Respiratory adaptations of a fossorial mammal, the pocket gopher (Thomomys bottae)

Abstract

1. Fossorial rodent burrows exhibit relatively stable environmental conditions with regard to light, y. However, vastly different concentrations of CO2 and O2 are encountered in these burrows. Field observations of shallow pocket gopher burrows (Thomomys bottae) reveal CO2 concentrations to 3.8%, and O2 concentrations from 15.5% to 20.5% (Darden, 1970). Values similar to these have been reported for another genus of gopher,Geomys, by Kennerly (1964) and McNab (1966). 2. The sensitivity of the respiratory control mechanisms of the pocket gopher (T. bottae) O2 was tested and expressed as percent increase in minute volume as a function of the level of inspired CO2 (2% to 8%). The CO3 response curve is markedves for other terrestrial and diving mammals (Figs. 1 and 3). 3. Except for a reduction in slope, the respiratory response to CO2 of gophers can be described as similar to that recorded for humans. Carbon dioxide stimulates both increased ventilatory frequency and tidal volume in a near linear fashion. Individual difference in CO2 sensitivity among gophers was demonstrated (Table 2). 4. The level of alveolar CO2 (PA,CO2) in anesthetized pocket gophers is not significantly altered from values normally observed in man at sea level (Table 4). The reduced ventilatory response is due to a reduction in the slope of the response curve. The possible causes for the decreased sensitivity are discussed. 5. Comparisons of predicted and observed values of tidal volume (VT), rate of ventilation (f), minute volume (\(\dot V_{\min } \)) and respiratory dead space (VD) were made (Table 3). Of these,VD and f and consequently\(\dot V_{\min } \) were smaller than expected. The reduced value ofVD offsets the low\(\dot V_{\min } \) and thus alveolar ventilation (\(\dot V_A \)) is only slightly lower than expected. The possible biological significance of the alterations in f andVD are discussed.