VENTILATORY AND METABOLIC RESPONSES OF A BAT, PHYLLOSTOMUS DISCOLOR, TO HYPOXIA AND CO2 - IMPLICATIONS FOR THE ALLOMETRY OF RESPIRATORY CONTROL

The ventilatory and metabolic responses of lesser spear-nosed bats to hypoxia and hypercapnia were measured to determine whether those corre sponded to preliminary allometries and a positive relationship between hypoxic ventilatory threshold and P-50. Ventilatory responses of less er spear-nosed bats to 3, 5 and 7% CO2 differed significantly from ven tilation on air and each other. The magnitude of their ventilatory res ponse to CO2 is consistent with the prediction of a smaller ventilator y response to hypercapnia in small compared to large mammals [%Delta V over dot proportional to M(B)(0.130); Williams et al. (1994)]. Among 12, 10 and 8% O-2 treatments only the ventilatory response to 8% O-2 d iffered significantly from ventilation on air or the other treatments. Metabolic rate was significantly reduced at both 10 and 8% O-2. The h ypoxic ventilatory response of these bats does not support the predict ion of a greater response in small compared to large mammals [%Delta V over dot proportional to M(B)(0.273); Boggs and Tenney (1984)]. Their metabolic response is consistent with the hypoxic hypometabolism typi cal of small mammals, though not of comparable magnitude. The response , expressed as percent change in convection requirement (V over dot/V over dot O-2), is also less than that observed in other small mammals. This relative insensitivity to hypoxia may be associated with this ba t's unusually high affinity hemoglobin (P-50 = 27.5 torr).