Search

One of the central aims of ecology is to identify mechanisms that maintain biodiversity. Numerous theoretical models have shown that competing species can coexist if ecological processes such as dispersal, movement, and interaction occur over small spatial scales. In particular, this may be the case for non-transitive communities, that is, those without strict competitive hierarchies. The classic non-transitive system involves a community of three competing species satisfying a relationship similar to the children's game rock-paper-scissors, where rock crushes scissors, scissors cuts paper, and paper covers rock. Such relationships have been demonstrated in several natural systems. Some models predict that local interaction and dispersal are sufficient to ensure coexistence of all three species in such a community, whereas diversity is lost when ecological processes occur over larger scales. Here, we test these predictions empirically using a non-transitive model community containing three populations of Escherichia coli. We find that diversity is rapidly lost in our experimental community when dispersal and interaction occur over relatively large spatial scales, whereas all populations coexist when ecological processes are localized.

High-profile reports claiming an easy way to create pluripotent cells were flawed, Nature announces.

Change of journal does not convince critics that rat diseases were caused by genetically modified maize.

MANY species exhibit colour polymorphisms associated with alternative male reproductive strategies, including territorial males and 'sneaker males' that behave and look like females1–3. The prevalence of multiple morphs is a challenge to evolutionary theory because a single strategy should prevail unless morphs have exactly equal fitness4,5 or a fitness advantage when rare6,7. We report here the application of an evolutionary stable strategy model to a three-morph mating system in the side-blotched lizard. Using parameter estimates from field data, the model predicted oscillations in morph frequency, and the frequencies of the three male morphs were found to oscillate over a six-year period in the field. The fitnesses of each morph relative to other morphs were non-transitive in that each morph could invade another morph when rare, but was itself invadable by another morph when common. Concordance between frequency-dependent selection and the among-year changes in morph fitnesses suggest that male interactions drive a dynamic 'rock–paper–scissors' game7.

Biodiversity is essential to the viability of ecological systems. Species diversity in ecosystems is promoted by cyclic, non-hierarchical interactions among competing populations. Such non-transitive relations lead to an evolution with central features represented by the `rock-paper-scissors' game, where rock crushes scissors, scissors cut paper, and paper wraps rock. In combination with spatial dispersal of static populations, this type of competition results in the stable coexistence of all species and the long-term maintenance of biodiversity. However, population mobility is a central feature of real ecosystems: animals migrate, bacteria run and tumble. Here, we observe a critical influence of mobility on species diversity. When mobility exceeds a certain value, biodiversity is jeopardized and lost. In contrast, below this critical threshold all subpopulations coexist and an entanglement of travelling spiral waves forms in the course of temporal evolution. We establish that this phenomenon is robust, it does not depend on the details of cyclic competition or spatial environment. These findings have important implications for maintenance and evolution of ecological systems and are relevant for the formation and propagation of patterns in excitable media, such as chemical kinetics or epidemic outbreaks., Comment: Final submitted version; the printed version can be found at http://dx.doi.org/10.1038/nature06095 Supplementary movies are available at http://www.theorie.physik.uni-muenchen.de/lsfrey/images_content/movie1.AVI and http://www.theorie.physik.uni-muenchen.de/lsfrey/images_content/movie2.AVI

Colicins are narrow-spectrum antibiotics produced by and active against Escherichia coli and its close relatives. Colicin-producing strains cannot coexist with sensitive or resistant strains in a well-mixed culture, yet all three phenotypes are recovered in natural populations. Recent in vitro results conclude that strain diversity can be promoted by colicin production in a spatially structured, non-transitive interaction, as in the classic non-transitive model rock-paper-scissors (RPS). In the colicin version of the RPS model, strains that produce colicins (C) kill sensitive (S) strains, which outcompete resistant (R) strains, which outcompete C strains. Pairwise in vitro competitions between these three strains are resolved in a predictable order (C beats S, S beats R, and R beats C), but the complete system of three strains presents the opportunity for dynamic equilibrium. Here we provide conclusive evidence of an in vivo antagonistic role for colicins and show that colicins (and potentially other bacteriocins) may promote, rather than eliminate, microbial diversity in the environment.

Authors, institutions and editors did not act on findings of inquiry into organ harvesting.

RECENTLY, several workers1 have tried to fractionate gamma-globulins and immune sera by electrophoresis. Such experiments have only given the mean properties of all gamma-globulin proteins, since non-antibody as well as antibody proteins occur in immune sera. We have now carried out paper electrophoresis of a purified specific antibody.

IT has been shown by paper electrophoresis that xanthine dehydrogenase activity is bound to the globulin fractions of rat serum1. Using differential centrifugation, it was demonstrated that xanthine oxidase and xanthine dehydrogenase activities are present in the supernatant fluid corresponding to the ‘cell sap’ containing the soluble proteins of the rat liver2.

WE have studied a strain of Chaetomium globosum which was cultured on the basal medium of Buston and Basu1 (NaNO3, 2 gm.; KH2PO4, 1 gm.; KCl, 0.5 gm.; MgSO4.7H2O, 0.5 gm. ; FeSO4, 0.01 gm., in 1,000 ml. water) with the addition of 5 per cent sucrose and 2 per cent yeast extract. 50-ml. portions contained in 500-ml. flasks were inoculated with 1 ml. of a spore suspension and incubated at 25°. Samples were withdrawn aseptically from the culture flasks at intervals and spotted on a paper chromatogram2 and developed with n-butanol – water for 56 hr.

ON electropapergrams, the alpha-2-globulin protein peak has been shown to coincide exactly with the locus of maximum non-specific alkaline phosphatase activity1. This enzyme may be detected during the run by an adaptation of the Huggins and Talalay sodium phenolphthalein phosphate method, which determines alkaline phosphatase by ascertaining the colour due to free phenolphthalein produced at pH. 9.2 by incubating a serum sample with the colourless substrate (a blank correction is made for non-enzymatic substrate hydrolysis). Because of its broad optimum pH range, alkaline phosphatase has considerable activity at pH. 8.6, which is most often used for paper electrophoresis, and a significant proportion of free phenolphthalein is coloured at this pH. To detect alkaline phosphatase during paper electrophoresis, 0.1–1.0 per cent of sodium phenolphthalein phosphate is included in the buffer; the region of enzymatic activity is seen as a well-localized red band. At pH 9.2 the band is considerably more impressive in colour.

SEEGERS et al. 1 have very recently made an analysis on the amino-acid content, particularly tyrosine and tryptophan, of purified prothrombin. They have also shown by electrophoresis that their prothrombin preparation contains approximately 90 per cent of the protein in one component1. Several other workers2–4 have investigated the nature of the protein in prothrombin. Astrup and Darling4 have reported prothrombin to be a protein of globulin character. But the complete analysis of the prothrombin molecule with respect to different amino-acid contents is lacking.

THE monosaccharide composition of isolated cell walls of strain 7–11–05 of Chlorella pyrenoidosa Chick, an organism proposed for life-support systems in space travel, was examined. The two principal methods used were thin-layer chromatography and paper chromatography, accompanied by appropriate staining.

THE task of testing and localizing enzymes in a protein mixture subjected to paper electrophoresis is a tedious one. This is particularly true in a fractionation study where the number of tests may be numerous. During the course of such an investigation of the various carbohydrases in an Aspergillus niger fermentation, it became necessary to employ a rapid qualitative test for the detection of these enzymes. Keilin and Hartree1 have reported that glucose oxidase (notatin) can be successfully used for the quantitative assay of various carbohydrases. Monod and Torriani2 employed notatin to determine glucose in their studies of amylomaltase. Recently, Whistler et al. 3 showed that D-glucose in corn syrups can also be quantitatively estimated by using notatin. The latter enzyme oxidizes glucose to yield two products—gluconic acid and hydrogen peroxide.

THE study of animal haemoglobin types is developing rapidly and the results obtained in various species have recently been summarized by Huisman, van der Helm, Visser and van Vliet1. However, the electrophoretic mobility of hippopotamus haemoglobin does not seem to have been studied before, possibly because of scarcity of materials. We have had the opportunity to examine haemoglobin samples from the East African hippopotamus, Hippopotamus amphibius L.2, obtained during a controlled reduction in a hippopotamus population.

PAPER-PARTITION chromatography of tissues of genetically known strains of Drosophila melanogaster as well as those of certain plants has shown that each strain gives a constant and distinctive pattern. The chromatographic patterns of heterozygotes carrying recessive genes can be easily distinguished from those of either parental homozygous strain, even though the phenotype of the heterozygote is indistinguishable from that of the homozygous dominant. This is the case for: (a) the fluorescent patterns observed under ultra-violet light in the chromatograms of adult Drosophila melanogaster heterozygous for the following mutants: bent, eyeless2, short-vein, spineless-aristapedia, vestigial; (b) the ultra-violet-fluorescent and the ninhydrin-positive patterns of root-tip smears of heterozygotes for the mutant male-sterile2 in tomato1; (c) the ultra-violet-fluorescent and the ninhydrin-positive patterns of root-tip smears and leaf extracts of heterozygotes for the yellow-green mutant of musk melon2 (see also chromatogram).

ELECTROPHORETIC fractionation of pancreatic juice components in a dog has been described in the literature1–4. Some of the authors2,3 isolated part of the fractions and studied their enzymatic activities. All authors used the free electrophoresis method with the exception of Delcourt and Delcourt4, who employed paper electrophoresis for the separation of the different fractions.

THE use of 'Gammexane' has been recommended for controlling insect pests in libraries and record offices, where insect infestation is a serious problem especially in a tropical climate. 'Gammexane' smoke generators appeared to be particularly suitable for this purpose owing to the ease and safety with which they can be handled. But no information about its effect on paper1 was available, and the use of a new insecticide for the disinfestation of documents of a unique and irreplaceable nature had therefore to be scrutinized from the preservation point of view.

XANTHINE dehydrogenase from Drosophila melanogaster is of particular interest since mutants at two separate loci lack this enzyme1 while a mutant at a third locus produces about 25 per cent of normal activity2. In an effort to detect strains of flies with genetically altered forms of xanthine dehydrogenase we devised a technique involving paper-strip electrophoresis in which this enzyme is located after electrophoresis by spraying the strip with the enzyme's substrates, incubating it at 25° C, and then using paper chromatography to separate the fluorescent product from the substrate which also fluoresces. This technique is very simple, and has potential application to other enzymes. Paper electrophoresis of xanthine dehydrogenase in rat serum has previously been reported using the technique of elution and direct assay3,4.

WE have already described a fortuitous combination of events which led to the discovery that American newspapers and other paper products contain a potent analogue of the juvenile hormone of the European bug, Pyrrhocoris apterus L. (Heteroptera ; Pyrrhocoridae)1. When reared in contact with ‘active paper’ or when exposed to surfaces impregnated with extracts of the ‘paper factor’ (PF), fifth-stage Pyrrhocoris larvae undergo one or more supernumerary larval moults and finally die without completing metamorphosis or attaining sexual maturity. This same result is observed when 1 µg of partially purified PF is topically applied to young fifth instar larvae1,2.

IN the first report1,2, on ‘crossing paper electrophoresis’, a direct demonstration of enzyme-substrate complex has been described. The enzymes tested included crystallized pure trypsin, chymotrypsin and ribonuclease.

IN several recent publications, separation of the alkaloids of the South American Strychnos into a great number of constituents by paper chromatography has been recorded1,2. The most successful solvents for two-dimensional analysis yield, however, almost the same sequence of spots. Thus it was considered desirable to find methods of separation which gave sequences different from those obtained by partition chromatography.

IN a communication under the above title, Giri1 describes the use of a starch agar gel for the location of amylases on the paper chromatogram. The technique seems to be essentially the same as that used in this Department, and previously described in Nature2.