title: Coping with cyclic oxygen availability: evolutionary aspects.
abstract: Both the gradual rise in atmospheric oxygen over the Proterozoic Eon as well as episodic fluctuations in oxygen over several million-year time spans during the Phanerozoic Era, have arguably exerted strong selective forces on cellular and organismic respiratory specialization and evolution. The rise in atmospheric oxygen, some 2 billion years after the origin of life, dramatically altered cell biology and set the stage for the appearance of multicelluar life forms in the Vendian (Ediacaran) Period of the Neoproterozoic Era. Over much of the Paleozoic, the level of oxygen in the atmosphere was near the present atmospheric level (21%). In the Late Paleozoic, however, there were extended times during which the level of atmospheric oxygen was either markedly lower or markedly higher than 21%. That these Paleozoic shifts in atmospheric oxygen affected the biota is suggested by the correlations between: (1) Reduced oxygen and the occurrences of extinctions, a lowered biodiversity and shifts in phyletic succession, and (2) During hyperoxia, the corresponding occurrence of phenomena such as arthropod gigantism, the origin of insect flight, and the evolution of vertebrate terrestriality. Basic similarities in features of adaptation to hyopoxia, manifest in living organisms at levels ranging from genetic and cellular to physiological and behavioral, suggest the common and early origin of a suite of adaptive mechanisms responsive to fluctuations in ambient oxygen. Comparative integrative approaches addressing the molecular bases of phenotypic adjustments to cyclic oxygen fluctuation provide broad insight into the incremental steps leading to the early evolution of homeostatic respiratory mechanisms and to the specialization of organismic respiratory function.
authors.affiliation: *Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager, UK; Institute of Anatomy, University of Berne, Berne, Switzerland; Vascular Biology Institute, University of Miami, Miami (FL), USA; Center for Marine Biotechnology and Biomedicine and Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA; Department of Biology, University of Padova, Padova, Italy; Institute of Molecular Genetics, University of Mainz, Mainz, Germany; Institute of Zoology, Biocenter Grindel, University of Hamburg, Hamburg, Germany; **Institute of Zoology, Rheinische Friedrich-Wilhelms-University Bonn, Bonn, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Flück
authors.forename: Keith A
authors.initials: KA
authors.lastname: Webster
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Graham
authors.forename: Folco
authors.initials: F
authors.lastname: Giomi
authors.forename: Frank
authors.initials: F
authors.lastname: Gerlach
authors.forename: Anke
authors.initials: A
authors.lastname: Schmitz