Coexistence of natural enemies in a multitrophic host–parasitoid system

Abstract.  1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host–parasitoid assemblage.
2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored.
3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae , was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid.
4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence.     

The use of clip cages to restrain insects reduces leaf expansion systemically in Rumex obtusifolius

Abstract. 1. Clip cages have been used widely by experimental ecologists to contain insects on plants.
2. Under controlled conditions, the effect of applying clip cages alone and clip cages and the chrysomelid beetle Gastrophysa viridula on systemic leaf expansion of Rumex obtusifolius was investigated. Treatments were applied to the fully expanded fourth leaf and expansion of leaf 8 was measured over a period of 22 days.
3. The application of clip cages reduced the rate at which leaf area increased and led to reductions in final leaf areas.
4. Clip cages have systemic effects on plant development and these effects are sustained even after the clip cage is removed. Investigators should take this into account in designing experiments.     

Torsional constant of 27-mer DNA oligomers of different sequences.

We have studied the torsional elastic constant (alpha) of short DNA (27mer) oligomers of various sequence by fluorescence polarization anysotropy (FPA) measurements. The lowest alpha values were found in samples with sequence rich in AA dinucleotides or containing the alternating d(A-T) x d(A-T) motif. The torsional rigidity of our DNA samples was compared to that calculated according to the current values of twist angle fluctuations derived for ten dinucleotide steps by recent analyses of DNA crystal structure database. The values of torsional rigidity derived from crystals are higher than our experimental ones, obtained by FPA analysis, suggesting that packing force in crystals may notably hinder the dinucleotide twist angle fluctuations that occur in solution. This behaviour is more evident for samples containing AA, TA and AT steps. In all the samples there is about a twofold change of the alpha value in the 10-40 degrees C range. An activation enthalpy (Delta H (#)) of about 17.4 kJ mol(-1), on average, was obtained for the temperature dependence of eight of the ten samples studied. A correlation with the stacking energy is discussed.     

Fine structural recognition specificities of IgE antibodies distinguishing amoxicilloyl and amoxicillanyl determinants in allergic subjects.

IgE antibodies in the sera of subjects allergic to beta-lactam antibiotics detect a spectrum of specificities ranging from side-chain groups to an entire penicillin or cephalosporin molecule. In addition to such structural heterogeneity of allergenic determinants, IgE antibodies in the sera of different allergic subjects show heterogeneous recognition responses. Detailed immunochemical studies were carried out on the sera of penicillin-allergic subjects that showed selective and unexpected reactions with the frequently prescribed penicillin, amoxicillin. Antibodies from one subject reacted only with the amoxicilloyl determinant while IgE from another subject showed multiple reactivity with penicilloyl and penicillanyl determinants of different penicillins but not with the amoxicilloyl determinant. Quantitative hapten inhibition studies revealed that the combining sites of the former antibodies were complementary to amoxicillin in a form that permits binding to the hydroxyaminobenzyl side-chain and the thiazolidine ring carboxyl. These conditions are satisfied with the drug in the '-oyl' but not in the '-anyl' form which involves linkage through the 2-carboxyl of the thiazolidine ring. With the second serum, adsorption studies showed that the wide-ranging reactivity of IgE was due to a single population of antibodies that detected a common specificity on the different penicillins. Combining site studies revealed clear recognition of the benzyl portion of the side-chain of benzylpenicilloyl, benzylpenicillanyl, ampicilloyl, ampicillanyl and amoxicillanyl determinants when free antibody access to the side-chain was possible but little or no recognition of the ring hydroxyl of amoxicillin. Such uninhibited access may not occur, however, when amoxicillin is conjugated in the '-oyl' form since opening the beta-lactam ring allows increased flexibility and rotation of the molecule and the possibility of close association of the hydroxyaminobenzyl side-chain of amoxicillin with the linked peptide carrier. In such close steric association, H-bonding involving the ring hydroxyl and amino acids of the carrier may prevent antibody access to the side-chain region of the amoxicilloyl determinant.     

Exopolysaccharide-producing strains of thermophilic lactic acid bacteria cluster into groups according to their EPS structure

AIMS: To compare galactose-negative strains of Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs). METHODS AND RESULTS: The structures of the EPSs were determined using nuclear magnetic resonance (NMR) and their genetic relationships determined using restriction endonuclease analysis (REA) and random amplification of polymorphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and each group produced an EPS with a particular subunit structure. CONCLUSION: Although none of the strains assimilated galactose, all inserted a high proportion of galactose into their EPS when grown in skimmed milk, and fell into three distinct groups. Significance and Impact of the Study: This information should help in an understanding of genetic exchanges in lactic acid bacteria.     

Three C. elegans Rac proteins and several alternative Rac regulators control axon guidance, cell migration and apoptotic cell phagocytosis.

The Caenorhabditis elegans genome contains three rac-like genes, ced-10, mig-2, and rac-2. We report that ced-10, mig-2 and rac-2 act redundantly in axon pathfinding: inactivating one gene had little effect, but inactivating two or more genes perturbed both axon outgrowth and guidance. mig-2 and ced-10 also have redundant functions in some cell migrations. By contrast, ced-10 is uniquely required for cell-corpse phagocytosis, and mig-2 and rac-2 have only subtle roles in this process. Rac activators are also used differentially. The UNC-73 Trio Rac GTP exchange factor affected all Rac pathways in axon pathfinding and cell migration but did not affect cell-corpse phagocytosis. CED-5 DOCK180, which acts with CED-10 Rac in cell-corpse phagocytosis, acted with MIG-2 but not CED-10 in axon pathfinding. Thus, distinct regulatory proteins modulate Rac activation and function in different developmental processes.     

Formation of wine aroma: tones and imperfections caused by minor components (a review)]

Mechanisms of formation of primary and secondary wine aroma and processes associated with wine maturation and ageing are reviewed. Compounds determining brand- or technology-specific aroma tones (floral, fruit, honey, black-currant, nightshade, yeast, oak-cask, thermal, etc.) are identified. Chemical background of unacceptable, foul tones (oxidized, murine, acetic, hydrogen-sulfide, saprogenic, cabbage, hospital, mold, vulpine, etc.) is presented.     

Fertility after bilateral cryptorchidism. Evaluation by paternity, hormone, and semen data.

PURPOSE: Evaluation of the fertility of a cohort of formerly bilaterally cryptorchid men in comparison with a group of formerly unilaterally cryptorchid men, and a group of control men. MATERIALS AND METHODS: Using a detailed questionnaire concerning paternity and factors related to paternity, a cohort of formerly bilateral cryptorchid men were studied and compared with men who had undergone orchiopexy for unilateral cryptorchidism, and a group of control men. All study subjects had had surgery at the Children's Hospital of Pittsburgh, Pittsburgh, Pa., between 1955 and 1975. A subset of the full cohort underwent clinical evaluation that included a physical examination, serum hormonal determination and semen analyses. RESULTS: Paternity rates are significantly lower among the formerly bilaterally cryptorchid men who have attempted to father a child (65.3%) as compared to the formerly unilaterally cryptorchid (89.7%; p < 0.001) and control men (93.2%; p < 0.001). Differences in the ability to father children are also apparent when semen and hormone levels are compared between the three groups. The bilateral group has significantly lower sperm density and inhibin B levels, and higher FSH and LH levels, than the unilateral and control groups. CONCLUSIONS: Men born with bilateral cryptorchidism have severely compromised fertility in adulthood. This reduction in fertility is clearly shown in comparisons of both paternity rates, and in semen and hormone analyses, between the formerly bilateral, formerly unilateral, and control groups.