title: Evolution of lung breathing from a lungless primitive vertebrate.
abstract: Air breathing was critical to the terrestrial radiation and evolution of tetrapods and arose in fish. The vertebrate lung originated from a progenitor structure present in primitive boney fish. The origin of the neural substrates, which are sensitive to metabolically produced CO2 and which rhythmically activate respiratory muscles to match lung ventilation to metabolic demand, is enigmatic. We have found that a distinct periodic centrally generated rhythm, described as "cough" and occurring in lamprey in vivo and in vitro, is modulated by central sensitivity to CO2. This suggests that elements critical for the evolution of breathing in tetrapods, were present in the most basal vertebrate ancestors prior to the evolution of the lung. We propose that the evolution of breathing in all vertebrates occurred through exaptations derived from these critical basal elements.
authors.affiliation: Department of Veterinary Medicine, University of Alaska Fairbanks, United States.
authors.forename: M
authors.initials: M
authors.lastname: Hoffman
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, United States; Department of Biology and Wildlife, University of Alaska Fairbanks, United States.
authors.forename: B E
authors.initials: BE
authors.lastname: Taylor
authors.affiliation: Department of Veterinary Medicine, University of Alaska Fairbanks, United States; Institute of Arctic Biology, University of Alaska Fairbanks, United States; Department of Biology and Wildlife, University of Alaska Fairbanks, United States. Electronic address: mbharris@alaska.edu.
authors.forename: M B
authors.initials: MB
authors.lastname: Harris
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001933:Brain Stem / Q000502:physiology*; D007798:Lampreys / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D010991:Plethysmography; D012119:Respiration; D012143:Respiratory Physiological Phenomena
keywords: Breathing; CO(2); Cough; Evolution; Exaptation; Lamprey