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The initiation of pulmonary respiration in a bird embryo: tidal volume and frequency
Insights
Wedge-tailed Shearwater embryos show increasing lung ventilation as they develop. Their respiratory system adapts to high CO2 levels during internal pipping, preparing them for hatching.
Area of Science:
- Physiology
- Embryology
- Avian Biology
Background:
- Pulmonary ventilation changes are critical for avian embryonic development and hatching success.
- Understanding respiratory adaptations in seabirds like the Wedge-tailed Shearwater (Puffinus pacificus) provides insights into developmental physiology.
Purpose of the Study:
- To investigate the changes in pulmonary ventilation (tidal volume and minute volume) in Wedge-tailed Shearwater embryos and hatchlings.
- To assess the respiratory response of Shearwater embryos and hatchlings to varying concentrations of carbon dioxide (CO2).
Main Methods:
- Barometric plethysmography was used to measure pulmonary ventilation in Wedge-tailed Shearwater embryos and hatchlings.
- Embryos at different developmental stages, including internally pipped eggs and those with pip-holes, were analyzed.
- Ventilatory responses to acute exposure to 2%, 5%, and 10% CO2 in air were recorded.
Main Results:
- Tidal volume and minute volume significantly increased from internally pipped eggs to hatchlings.
- Ventilation was significantly higher in eggs with pip-holes compared to internally pipped eggs.
- Shearwater embryos showed a blunted response to CO2, with increased tidal volume and decreased respiratory frequency only at 10% CO2.
- Hatchlings exhibited significant increases in tidal volume with all tested CO2 levels and increased minute volume at 5% CO2.
Conclusions:
- The Wedge-tailed Shearwater embryo exhibits a relative insensitivity to high CO2 levels, indicating a physiological adaptation to the gas composition within the air cell during internal pipping.
- These findings suggest a developmental respiratory strategy that prepares the embryo for hatching and the challenges of rebreathing within the egg.
Abstract:
Pulmonary ventilation in embryos and hatchlings of the Wedge-tailed Shearwater (Puffinus pacificus), measured with a barometric plethysmograph, revealed a progressive rise in tidal volume (VT) and minute volume (VE) during the paranatal period to achieve hatchling levels. VT and VE in internally pipped eggs (penetration of air cell) was 0.06 ml +/- 0.03 (SD) and 3.11 ml . min-1 +/- 1.80, respectively. Ventilation was significantly higher (P less than 0.05) in eggs with pip-holes (VT = 0.15 ml +/- 0.04 and VE = 7.09 ml . min-1 +/- 2.76). A significant difference (P less than 0.05) was also obtained for VT and VE between embryos and hatchling chicks. The respiratory frequency (f) was approximately 47 breaths . min-1 for both embryos and chicks. Acute changes in ventilation were examined in response to 2% CO2, 5% CO2, and 10% CO2 in air. For embryos, VT increased significantly (P less than 0.05) only with 10% CO2 and was accompanied by a significant decrease (P less than 0.05) in f. Hatchling VT increased significantly (P less than 0.05) with each test gas and VE increased significantly (P less than 0.05) with acute exposure to 5% CO2, from 16.5 ml . min-1 +/- 2.0 in normoxic air to 53.9 ml . min-1 +/- 8.6. The shearwater embryo is relatively insensitive to high levels of CO2, suggesting a respiratory adaptation to naturally inspired air cell gas concentrations during the internal pipping phase and rebreathing.