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Two new biomechanical challenges faced cetacean lungs compared to their terrestrial ancestors. First, hydrostatic pressures encountered during deep dives are sufficient to cause nearly full lung collapse, risking substantial barotrauma during surfacing if air is trapped in the fragile smaller airways. Second, rapid ventilation in large cetaceans requires correspondingly high ventilatory flow rates. In order to investigate how airway geometry evolved in response to these challenges, we characterized airway geometry from 12 species of cetaceans that vary in common dive depth and ventilatory behavior and a domestic pig using computed tomography. After segmenting the major airways, we generated centerline networks models for the larger airways and computed geometric parameters for each tree including mean branching angle, percent volume fraction, and Strahler branching, diameter, and length ratios. When airway geometry was regressed against ventilatory and diving parameters with phylogenetic least squares, neither average branching angle, percent volume fraction, Strahler length ratio or Strahler branching ratio significantly varied with common ventilatory mode or common diving depth. Higher Strahler diameter ratios were associated with slower ventilation and deeper diving depth, suggesting that cetacean lungs have responded to biomechanical pressures primarily with changes in airway diameter. High Strahler diameter ratios lungs in deeper diving species may help to facilitate more complete collapse of the delicate terminal airways by providing for a greater incompressible volume for air storage at depth. On the other hand, lungs with low Strahler diameter ratios would be better for fast ventilation because the gradual decrease in diameter moving distally should keep peripheral flow resistance low, maximizing ventilatory flow rates.
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Effect of parabranchial position on ventilatory pressures in the Pacific spiny dogfish (Squalus suckleyi)
The mechanics of ventilation in elasmobranchs have been described as a two-pump system which is dependent on the generation of differential pressures between the orobranchial and parabranchial cavities. However, this general model does not take into account sources of variation in parabranchial form and function. For example, the relative pressures that drive flow in each parabranchial chamber during ventilation remain largely unexplored. To address this gap, parabranchial pressures were collected from the Pacific spiny dogfish (Squalus suckleyi, n = 12) during routine ventilation using transducers inserted into parabranchial chambers 2, 3, and 5, numbered anteriorly to posteriorly. Pressure amplitudes collected from the three chambers displayed an attenuation of pressure amplitudes posteriorly, as well as differential, modular use of parabranchial chamber five. These observations have implications for the functioning of the ventilatory pump and indicate distinct ventilatory modes, leading us to propose a new model to describe ventilation in Squalus suckleyi.
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- Award ID(s):
- 2000268
- PAR ID:
- 10472731
- Publisher / Repository:
- Zoology
- Date Published:
- Journal Name:
- Zoology
- Volume:
- 159
- Issue:
- C
- ISSN:
- 0944-2006
- Page Range / eLocation ID:
- 126106
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.zool.2023.126106
