Delayed effects in aphid-parasitoid systems: Consequences for evaluating biological control species and their use in augmentation strategies

A particular feature of aphid-parasitoid systems is the existence of a delay between parasitisation (sting) and the death of the host (i.e. mummification). This biological trait is generally not considered important for population stability, except if the delay is very long, and hence it is ignored in most population dynamics studies. However, many crops have relatively short durations, and these time delays may have important consequences and cannot be ignored in a dynamics model. In this study, we are looking for the key-factors that influence an aphidparasitoid system population dynamics during a cropping cycle. Specifically, a simple model based on ordinary and delay differential equations and including biologically meaningful parameters was developed for aphidparasitoid systems and used to examine: (1) effect of biological characteristics of both the aphid and the parasitoid on their dynamics, (2) the effect of parasitoid augmentation on the dynamics of the system (e.g.: date, number and importance of the releases of parasitoids), and (3) to compare observedAphis gossypii — Lysiphlebus testaceipes dynamics in a cucumber crop to the predictions of the model. Good fits between the model and the field data were obtained and suggest that this model may be a powerful tool for selecting species of parasitoid and strategies for their use in biological control augmentation programs for aphid pest management.     

Recombination in Escherichia coli and the definition of biological species.

The DNA sequence of part of the gnd (6-phosphogluconate dehydrogenase) gene was determined for eight wild strains of Escherichia coli and for Salmonella typhimurium. Since a region of the trp (tryptophan) operon and the phoA (alkaline phosphatase) gene have been sequenced from the same strains, the gene trees for these three regions were determined and compared. Gene trees are different from species or strain trees in that a gene tree is derived from a particular segment of DNA, whereas a species or strain tree should be derived from many such segments and is the tree that best represents the phylogenetic relationship of the species or strains. If there were no recombination in E. coli, the gene trees for different genes would not be statistically different from the strain tree or from each other. But, if the gene trees are significantly different, there must have been recombination. Methods are proposed that show these gene trees to be statistically different. Since the gene trees are different, we conclude that recombination is important in natural populations of E. coli. Finally, we suggest that gene trees can be used to create an operational means of defining bacterial species by using the biological species definition.     

Endophytic Phomopsis species: host range and implications for diversity estimates

Foliar endophyte assemblages of teak trees growing in dry deciduous and moist deciduous forests of Nilgiri Biosphere Reserve were compared. A species of Phomopsis dominated the endophyte assemblages of teak, irrespective of the location of the host trees. Internal transcribed spacer sequence analysis of 11 different Phomopsis isolates (ten from teak and one from Cassia fistula) showed that they fall into two groups, which are separated by a relatively long branch that is strongly supported. The results showed that this fungus is not host restricted and that it continues to survive as a saprotroph in teak leaf, possibly by exploiting senescent leaves as well as the litter. Although the endophyte assemblage of a teak tree growing about 500 km from the forests was also dominated by a Phomopsis sp., it separated into a different group based on internal transcribed spacer sequence analysis. Our results with an endophytic Phomopsis sp. reinforce the earlier conclusions reached by others for pathogenic Phomopsis sp., i.e., that this fungus is not host specific, and the species concept of Phomopsis needs to be redefined.     

DNA-protein crosslinks: their induction, repair, and biological consequences

The covalent crosslinking of proteins to DNA presents a major physical challenge to the DNA metabolic machinery. DNA-protein crosslinks (DPCs) are induced by a variety of endogenous and exogenous agents (including, paradoxically, agents that are known to cause cancer as well as agents that are used to treat cancer), and yet they have not received as much attention as other types of DNA damage. This review summarizes the current state of knowledge of DPCs in terms of their induction, structures, biological consequences and possible mechanisms of repair. DPCs can be formed through several different chemistries, which is likely to affect the stability and repair of these lesions, as well as their biological consequences. The considerable discrepancy in the DPC literature reflects both the varying chemistries of this heterogeneous group of lesions and the fact that a number of different methods have been used for their analysis. In particular, research in this area has long been hampered by the inability to chemically define these lesions in intact cells and tissues. However, the emergence of proteomics as a tool for identifying specific proteins that become crosslinked to DNA has heralded a new era in our ability to study these lesions. Although there are still many unanswered questions, the identification of specific proteins crosslinked to DNA should facilitate our understanding of the down-stream effects of these lesions.     

Eukaryotic DNA methylases and their use for in vitro methylation

DNA methylases from mouse and pea have been purified and characterized. Both are high molecular mass enzymes that show greater activity with hemimethylated than unmethylated substrate DNA. Both methylate cytosines in CpG preferentially, but not exclusively and show similar kinetics of methylation, which makes it difficult to saturate all possible sites on the DNA, but procedures are described that circumvent this problem.     

Successional phases and species replacements in freshwater rock pools: towards a biological definition of ephemeral systems

1. In temporary aquatic habitats, time is probably the dominant environmental factor affecting community composition, mainly by setting constraints on colonization success and the replacement of taxa over time. The mechanism and effect of a decreasing inundation period on community development, mostly in terms of truncation, are still poorly documented. The permanent and ephemeral components of temporary communities are expected to be differently influenced by the degree of persistence of the habitat. 2. To study the effect of time on invertebrate community assembly and dynamics in a short duration type of temporary aquatic habitat, we monitored 16 ephemeral rock pools which persisted from less than a week to about 1 month at two rock pool sites in semi‐arid south‐eastern Botswana. Data were collected every 2 days during a full inundation cycle. 3. All communities were initially assembled by permanent residents recolonizing the habitat from egg banks and were later joined by actively dispersing ephemeral taxa. Species replacements only occurred in two pools. Concurrent with a decrease in the densities of Branchipodopsis wolfi, population sizes of Leberis sp. and Culicidae (Aedes sp. and Anopheles sp.) increased in these pools. Although it was possible to distinguish two successive phases at one rock pool site, community assembly was generally a gradual process determined by dispersal strategies of the inhabitants. Additional rains after initial filling triggered dispersal by ephemeral taxa, mainly Micronecta youngiana and Hydroglyphus infirmus, and positively influenced colonization success. 4. Decreasing persistence shortens community development down to a critical point below which lack of time eliminates the possibility of species replacement. Based on these findings, we define ephemeral waters as aquatic habitats lacking species replacements. Other temporary water types have a relatively longer persistence, permitting successional replacement of species.     

Hiroshima-like neutrons from A-bomb replica: physical basis for their use in biological experiments

The lineal energy distribution and several other dosimetric parameters were measured for the neutrons emitted from a replica of the Hiroshima bomb to determine their usefulness in biological experiments designed to estimate the effectiveness of actual Hiroshima neutrons. The "Little-Boy" replica (LBR) was constructed at the Los Alamos National Laboratory in support of the recent atomic-bomb dose reevaluation and was made of identical materials and had nearly identical dimensions and geometry as the Hiroshima bomb. However, the LBR was operated as a steady-state nuclear reactor, which permitted measurements under controlled conditions. Detailed dosimetric measurements and calculations were made at distances of up to 2.1 m from the center of the LBR uranium core. At these distances, the in-air kerma was approximately 97% from neutrons and kerma rates were shown to be particularly useful for biological experiments (up to approximately 7 Gy/h was possible). Quantitative intercomparisons of neutron energy spectra, lineal energy distributions, and measured cytogenetic results for several fission-neutron sources indicate that Hiroshima and LBR neutrons should be of similar biological effectiveness. Based on these evaluations, and cytogenetic results for LBR neutrons reported in a companion paper (this issue), it is estimated that Hiroshima neutrons were 20 to 30% more effective than the fission neutrons commonly used in radiobiology.     

Gene-sequence-based criteria for species definition in bacteriology: the Bartonella paradigm

The definition of new species is currently based on polyphasic classification that includes both determination of phenotypic characteristics and DNA-DNA homology. However, none of these techniques is convenient for the rapid characterization of fastidious or non-culturable bacteria. Using sequences available in the GenBank database, we compared the similarities of gene fragments among the currently recognized Bartonella species. This comparison led to both the definition of similarity values that discriminated Bartonella at the species level and assessment of the relative discriminatory power of each gene examined. In this perspective, rpoB and gltA were found to be the most potent.     

Life history comparison between two competitive Aleochara species in the cabbage root fly, Delia radicum: implications for their use in biological control

This study evaluates the efficacy of Aleochara bilineata Gyll and Aleochara bipustulata L. (Coleoptera: Staphylinidae) as biological control agents against the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae). Biological and demographic characters are documented and comparisons made between the two species. The following results were obtained:(1) The reproductive potential and longevity of A. bipustulata females are significantly higher than those of A. bilineata. These differences are correlated with the biology and ecology of the hosts of both species.(2) Under laboratory conditions the rate of increase (r_m) of both staphylinids species is significantly higher than that of the pest and their major competitor Trybliographa rapae West. (Hymenoptera:Figitidae). This may indicate that A. bilineata and A. bipustulata can be effective biological control agents.(3) Aleochara bilineata appears to be the most interesting biological control agent against D. radicum, because of its higher rate of increase, higher host specificity and host acceptance, and a development time which is well synchronised with that of its host. With its higher competitive ability, a population of A. bilineata may increase even if competition occurs. However, A. bipustulata presents interesting biocontrol characteristics, but the best strategy may be only to use the potential of its natural populations.     

Redox properties of iron-dithiocarbamates and their nitrosyl derivatives: implications for their use as traps of nitric oxide in biological systems

While the Fe(2+)-dithiocarbamate complexes have been commonly used as NO traps to estimate NO production in biological systems, these complexes can undergo complex redox chemistry. Characterization of this redox chemistry is of critical importance for the use of this method as a quantitative assay of NO generation. We observe that the commonly used Fe(2+) complexes of N-methyl-D-glucamine dithiocarbamate (MGD) or diethyldithiocarbamate (DETC) are rapidly oxidized under aerobic conditions to form Fe(3+) complexes. Following exposure to NO, diamagnetic NO-Fe(3+) complexes are formed as demonstrated by the optical, electron paramagnetic resonance and gamma-resonance spectroscopy, chemiluminescence and electrochemical methods. Under anaerobic conditions the aqueous NO-Fe(3+)-MGD and lipid soluble NO-Fe(2+)-DETC complexes gradually self transform by reductive nitrosylation into paramagnetic NO-Fe(2+)-MGD complexes with yield of up to 50% and the balance is converted to Fe(3+)-MGD and nitrite. In dimethylsulfoxide this process is greatly accelerated. More efficient transformation of NO-Fe(3+)-MGD into NO-Fe(2+)-MGD (60-90% levels) was observed after addition of reducing equivalents such as ascorbate, hydroquinone or cysteine or with addition of excess Fe(2+)-MGD. With isotope labeling of the NO-Fe(3+)-MGD with (57)Fe, it was shown that these complexes donate NO to Fe(2+)-MGD. NO-Fe(3+)-MGD complexes were also formed by reversible oxidation of NO-Fe(2+)-MGD in air. The stability of NO-Fe(3+)-MGD and NO-Fe(2+)-MGD complexes increased with increasing the ratio of MGD to Fe. Thus, the iron-dithiocarbamate complexes and their NO derivatives exhibit complex redox chemistry that should be considered in their application for detection of NO in biological systems.     

A method for hormonal induction of sperm release in anurans (eight species) and in vitro fertilization in Lepidobatrachus species

Injections of synthetic human gonadotropin releasing hormone (GnRH) into the dorsal pelvic area were used in an attempt to stimulate sperm release in isolated males of eight anuran species including Xenopus laevis, Rana pipiens and Lepidobatrachus laevis . Sperm were obtained within 1–5 h post injection either by mechanical stimulation or by cloacal lavage. Sperm suspensions varied from 8 μL to 7 mL and the cell densities ranged from 4 × 10⁵ to 4 × 10⁷ sperm/mL. The sperm obtained from seven species using GnRH-induced release were viable based on light microscopic observations of motility. In addition, sperm preparations fertilized eggs in vitro and produced normal tadpoles in the case of L. laevis and L. llanensis . This hormonal method of anuran sperm collection will provide a convenient non-injurious way to obtain anuran sperm for basic studies of reproduction and development.     

Metallothioneins in terrestrial invertebrates: structural aspects, biological significance and implications for their use as biomarkers.

During the last few years the subject of metallothioneins (MTs) in terrestrial invertebrates has gained increasing attention. One reason for this may be that terrestrial invertebrates provide new insights into the biological diversity of MTs, with the potential of discovering alternative models of structural and functional relationships. Four groups of terrestrial invertebrates have been studied in detail, namely nematodes, insects, snails and earthworms, with the present article focusing on MTs from the latter two groups. Snails are interesting because they possess distinct MT isoforms involved in different metal-specific tasks. In the Roman snail (Helix pomatia), for example, one isoform is predominantly expressed in the midgut gland, accounting for the accumulation, binding and detoxification of cadmium. The second isoform, which is present in the snail's mantle, is substantially different regarding its primary structure. Furthermore, it binds nearly exclusively copper, and thus is probably involved in the homeostatic regulation of essential trace elements. Earthworm MTs merit our attention because of another peculiarity: they seem to be much more unstable than snail MTs, particularly under conventional conditions of preparation. The cDNA of the brandling worm (Eisenia foetida), for instance, codes for a putative MT, which is about twice the size of the actual protein. The isolated MT peptide binds four Cd2+ ions and represents a one-domain MT entity that is stable and functional in vitro. This strongly suggests that earthworm MTs are either posttranslationally modified, or subjected to enzymatic cleavage during preparation. Both snail and earthworm MTs are inducible by metal exposure, especially by cadmium, thus supporting the idea of using them as potential biomarkers for environmental metal pollution. Whilst snail MTs have already been tested in this respect with some success, the use of earthworm MTs as biomarkers still remains to be evaluated, especially in the light of the unknown significance of their posttranslational instability.     

Interaction of nonsteroidal anti-inflammatory drugs with membranes: In vitro assessment and relevance for their biological actions

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used drugs in the world due to their anti-inflammatory, analgesic and antipyretic properties. Nevertheless, the consumption of these drugs is still associated with the occurrence of a wide spectrum of adverse effects. Regarding the major role of membranes in cellular events, the hypothesis that the biological actions of NSAIDs may be related to their effect at the membrane level has triggered the in vitro assessment of NSAIDs-membrane interactions. The use of membrane mimetic models, cell cultures, a wide range of experimental techniques and molecular dynamics simulations has been providing significant information about drugs partition and location within membranes and also about their effect on diverse membrane properties. These studies have indeed been providing evidences that the effect of NSAIDs at membrane level may be an additional mechanism of action and toxicity of NSAIDs. In fact, the pharmacokinetic properties of NSAIDs are closely related to the ability of these drugs to interact and overcome biological membranes. Moreover, the therapeutic actions of NSAIDs may also result from the indirect inhibition of cyclooxygenase due to the disturbing effect of NSAIDs on membrane properties. Furthermore, increasing evidences suggest that the disordering effects of these drugs on membranes may be in the basis of the NSAIDs-induced toxicity in diverse organ systems. Overall, the study of NSAIDs-membrane interactions has proved to be not only important for the better understanding of their pharmacological actions, but also for the rational development of new approaches to overcome NSAIDs adverse effects.     

基于生物学物种定义探讨物种形成理论与验证的研究进展

物种形成是进化生物学研究的一个永恒主题, 由于生物群体进化是连续和动态的, 物种界限变得难于界定。本文首先讨论了3种地理物种形成模式(同域、邻域及异域), 并分析了近期报道的研究证据。其次, 评述了合子后生殖隔离机制的分子遗传基础和应用群体基因组数据分析的证据, 包括BDMI模型(Bateson-Dobzhansky-Muller incompatibility)、QTLs (quantitative trait loci)、霍尔丹法则及大X染色体效应。最后, 探讨了交配系统作为合子前隔离机制之一与物种形成的关系, 认为近交或自交通过扩大种群遗传结构分化, 增强不同交配系统的种群间不对称基因渐渗, 或种群间无基因渐渗等途径, 促进新物种形成。已知植物交配系统的演化更倾向于从异交(或自交不亲和)向自交(或近交亲和)方式, 花性状和基因组的分化推动形成所谓的自交综合征, 研究交配系统驱动或强化物种形成模式对认识植物物种形成机制有重要意义。     

Theory for the systemic definition of metabolic pathways and their use in interpreting metabolic function from a pathway-oriented perspective

Cellular metabolism is most often described and interpreted in terms of the biochemical reactions that make up the metabolic network. Genomics is providing near complete information regarding the genes/gene products participating in cellular metabolism for a growing number of organisms. As the true functional units of metabolic systems are its pathways, the time has arrived to define metabolic pathways in the context of whole-cell metabolism for the analysis of the structural design and capabilities of the metabolic network. In this study, we present the theoretical foundations for the identification of the unique set of systemically independent biochemical pathways, termed extreme pathways, based on system stochiometry and limited thermodynamics. These pathways represent the edges of the steady-state flux cone derived from convex analysis, and they can be used to represent any flux distribution achievable by the metabolic network. An algorithm is presented to determine the set of extreme pathways for a system of any complexity and a classification scheme is introduced for the characterization of these pathways. The property of systemic independence is discussed along with its implications for issues related to metabolic regulation and the evolution of cellular metabolic networks. The underlying pathway structure that is determined from the set of extreme pathways now provides us with the ability to analyse, interpret, and perhaps predict metabolic function from a pathway-based perspective in addition to the traditional reaction-based perspective. The algorithm and classification scheme developed can be used to describe the pathway structure in annotated genomes to explore the capabilities of an organism.     

Redox properties of iron–dithiocarbamates and their nitrosyl derivatives: implications for their use as traps of nitric oxide in biological systems

While the Fe²⁺–dithiocarbamate complexes have been commonly used as NO traps to estimate NO production in biological systems, these complexes can undergo complex redox chemistry. Characterization of this redox chemistry is of critical importance for the use of this method as a quantitative assay of NO generation. We observe that the commonly used Fe²⁺ complexes of N-methyl-D-glucamine dithiocarbamate (MGD) or diethyldithiocarbamate (DETC) are rapidly oxidized under aerobic conditions to form Fe³⁺ complexes. Following exposure to NO, diamagnetic NO–Fe³⁺ complexes are formed as demonstrated by the optical, electron paramagnetic resonance and gamma-resonance spectroscopy, chemiluminescence and electrochemical methods. Under anaerobic conditions the aqueous NO–Fe³⁺–MGD and lipid soluble NO–Fe²⁺–DETC complexes gradually self transform by reductive nitrosylation into paramagnetic NO–Fe²⁺–MGD complexes with yield of up to 50% and the balance is converted to Fe³⁺–MGD and nitrite. In dimethylsulfoxide this process is greatly accelerated. More efficient transformation of NO–Fe³⁺–MGD into NO–Fe²⁺–MGD (60–90% levels) was observed after addition of reducing equivalents such as ascorbate, hydroquinone or cysteine or with addition of excess Fe²⁺–MGD. With isotope labeling of the NO–Fe³⁺–MGD with ⁵⁷Fe, it was shown that these complexes donate NO to Fe²⁺–MGD. NO–Fe³⁺–MGD complexes were also formed by reversible oxidation of NO–Fe²⁺–MGD in air. The stability of NO–Fe³⁺–MGD and NO–Fe²⁺–MGD complexes increased with increasing the ratio of MGD to Fe. Thus, the iron–dithiocarbamate complexes and their NO derivatives exhibit complex redox chemistry that should be considered in their application for detection of NO in biological systems.     

Citrinin,ochratoxin A and iron. Possible implications for their biological function and induction of nephropathy

Experiments with Neisseria meningitidis have shown that Fe³⁺ to some extent can reverse the toxicity of ochratoxin A and citrinin, as measured by inhibition zones around impregnated paper discs. Similar phenomena were observed with the less toxic ochratoxin B. Zearalenone also inhibited growth, but its effect was not counteracted by iron. The mycotoxins aflatoxin B₁ and deoxynivalenol did not inhibit bacterial growth at all. Desferal (deferoxamine) also inhibited growth of meningococci, but iron totally abolished this inhibition. The results indicate that ochratoxin A and citrinin interfere with iron metabolism in this organism but that other additional toxic mechanisms are involved as well since a marked growth inhibition by both toxins was also observed in the presence of iron. One function of ochratoxin A and citrinin in nature could consequently be to affect the iron uptake of other competing microorgansms.Since both toxins interfere with iron and both cause nephropathy, a possible connection between these properties and lipid peroxidation is also briefly discussed.Abbreviations DON deoxynivalenol - OA ochratoxin A - OB ochratoxin B