Reptile thermogenesis and the origins of endothermy

Extant endotherms have high rates of metabolism, elevated body temperatures, usually tight control over body temperature, and a reasonable scope for further increases in metabolism through locomotor activity. Vertebrate ectotherms, on the other hand, rely on behavioural thermoregulation and cardiovascular adjustments to facilitate warming, and generally lack specific biochemical and cellular mechanisms for sustained, elevated metabolism. Nevertheless, the ancestral condition to endothermy is thought to resemble that of many extant reptiles, which raises the question of the origins and selection pressures relevant to the transitional state. Numerous hypotheses have emerged to explain the multiple origins of endothermy in vertebrates, including thermoregulatory, locomotory, and reproductive activity as possible drivers for these sustained and elevated metabolic rates. In this article, I discuss recent evidence for facultative endothermy in an extant lepidosaur, the tegu lizard. Since lepidosaurs are a sister group to the archosaurs, understanding how a novel form of endothermy evolved will open up opportunities to test the compatibility or incompatibility of the various endothermy hypotheses, with potential to elucidate and resolve long contentious ideas in evolutionary physiology

Infrared thermography: A non-invasive window into thermal physiology

Infrared thermography is a non-invasive technique that measures mid to long-wave infrared radiation emanating from all objects and converts this to temperature. As an imaging technique, the value of modern infrared thermography is its ability to produce a digitized image or high speed video rendering a thermal map of the scene in false colour. Since temperature is an important environmental parameter influencing animal physiology and metabolic heat production an energetically expensive process, measuring temperature and energy exchange in animals is critical to understanding physiology, especially under field conditions. As a non-contact approach, infrared thermography provides a non-invasive complement to physiological data gathering. One caveat, however, is that only surface temperatures are measured, which guides much research to those thermal events occurring at the skin and insulating regions of the body. As an imaging technique, infrared thermal imaging is also subject to certain uncertainties that require physical modeling, which is typically done via built-in software approaches. Infrared thermal imaging has enabled different insights into the comparative physiology of phenomena ranging from thermogenesis, peripheral blood flow adjustments, evaporative cooling, and to respiratory physiology. In this review, I provide background and guidelines for the use of thermal imaging, primarily aimed at field physiologists and biologists interested in thermal biology. I also discuss some of the better known approaches and discoveries revealed from using thermal imaging with the objective of encouraging more quantitative assessment

Vocalization-associated respiration patterns: thermography-based monitoring and detection of preparation for calling

Vocal emission requires coordination with the respiratory system. Monitoring the increase in laryngeal pressure, which is needed for vocal production, allows detection of transitions from quiet respiration to vocalization-supporting respiration. Characterization of these transitions could be used to identify preparation for vocal emission and to examine the probability of it manifesting into an actual vocal production event. Specifically, overlaying the subject's respiration with conspecific calls can highlight events of call initiation and suppression, as a means of signalling coordination and avoiding jamming. Here, we present a thermal imaging-based methodology for synchronized respiration and vocalization monitoring of free-ranging meerkats. The sensitivity of this methodology is sufficient for detecting transient changes in the subject's respiration associated with the exertion of vocal production. The differences in respiration are apparent not only during the vocal output, but also prior to it, marking the potential time frame of the respiratory preparation for calling. A correlation between conspecific calls with elongation of the focal subject's respiration cycles could be related to fluctuations in attention levels or in the motivation to reply. This framework can be used for examining the capability for enhanced respiration control in animals during modulated and complex vocal sequences, detecting ‘failed’ vocalization attempts and investigating the role of respiration cues in the regulation of vocal interactions

Novel energy savings to multiple stressors in birds: The ultradian regulation of body temperature

This study aimed to examine thermoregulatory responses in birds facing two commonly experienced stressors, cold and fasting. Logging devices allowing long-term and precise access to internal body temperature were placed within the gizzards of ducklings acclimated to cold (CA) (5°C) or thermoneutrality (TN) (25°C). The animals were then examined under three equal 4-day periods: ad libitum feeding, fasting and re-feeding. Through the analysis of daily as well as short-term, or ultradian, variations of body temperature, we showed that while ducklings at TN show only a modest decline in daily thermoregulatory parameters when fasted, they exhibit reduced surface temperatures from key sites of vascular heat exchange during fasting. The CA birds, on the other hand, significantly reduced their short-term variations of body temperature while increasing long-term variability when fasting. This phenomenon would allow the CA birds to reduce the energetic cost of body temperature maintenance under fasting. By analysing ultradian regulation of body temperature, we describe a means by which an endotherm appears to lower thermoregulatory costs in response to the combined stressors of cold and fasting

Bearded dragons (Pogona vitticeps) with reduced scalation lose water faster but do not have substantially different thermal preferences.

Whether scales reduce cutaneous evaporative water loss in lepidosaur reptiles (Superorder Lepidosauria) such as lizards and snakes has been a contentious issue for nearly half a century. Furthermore, while many studies have looked at whether dehydration affects thermal preference in lepidosaurs, far fewer have examined whether normally hydrated lepidosaurs can assess their instantaneous rate of evaporative water loss and adjust their thermal preference to compensate in an adaptive manner. We tested both of these hypotheses using three captive-bred phenotypes of bearded dragon (Pogona vitticeps) sourced from the pet trade: ‘Wild Types’ with normal scalation, ‘Leatherbacks’ exhibiting scales of reduced prominence, and scaleless bearded dragons referred to as ‘Silkbacks’. Silkbacks on average lost water evaporatively at about twice the rate that Wild Types did. Leatherbacks on average were closer in their rates of evaporative water loss to Silkbacks than they were to Wild Types. Additionally, very small (at most ~1°C) differences in thermal preference existed between the three phenotypes that were not statistically significant. This suggests a lack of plasticity in thermal preference in response to an increase in rate of evaporative water loss, and may be reflective of a thermal ‘strategy’ as employed by thermoregulating bearded dragons that prioritises immediate thermal benefits over the threat of future dehydration. The results of this study bolster an often-discounted hypothesis regarding the present adaptive function of scales and have implications for the applied fields of animal welfare and conservation.Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada (Grant RGPIN-2014-05814)

Systematic review of the efficacy of antiemetics in the treatment of nausea in patients with far advanced cancer

Objectives: To systematically review studies of antiemetics used in the treatment of nausea in patients with far-advanced cancer. Data sources: Randomized controlled trials (RCT) and uncontrolled studies identified by electronic and hand searching. Review methods: Identified studies were appraised for quality and effect size. Results: Of 21 studies included, 2 were systematic reviews, 7 were RCT and 12 were uncontrolled studies or case series. Differences in interventions and outcomes amongst the RCT precluded any quantitative data synthesis and all seven studies were prone to bias. Whereas uncontrolled studies indicated a high response rate to standard regimens (75-93% for both nausea and vomiting), RCT showed much lower response rates to these agents (23-36% for nausea, 18-52% for vomiting). The two methods of antiemetic choice (choice based either on the inferred mechanism or empirical) were equally effective. There is reasonably strong evidence for the use of metoclopramide in cancer-associated dyspepsia and steroids in malignant bowel obstruction. There was conflicting evidence about the efficacy of serotonin antagonists compared with standard treatments (e.g. metoclopramide, dopamine antagonists and dexamethasone). There was little or no evidence of the efficacy of some commonly used and seemingly effective drugs such as haloperidol, cyclizine, and methotrimeprazine. Conclusion: Evidence supporting the existing consensus-based guidelines for management of nausea and vomiting in advanced cancer is sparse. Current approaches to treatment based on the neuropharmacology of the emetic pathway may be inappropriate in this setting. Well-designed studies of the impact of "standard" management and novel agents on nausea and vomiting in palliative populations are needed

Geographical variation in bill size across bird species provides evidence for Allen\u27s rule

Allen&rsquo;s rule proposes that the appendages of endotherms are smaller, relative to body size, in colder climates, in order to reduce heat loss. Empirical support for Allen&rsquo;s rule is mainly derived from occasional reports of geographical clines in extremity size of individual species. Interspecific evidence is restricted to two studies of leg proportions in seabirds and shorebirds. We used phylogenetic comparative analyses of 214 bird species to examine whether bird bills, significant sites of heat exchange, conform to Allen&rsquo;s rule. The species comprised eight diverse taxonomic groups&mdash;toucans, African barbets, Australian parrots, estrildid finches, Canadian galliforms, penguins, gulls, and terns. Across all species, there were strongly significant relationships between bill length and both latitude and environmental temperature, with species in colder climates having significantly shorter bills. Patterns supporting Allen&rsquo;s rule in relation to latitudinal or altitudinal distribution held within all groups except the finches. Evidence for a direct association with temperature was found within four groups (parrots, galliforms, penguins, and gulls). Support for Allen&rsquo;s rule in leg elements was weaker, suggesting that bird bills may be more susceptible to thermoregulatory constraints generally. Our results provide the strongest comparative support yet published for Allen&rsquo;s rule and demonstrate that thermoregulation has been an important factor in shaping the evolution of bird bills.<br /

Identification of a lipid-rich depot in the orbital cavity of the thirteen-lined ground squirrel

We discovered a previously undescribed orbital lipid depot in the thirteen-lined ground squirrel during the first ever magnetic resonance image (MRI) of this common experimental model of mammalian hibernation. In animals housed at constant ambient temperatures (5°C or 25°C, 12 h:12 h light:dark photoperiod), the volume of this depot increased in the autumn and decreased in the spring, suggesting an endogenous circannual pattern. Water-fat MRI revealed that throughout the year this depot is composed of ∼40% lipid, similar to brown adipose tissue (BAT). During arousal from torpor, thermal images showed higher surface temperatures near this depot before the rest of the head warmed, suggesting a thermoregulatory function. This depot, however, does not contain uncoupling protein 1, a BAT biomarker, or uncoupling protein 3. Histology shows blood vessels in close proximity to each other, suggesting it may serve as a vascular rete, perhaps to preferentially warm the eye and brain during arousals

Development of homeothermic endothermy is delayed in high-altitude native deer mice (Peromyscus maniculatus)

Altricial mammals begin to independently thermoregulate during the firstfew weeks of postnatal development. In wild rodent populations, this isalso a time of high mortality (50–95%), making the physiological systemsthat mature during this period potential targets for selection. High altitude(HA) is a particularly challenging environment for small endotherms owingto unremitting low O2and ambient temperatures. While superior thermo-genic capacities have been demonstrated in adults of some HA species, itis unclear if selection has occurred to survive these unique challengesearly in development. We used deer mice (Peromyscus maniculatus) nativeto high and low altitude (LA), and a strictly LA species (Peromyscus leucopus),raised under common garden conditions, to determine if postnatal onset ofendothermy and maturation of brown adipose tissue (BAT) is affected byaltitude ancestry. We found that the onset of endothermy correspondswith the maturation and activation of BAT at an equivalent age in LAnatives, with 10-day-old pups able to thermoregulate in response to acutecold in both species. However, the onset of endothermy in HA pups wassubstantially delayed (by approx. 2 days), possibly driven by delayedsympathetic regulation of BAT. We suggest that this delay may be part ofan evolved cost-saving measure to allow pups to maintain growth ratesunder the O2-limited conditions at HA

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

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