Resting Metabolic Rate and Lung Function in Wild Offshore Common Bottlenose Dolphins, Tursiops truncatus, Near Bermuda

Abstract

Diving mammals have evolved a suite of physiological adaptations to manage respiratory gases during extended breath-hold dives. To test the hypothesis that offshore bottlenose dolphins have evolved physiological adaptations to improve their ability for extended deep dives and as protection for lung barotrauma, we investigated the lung function and respiratory physiology of four wild common bottlenose dolphins (Tursiops truncatus) near the island of Bermuda. We measured blood hematocrit (Hct, %), resting metabolic rate (RMR, l O2 ⋅ min-1), tidal volume (VT, l), respiratory frequency (fR, breaths ⋅ min-1), respiratory flow (l ⋅ min-1), and dynamic lung compliance (CL, l ⋅ cmH2O-1) in air and in water, and compared measurements with published results from coastal, shallow-diving dolphins. We found that offshore dolphins had greater Hct (56 ± 2%) compared to shallow-diving bottlenose dolphins (range: 30–49%), thus resulting in a greater O2 storage capacity and longer aerobic diving duration. Contrary to our hypothesis, the specific CL (sCL, 0.30 ± 0.12 cmH2O-1) was not different between populations. Neither the mass-specific RMR (3.0 ± 1.7 ml O2 ⋅ min-1 ⋅ kg-1) nor VT (23.0 ± 3.7 ml ⋅ kg-1) were different from coastal ecotype bottlenose dolphins, both in the wild and under managed care, suggesting that deep-diving dolphins do not have metabolic or respiratory adaptations that differ from the shallow-diving ecotypes. The lack of respiratory adaptations for deep diving further support the recently developed hypothesis that gas management in cetaceans is not entirely passive but governed by alteration in the ventilation-perfusion matching, which allows for selective gas exchange to protect against diving related problems such as decompression sickness.

Modeling Tissue and Blood Gas Kinetics in Coastal and Offshore Common Bottlenose Dolphins, Tursiops truncatus

“… The parameters for Equations (4) and (5) in Bostrom et al ( 2008 ) were revised using previously published compliance data from the bottlenose dolphin (Fahlman et al, 2018b ). Old values are in parentheses .…”

“…Coastal bottlenose dolphins inhabit coastal areas and generally perform short (<60 s), shallow (<10 m) dives (Mate et al, 1995 ), while offshore bottlenose dolphins inhabit offshore, deep-water habitats and regularly dive below 200 m (Klatsky et al, 2007 ). Interestingly, neither resting metabolic rate nor lung compliance differed between the two ecotypes (Fahlman et al, 2018a , b ), but blood hematocrit was significantly higher in the offshore ecotype (Klatsky et al, 2007 ; Schwacke et al, 2009 ; Fahlman et al, 2018a ). In addition, the offshore ecotype is generally larger (Klatsky et al, 2007 ), possibly due to larger muscle mass to help increase the available O 2 stores and diving capacity.…”

Comparative Respiratory Physiology in Cetaceans

“…The differential pressure transducer was connected to a data acquisition system (Powerlab 8/35, ADInstruments, Colorado Springs, CO, United States), and the data was captured at 400 Hz and displayed on a laptop computer running LabChart (v. 8.1, ADInstruments, Colorado Springs, CO, United States). A low resistance diffuser was added to homogenize the flow (Fahlman et al, 2018b), which helped resolve the difference in calibration factors for inspired (V insp ) and expired (V exp ) flow (Fahlman et al, 2015). To assess the flow range over which the flow was linear, we used an industrial fan (Atmosphere Vortex 728 CFM S Line S-800 Fan, 8 ) to generate laminar flow up to 120 l • s −1 , as measured by a calibrated industrial flow meter (Merriam Process Technologies, Serial No.…”

“…Respiratory flow (V) is also generally greater in marine mammals as compared with terrestrial species, especially in cetaceans, that have been shown to be able to generate expiratory flows (V exp ) that are at least one order of magnitude greater than in humans (Olsen et al, 1969a;Kooyman et al, 1971Kooyman et al, , 1975Kooyman and Cornell, 1981;Piscitelli et al, 2013;Fahlman et al, 2015Fahlman et al, , 2017Fahlman et al, , 2019b). There appears to be great variability in the mechanical properties of the respiratory system, but in general marine mammals appear to have more compliant lung parenchyma as compared with terrestrial species, and a rib cage that allows the alveoli to compress and collapse without apparent trauma (Olsen et al, 1969b;Leith, 1976Leith, , 1989Fahlman et al, 2011Fahlman et al, , 2017Fahlman et al, , 2018bDenk et al, 2020).…”

Ventilation and gas exchange before and after voluntary static surface breath-holds in clinically healthy bottlenose dolphins, Tursiops truncatus

“…Z9A887-2, Merriam Process Technologies, Cleveland, OH, USA). A low-resistance diffuser was added to homogenize the flow (Fahlman et al, 2018c), which helped resolve the difference in calibration factors for inspired (Vi nsp ) and expired (Vė xp ) flow . A differential pressure transducer (Spirometer Pod, ML 311, ADInstruments, Colorado Springs, CO, USA) was connected to the pneumotachometer with two firm-walled, flexible tubes (310 cm length×2 mm i.d.).…”