Differential effects of food availability on minimum and maximum rates of metabolism

Metabolic rates reflect the energetic cost of living but exhibit remarkable variation among conspecifics, partly as a result of the constraints imposed by environmental conditions. Metabolic rates are sensitive to changes in temperature and oxygen availability, but effects of food availability, particularly on maximum metabolic rates, are not well understood. Here, we show in brown trout (Salmo trutta) that maximum metabolic rates are immutable but minimum metabolic rates increase as a positive function of food availability. As a result, aerobic scope (i.e. the capacity to elevate metabolism above baseline requirements) declines as food availability increases. These differential changes in metabolic rates likely have important consequences for how organisms partition available metabolic power to different functions under the constraints imposed by food availability

Kinematics of hovering hummingbird flight along simulated and natural elevational gradients

Hovering flight is one of the most energetically demanding forms of animal locomotion. Despite the cost, hummingbirds regularly hover at high elevations, where flight is doubly challenging because of reduced air density and oxygen availability. We performed three laboratory experiments to examine how air density and oxygen partial pressure influence wingbeat kinematics. In the first study, we experimentally lowered air density but maintained constant oxygen partial pressure. Under these hypodense but normoxic conditions, hummingbirds increased stroke amplitude substantially and increased wingbeat frequency slightly. In the second experiment, we maintained constant air density but decreased oxygen partial pressure. Under these normodense but hypoxic conditions, hummingbirds did not alter stroke amplitude but instead reduced wingbeat frequency until they could no longer generate enough vertical force to offset body weight. In a final combined experiment, we decreased air density but increased oxygen availability, and found that the wingbeat kinematics were unaffected by supplemental oxygen. We also studied hovering and maximally loaded flight performance for 43 hummingbird species distributed along a natural elevational gradient in Peru. During free hovering flight, hummingbirds showed increased stroke amplitude interspecifically at higher elevations, mirroring the intra-individual responses in our first laboratory experiment. During loaded flight, hummingbirds increased both wingbeat frequency and wing stroke amplitude by 19% relative to free-flight values at any given elevation. We conclude that modulation of wing stroke amplitude is a major compensatory mechanism for flight in hypodense or hypobaric environments. By contrast, increases in wingbeat frequency impose substantial metabolic demands, are only elicited transiently and anaerobically, and cannot be used to generate additional sustained lift at high elevations

Effects of diamagnetic levitation on bacterial growth in liquid

Diamagnetic levitation is a technique that uses a strong, spatially-varying magnetic field to levitate diamagnetic materials, such as water and biological cells. This technique has the potential to simulate aspects of weightlessness, on the Earth. In common with all ground-based techniques to simulate weightlessness, however, there are effects introduced by diamagnetic levitation that are not present in space. Since there have been few studies that systematically investigate these differences, diamagnetic levitation is not yet being fully exploited. For the first time, we critically assess the effect of diamagnetic levitation on a bacterial culture in liquid. We used a superconducting magnet to levitate growing bacterial cultures for up to 18 hours, in a series of experiments to determine the effect of diamagnetic levitation on all phases of the bacterial growth cycle. We find that diamagnetic levitation increases the rate of population growth in a liquid culture. The speed of sedimentation of the bacterial cells to the bottom of the container is considerably reduced. Further experiments and microarray gene analysis show that the growth enhancement is due to greater oxygen availability in the magnetically levitated sample. We demonstrate that the magnetic field that levitates the cells also induces convective stirring in the liquid, an effect not present in microgravity. We present a simple theoretical model, showing how the paramagnetic force on dissolved oxygen can cause the liquid to become unstable to convection when the consumption of oxygen by the bacteria generates an oxygen concentration gradient. We propose that this convection enhances oxygen availability by transporting oxygen around the sample. Since convection is absent in space, these results are of significant importance and timeliness to researchers considering using diamagnetic levitation to explore weightless effects on living organisms and a broad range of other topics in the physical and life sciences

Use of lunar produced propellants for manned Mars missions

Manned Mars Mission departures from low lunar orbit (LLO), L2, and low Earth orbit (LEO), using oxygen or oxygen and hydrogen produced on the Lunar surface; or Phobos produced propellants; are compared to departures from LEO using Earth produced propellants. The economy of a given scheme is a function of the ratio of Earth launch to lunar launch costs per unit mass. To achieve savings on the order of 40% of total Earth launch costs for steady state operations requires the availability of both oxygen and hydrogen on the Moon and launch per unit mass costs of lunar surface to LLO in the range of 25% of Earth to LEO costs

Regulation of the Aspergillus nidulans cytochrome C gene : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Molecular Genetics at Massey University, Palmerston North, New Zealand

The filamentous fungus Aspergillus nidulans has been genetically and biochemically well-characterised and thus provides an attractive model for studies on the regulation of eukaroytic gene expression. This study was undertaken to investigate the factors affecting respiratory function in A. nidulans. Due to the central role of cytochrome c in oxidative respiration, this study was focused on the cytochrome c gene and primarily upon how oxygen availability affects its expression. The Aspergillus nidulans cytochrome c gene (eyeA) appears to be transcriptionally activated in response to oxygen availability (Raitt et al., 1994). In the yeast S. cerevisiae, oxygen availability activates its cytochrome c genes via a heme-activated protein HAP1, which binds to the promoter region of each gene (Pfiefer et al., 1989). Since heme is only synthesised in the presence of oxygen, activity of the HAP1 protein serves as an intracellular signal of oxygen availability. In the upstream region of the cycA gene, a sequence with homology to the S. cerevisiae HAP1 binding site was present (Raitt, 1992). To determine the significance of the putative HAP1 binding site and the role of other promoter sequences in the A. nidulans cycA gene, a promoter-reporter vector was constructed. However, upon sequencing of the cycA promoter in the reporter vector, a sequencing error was discovered in the published cycA gene by Raitt et al. (1994) which affected the position of the major translational start site. Further examination of the cycA sequence also revealed a possible undetected intron (Intron I). To determine the number of introns in the cycA gene, RT- PCR was performed on cycA RNA. Sequencing of the RT-PCR amplified products showed that the previously undetected intron (Intron I) was present, and that the cycA gene contains three instead of two introns as published by Raitt et al. (1994). Since the published ATG start site was located within Intron I, a new translational start site was proposed. The major consequences of these changes to the cycA gene was that the putative HAP1 site was now located within the coding region of the gene, and therefore could not be a regulatory element. In addition only 247 bp of cycA promoter sequence remained cloned for analysis. To obtain additional promoter sequence, an A. nidulans genomic library was screened with a BamHI cDNA probe containing 224 bp of the 5' region of the cycA gene. Three positive clones were obtained, of which λLM9 and λLM5 were identical, and λLM19 was an overlapping clone with λLM9 and λLM5. Restriction enzyme and Southern blott analysis of the two overlapping cycA clones, revealed that 2.1 kb EcoRI fragments from both clones contained the 5' region. The 2.1 kb EcoRI fragment from λLM9 was cloned into pUC18 and sequenced. The completed upstream sequence of the A. nidulans cytochrome c gene was obtained, and putative regulatory signals including the HAP1 binding site were found, and compared with published promoter sequences which regulate the expression of respiratory-encoding genes from yeast

Coping with cyclic oxygen availability: evolutionary aspects

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 functio