论害虫种群的生态控制

本文根据保护生物圈与经济持续发展的要求,提出害虫种群的“生态控制’对策,以代替现在国内外采用的“综合防治”。文中根据生态学与经济学理论,不仅提出了“生态控制”应遵循的经济学与生态学的管理原则,并且提出了“生态控制”的指导思想与方法论,以及它的目标函数、约束条件与主要对策。进而根据国内外本领域的科技发展动态分析与生产实际需要,论述了本种对策在生产中的可行性与重要性。     

Bacterial swimming strategies and turbulence

Most bacteria in the ocean can be motile. Chemotaxis allows bacteria to detect nutrient gradients, and hence motility is believed to serve as a method of approaching sources of food. This picture is well established in a stagnant environment. In the ocean a shear microenvironment is associated with turbulence. This shear flow prevents clustering of bacteria around local nutrient sources if they swim in the commonly assumed "run-and-tumble" strategy. Recent observations, however, indicate a "back-and-forth" swimming behavior for marine bacteria. In a theoretical study we compare the two bacterial swimming strategies in a realistic ocean environment. The "back-and-forth" strategy is found to enable the bacteria to stay close to a nutrient source even under high shear. Furthermore, rotational diffusion driven by thermal noise can significantly enhance the efficiency of this strategy. The superiority of the "back-and-forth" strategy suggests that bacterial motility has a control function rather than an approach function under turbulent conditions.     

The influence of nest predation on mating strategies under polygyny

The mating status of an advertising male is one important factorfor female assessment. In species where already-mated malestry to attract additional females at some distance from theirmate, mating status may be difficult to assess. Limitationsin the time available to breed and a decrease in reproductivesuccess over the breeding season could make the costs outweighthe benefits of a time-consuming mate assessment process, whichautomatically postpones the onset of breeding. Time and energyconstraints will then limit the behavioral options for femalesin search of breeding opportunities, and females would suffera cost when assessing male mating status. Female choice maythen be better understood by analyzing the behavioral optionsfor females; the success of a strategy in which costly assessmentsare avoided and females choose mates indiscriminately, disregardingmating status ("fast" strategy), could be compared to the successof a strategy in which females carefully try to assess matingstatus ("coy" strategy). Nest predation should be included insuch an analysis because it influences the amount of male assistancefemales of polygynous males receive, as nest predation for onlyone of a polygynous male's two females leads to more male assistancefor the other female. In this study, I compare the outcome ofa "fast" strategy with that of a "coy" strategy under differentrates of nest predation. Although high probabilities of becominga mate of a polygynous male associated with a fitness reductiondecrease the relative success of a "fast" strategy, simulationsshow that high rates of nest predation considerably lower thedifference in the outcome of the two strategies. Therefore,the cost of assessing mating status must be relatively smallto be economical.     

Influence network linkages across implementation strategy conditions in a randomized controlled trial of two strategies for scaling up evidence-based practices in public youth-serving systems

Background

Given the importance of influence networks in the implementation of evidence-based practices and interventions, it is unclear whether such networks continue to operate as sources of information and advice when they are segmented and disrupted by randomization to different implementation strategy conditions. The present study examines the linkages across implementation strategy conditions of social influence networks of leaders of youth-serving systems in 12 California counties participating in a randomized controlled trial of community development teams (CDTs) to scale up use of an evidence-based practice.

Methods

Semi-structured interviews were conducted with 38 directors, assistant directors, and program managers of county probation, mental health, and child welfare departments. A web-based survey collected additional quantitative data on information and advice networks of study participants. A mixed-methods approach to data analysis was used to create a sociometric data set (n?=?176) to examine linkages between treatment and standard conditions.

Results

Of those network members who were affiliated with a county (n?=?137), only 6 (4.4%) were directly connected to a member of the opposite implementation strategy condition; 19 (13.9%) were connected by two steps or fewer to a member of the opposite implementation strategy condition; 64 (46.7%) were connected by three or fewer steps to a member of the opposite implementation strategy condition. Most of the indirect steps between individuals who were in different implementation strategy conditions were connections involving a third non-county organizational entity that had an important role in the trial in keeping the implementation strategy conditions separate. When these entities were excluded, the CDT network exhibited fewer components and significantly higher betweenness centralization than did the standard condition network.

Conclusion

Although the integrity of the RCT in this instance was not compromised by study participant influence networks, RCT designs should consider how influence networks may extend beyond boundaries established by the randomization process in implementation studies.

Trial registration

NCT00880126

     

Improving the efficiency of gene replacements in Neurospora crassa: a first step towards a large-scale functional genomics project

Here, we report the use of the mating type heterokaryon incompatibility system as a counterselection to increase the probability of identifying gene replacements in Neurospora crassa. We compared the frequencies of gene replacements observed among transformants obtained by using plasmids with or without the mat a-1(+) gene (hereby called "Toxic Gene") placed adjacent to disruption cassettes. On an average, we were 20x more likely to identify a correct gene replacement by incorporating the toxic gene in our constructs. Using this strategy, we constructed strains containing a deletion of the inl (1L-myo-inositol-1-phosphate synthase) gene. Finally, we demonstrated that we were able to remove the transformation marker (the hygromycin B phosphotransferase- thymidine kinase gene fusion [hph(+)::tk(+)]) from the genome by using a strategy similar to the "URA-blaster" strategy used in yeast, which we call "tk-blaster."     

Molecular vehicles for targeted drug delivery

Targeted drug delivery by cell-specific cytokines and antibodies promises greater drug efficacy and reduced side effects. We describe a novel strategy for assembly of drug delivery vehicles that does not require chemical modification of targeting proteins. The strategy relies on a noncovalent binding of standardized "payload" modules to targeting proteins expressed with a "docking" tag. The payload modules are constructed by linking drug carriers to an adapter protein capable of binding to a docking tag. Using fragments of bovine ribonuclease A as an adapter protein and a docking tag, we have constructed vascular endothelial growth factor (VEGF) based vehicles for gene delivery and for liposome delivery. Assembled vehicles displayed remarkable selectivity in drug delivery to cells overexpressing VEGF receptors. We expect that our strategy can be employed for targeted delivery of many therapeutic or imaging agents by different recombinant targeting proteins.     

The effect of insularity on the diversity of land birds in the Fiji islands: implications for refuge design

Ecologists have argued over rules of thumb that could be used to set priorities in configuring systems of reserves for preserving biological diversity. To evaluate these simple strategies, I assembled a particularly large and comprehensive data set on the land birds of the Fiji archipelago. I analyzed the species distribution on 220 islands to compare the running total of species preserved by differènt sequences of adding nature reserves to a hypothetical reserve system, treating each island as if it were a potential reserve. A strategy of maximizing the number of islands contributing to any given reserve area (maximum fragmentation) is much more effective at including species than a strategy of maximizing the size of the island components of a reserve (minimum fragmentation). Nevertheless the maximum fragmentation strategy is not a very good one. It is less effective than many random strategies, especially when about 2–10% of total area is to be set aside as reserve, and when only rare species are considered. A computer program was used to determine an optimal strategy by maximizing the number of additional species added for each unit of area added. This strategy is always substantially more effective at encompassing species diversity than either the maximum or minimum fragmentation strategies. It is suggested that the poor performance of the minimum fragmentation strategy is due principally to the presence of many smaller-island endemics within the Fiji archipelago. More generally, it is argued that the effect of fragmentation on species diversity depends on the geographic scale and isolation of the region under consideration. In these respects the Fiji Archipelago may be a particularly good model for continental reserve systems.     

Convergent maternal care strategies in ungulates and macropods

Mammals show extensive interspecific variation in the form of maternal care. Among ungulates, there is a dichotomy between species in which offspring follow the mother ("following" strategy) versus species in which offspring remain concealed ("hiding" strategy). Here we reveal that the same dichotomy exists among macropods (kangaroos, wallabies and allies). We test three traditional adaptive explanations and one new life history hypothesis, and find very similar patterns among both ungulates and macropods. The three traditional explanations that we tested were that a "following" strategy is associated with (1) open habitat, (2) large mothers, and (3) gregariousness. Our new life-history hypothesis is that a "following strategy" is associated with delayed weaning, and thus with the "slow" end of the slow-fast mammalian life-history continuum, because offspring devote resources to locomotion rather than rapid growth. Our comparative test strongly supports the habitat structure hypothesis and provides some support for this new delayed weaning hypothesis for both ungulates and macropods. We propose that sedentary young in closed habitats benefit energetically by having milk brought to them. In open habitats, predation pressure will select against hiding. Followers will suffer slower growth to independence. Taken together, therefore, our results provide the first quantitative evidence that macropods and ungulates are convergent with respect to interspecific variation in maternal care strategy. In both clades, differences between species in the form of parental care are due to a similar interaction between habitat, social behavior, and life history.     

Double-stranded RNA as a not-self alarm signal: to evade, most viruses purine-load their RNAs, but some (HTLV-1, Epstein-Barr) pyrimidine-load

For double-stranded RNA (dsRNA) to signal the presence of foreign (non-self) nucleic acid, self-RNA-self-RNA interactions should be minimized. Indeed, self-RNAs appear to have been fine-tuned over evolutionary time by the introduction of purines in clusters in the loop regions of stem-loop structures. This adaptation should militate against the "kissing" interactions which initiate formation of dsRNA. Our analyses of virus base compositions suggest that, to avoid triggering the host cell's dsRNA surveillance mechanism, most viruses purine-load their RNAs to resemble host RNAs ("stealth" strategy). However, some GC-rich latent viruses (HTLV-1, EBV) pyrimidine-load their RNAs. It is suggested that when virus production begins, these RNAs suddenly increase in concentration and impair host mRNA function by virtue of an excess of complementary "kissing" interactions ("surprise" strategy). Remarkably, the only mRNA expressed in the most fundamental form of EBV latency (the "EBNA-1 program") is purine-loaded. This apparent stealth strategy is reinforced by a simple sequence repeat which prefers purine-rich codons. During latent infection the EBNA-1 protein may evade recognition by cytotoxic T-cells, not by virtue of containing a simple sequence amino acid repeat as has been proposed, but by virtue of the encoding mRNA being purine-loaded to prevent interactions with host RNAs of either genic or non-genic origin.     

The Ecological Strategies of Sea Turtles

By employing concepts such as "option" and "strategy" from gametheory, this study derives an ecologically-oriented dendrogramof the probable evolutionary history and the present relationshipsof sea turtles. An "armored tank" strategy is seen as differentiatingthe first ancestral testudines from the stem reptiles and providingenduring advantages while simultaneously imposing basic restrictionson all later forms. A "flipper" strategy is postulated as basicto development of the sea turtle line, again imposing limitationswhile conferring selective advantage. Modern sea turtle speciesare grouped into three lineages representing strategies of habitat-typeresource partitioning (a split-habitat, migratory pattern, aneritic residence pattern, and a pelagic residence pattern).Within the split-habitat, migratory group, further resource-partitioningby food-type separates the herbivorous Chelonia mydas populationsfrom omnivorous Eretmochelys imbricata and the (apparently)carnivorous Chelonia depressa. Herbivory is seen as integralto the split-habitat, migratory strategy and C. mydas is consideredthe most "traditional" species, with the migratory habit secondarilylost in the other two. At the same time, the enhanced philopatryselected for by the migration strategy is viewed as responsiblefor the fact that C. mydas seems to have the most active race-formationof the three species. Further habitat-type partitioning in theneritic group, together with food-type partitioning, separatesCaretta caretta from the two Lepidochelys species. L. kempiis represented as a consequence of Panamanian separation fromL. olivacea following the last establishment of the isthmusas a land barrier. The third, pelagic residence, strategy isrepresented by Dermochelys coriacea, with little further differentiationof the line. The paper attempts to show that the evolution ofsea turtles has been ecologically logical, that most conceivableniches for marine turtles are presently filled successfully,and that some predictions may be made with regard to gaps inour existing information.     

农户生计策略转型及对环境的影响研究综述

随着我国经济形势的不断变化,越来越多的农户从传统的"单一生计"转向"生计多样化"和"优势生计"的发展方向。农户作为农村地区最基本的社会经济单元和行为决策主体,处于人口、经济与资源环境矛盾的核心,其生计策略与生计活动的动态变化势必对所处的自然-社会-经济复合生态系统带来一定的影响。在回顾农户生计研究的历史与现状的基础上,分别从农户生计策略的内涵与类型、农户生计策略转型及其驱动因素、生计策略转型对环境的影响3个方面,系统梳理了国内外学者对农户生计策略转型及对环境的影响的研究进展,尝试性地构建了农户生计策略转型及对环境的影响的基本研究框架,提出未来研究应当体现生计问题本身的动态性和复杂性,并注重可持续生计策略的界定与实现。     

Travelling waves and dominance of ESS's

We consider a simple two strategy game in which each pure strategy is an evolutionarily stable strategy (ESS). Under the usual dynamical equations, the large-time behaviour of the system will depend upon the initial conditions and the pay-off matrix. If spatial effects are included to give a reaction-diffusion system, we prove that travelling wavefronts can occur which in effect replace one ESS by another. The strength or dominance of each ESS which decides the winner in a precisely defined sense is determined by its pay-off and by its diffusion rate. Good strategies have large pay-offs and small diffusion rates.     

Application of "oxygen uptake rate-amino acids" associated mode in controlled-fed perfusion culture

Controlled-fed perfusion, a new operation mode, which combines the advantages of fed-batch and perfusion, has been reported to enhance monoclonal antibody productivity. The aim of the present study was to further enrich this mode by an "oxygen uptake rate-amino acids (OUR-AA)" strategy in which the feeding of amino acids was controlled according to the variation of OUR during perfusion. And the effects of this strategy on bioreactor productivity and product quality were evaluated. Experimental results indicated that by using this "OUR-AA" approach in controlled-fed perfusion mode a high viable cell density of more than 1.9 x 10(7)cells/ml was achieved and the productivity of mAb reached 325 mg/l/d, which was significantly increased by nearly twofold over those of the perfusion and fed-batch process. The residual concentrations of selected amino acids were controlled at a relative steady level by OUR during the culture. The immunoreactivity and the purity of the antibody were well preserved as the culture process was evolving from flask to the controlled-fed perfusion mode. The primary application of "OUR-AA" approach in controlled-fed perfusion mode may present a novel control strategy to enhance the culture performance and to display the potential of this approach in automatic control field.     

Detection of new transposable element families in Drosophila melanogaster and Anopheles gambiae genomes

The techniques that are usually used to detect transposable elements (TEs) in nucleic acid sequences rely on sequence similarity with previously characterized elements. However, these methods are likely to miss many elements in various organisms. We tested two strategies for the detection of unknown elements. The first, which we call "TBLASTX strategy," searches for TE sequences by comparing the six-frame translations of the nucleic acid sequences of known TEs with the genomic sequence of interest. The second, "repeat-based strategy," searches genomic sequences for long repeats and clusters them in groups of similar sequences. TE copies from a given family are expected to cluster together. We tested the Drosophila melanogaster genomic sequence and the recently sequenced Anopheles gambiae genome in which most TEs remain unknown. We showed that the "TBLASTX strategy" is very efficient as it detected at least 332 new TE families in D. melanogaster and 400 in A. gambiae. This was unexpected in Drosophila as TEs of this organism have been extensively studied. The "repeat-based strategy" appeared to be very inefficient because of two problems: (i) TE copies are heavily deleted and few copies share homologous regions, and (ii) segmental duplications are frequent and it is not easy to distinguish them from TE copies.     

Implicit frequency dependence and kin selection in fluctuating environments

Summary I consider a general model of a fluctuating environment in which the environmental state each year is drawn at random from some given distribution. Each year organisms must choose what action to perform before the environmental state for that year is known. There is no interaction with kin. In this scenario, natural selection will tend to produce organisms which maximize their geometric mean fitness. In this paper I introduce the idea of the profile of a strategy. This function quantifies how the strategy peforms for each environmental state. I show that there is a unique profile such that a strategy is optimal if and only if it has this profile. I then give a characterization of the optimal profile which generalizes previous work by others in this area. The characterization of the optimal profile has a game theoretical interpretation. Motivated by this I introduce a game in which individuals play the field in a constant environment. This game may be interpreted as a cooperative game between kin. The key result of this paper shows that a strategy maximizes geometric mean fitness in the original fluctuating environment problem if and only if it is an evolutionarily stable strategy of the deterministic environment game. It is well known that an optimal strategy in a fluctuating environment may be mixed, involving adaptive coin-flipping. Others have previously noted that this may result in some individuals sacrificing individual reproductive success for the good of the genotype. My analysis shows that one may regain the concept of individual optimization if the quantity maximized is suitably defined. Under an optimal strategy every action taken maximizes the expected number of offspring produced, where this expectation is not calculated using the true distribution of environmental states, but a distribution modified to take account of the actions of kin.     

The development of cooperative relationships: an experiment

Pairs of individuals frequently face situations in which they could do well if they cooperated, but each risks being exploited. The Prisoner's Dilemma is widely used for investigating such scenarios, but it is framed in terms of cooperating and defecting, whereas in reality cooperation is rarely "all or nothing". Recent models allowing for variable investment in cooperation indicated the success of a strategy of "raising-the-stakes" (RTS), which invests minimally at first and then increases its investment if its partner matches it. We tested whether this strategy was adopted by subjects participating in an experiment in which they could choose how much money to give to a partner, reciprocity being encouraged by doubling donations. Subjects did increase their donations over successive rounds, both when playing against a stooge who reciprocated with the same investment, and when playing with a partner who was free to choose their investment. Subjects showed a strong tendency to match variations in their partner's investments. Cooperation was therefore achieved through a combination of initial escalation (RTS strategy) and quantitative responsiveness ("give-as-good-as-you-get" strategy). Although initial offers were higher than predicted, our results were broadly consistent with theoretical expectations.     

Subgroup economic analysis for glioblastoma in a health resource-limited setting

Background

The aim of this research was to evaluate the economic outcomes of radiotherapy (RT), temozolomide (TMZ) and nitrosourea (NT) strategies for glioblastoma patients with different prognostic factors.

Methodology/Principal Findings

A Markov model was developed to track monthly patient transitions. Transition probabilities and utilities were derived primarily from published reports. Costs were estimated from the perspective of the Chinese healthcare system. The survival data with different prognostic factors were simulated using Weibull survival models. Costs over a 5-year period and quality-adjusted life years (QALYs) were estimated. Probabilistic sensitivity and one-way analyses were performed. The baseline analysis in the overall cohort showed that the TMZ strategy increased the cost and QALY relative to the RT strategy by $25,328.4 and 0.29, respectively; and the TMZ strategy increased the cost and QALY relative to the NT strategy by $23,906.5 and 0.25, respectively. Therefore, the incremental cost effectiveness ratio (ICER) per additional QALY of the TMZ strategy, relative to the RT strategy and the NT strategy, amounts to $87,940.6 and $94,968.3, respectively. Subgroups with more favorable prognostic factors achieved more health benefits with improved ICERs. Probabilistic sensitivity analyses confirmed that the TMZ strategy was not cost-effective. In general, the results were most sensitive to the cost of TMZ, which indicates that better outcomes could be achieved by decreasing the cost of TMZ.

Conclusions/Significance

In health resource-limited settings, TMZ is not a cost-effective option for glioblastoma patients. Selecting patients with more favorable prognostic factors increases the likelihood of cost-effectiveness.     

Female multiple mating as a genetic bet-hedging strategy when mate choice criteria are unreliable

Female multiple mating (or polyandry) is considered to act as a genetic bet-hedging mechanism, by which females can reduce the assessment error in regard to mates genetic quality when only uncertain information is available. In spite of frequent verbal arguments, no theoretical examination has been carried out to determine the effectiveness of bet-hedging by multiple mating. In the present paper, I show that three factors, female population size, remating costs and environmental fluctuation, all affect the effectiveness of bet-hedging. A mathematical model predicts that bet-hedging effectively works only in small populations, and computer simulations were used to confirm this prediction. The results of simulations differed according to the degree of environmental fluctuation. In relatively stable environments, if there is no remating cost, the fixation probability of a multiple mating strategy is slightly higher than that of a single mating strategy, independent of female population size. However, with very slight fitness costs, multiple mating drastically loses its advantage as population size increases, and almost always becomes extinct within large populations. This means that the evolution of polyandry solely by the mechanism of bet-hedging is unlikely in stable environments. However, in unpredictable environments, or when negative frequency-dependent selection on fitness-related loci is introduced, a multiple mating strategy is sometimes successful against a single mating strategy, even if it entails a small fitness cost. Therefore, female multiple mating may possibly evolve only in these limited conditions. In most cases, some deterministic mechanisms such as postcopulatory sperm selection by multiply mated females (or direct material benefits) are more reasonable as the evolutionary causes of polyandry.