Constant set points for pH and P(CO2) in cold-submerged skin-breathing frogs.
*Hydrogen-Ion Concentration; *Skin Physiological Phenomena; Acclimatization; Animals; Carbon Dioxide/blood/*metabolism; Cold Temperature; Immersion; Muscle; Oxygen/*metabolism; Partial Pressure; Rana temporaria/*physiology; Seasons; Skeletal/physiology
The low temperatures encountered by overwintering frogs result in a large downregulation of metabolism and behaviour. However, little is known about acid-base regulation in the extreme cold, especially when frogs become exclusive skin-breathers during their winter submergence. Blood and muscle tissue acid-base parameters (pH, P(CO2), bicarbonate and lactic acid concentrations) were determined in submerged frogs exposed to a range of low temperatures (0.2-7 degrees C). At overwintering temperatures between T = 0.2 and 4 degrees C plasma pH and P(CO2) were maintained constant, whereas intracellular pH regulation resulted in larger pH-temperature slopes occurring in the presumably more active heart muscle (deltapH/deltaT = -0.0313) than in the gastrocnemius muscle (deltapH/deltaT = -0.00799). Although blood pH was not significantly affected by submergence between 0.2 and 4 degrees C (pH = 8.220-8.253), it declined in the 7 degrees C frogs (pH = 8.086), a decrease not linked to the recruitment of anaerobiosis. Plasma P(CO2) and pH in the cold appear to be regulated at constant levels, implying that cutaneous CO2 conductance in submerged frogs is adjusted within the range of overwintering temperatures. This is likely geared toward facilitating the uptake of oxygen under conditions of greater metabolic demand, however there remains the possibility that acid-base balance itself is maintained at a constant set point at the frog's natural overwintering temperatures.
Tattersall G J; Boutilier R G
Respiration physiology
1999
1999-10
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1016/s0034-5687(99)00073-0" target="_blank" rel="noreferrer noopener">10.1016/s0034-5687(99)00073-0</a>
Behavioural oxy-regulation by cold-submerged frogs in heterogeneous oxygen environments
amphibians; blood-flow; bufo-marinus; bullfrogs rana-catesbeiana; cutaneous gas-exchange; dissolved-oxygen; fish; hypoxia; temperature; toad; Zoology
Amphibians overwintering in ice-covered aquatic environments encounter levels of hypoxia that present significant challenges to the maintenance of aerobic metabolism. Earlier laboratory experiments showed that cold-submerged frogs will seek out lower temperatures when confronted with severe hypoxia. This so-called behavioural hypothermia response effectively reduces the aerobic metabolic rate and thereby minimises the lactic acidosis associated with oxygen lack. The results of these previous experiments suggest that frogs overwintering in hypoxic environments have the capacity to exploit thermal gradients under the ice to forestall the onset of anaerobiosis. What is not yet known is whether overwintering frogs can detect and therefore react to the large isothermal oxygen gradients that also exist under the ice. To determine the behavioural response of frogs to dissolved oxygen, the movements of submerged animals were followed for 6 h in an aquatic chamber that presented a linear horizontal oxygen gradient (14-130 mmHg) at two constant temperatures (1.5 and 7 degrees C). At both temperatures, frogs spent significantly less time in regions of the tank that were hypoxic than they did in the same regions when no oxygen gradient was present. Submerged frogs also showed an overall preference for oxygen levels above their critical oxygen partial pressures for the aerobic metabolic rate (41 mmHg at 1.5 degrees C and 76 mmHg at 7 degrees C). Thus, cold-submerged frogs not only respond to oxygen gradients, but they do so in a fashion that favours oxygen uptake and aerobic metabolism. This "behavioural oxy-regulation," although slow-acting, would appear to be adequate for frogs responding to the progressively developing oxygen and temperature gradients in their natural overwintering environments.
Tattersall G J; Boutilier R G
Canadian Journal of Zoology-Revue Canadienne De Zoologie
1999
1999-06
Journal Article
<a href="http://doi.org/10.1139/cjz-77-6-843" target="_blank" rel="noreferrer noopener">10.1139/cjz-77-6-843</a>
Does behavioural hypothermia promote post-exercise recovery in cold-submerged frogs?
amphibian; anuran amphibians; behavioural hypothermia; body size; bufo-marinus; bullfrogs; exhaustive exercise; frog; hypoxia; Life Sciences & Biomedicine - Other Topics; maximal oxygen; mechanisms; metabolic recovery; overwintering; Rana; rana-catesbeiana; recovery; temperature; temperature selection; temporaria; thermoregulation
At the low temperatures of the overwintering environment of the frog Rana temporaria, small changes in ambient temperature have large effects on metabolism and behaviour, especially since Q(10) values are often greatly elevated in the cold. How the overwintering aquatic frog copes with variable thermal environments in terms of its overall activity metabolism and recovery from pursuit by predators is poorly understood, as is the role of behavioural thermoregulation in furthering recovery from intense activity, Exhaustive exercise was chosen as the method of evaluating activity capacity (defined by time to exhaustion, total distance swum and number of leg contractions before exhaustion) and was determined at 1.5 and 7 degrees C, Other cohorts of frogs were examined at both temperatures to determine the metabolic (acid-base, lactate, glucose, ATF and creatine phosphate) and respiratory responses to exercise in cold-submerged frogs. Finally, temperature preference before and after exercise was determined in a thermal gradient to define the importance of behavioural thermoregulation on the recovery rates of relevant metabolic and respiratory processes. Activity capacity was significantly reduced in frogs exercised at 1.5 versus 7 degrees C, although similar levels of tissue acid-base metabolites and lactate were reached, Blood pH, plasma PCO2 and lactate levels recovered more rapidly at 1.5 degrees C than at 7 degrees C; however, intracellular pH and the recovery of tissue metabolite levels were independent of temperature. Resting aerobic metabolic rates were strongly affected by temperature (Q(10)=3.82); however, rates determined immediately after exercise showed a reduced temperature sensitivity (Q(10)=1.67) and, therefore, a reduced factorial aerobic scope, Excess oxygen consumption recovered to resting values after 5-6.25 h, and 67% recovery times tended to be slightly faster at the lower temperatures, Exercise in the cold, therefore, provided an immediately higher factorial scope, which could be involved in the faster rate of recovery of blood lactate levels in the colder frogs, In addition, exercise significantly lowered the preferred temperature of the frogs from 6.7 to 3.6 degrees C for nearly 7 h, after which they returned to their normal, unstressed preferred temperatures. Thus, a transient behavioural hypothermia in the skin-breathing, overwintering frog may be an important strategy for minimising post-exercise stress and maintaining aerobic metabolism during recovery from intense activity.
Tattersall G J; Boutilier R G
Journal of Experimental Biology
1999
1999-03
Journal Article
n/a
Metabolic consequences of behavioural hypothermia and oxygen detection in submerged overwintering frogs
hypoxia; exercise; oxygen; recovery; Zoology; temperature; amphibians; rana-catesbeiana; bullfrogs; metabolic fuels; metabolic suppression; muscosa; temperature gradients
The common frog, Rana temporaria, overwinters under the ice of frozen lakes and ponds, during which time metabolic, respiratory and behavioural adjustments act in concert to conserve metabolic fuels by promoting aerobic metabolism. Animal behaviour under the ice is poorly understood, but given that spatial and temporal gradients for temperature and oxygen develop throughout the winter, behavioural thermoregulation may allow the selection of aerobic microenvironments that are conducive to overwintering survival. Accordingly, we have examined the thermoregulatory behaviour and metabolism of cold-submerged frogs in an experimental 'gradient chamber' designed to mimic overwintering conditions in nature. The preferred temperature of 7 degrees C in normoxia decreases to 1.5 degrees C in severe hypoxia, and coincides: with an aerobic metabolic saving of 70-85% and a delay in the onset of a runaway lactacidosis. Following intense exercise, temperature preferences are also lowered from 6.7 degrees C to 3.6 degrees C for upwards of 7 hours in a fashion reminiscent of the 'behavioural hypothermia' response to hypoxia. Cold-submerged frogs are also able to detect isothermal variations in dissolved oxygen and spend 70% of their time at oxygen partial pressures that promote aerobic metabolism. The ability to exploit gradients of oxygen and temperature has strong ecological relevance to over-wintering since the behavioural selection of preferred microhabitats is consistent with minimising the metabolic stresses associated with either hypoxia or hypothermia and promoting survival.
Boutilier R G; Tattersall G J; Donohoe P H
Zoology-Analysis of Complex Systems
2000
2000
Journal Article or Conference Abstract Publication
n/a