis merianae) at Various Levels of Activity

      Piercy, Joanna; Rogers, Kip; Reichert, Michelle; Andrade, Denis V; Abe, Augusto S; Tattersall, Glenn J; Milsom, William K (2015)
      The present study determined whether EEG and/or EMG recordings could be used to reliably define activity states in the Brazilian black and white tegu lizard (Tupinambis merianae) and then examined the interactive effects of temperature and activity states on strategies for matching O2 supply and demand. In a first series of experiments, the rate of oxygen consumption (V˙O2), breathing frequency (f R), heart rate (f H), and EEG and EMG (neck muscle) activity were measured in different sleep/wake states (sleeping, awake but quiet, alert, or moving). In general, metabolic and cardio-respiratory changes were better indictors of the transition from sleep to wake than were changes in the EEG and EMG. In a second series of experiments, the interactive effects of temperature (17, 27 and 37 °C) and activity states on f R, tidal volume (V T), the fraction of oxygen extracted from the lung per breath (FIO2–FEO2), f H, and the cardiac O2 pulse were quantified to determine the relative roles of each of these variables in accommodating changes in V˙O2. The increases in oxygen supply to meet temperature- and activity-induced increases in oxygen demand were produced almost exclusively by increases in f H and f R. Regression analysis showed that the effects of temperature and activity state on the relationships between f H, f R and V˙O2 was to extend a common relationship along a single curve, rather than separate relationships for each metabolic state. For these lizards, the predictive powers of f R and f H were maximized when the effects of changes in temperature, digestive state and activity were pooled. However, the best r 2 values obtained were 0.63 and 0.74 using f R and f H as predictors of met abolic rate, respectively.
    • Seasonal reproductive endothermy in tegu lizards

      Tattersall, Glenn J; Leite, Cleo A.C.; Sanders, Colin E; Cadena, Viviana; Andrade, Denis V; Abe, Augusto S; Milsom, William K (Science Advances, 2016-01)
    • Seasonal reproductive endothermy in tegu lizards

      Tattersall, Glenn J; Leite, Cleo A.C.; Sanders, Colin E; Cadena, Viviana; Andrade, Denis V; Abe, Augusto S; Milsom, William K (2016)
      With some notable exceptions, small ectothermic vertebrates are incapable of endogenously sustaining a body temperature substantially above ambient temperature. This view was challenged by our observations of nighttime body temperatures sustained well above ambient (up to 10°C) during the reproductive season in tegu lizards (~2 kg). This led us to hypothesize that tegus have an enhanced capacity to augment heat production and heat conservation. Increased metabolic rates and decreased thermal conductance are the same mechanisms involved in body temperature regulation in those vertebrates traditionally acknowledged as “true endotherms” : the birds and mammals. The appreciation that a modern ectotherm the size of the earliest mammals can sustain an elevated body temperature through metabolic rates approaching that of endotherms enlightens the debate over endothermy origins, providing support for the parental care model of endothermy, but not for the assimilation capacity model of endothermy. It also indicates that, contrary to prevailing notions, ectotherms can engage in facultative endothermy, providing a physiological analog in the evolutionary transition to true endothermy.