Transient dynamics of an altered large marine ecosystem

Overfishing of large-bodied benthic fishes and their subsequent population collapses on the Scotian Shelf of Canada's east coast and elsewhere resulted in restructuring of entire food webs now dominated by planktivorous, forage fish species and macroinvertebrates. Despite the imposition of strict management measures in force since the early 1990s, the Scotian Shelf ecosystem has not reverted back to its former structure. Here we provide evidence of the transient nature of this ecosystem and its current return path towards benthic fish species domination. The prolonged duration of the altered food web, and its current recovery, was and is being governed by the oscillatory, runaway consumption dynamics of the forage fish complex. These erupting forage species, which reached biomass levels 900% greater than those prevalent during the pre-collapse years of large benthic predators, are now in decline, having outstripped their zooplankton food supply. This dampening, and the associated reduction in the intensity of predation, was accompanied by lagged increases in species abundances at both lower and higher trophic levels, first witnessed in zooplankton and then in large-bodied predators, all consistent with a return towards the earlier ecosystem structure. We conclude that the reversibility of perturbed ecosystems can occur and that this bodes well for other collapsed fisheries.     

Family of disulphide-linked dimers containing the zeta and eta chains of the T-cell receptor and the gamma chain of Fc receptors

Stimulation of T cells by antigen activates many signalling pathways. The capacity for this range of biochemical responses may reside in the complex structure of the seven-chain T-cell antigen receptor (TCR). In addition to the complexity shared by all TCRs, coexpression of zeta (zeta) and the distinct but related eta (eta) chains creates structural diversity among the TCR complexes expressed on a given cell. In most murine T cells that we have studied, about 90% of the heptameric receptor complexes contain a zeta zeta disulphide homodimer, whereas 10% contain a zeta eta disulphide heterodimer. Recent studies suggest that zeta has a critical role in allowing antigen to activate the cell, whereas eta expression has been correlated with the capacity for antigen-induced phosphoinositide turnover. A third zeta-related protein, the gamma (gamma) chain of the Fc epsilon and some Fc gamma receptors, exists as a disulphide homodimer in those complexes. The structural relatedness of zeta and gamma is emphasized by the recent demonstration of zeta zeta in association with CD16 in TCR-negative natural killer cells. Here we identify T cells lacking Fc receptors but coexpressing zeta, gamma, and eta, document the formation of novel heterodimers between zeta and gamma and between eta and gamma and show their association with the TCR. A greater range of homologous coupling structures than previously thought may be one way of achieving the variety of TCR-mediated (and possibly Fc receptor-mediated) biochemical responses and effector functions.     

A preliminary study of optimal variable weighting in k-means clustering

Recently, algorithms for optimally weighting variables in non-hierarchical and hierarchical clustering methods have been proposed. Preliminary Monte Carlo research has shown that at least one of these algorithms cross-validates extremely well.The present study applies a k-means, optimal weighting procedure to two empirical data sets and contrasts its cross-validation performance with that of unit (i.e., equal) weighting of the variables. We find that the optimal weighting procedure cross-validates better in one of the two data sets. In the second data set its comparative performance strongly depends on the approach used to find seed values for the initial k-means partitioning.The authors would like to acknowledge the support of the Citibank Fellowship from the Sol C. Snider Entrepreneurial Center at the Wharton School. The authors would like to express their appreciation to J. Douglas Carroll and Abba M. Kreiger for comments on an earlier version of the paper.     

Calf thymus ribonuclease H IIa activity lacks ribonuclease H specificity.

Less purified fractions of ribonuclease H IIa activity of calf thymus display divalent cation-dependent ribonuclease H activity and divalent cation-independent ribonuclease activity. Because the ratio of the two enzyme activities does not change during successive chromatographic procedures, we suggest that ribonuclease H IIa activity is indeed able to degrade both ssRNA and the RNA moiety of RNA.DNA-hybrids. Ribonuclease H IIa activity can therefore be differentiated from calf thymus ribonuclease H I and H IIb by its lack of ribonuclease H specificity. The native molecular mass of ribonuclease H IIa activity is between 23 and 28 kDa. Under denaturing conditions a 23 kDa-protein band copurifies with the enzyme activity suggesting that this enzyme is monomeric.     

Isolation and structure of a human fibroblast interferon gene

Chimaeric plasmids containing double-stranded cDNA copies of mRNA induced in human fibroblasts by poly I . C were screened by an RNA selection method. A series of clones to which human fibroblast interferon mRNA selectively hybridized was identified. From the nucleotide sequence of the gene, the complete amino acid sequence of human fibroblast interferon was deduced. The protein is 166 amino acids long and is preceded by a 21-amino acid signal sequence.     

Investigations on carcinogenic effects of Penicillium caseicolum and P. roqueforti in rats

Summary A feeding test over the whole life span of 800 Sprague-Dawley rats with commercial starters for camembert- and blue-cheese, with commercial cheese and test cheese, as well as subcutaneous application of the mycelia, did not yield any indication for a detrimental or carcinogenic effect.The authors wish to thank the Federal Minister for Youth, Family and Health in Bonn for support of this work.     

Ecosystem energetic implications of parasite and free-living biomass in three estuaries

Parasites can have strong impacts but are thought to contribute little biomass to ecosystems. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.     

Superconducting quantum bits

Superconducting circuits are macroscopic in size but have generic quantum properties such as quantized energy levels, superposition of states, and entanglement, all of which are more commonly associated with atoms. Superconducting quantum bits (qubits) form the key component of these circuits. Their quantum state is manipulated by using electromagnetic pulses to control the magnetic flux, the electric charge or the phase difference across a Josephson junction (a device with nonlinear inductance and no energy dissipation). As such, superconducting qubits are not only of considerable fundamental interest but also might ultimately form the primitive building blocks of quantum computers.