Hypoxic metabolic response of the golden-mantled ground squirrel

SUMMARYThe decrease in body temperature (T b ) observed in most vertebrate classes in response to hypoxia has been attributed to a regulated decrease in set-point, protecting organs against tissue death due to oxygen depletion. Hypoxia, however, imparts particular challenges to metabolic function which may, in turn, affect thermoregulation. In ectotherms, where thermoregulation is mainly behavioural, stressors that influence the propensity to move and respond to temperature gradients are expected to have an impact on thermoregulatory control. Using low oxygen as a potent stressor, we evaluated the variability and level of thermoregulation of inland bearded dragons. To examine the source of thermoregulatory variability, we studied their behaviour in an electronically controlled temperature-choice shuttle box, a constant temperature dual-choice shuttle box, and a linear thermal gradient. A significant increase in the size of the T b range was observed at the lowest oxygen concentration (4% O 2 ), reflecting a decrease in thermoregulatory precision in the temperature-choice shuttle box. This was also accompanied by a drop of ~2-4°C in T b , the drop being greatest in situations where T b must be actively defended. Situations that force the lizards to continually choose temperatures, rather than passively remain at a given temperature, lead to an increase in the variability in the manifested T b , which is further exaggerated in hypoxia. This study reveals that a decrease in thermoregulatory precision caused by a diminished propensity to move or effect appropriate thermoregulatory responses may be a contributing component in the lowering of selected body temperatures observed in many hypoxic ectotherms.

Section: Discussionsupporting

confidence: 90%

Decreased precision contributes to the hypoxic thermoregulatory response in lizards

Cadena

Tattersall

2009

“…This response is typically seen as being protective and contributes to the preservation of arterial oxygen pressure in hypoxia. This is an active process resulting from a reduction of the thermoregulatory set point, regulated within the preoptic hypothalamic nucleus (Barros et al, 2001;Steiner et al, 2002). It is possible to ask whether the drop in rectal temperature accounted for the fall in metabolic rate or whether is there evidence of metabolic suppression beyond that due to a resetting of the body temperature set point (Barros et al, 2001).…”

Section: Respiratory and Metabolic Responses To Hypoxia In High Altitmentioning

confidence: 99%

Divergent physiological responses in laboratory rats and mice raised at high altitude

Jochmans-Lemoine

Villalpando

Gonzales

et al. 2015

Ecological studies show that mice can be found at high altitude (HAup to 4000 m) while rats are absent at these altitudes, and there are no data to explain this discrepancy. We used adult laboratory rats and mice that have been raised for more than 30 generations in La Paz, Bolivia (3600 m), and compared their hematocrit levels, right ventricular hypertrophy (index of pulmonary hypertension) and alveolar surface area in the lungs. We also used whole-body plethysmography, indirect calorimetry and pulse oxymetry to measure ventilation, metabolic rate (O 2 consumption and CO 2 production), heart rate and pulse oxymetry oxygen saturation (p O2,sat ) under ambient conditions, and in response to exposure to sea level P O2 (32% O 2 =160 mmHg for 10 min) and hypoxia (18% and 15% O 2 =90 and 75 mmHg for 10 min each). The variables used for comparisons between species were corrected for body mass using standard allometric equations, and are termed mass-corrected variables. Under baseline, compared with rats, adult mice had similar levels of p O2,sat , but lower hematocrit and hemoglobin levels, reduced right ventricular hypertrophy and higher mass-corrected alveolar surface area, tidal volume and metabolic rate. In response to sea level P O2 and hypoxia, mice and rats had similar changes of ventilation, but metabolic rate decreased much more in hypoxia in mice, while p O2,sat remained higher in mice. We conclude that laboratory mice and rats that have been raised at HA for >30 generations have different physiological responses to altitude. These differences might explain the different altitude distribution observed in wild rats and mice.

“…In numerous taxa, hypoxic exposure augments external heat exchange (Tattersall and Milsom, 2003), lowers thermal preference (Dupré and Wood, 1988;Dupré and Owen, 1992;Tattersall and Boutilier, 1997;Wiggins and Frappell, 2002;Cadena and Tattersall, 2009), reduces metabolic rate (Barros et al, 2001), and inhibits shivering (Barros et al, 2001) and non-shivering heat production (Madden and Morrison, 2005). The prevailing hypothesis is that low environmental oxygen reduces thermoregulatory thresholds for the activation of thermoeffector responses (Steiner and Branco, 2002;Bicego et al, 2007;Tattersall and Milsom, 2009).…”

Section: Introductionmentioning

confidence: 99%

Fluctuations in oxygen influence facultative endothermy in bumblebees

Dzialowski

Tattersall

Nicol

et al. 2014

Bumblebees are facultative endotherms, having the ability to elevate thorax temperature above ambient temperature by elevating metabolism. Here, we investigated the influence of hypoxia on metabolic demands and thermoregulatory capabilities of the bumblebee Bombus terrestris. We measured thorax temperature, rates of oxygen consumption and carbon dioxide production, and abdominal pumping rates of bees randomly exposed to oxygen levels of 20, 15, 10 and 5 kPa at 26°C. Under normoxia, bumblebees maintained an elevated mean thorax temperature of 35.5°C. There was no significant change in thorax temperature at 15 kPa O 2 (33.4°C). Mean thorax temperature decreased significantly at 10 kPa O 2 (31.6°C) and 5 kPa O 2 (27.3°C). Bees were able to maintain an elevated metabolic rate at 15 and 10 kPa O 2 . In normoxia, endothermic bees exhibited periods of rapid abdominal pumping (327 min −1 ) interspaced by periods of no abdominal pumping. At 10 kPa O 2 , abdominal pumping rate decreased (255 min −1 ) but became more continuous. Upon exposure to 5 kPa, metabolic rate and abdominal pumping rate (152 min −1 ) decreased, although the animals continued abdominal pumping at the reduced rate throughout the exposure period. Bumblebees are able to meet the energetic demands of endothermy at 15 kPa O 2 , but become compromised at levels of 10 kPa O 2 and below.