Behavioural oxy-regulation by cold-submerged frogs in heterogeneous oxygen environments

Behavioural oxy-regulation by cold-submerged frogs in heterogeneous oxygen environments

Tattersall G J; Boutilier R G

Canadian Journal of Zoology-Revue Canadienne De Zoologie

1999

1999-06

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.

amphibians; blood-flow; bufo-marinus; bullfrogs rana-catesbeiana; cutaneous gas-exchange; dissolved-oxygen; fish; hypoxia; temperature; toad; Zoology

Journal Article

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