Effects of different levels of hypoxia and hypercarbia on ventilation and gas exchange in Boa constrictor amaralis and Crotalus durissus (Squamata: Serpentes).

Ventilation and gas exchange have been studied in relatively few species of snakes, especially regarding their response to environmental hypoxia or hypercarbia. We exposed Crotalus durissus (N = 6) and Boa constrictor (N = 6) to decreasing levels of oxygen (12, 9, 6, 3 % O) and increasing levels of carbon dioxide (1.5, 3.0, 4.5, 6.0 % CO) and analyzed the effect of the different gas mixtures on ventilation and gas exchange using open-flow respirometry. Neither hypoxia nor hypercarbia significantly altered the duration of expiration or inspiration, nor their proportions. Both hypoxia and hypercarbia increased minute ventilation, but the decrease in oxygen had a less pronounced effect on ventilation. Gas exchange under normoxic conditions was low and was not significantly affected by hypoxia, but hypercarbia decreased gas exchange significantly in both species. While B. constrictor maintained its respiratory exchange ratio (RER) under hypercarbia between 0.5 and 1.0, C. durissus showed a RER above 1.0 during hypercarbia, due to a significantly greater CO excretion. The overall responses of both species to hypercarbia and especially to hypoxia were very similar, which could be associated to similar lifestyles as ambush hunting sit-and-wait predators that are able to ingest large prey items. The observed differences in gas exchange could be related to respiratory systems with macroscopically different structures, possessing only a tracheal lung in C. durissus, but two functional lungs in B. constrictor.