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

Abstract

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 (fH), respiration rate (fR), and deep body temperature (Tb) 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 Tb, 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, Tb (day and night) fell to match burrow temperature, accompanied by a further reduction in fH and fR. Tegus, under the conditions of this study, did arouse periodically during dormancy. There was a complex interplay between changes in fH and Tb 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 fH/Tb relationship reflective of the physiological changes associated with warming and cooling as preferred Tb 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.

Beyond body size: muscle biochemistry and body shape explain ontogenetic variation of anti-predatory behaviour in the lizard Salvator merianae (Squamata: Teiidae)

“…In the ecological context of predator avoidance in natural habitats, adults are big and therefore might rely on strong bites during combat -a strategy that is inefficient in juveniles, which are comparatively smaller than adults. When tegus emerge from their shelters early in the morning to feed and/or thermoregulate, they experience body temperatures that can vary from 18 to 26°C depending on the season, reaching 33-37°C later in the day (Sanders et al, 2015) -the second range encompassing their preferential temperatures (Cecchetto and Naretto, 2015). Therefore, these animals may in fact face predators when their body temperatures are below their preferred range.…”

“…During the night, T b decreases very slowly, especially in the summer, when nocturnal temperatures are higher -an effect that is more prominent in larger tegus because of thermal inertia (Tattersall et al, 2016). In colder months, however, the night-time minimum T b in tegus remains low but maximum daily voluntary temperatures also decline, a pattern related to dormancy (Sanders et al, 2015). During this period, although tegus remain inside their burrows most of the time, they also emerge for briefly periods, and their T b remains between 18 and 22°C (Andrade, 2016;Sanders et al, 2015).…”

“…Early in the morning, the T b of tegus is mainly influenced by temperature changes inside their shelters and, because this parameter is variable throughout the year (Sanders et al, 2015;Tattersall et al, 2016), in hotter seasons the lizards might avoid emerging from their shelters if T b is too low. During the night, T b decreases very slowly, especially in the summer, when nocturnal temperatures are higher -an effect that is more prominent in larger tegus because of thermal inertia (Tattersall et al, 2016).…”

“…In colder months, however, the night-time minimum T b in tegus remains low but maximum daily voluntary temperatures also decline, a pattern related to dormancy (Sanders et al, 2015). During this period, although tegus remain inside their burrows most of the time, they also emerge for briefly periods, and their T b remains between 18 and 22°C (Andrade, 2016;Sanders et al, 2015). Such a condition represents a critical situation for survival, because animals may face predators when their T b is below the preferred temperature and locomotion could be impaired.…”

Winter metabolic depression does not change arterial baroreflex control of heart rate in the tegu lizard (Salvator merianae)

“…In contrast, there are situations when metabolic rate can be downregulated independent of temperature in ectotherms; for example, when they are seasonally exposed to adverse environmental conditions and enter the physiological/behavioural state of hibernation or aestivation (Abe, 1995;Glass et al, 1997;Bícego-Nahas et al, 2001;Andrade et al, 2004;Milsom et al, 2008;Navas and Carvalho, 2010). Seasonal reductions in metabolic rate of ectotherms is marked by profound temperature-independent suppression of many physiological and biochemical processes (Navas and Carvalho, 2010), including reduction in f H (Delaney et al, 1974;Glass et al, 1997;Bícego-Nahas et al, 2001;da Silva et al, 2008;Sanders et al, 2015).…”