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.

Upper Thermal Limits of Insects Are Not the Result of Insufficient Oxygen Delivery

“…Intermediate hypoxia and hyperoxia treatments are useful because they delimit the natural changes in atmospheric oxygen content believed to have taken place over the past 500 million years of insect history (reviewed in Dudley 2000;Fluck et al 2007;Harrison et al 2010). Although the particular details of the competing geochemical models of paleoatmospheric composition differ slightly, what is clear is that insects have been exposed to radical changes in oxygen availability, including periods where levels may have been more than 60% higher than present levels (Berner and Canfield 1989;Bergman et al 2004;Berner 2006).…”

Critical oxygen levels and metabolic suppression in oceanic oxygen minimum zones

“…Possible adjustments include increased heart rate, enhanced gill surface area via remodeling (Mitrovic et al, 2009), increased blood pigment levels, adjustment of enzyme systems, and elevated rates of ventilation. Some of these adjustments are triggered by hypoxia-mediated upregulation of gene expression patterns (Flück et al, 2007) while others are regulated physiologically. By contrast, animals whose metabolic rate drops with declining P O 2 are termed 'oxyconformers'.…”

“…This is the largest mass animal migration on Earth (Robison, 2009) and is driven predominantly by predator avoidance (although some organisms gain considerable energetic advantage by migrating into cool, hypoxic waters) (Rosa and Seibel, 2010;Svetltichny et al, 2000). Diel vertical migrators living in areas of oceanic OMZs migrate through a gradient of relatively stable O 2 environments and so possess adaptations for enhanced anaerobic metabolism and metabolic suppression similar to those from unstable O 2 environments (Flück et al, 2007;Richards, 2011). By contrast, organisms from stable O 2 environments tend to rely more on aerobic adaptations for extraction of O 2 sufficient to maintain routine metabolic rates (Childress and Seibel, 1998).…”

Should Oxygen Therapy Be Tightly Regulated to Minimize Hyperoxia in Critically Ill Patients?

“…Moreover, many ancestral species dwelled predominantly in subterranean habitats that probably enhanced their ability to adapt to hypoxic environments. 20 It is very likely that these genetically coded strategies influence all current organisms' responses to hyperoxia in ways that we do not yet fully comprehend.…”

“…As described in the pro argument, the toxicity of oxygen in animal models is well known, and further discussion on that point is unwarranted. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] The argument here is: Should we use conservative oxygen therapy and avoid hyperoxemia in mechanically ventilated patients?…”