Augmentation of beneficial arthropods by strip-management

Summary A 5-year-field experiment was performed in a meadow to test the effect of strip-management (small unmown strips alternating with broad mown strips, Fig. 1) on the abundance and composition of arthropods. The species number and density of most predator groups increased from year to year. The succession (parallel to the development of the unmown strips) favoured more specialized species, so that the initial pioneer species become less abundant in consecutive years. In spiders, this succession leads from a dominance of Linyphiidae to a dominance of Lycosidae; the spider biomass increases and probably predator pressure by spiders is augmented. The stability of the predator community (measured as the variance of their frequency in successive years) is higher than that of the phytophagous groups. Under strip-managed conditions the abundance (activity density) of most arthropod groups decreases by an average of ca. 12%. The trophic levels, however, are affected to different extents and strong species-specific preferences were found as well. These combined effects lead to constant increase in the ratio of predacious and parasitic to phytophagous insects in the strip-managed area and probably lead also to an increase of the predator pressure facing phytophagous insects. Strip-management is discussed as an important technique among integrated methods for the biological control of pests.     

A structural model for elongation factor 1 (EF-1) and phosphorylation by protein kinase CKII

EF-1a binds aminoacyl-tRNA to the ribosome with the hydrolysis of GTP; the complex facilitates the exchange of GDP for GTP to initiate another round of elongation. To examine the subunit structure of EF-1 and phosphorylation by protein kinase CKII, recombinant , , and subunits from rabbit were expressed in E. coli and the subunits were reconstituted into partial and complete complexes and analyzed by gel filtration. To determine the availability of the and subunits for phosphorylation by CKII, the subunits and the reconstituted complexes were examined as substrates for CKII. Formation of the nucleotide exchange complex increased the rate of phosphorylation of the subunit and reduced the Km, while addition of to or the complex inhibited phosphorylation by CKII. However, a had little effect on phosphorylation of . Thus, the and subunits in EF-1 were differentially phosphorylated by CKII, in that phosphorylation of was altered by association with other subunits, while the site on was always available for phosphorylation by CKII. From the availability of the subunits for phosphorylation by CKII and the composition of the reconstituted partial and complete complexes, a model for the subunit structure of EF-1 consisting of (22)2 is proposed and discussed.     

A comparative analysis of food-niche relationships and trophic guild structure in two assemblages of vertebrate predators differing in species richness: causes,correlations, and consequences

Summary We conducted a comparative analysis of foodniche relationships and trophic guild structure in two assemblages of vertebrate predators (including hawks, owls, snakes, and carnivores) living in similar habitats of Chile and Spain, which differed in species richness (11 and 25 predator species, respectively), to explore how the structure of predator assemblages reflects an increase (or decrease) in the number of coexisting species. Our results indicate that the Spanish assemblage appears enriched by the symmetrical addition of species with disparately large and small values of body weight, diet breadth, and mean prey size, around the same median value found in Chile. Or, alternatively, the Chilean assemblage appears impoverished by the symmetrical loss of peripheral species — those at both tails of the frequency distribution of the above trophic estimators. Spanish predators overlap less extensively among themselves, and with smaller variance, than Chilean predators. Consequently, the higher predator richness in Spain is not ascribable to their narrower diet breadths or more extensive diet overlaps as predicted by some theoretical models. Instead, it is associated with a more spread-out use of the available resources. Trophic guilds can be recognized in the two countries, but in Spain guilds are less tightly packed. Some taxomically unrelated species are close diet analogues between Spain and Chile, whereas some closely related species cannot be matched well between countries. Circumstantial evidence suggests that the presence of some trophic guilds and of some specialist predators in either country is based on the high abundance attained by some particular prey types.     

Polymorphism of the HLA DR1 haplotype in the Israeli population investigated at the serological,cellular, and genomic levels

In the present report, we used serological, cellular, and restriction fragment length polymorphism (RFLP) to investigate the DR1 haplotype in the Israeli population. We describe an Israeli homozygous typing cell (HTC), HLA-DwLVA, which defines a new lymphocyte-activating determinant associated with Bw65, DR1 and distinct from Dwl. The parents of this donor, non-Ashkenazi Algerian Jews, are first cousins and share HLA-Cw8, Bw65, BfS, DR1, DQw1, DPw4. No specificity could be assigned to HLA-DwLVA using the 91 Ninth Workshop HTCs. Two families and forty unrelated DR1 individuals were studied with DwLVA and a panel of DR1/Dw1 HTCs. HLA-DwLVA showed segregation as a single determinant within families. This new specificity was present in 24 out of 40 (60%) unrelated DR1 individuals, indicating that in the Israeli population DwLVA is the main lymphocyte-defined determinant associated with the serologically defined DRI specificity, in contrast to non-Jewish Caucasoids where DR1 is significantly associated with Dw1. The vast majority of DwLVA-positive carriers were also Bw65 carriers, indicating that Bw65, DR1, DwLVA may represent a typical allele combination in the Israeli population. The RFLP analysis established the correlation of certain RFLPs with Dw1 and DwLVA. In addition, we describe a cluster of RFLPs that may correspond to a new Dw subtype associated with DR1, for which no serological and cellular reagents have been described so far.     

Effects of Seed Predators of Different Body Size on Seed Mortality in Bornean Logged Forest

Background

The Janzen-Connell hypothesis proposes that seed and seedling enemies play a major role in maintaining high levels of tree diversity in tropical forests. However, human disturbance may alter guilds of seed predators including their body size distribution. These changes have the potential to affect seedling survival in logged forest and may alter forest composition and diversity.

Methodology/Principal Findings

We manipulated seed density in plots beneath con- and heterospecific adult trees within a logged forest and excluded vertebrate predators of different body sizes using cages. We show that small and large-bodied predators differed in their effect on con- and heterospecific seedling mortality. In combination small and large-bodied predators dramatically decreased both con- and heterospecific seedling survival. In contrast, when larger-bodied predators were excluded small-bodied predators reduced conspecific seed survival leaving seeds coming from the distant tree of a different species.

Conclusions/Significance

Our results suggest that seed survival is affected differently by vertebrate predators according to their body size. Therefore, changes in the body size structure of the seed predator community in logged forests may change patterns of seed mortality and potentially affect recruitment and community composition.     

Snake communities of moist rainforest and derived savanna sites of Nigeria: biodiversity patterns and conservation priorities

The taxonomic composition and the abundance of two communities of snakes were studied in two different areas of southern Nigeria. One community was studied in a derived savanna area (environs of Ejule, 06°54N, 07°23E), and one community was studied in a moist rainforest area (environs of Eket, 04°50N, 07°59E). Both the specific diversity and the mean frequency of observation of snakes were significantly higher in the forest area than in the savanna area, and the dominance index was higher in the savanna than in the forest site. However, most of the species were found in only one of the two areas, depending on their habitat requirements (e.g. Gastropyxis smaragdina, Dispholidus typus, Thelotornis kirtlandii, Dendroaspis jamesoni, Bitis nasicornis, Causus maculatus, etc). The forest community housed a significant number of arboreal and semiaquatic taxa, but in both sites most of the species were terrestrial. The commonest species in the forest area was an oviparous, semiaquatic, batracophagous natricine snake (Afronatrix anoscopus), whereas the commonest species in the savanna area was an oviparous terrestrial lacertophagous psammophine snake (Psammophis phillipsi). Some conservation implications of our biodiversity analyses are presented. It is suggested that the moist rainforest represents a critically endangered habitat, and should deserve special attention by the international scientific community. Oil industry activity is especially dangerous for snake communities, especially in the southernmost regions of Nigeria.     

Ecological impact of a fresh-water “reef kill” in Kaneohe Bay,Oahu, Hawaii

Storm floods on the night of December 31, 1987 reduced salinity to 15 in the surface waters of Kaneohe Bay, resulting in massive mortality of coral reef organisms in shallow water. A spectacular phytoplankton bloom occurred in the following weeks. Phytoplankton growth was stimulated by high concentrations of plant nutrients derived partially from dissolved material transported into the bay by flood runoff and partially by decomposition of marine organisms killed by the flood. Within two weeks of the storm, chlorophyll a concentrations reached 40 mg m^-3, one of the highest values ever reported. The extremely rapid growth rate of phytoplankton depleted dissolved plant nutrients, leading to a dramatic decline or crash of the phytoplankton population. Water quality parameters returned to values approaching the long-term average within 2 to 3 months. Corals, echinoderms, crustaceans and other creatures suffered extremely high rates of mortality in shallow water. Virtually all coral was killed to depths of 1–2m in the western and southern portions of the bay. Elimination of coral species intolerant to lowered salinity during these rare flood events leads to dominance by the coral Porites compressa. After a reef kill, this species can eventually regenerate new colonies from undifferentiated tissues within the dead perforate skeleton. Catastrophic flood disturbances in Kaneohe Bay are infrequent, probably occurring once every 20 to 50 years, but play an important role in determination of coral community structure. The last major fresh water reef kill occurred in 1965 when sewage was being discharged into Kaneohe Bay. Coral communities did not recover until after sewage abatement in 1979. Comparison between recovery rate after the two flood events suggests that coral reefs can recover quickly from natural disturbances, but not under polluted conditions.     

Composition of Endemic Fish Assemblages in Relation to Exotic Species and River Regulation in a Temperate Stream

Spatial variation in the fish community of the regulated Raia stream (Portugal) was examined during the summer of 1995. Variation in the native fish community (abundance of species-size combinations) was explicitly related to both the abundance of exotic species and habitat variables. The fish community changed in space from assemblages characterised by the high relative abundance of Leuciscus pyrenaicus, Leuciscus alburnoides and the smaller size classes of Barbus bocagei (all Iberian endemics with total length, TL, < 100mm to assemblages characterised by the high relative abundance of Chondrostoma polylepis (Iberian endemic) and B. bocagei with TL > 200mm and of exotics Micropterus salmoides and Lepomis gibbosus (> 100mm TL). The former assemblages used shallow sites far from downstream dams with some current whereas the latter assemblages used deeper sites closer to downstream dams without current velocity and with abundant floating macrophytes. Both exotic species and habitat variables were significant correlates of endemic assemblage composition in the Raia stream and the abundance of M. salmoides > 150mm in TL was the best biotic predictor of endemic assemblage composition. The total variation in the community of endemic fish was partitioned into four components: (i) associated uniquely with exotic species - 12.6%, (ii) associated uniquely with habitat variables - 27.6%, (iii) associated both with exotic species and habitat variables - 14.5%, and (iv) that unexplained - 45.3%. A significant association of exotic species with the endemic fish community remained after accounting for the selected environmental variables and a strong (habitat) x (exotic species) interaction was indicated.     

Additive partition of parametric information and its associated beta-diversity measure

A desirable property of a diversity index is strict concavity. This implies that the pooled diversity of a given community sample is greater than or equal to but not less than the weighted mean of the diversity values of the constituting plots. For a strict concave diversity index, such as species richness S, Shannon's entropy H or Simpson's index 1-D, the pooled diversity of a given community sample can be partitioned into two non-negative, additive components: average within-plot diversity and between-plot diversity. As a result, species diversity can be summarized at various scales measuring all diversity components in the same units. Conversely, violation of strict concavity would imply the non-interpretable result of a negative diversity among community plots. In this paper, I apply this additive partition model generally adopted for traditional diversity measures to Aczél and Daróczy's generalized entropy of type . In this way, a parametric measure of -diversity is derived as the ratio between the pooled sample diversity and the average within-plot diversity that represents the parametric analogue of Whittaker's -diversity for data on species relative abundances.     

Evaluating predation pressure on green treefrog larvae across a habitat gradient

The effect of a predator on the abundance of a prey species depends upon the predators abundance and its ability to capture that prey. The objectives of this research were to evaluate the community structure of predators of green treefrog (Hyla cinerea) tadpoles across habitat types and evaluate the effectiveness of individual predators on H. cinerea tadpoles. Correspondence and cluster analyses of predator frequencies across 23 aquatic habitats indicated that the majority of variance in predator communities was due to a division between permanent and temporary habitats. Experimental work demonstrated that survival of the smallest H. cinerea tadpoles was significantly lower than survival of medium and large tadpoles with the most effective predators, indicating that H. cinerea tadpoles attain a refuge from predation at larger body sizes. We combined the effectiveness of predators in experiments with the abundance of each predator species from the predator community survey to demonstrate that predation pressure on H. cinerea tadpoles is higher in temporary ponds. This pattern may explain in part why this species generally breeds successfully only in permanent habitats. It also confirms that discussions about an increasing gradient of predation pressure from temporary to permanent aquatic habitats should be restricted to individual prey species for which such a gradient has been demonstrated.     

Structure and evolution of the HLA Class II SXβ gene

The class II major histocompatibility complex antigens are cell-surface heterodimers consisting of an a and a chain. Cosmid cloning has shown that the three families of clas II antigens, DR, DQ, and DP, are encoded within the HLA-D region of chromosome 6 as a series of discrete gene clusters. The DP cluster contains two pairs of a and genes, one of which encodes the biochemically-defined DP antigen. In order to assess whether the other two genes, SXa and SX, are also expressed, potential coding regions have been subcloned and sequenced. The SX3 gene is shown to contain region closely homologous to all six exons of DP. A 1 bp deletion in the 2 exon, also observed for the SX4 allele, causes a translation frameshift, suggesting that SX is a pseudogene. However, all the other exons, as well as their splice sites and the putative promoter region, appear to be intact.     

Disturbance and predation in an assemblage of herbivorous Diptera and algae on rocky shores

Summary Speculation about the effects of disturbance in marine benthic communities is often based on competition theory. Disturbances are thought to provision numerically depleted or competitively inferior species with resources associated with open substrate. However, disturbances that remove entire assemblages of sessile species also alter trophic structure, and thereby, influence the outcome of predator/prey relations. Aspects of community structure may be determined by patterns of disturbance and predation.The influence of disturbance and predation on the distribution and seasonality of blooms of ephemeral algae and associated Diptera was investigated with field experiments at several rocky beaches in central California. Blooms of ephemeral algae developed on high intertidal rock faces that were subject to severe seasonal disturbances caused by shifting sediment. These were subsequently colonized by the herbivorous larvae of several Diptera species for predictable periods each year. Other areas, without blooms, were not so disturbed.Experiments were done to determine if seasonal blooms were caused by seasonal disturbances that remove predators which otherwise might prevent the establishment of the Diptera/algae assemblage. The predators were crabs and limpets which eat both algae and larvae while foraging. Blooms of algae and larvae did not develop when limpets were transplanted to disturbed areas in periods between disturbances. Adjacent control areas did support blooms. Transplanted limpets did not survive periods of burial. When both limpets and crabs were excluded from treatment plots in undisturbed areas, blooms developed where they would not otherwise have occurred; controls remaied unchanged. Crabs and limpets differed in their effects on this assemblage. Crabs recruited quickly to the site of a bloom, but did not crop algal cover as closely, nor decrease larval density as much as the slowly recruiting limpets.The results suggest that disturbances favor blooms of some species by reducing predation. Severe localized disturbances increased the variability of the upper shore community by creating a patchwork of differing predator/prey abundances.     

Establishment and characterization of Rubus tissue culture systems for in vitro bioassays against phytotoxins from Rubus fungal pathogens

The Rubus species R. parviflorus, R. spectabilis and R. strigosus interfere with conifer seedling establishment on forest regeneration sites in Canada and the United States. As a first step towards microbial metabolite-based control, callus and cell suspension cultures of the Rubus species were developed as a bioassay system to detect phytotoxic compounds that may have relevance in a vegetation control context. Rapidly growing friable callus and suspension cultures were obtained from leaf disks of the three weedy Rubus species using similar culture media conditions (modified Murashige and Skoog) but required different plant growth regulators (R. parviflorus, 4.5 M 2,4-D; R. spectabilis, 26.9 M NAA/0.5 M zeatin; and R. strigosus, 12.4 M picloram). Cell growth and health attributes including callus circumference, degree of browning and suspension culture cell viability as measured by the TTC vital stain assay were developed and were rapid and convenient to use. We have established Rubus tissue culture systems that will make it possible for large scale screening of phytotoxic metabolites.     

Invertebrate predator-prey body size relationships: an explanation for upper triangular food webs and patterns in food web structure?

Summary It has been suggested by Cohen and Newman (1985) that many of the patterns in published food webs can be derived from a stochastic model in which the species are arranged in a trophic hierarchy (the cascade model). We suggest that, if predators are larger than their prey, a trophic hierarchy can be generated on the basis of body size Empirical evidence from the literature shows that there is a positive relationship between predator and prey size for a range of invertebrates and that predators are usually larger than their prey. Using experimental data on an aquatic food web we show that body size can lead to the type of trophic hierarchy used in the cascade model, suggesting that many food web patterns may be a product of body size. This conclusion is discussed with respect to the limitations of the food web data and the relationship between static and dynamic models of web structure.     

Effects of exercise training and diabetes on cardiac myosin heavy chain composition

This study determined whether the beneficial effects of exercise training on the diabetic heart previously observed are associated with alterations in ventricular myosin heavy chain (MHC) isoform composition. Diabetes was induced in rats by i.v. streptozotocin. Trained rats were run on a treadmill for 60 min/day, 27 m/min, 10% grade. After 10 wks, ventricular MHC isoenzyme protein composition was analyzed for MHC composition using gel electrophoresis. -MHC and -MHC mRNA were determined by Northern and slot blot hybridization techniques. Both protein and mRNA analyses indicated that sedentary control rats exhibited a predominance of -MHC. Sedentary diabetics exhibited a shift to -MHC. Exercise trained diabetic rats showed a predominance of -MHC. The results indicate that treadmill exercise training of diabetic rat does not prevent the diabetes-induced shift in MHC composition towards the -MHC isoform, thus it is unlikely that the beneficial effects of exercise training on the diabetic heart, previously shown, are due to a normalization of the myosin isoform composition.     

The sialyl-α2,6-lactosaminyl-structure: Biosynthesis and functional role

Sialylation represents one of the most frequently occurring terminations of the oligosaccharide chains of glycoproteins and glycolipids. Sialic acid is commonly found ,3- or ,6-linked to galactose (Gal), ,6-linked to N-acetylgalactosamine (GalNAc) or ,8-linked to another sialic acid. The biosynthesis of the various linkages is mediated by the different members of the sialyltransferase family. The addition of sialic acid in ,6-linkage to the galactose residue of lactosamine (type 2 chains) is catalyzed by -galactoside ,6-sialyltransferase (ST6Gal.I). Although expressed by a single gene, this enzyme shows a complex pattern of regulation which allows its tissue- and stage-specific modulation. The cognate oligosaccharide structure, NeuAc,6Gal1,4GIcNAc, is widely distributed among tissues and is involved in biological processes such as the regulation of the immune response and the progression of colon cancer. This review summarizes the current knowledge on the biochemistry of ST6Gal.I and on the functional role of the sialyl-,6-lactosaminyl structure.     

A study of the HLA-D region in patients with classic Kaposi's sarcoma

The HLA-D region in nine Sardinian patients with classic Kaposi's sarcoma was studied with two restriction enzymes, Eco RI and Eco RV, and two cDNA probes, DR and DQ. A total of 41 polymorphic restriction fragments were identified. One, an 11.5 kb Eco RV DQ fragment, was present in three of the patients but in none of the controls; a second, an 8.0 kb Eco RV DR fragment, was present in six patients and all the controls. No single fragment was identified which was significantly over or under-represented in either group.     

The organ-specific rRNA gene number in Drosophila hydei is controlled by sex heterochromatin

Genotypes of Drosophila hydei having deficiencies of specific sections of X or Y chromosomal heterochromatin are characterized by heterogeneous rRNA gene numbers in their nonpolyploid organs. Depending on which sex heterochromatin portion is deleted, the rDNA amount in either brain or thoracic muscle cells or in both is increased threefold. This rDNA overreplication cannot be a compensation for a deficiency in ribosomal gene number, since the phenomenon also occurs in genotypes with a high initial rRNA gene numbers.     

Generalist Natural Enemies of a Willow Leaf Beetle (Phratora vulgatissima): Abundance and Feeding Habits

The natural enemies attacking eggs (and young larvae) of the willow leaf beetle Phratora vulgatissima were identified in the field. Three heteropterans were common natural enemies. The mirid Orthotylus marginalis was the most abundant and had an intermediate consumption rate in the lab, whereas the mirid Closterotomus fulvomaculatus was the least abundant but had the highest consumption rate. The anthocorid Anthocoris nemorum was intermediate in abundance but had the lowest consumption rate. However, the experimental situation (in petridish or on shoot) affected the ranking of the predators and illustrates behavioral differences. The anthocorid was very mobile and could be characterized as a run and eat predator, whereas the mirids were less mobile and behaved to a find and stay principle. Possible consequences of interspecific variation in behavior, from a biological control perspective, are discussed.     

Plathelminth abundance in North Sea salt marshes: environmental instability causes high diversity

Although supralittoral salt marshes are habitats of high environmental instability, the meiofauna is rich in species and abundance is high. The community structure of free-living Plathelminthes (Turbellaria) in these salt marshes is described. On an average, 104 individuals are found below an area of 10 cm². The average species density in ungrazed salt marshes is 11.3 below 10 cm² and 45.2 below 100 cm², indicating strong small-scale heterogenity. The faunal similarity between sediment and the corresponding above-ground vegetation is higher than between adjacent sample sites. Species prefer distinct ranges of salinity. In the lower part of the supralittoral salt marshes, the annual fluctuations of salinity are strongest and highly unpredictable. This region is richest in plathelminth species and abundance; diversity is highest, and the faunal composition of parallel samples is quite similar. In the upper part of the supralittoral salt marshes, the annual variability of salinity is lower, plathelminths are poor in species diversity and abundance. Parallel samples often have no species in common. Thus, those salt marsh regions with the most unstable environment are inhabited by the most diverse species assemblage. Compared to other littoral zones of the North Sea, however, plathelminth diversity in salt marshes is low. The observed plathelminth diversity pattern can apparently be explained by the dynamic equilibrium model (Huston, 1979).