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

https://doi.org/10.1016/j.resp.2021.103747Get rights and content
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Highlights

  • Ventilation and gas exchange have been analyzed in Boa constrictor and Crotalus durissus under hypoxia and hypercarbia.

  • Hypoxia produced very similar effects in both species.

  • Hypercarbia did not affect durations of the breathing cycle..

  • CO2 increased ventilation, with air convection requirements being greater in B. constrictor than in C. durissus.

Abstract

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 % O2) and increasing levels of carbon dioxide (1.5, 3.0, 4.5, 6.0 % CO2) 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 CO2 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.

Keywords

Reptilia
Respiratory system
Oxygen consumption
Carbon dioxide release
Breathing pattern

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