Control of lung ventilation following overwintering conditions in bullfrogs, Lithobates catesbeianus.
Ranid frogs in northern latitudes survive winter at cold temperatures in aquatic habitats often completely covered by ice. Cold-submerged frogs survive aerobically for several months relying exclusively on cutaneous gas exchange while maintaining temperature-specific acid-base balance. Depending on the overwintering hibernaculum, frogs in northern latitudes could spend several months without access to air, the need to breathe or the chemosensory drive to use neuromuscular processes that regulate and enable pulmonary ventilation. Therefore, we performed experiments to determine whether aspects of the respiratory control system of bullfrogs, Lithobates catesbeianus, are maintained or suppressed following minimal use of air breathing in overwintering environments. Based on the necessity for control of lung ventilation in early spring, we hypothesized that critical components of the respiratory control system of bullfrogs would be functional following simulated overwintering. We found that bullfrogs recently removed from simulated overwintering environments exhibited similar resting ventilation when assessed at 24°C compared with warm-acclimated control bullfrogs. Additionally, ventilation met resting metabolic and, presumably, acid-base regulation requirements, indicating preservation of basal respiratory function despite prolonged disuse in the cold. Recently emerged bullfrogs underwent similar increases in ventilation during acute oxygen lack (aerial hypoxia) compared with warm-acclimated frogs; however, CO2-related hyperventilation was significantly blunted following overwintering. Overcoming challenges to gas exchange during overwintering have garnered attention in ectothermic vertebrates, but this study uncovers robust and labile aspects of the respiratory control system at a time point correlating with early spring following minimal to no use of lung breathing in cold-aquatic overwintering habitats.
Wright State University, Department of Biological Sciences, 3640 Colonel Glenn. Hwy, Dayton, OH 45435, USA Wright State University, Biomedical Sciences PhD Program, 3640 Colonel Glenn. Hwy, Dayton, OH 45435, USA santin.2@wright.edu.
Joseph M
0000-0003-1308-623X
JM
Santin
Wright State University, Department of Biological Sciences, 3640 Colonel Glenn. Hwy, Dayton, OH 45435, USA.
Lynn K
LK
Hartzler
D000818:Animals; D001481:Basal Metabolism; D001784:Blood Gas Analysis; D003080:Cold Temperature; D005260:Female; D005740:Gases / Q000097:blood; D006706:Homeostasis; D010100:Oxygen / Q000378:metabolism*; D012123:Pulmonary Ventilation; D011892:Rana catesbeiana / Q000502:physiology*; D011897:Random Allocation; D012119:Respiration; D012621:Seasons
D005740:Gases; D010100:Oxygen
Bullfrog; Control of breathing; Environmental physiology; Hypercarbia; Hypoxia; Temperature acclimation