Biometrical variability of foliage and cone characters inCupressus bakeri (Cupressaceae)

Biometrical variability of foliage, cones, and seeds were analyzed in 8 native populations (throughout the range) of a relictual species,Cupressus bakeri Jeps. (Cupressaceae) from California and Oregon. The partition of variation within and among populations for this rare plant was investigated and the justification for subspecies status was reviewed. Morphological characters varied significantly, with more of the variation among populations than at the population level. Multivariate analyses indicated close affinities among populations on serpentine sites suggesting the presence of a serpentine race. However, the high degree of variation among populations did not permit their clear separation into the two subspecies described byWolf (1948). We conclude thatC. bakeri should be treated as a monotypic species.     

Modelling mitochondrial site polymorphisms to infer the number of segregating units and mutation rate

We present a mathematical model of mitochondrial inheritance evolving under neutral evolution to interpret the heteroplasmies observed at some sites. A comparison of the levels of heteroplasmies transmitted from mother to her offspring allows us to estimate the number N_x of inherited mitochondrial genomes (segregating units). The model demonstrates the necessity of accounting for both the multiplicity of an unknown number N_x, and the threshold θ, below which heteroplasmy cannot be detected reliably, in order to estimate the mitochondrial mutation rate μ_m in the maternal line of descent. Our model is applicable to pedigree studies of any eukaryotic species where site heteroplasmies are observed in regions of the mitochondria, provided neutrality can be assumed. The model is illustrated with an analysis of site heteroplasmies in the first hypervariable region of mitochondrial sequence data sampled from Adélie penguin families, providing an estimate N_x and μ_m. This estimate of μ_m was found to be consistent with earlier estimates from ancient DNA analysis.     

Incidence of exercise induced hypoxemia in elite endurance athletes at sea level

Recent evidence suggests that exercise-induced hypoxemia (EIH) may occur in healthy trained endurance athletes. However, at present, no data exist to describe the regularity of EIH in athletes or non-athletes. Therefore, the purpose of the present investigation was to determine the incidence of EIH during exercise in healthy subjects varying in physical fitness. Subjects (N = 68) performed an incremental cycle ergometer test to volitional fatigue with percent arterial oxyhemoglobin saturation (%SaO2) measured min-by-min. For the purpose of data analysis subjects were divided into three groups according to their level of physical training: 1) untrained (N = 16), 2) moderately trained (N = 27), and 3) elite highly trained endurance athletes (N = 25). EIH was defined as a %SaO2 of less than or equal to 91% during exercise. EIH did not occur in any of the untrained subjects or the moderately trained subjects. However, EIH occurred in 52% of the highly trained endurance athletes tested and was highly reproducible (r = 0.95; P less than 0.05). These findings further confirm the existence of EIH in healthy highly trained endurance athletes and suggests a rather high incidence of EIH in this healthy population. Hence, it is important that the clinician or physiologist performing exercise testing in elite endurance athletes recognize that EIH can and does occur in the elite endurance athlete in the absence of lung disease.     

Rapid Method for the Isolation of Plasma Membranes from a Murine Fibrosarcoma Using an Aqueous Two-Phase Polymer System

An aqueous two-phase polymer system was used to isolate plasma membranes from a palpable mouse fibrosarcoma. The excised tumor tissue was washed with sterile saline and pushed through nylon screens of decreasing mesh size. This cell suspension was placed in Tris-buffered, isotonic sucrose plus MgSo₄ and homogenized by nitrogen cavitation. A pellet was collected from the homogenate by low-speed centrifugation and was added to the aqueous two-phase polymer system. After several brief, low-speed centrifugations, the interfacial material between the polymer phases was collected. Data from enzyme and biochemical assays demonstrated that this fraction was plasma membrane. This method provided a high yield of the surface membrane in less than three hours.