Evidence for top predator control of a grazing ecosystem

The importance of top predators in controlling ecological processes in large, intact ecosystems is unclear. In grasslands that support abundant ungulates, top–down control by predators may be particularly important, because of the tight biogeochemical linkages of ungulate prey with plants and soil microbes. Here, I examined the effects of the recent reintroduction of the gray wolf Canis lupus on ecosystem processes in Yellowstone National Park, where herds of grazing ungulates previously have been shown to stimulate several processes, including soil net nitrogen (N) mineralization. Rates of ungulate grazing intensity and soil net N mineralization were compared before and after wolf reintroduction in grasslands ranging five‐fold in aboveground production. Grazing intensity and grassland net N mineralization declined after wolf reintroduction, a likely partial function of fewer ungulates; wolf predation has been one of several factors implicated in causing the decline in Yellowstone ungulates. In addition, the spatial pattern of grazing and net N mineralization changed after reintroduction. A shift in the spatial patterns of grazer‐associated processes is consistent with a growing body of work indicating that wolves have changed habitat use patterns of ungulates in Yellowstone National Park. These findings suggest widespread wolf effects on ungulate prey, plants, and microbial activity that have spatially reorganized grassland energy and nutrient dynamics in Yellowstone Park.     

Cartilage electromechanics--II. A continuum model of cartilage electrokinetics and correlation with experiments

We have formulated a continuum model for linear electrokinetic transduction in cartilage. Expressions are derived for the streaming potential and streaming current induced by oscillatory, uniaxial confined compression of the tissue, as well as the mechanical stress generated by a current density or potential difference applied to the tissue. The experimentally observed streaming potential and current-generated stress response, measured on the same specimens, are compared with the predictions of the theory over a wide frequency range. The theory compares well with the data for reasonable values of cartilage intrinsic mechanical parameters and electrokinetic coupling coefficients. Experiments also show a linear relationship between the stimulus amplitude and the transduction response amplitude, within the range of stimulus amplitudes of interest. This observation is shown to be consistent with the predictions of the linear theory.     

Elevated levels of plasma lipofuscins in patients with chronic renal failure

The fluorescence excitation and emission spectra observed in plasma from patients with chronic renal failure were reproduced by the generation of soluble lipofuscins in normal plasma samples by incubation with mixtures of L-dopa, dopamine, L-norepinephrine, L-epinephrine, 3-hydroxy-DL-kynurenine and 3-hydroxy-anthranilic acid for 24 h at 37 degrees C. Relative fluorescence intensity measurements consistently showed elevated plasma levels of the soluble lipofuscins in chronic renal failure: the means (n = 27) were 73.9 +/- 33.4 (SD) and 71.1 +/- 14.8 at emissions 413 nm and 445 nm respectively, in contrast to those of normal plasma samples (n = 11), 18.2 +/- 5.3 and 23.1 +/- 5.6. The maximum or shoulder at approximately 413 nm represents soluble lipofuscin that can be generated from 3-hydroxyanthranilic acid and the maximum or shoulder at approximately 445 nm represents soluble lipofuscins derived from the precursors listed above and probably from other related precursors. Gravimetric measurements also showed elevated levels of melanins in the plasma samples of patients with chronic renal failure: 2.72 +/- 0.38 mg/ml (n = 16), as compared to normal values: 1.70 +/- 0.10 mg/ml (n = 6). In individual patients haemodialysis reduced the fluorescence intensities to a range of 65-99% and the melanin levels to a range of 86-99% of the pre-dialysis values.     

Proceedings of the fifty-fourth Annual Meeting of the American Association of physical anthropologists to be held in Knoxville,Tennessee—Holiday Inn World's fair April 10–13, 1985

Empirical analyses and models of the lineal effects of fission indicate that considerable genetic differentiation may occur at the time of group formation, thus confusing the usual positive relationship between historical affiliation and genetic differentiation. We analyze the effects of fission pattern on variation in highly heritable morphological traits among eight social groups on Cayo Santiago. The analysis is performed using general network autocorrelation methods that quantitatively and directly measure the amount of variation in social group mean morphology that can be explained by fission. All of the fission autocorrelation coefficients are strongly negative, indicating that groups most recently formed by fission are most dissimilar. Also, most of the variation between groups can be explained by the fission pattern, indicating that lineal fission is the most important process generating between-group variation on Cayo Santiago.     

Spin probe clustering in human erythrocyte ghosts

Summary A model has been developed for 5-nitroxide stearate, I(12,3), distribution in human erythrocyte ghosts which accurately predicts ESR spectral alterations observed with increased probe/total lipid (P/L) at 37°C. This spin probe occupies a class of high-affinity, noninteracting sites at low loading. Saturation occurs with increasing probe concentration, and, at higher loading, the probe inserts itself at initially dilute sites to form membranebound clusters of variable size. No low probe remains at high P/L where all I(12,3) clusters in a concentrated phase. This model allows determination of the dilute/clustered probe ratio, and shows that I(12,3) segregates in erythrocytes at what might otherwise be considered low P/L (e.g., 1/359). These findings validate the earlier use of empirical parameters to estimate probe sequestration in biological membranes.     

Computer-Assisted Image Analysis of Plant Growth, Thigmomorphogenesis, and Gravitropism

A nonintrusive auxonometric system, based on the DARWIN image processor (Telewski et al. 1983 Plant Physiol 72: 177-181), is described and demonstrated in the analysis of gravitropism and thigmomorphogenesis in corn seedlings (Zea mays). Using this system, growth and bending of regularly shaped plants or organs can be quickly and accurately measured without, in any way, interfering with the plant. Furthermore, the growth and bending curves are automatically plotted. Thigmomorphogenesis in the aerial part of corn seedlings involves growth promotion at a low force load and growth retardation at higher force loads. The time courses of the two kinds of response are somewhat different, with retardation occurring immeditely after mechanical perturbation and growth promotion taking somewhat longer to begin. Gravitropic experiments show that when dark-grown corn seedlings are placed on their side in the light, the resulting curvature is due to two consecutive morphological mechanisms. In the first instance, lasting for about 15 minutes, the elongation of the bottom edge of the plant accelerates, while the elongation of the top edge remains constant. After that, for the next 1.75 hours, the elongation of the top edge decelerates and stops while that of the bottom edge remains constant at the increased rate for most of the period. The measurements taken from both experiments at relatively high resolution (0.08-0.1 millimeter) show that the growth curves are not smooth but show many small irregularities which may or may not involve micronutations.     

A selenomethionine-containing azurin from an auxotroph of Pseudomonas aeruginosa

The production and spectroscopic properties of an L-selenomethionine-containing homolog of Pseudomonas aeruginosa azurin are described. The amino acid substitution was carried out by developing an L-methionine-dependent bacterial strain from a fully functional ATCC culture. Uptake studies monitored using L-[75Se]methionine indicated that L-selenomethionine was incorporated into the protein synthetic pathway of Pseudomonas bacteria in a manner analogous to L-methionine. Several batches of bacteria were grown, and one sample of isolated and purified selenoazurin (azurin in which methionine was substituted by selenomethionine) was found (by neutron activation analysis) to contain 5.2 +/- 0.8 seleniums/copper. Correspondingly, a residual 0.35 methionines, relative to 6.0 in the native protein, were found by amino acid analysis in this azurin sample. The redox potential and extinction coefficient of this selenoazurin were found to be 333 +/- 1 mV (pH 7.0, I = 0.22) and 5855 +/- 160 M-1 cm-1 at 626 +/- 1 nm, respectively. Visible electronic, CD, and EPR spectra are reported and Gaussian curve fitting to the former spectrum allowed assignment of the selenomethionine Se----Cu(II) transition to a band found at 18034 cm-1, based upon an observed 450 cm-1 shift to the red from the analogous band position in the native protein. The data are consistent with a relatively more covalent copper site stabilizing the reduced, Cu(I), form in the selenoprotein. A role for the methionine as a modulator of the blue copper site redox potential by metal----ligand back bonding from Cu(I) is discussed in terms of a ligand sphere which limits the valence change at copper to much less than 1 during a redox cycle.     

Purification and regulation of glutamine synthetase in a collagenolytic Vibrio alginolyticus strain

Glutamine synthetase (EC 6.3.1.2) has been purified from a collagenolytic Vibrio alginolyticus strain. The apparent molecular weight of the glutamine synthetase subunit was approximately 62,000. This indicates a particle weight for the undissociated enzyme of 744,000, assuming the enzyme is the typical dodecamer. The glutamine synthetase enzyme had a sedimentation coefficient of 25.9 S and seems to be regulated by a denylylation and deadenylylation. The pH profiles assayed by the -glutamyltransferase method were similar for NH₄-shocked and unshocked cell extracts and isoactivity point was not obtained from these eurves. The optimum pH for purified and crude cell extracts was 7.9. Cell-free glutamine synthetase was inhibited by some amino acids and AMP. The transferase activity of glutamine synthetase from mid-exponential phase cells varied greatly depending on the sources of nitrogen or carbon in the growth medium. Glutamine synthetase level was regulated by nitrogen catabolite repression by (NH₄)₂SO₄ and glutamine, but cells grown, in the presence of proline, leucine, isoleucine, tryptophan, histidine, glutamic acid, glycine and arginine had enhanced levels of transferase activity. Glutamine synthetase was not subject to glucose, sucrose, fructose, glycerol or maltose catabolite repression and these sugars had the opposite effect and markedly enhanced glutamine synthetase activity.Abbreviations GS glutamine synthetase - SMM succinate minimal medium - ASMM ammonium/succinate minimal medium - GT -glutamyl transferase - SVP snake venom phosphodiesterase