Ventilatory and metabolic responses of a bat,Phyllostomus discolor, to hypoxia and CO₂: implications for the allometry of respiratory control

Abstract

The ventilatory and metabolic responses of lesser spear-nosed bats to hypoxia and hypercapnia were measured to determine whether these corresponded to preliminary allometries and a positive relationship between hypoxic ventilatory threshold andP₅₀. Ventilatory responses of lesser spear-nosed bats to 3, 5 and 7% CO₂ differed significantly from ventilation on air and each other. The magnitude of their ventilatory response to CO₂ is consistent with the prediction of a smaller ventilatory response to hypercapnia in small compared to large mammals [\(\% \Delta \dot V \propto M_B^{0.130}\); Williams et al. (1994)]. Among 12, 10 and 8% O₂ treatments only the ventilatory response to 8% O₂ differed significantly from ventilation on air or the other treatments. Metabolic rate was significantly reduced at both 10 and 8% O₂. The hypoxic ventilatory response of these bats does not support the prediction of a greater response in small compared to large mammals [\(\% \Delta \dot V \propto M_B^{0.273}\); Boggs and Tenney (1984)]. Their metabolic response is consistent with the hypoxic hypometabolism typical of small mammals, though not of comparable magnitude. The response, expressed as percent change in convection requirement (\(({{\dot V} \mathord{\left/ {\vphantom {{\dot V} {\dot VO_2 )}}} \right. \kern-\nulldelimiterspace} {\dot VO_2 )}}\)), is also less than that observed in other small mammals. This relative insensitivity to hypoxia may be associated with this bat's unusually high affinity hemoglobin (P₅₀=27.5 torr).