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

Summary

• 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 (P _A,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 (V _T), rate of ventilation (f), minute volume ($\dot V_{\min }$) and respiratory dead space (V _D) were made (Table 3). Of these,V _D and f and consequently$\dot V_{\min }$ were smaller than expected. The reduced value ofV _D 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 andV _D are discussed.