Environmentally-induced fluctuations in year-class strength and their implications for management

Data for river populations of common freshwater species including dace, chub, roach, gudgeon and pike are examined to assess the magnitude of natural density-independent fluctuations in the strength of year-classes. Both in the cyprinid populations and in those of some salmonids, only occasional years give rise to large cohorts of adult fish. Correlations with temperature indicate that for the cyprinid populations these are often years when temperatures are high. In the River Frome, Dorset there is a significant relationship between the growth of O-group dace and subsequent year-class strength. Faster-growing larvae may be better able to avoid predation. Both the habitat and feeding requirements of these young fish are different from those of the adults. A practical approach to improving recruitment in a population of a given species would be to first characterize, and then increase, the availability of suitable habitats and food organisms for the larval stages.     

A pike management strategy for a trout fishery

The efficiency of pike removal from a chalkstream trout fishery, by an angling society using electrofishing, was estimated over five successive autumns using mark-recapture methods. It averaged c . 50% for pike aged 1+ years or more. Numbers of 3+ and older pike decreased from 3.7 ha^-1 (1980) to 1.4 ha^-1 (1984), but there was no corresponding reduction in recruitment success. Both pike immigration and an inverse relationship between natural and fishing mortality could have reduced the effect of the pike culls. The mean weight of 0+ pike increased from 19.4 g to 48.2 g over the 5 years, but there was no change in the growth rates of older pike. Only the larger pike were able to eat the larger trout stocked, and the reduction in numbers of 3 + and older pike appears to have reduced the predation pressure on the trout population. Angling effort increased more than three-fold over the 5 years studied and rod-catches more than doubled, but catch-per-unit-effort was extremely variable between years. The increased rod catch occurred despite the decrease in numbers of large (> 33 cm) trout stocked in the spring and early summer. Compared with pre-cull years, the angling society saved about ş850 (present day prices) by stocking fewer trout.     

Murine interstitial nephritis. III. The selection of phenotypic (Lyt and L3T4) and idiotypic (RE-Id) T cell preferences by genes in Igh-1 and H-2K characterizes the cell-mediated potential for disease expression: susceptible mice provide a unique effector T cell repertoire in response to tubular antigen

The effector T cell repertoire in experimental interstitial nephritis was examined in a variety of susceptible and nonsusceptible mice. We observed that L3T4+ effector T cells in disease-susceptible mice disappear soon after immunization in preference to the emergence of Lyt-2+ effector cells. These latter cells respond with delayed-type hypersensitivity to tubular antigen in the context of H-2K. Such cells also express idiotypes (RE-Id) shared with kidney-bound alpha TBM-Ab that are regulated by an interactional effect of genes in Igh-1 and H-2K. These Lyt-2+ effector cells can be removed from renal infiltrates, and the transfer of similar cells under the renal capsule of naive mice results, within 5 days, in local interstitial nephritis. Nonsusceptible mice, however, not having these immune response genes, produce either L3T4+, Lyt-1+, RE-Id- effector T cells, which only respond to tubular antigen in the context of I-A, or Lyt-2+, RE-Id- T cells, which may lack very fine specificity. These findings suggest that susceptible mice carry a unique set of immune response genes that promote a T cell selection process that operates after induction, during the differentiation and development of disease-producing effector T cells.     

A nuclear-magnetic-resonance study of the binding of novel N-hydroxybenzenesulphonamide carbonic anhydrase inhibitors to native and cadmium-111-substituted carbonic anhydrase

Various ring- and nitrogen-substituted benzenesulphonamides have been prepared and tested as potential inhibitors of carbonic anhydrase. N-Methoxysulphonamides showed no inhibitory activity, as predicted by the classic work of Krebs on N-substituted inhibitors. By contrast, N-hydroxysulphonamides proved to be very effective inhibitors of carbonic anhydrase. Using 111Cd-NMR it has been possible to analyse the molecular interaction of 4-fluoro-N-hydroxybenzenesulphon[15N]amide, with 111Cd-substituted bovine carbonic anhydrase. A large cadmium-111:nitrogen-15 spin-coupling shows that this inhibitor is directly bound to the metal via its nitrogen rather than through an oxygen atom. The mode of this binding is similar to that for the unsubstituted sulphonamide inhibitor, 4-fluorobenzenesulphon[15N]amide. The 111Cd-chemical shift of the signal for the inhibited enzyme shows that the N-hydroxysulphonamide is bound as its anion. From the relative intensities of free and complexed enzyme signals it can be deduced that the cadmium enzyme complex with the N-hydroxysulphonamide has a longer life-time than that formed with the unsubstituted sulphonamide. By contrast, native zinc-containing bovine carbonic anhydrase shows similar I50 values with both of these sulphonamides. Attempts to monitor the binding using 15N-NMR were unsuccessful, possibly due to a very long relaxation time for the nitrogen nucleus in the N-hydroxysulphonamide when bound to the enzyme leading to loss of the 15N signal.     

Variations in the sizes of gonads,eggs and larvae of the dace,Leuciscus leuciscus

Synopsis Prespawning female dace were examined in 7 successive years; in 6 years mean egg size (mm³) and egg number were inversely related and hence the ovary weights of equivalent-sized females were constant. Fecundity increased logarithmically with fish length, and an index of reproductive effort (ovary weight ÷ length cubed) also increased. The number of eggs per gram of ovarian tissue decreased with fish length; this was because mean egg size (mm³) increased and not because of a change in the proportion of connective tissue in the ovary. But in 1977, both egg number and mean egg size were low, although very high somatic growth had occurred in the previous, very warm, summer of 1976. Eggs from different-sized female dace were artificially fertilized, and incubated at a constant temperature. Dry weights of larvae, egg dry weights, mean egg size and larval starvation times showed linear correlations with each other and with parental (female) lengths. The progeny from the very smallest parent died several days earlier than those from the other parents. Size-related predation rates may be of more consequence than starvation death in natural populations. The optimum position of dace along the continuum between many small eggs and fewer larger eggs may vary at different levels of reproductive effort.     

Rapid transfer of DNA from agarose gels to nylon membranes.

The unique properties of nylon membranes allow for dramatic improvement in the capillary transfer of DNA restriction fragments from agarose gels (Southern blotting). By using 0.4 M NaOH as the transfer solvent following a short pre-treatment of the gel in acid, DNA is depurinated during transfer. Fragments of all sizes are eluted and retained quantitatively by the membrane; furthermore, the alkaline solvent induces covalent fixation of DNA to the membrane. The saving in time and materials afforded by this simple modification is accompanied by a marked improvement in resolution and a ten-fold increase in sensitivity of subsequent hybridization analyses. In addition, we have found that nylon membrane completely retains native (and denatured) DNA in transfer solvents of low ionic strength (including distilled water), although quantitative elution of DNA from the gel is limited to fragments smaller than 4 Kb. This property can be utilized in the direct electrophoretic transfer of native restriction fragments from polyacrylamide gels. Exposure of DNA to ultraviolet light, either in the gel or following transfer to nylon membrane, reduces its ability to hybridize.     

"Clotspeed," a mathematical simulation of the functional properties of prothrombinase

Prothrombinase is a Ca2+-dependent, 1:1, enzymatic complex of Factor Xa and Factor Va that assembles on the surface of negatively charged phospholipid vesicles or platelets. It catalyzes the proteolytic conversion of prothrombin to the blood-clotting enzyme thrombin. Experimentally determined kinetic parameters, plus Kd and n values for the interaction of substrate, cofactor (Factor Va), and serine protease (Factor Xa) for both phospholipid and each other, were used to develop a model that simulates the functional properties of the enzymatic complex. Through the use of a desk-top computer and a program designated "Clotspeed," the distribution of enzymatic components and substrate between the bulk fluid and phospholipid is determined for a given set of initial concentrations of reaction components. Simulated reaction rates are then calculated from the calculated distributions, fractional binding, and local and bulk concentration of reactants. Predicted behavior includes formal Michaelis-Mentenlike properties for the reaction, increasing apparent Km with increased levels of phospholipid, and apparent inhibition by excess substrate, enzyme, and phospholipid. Inhibition by excess enzyme and phospholipid was demonstrated experimentally in quantitative agreement with predicted results. The model is useful in that it rationalizes well the seemingly unusual properties of prothrombinase in straightforward physical terms, provides a means of rationally choosing experimental conditions to both further test and refine the model, and explores the properties not only of prothrombinase but also other blood-clotting or surface-bound enzymatic complexes.     

Use of niflumic acid to determine the nature of the asymmetry of the human erythrocyte anion exchange system

Niflumic acid is a noncompetitive inhibitor of chloride exchange, which binds to a site different from the transport or modifier sites. When the internal Cl- concentration is raised, at constant extracellular Cl- , the inhibitory potency of niflumic acid increases. This effect cannot be attributed to changes in membrane potential, but rather it suggests that niflumic acid binds to the anion exchange protein band 3 only when the transport site faces outward. When the chloride gradient is reversed, with Clo greater than Cli , the inhibitory potency of niflumic acid decreases greatly, which indicates that the affinity of niflumic acid for band 3 with the transport site facing inward is almost 50 times less than when the transport site faces outward. Experiments in which Cli = Clo show no significant change in the inhibition by niflumic acid when Cl- is lowered from 150 to 10 mM. These data suggest that the intrinsic dissociation constants for Cl- at the two sides of the membrane are nearly equal. Thus, the chloride- loaded transport sites have an asymmetric orientation like that of the unloaded transport sites, with approximately 15 times more sites facing the inside than the outside. The asymmetry reflects an approximately 1.5 kcal/mol free energy difference between the inward-facing and outward-facing chloride-loaded forms of band 3. High concentrations of chloride (with Cli = Clo), which partially saturate the modifier site, have no effect on niflumic acid inhibition, which indicates that chloride binds equally well to the modifier site regardless of the orientation of the transport site.     

Yeasts in molecular biology. Spheroplast preparation withCanadida utilis,Schizosaccharomyces pombe andSaccharomyces cerevisiae

Efficient preparation of spheroplasts fromCandida utilis, Saccharomyces cerevisiae, andSchizosaccharomyces pombe, using a purified mixture of enzymes fromTrichoderma harzianum, is described. Limitations of other methods, and differences between yeasts are demonstrated.