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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 131 (1999), S. 57-64 
    ISSN: 1436-5073
    Keywords: Key words: dye-encapsulating liposomes; pH sensing; oxygen sensing; optochemical nanosensors.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  This paper describes the optochemical pH and oxygen sensing properties of dye-encapsulating and fluorescently labeled nano-sized unilamellar liposomes. To prepare the oxygen sensitive liposomes a lipid mixture consisting of dimyristoylphospatidylcholine, cholesterol, and dihexadecyl phosphate (molar ratio 5:4:1) all dissolved in dry isopropyl alcohol is injected into a sensing dye solution. The mixture is then sonicated with a liposome maker to form dye-encapsulating liposomes. A lipid mixture consisting of dimyristoylphospatidylcholine, N-(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (fluorescein DHPE), cholesterol, and dihexadecyl phosphate (molar ratio 20:1:16:4) is used to prepare the pH sensitive liposomes by the same sonication technique. Fluorescein labeled DHPE phospholipids are combined with DMPC phospholipids in a 1:20 ratio to incorporate the sensing dye directly into the bilayer membrane, virtually eliminating any instability due to dye leakage. Oxygen sensing liposomes are created by encapsulating the oxygen sensitive ruthenium tris(1,10)-phenanthroline complex [Ru(phen)3]. The dye is believed to exist both in free solution within the liposome, and as an adherent on the inner membrane of the liposome. High uniformity of the liposomes is realized by extruding them back and forth through a 100 nm pore-size polycarbonate membrane. TEM images of the liposomes, stained with uranyl acetate, show that the liposomes are unilamellar, spherical in shape, maintain high structural integrity, and average 70 nm in diameter. The liposomes show high stability with respect to dye leaking at room temperature for 8 days, and high photostability when exposed to the excitation light. Individual liposomes are used to monitor the pH and oxygen level in their vicinity during the enzymatic oxidation of glucose by the enzyme glucose oxidase. The newly prepared environmentally sensitive liposomes can be applied for non-invasive pH and oxygen determination in tissues and single biological cells.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Behavioral ecology and sociobiology 19 (1986), S. 313-322 
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Optimal foraging theory was first looked upon as a tool to study the evolution of niches in community ecology. Isoleg theory is being developed to reestablish it as such a tool. Isoleg theories are maps of isolegs in a graph whose axes are population densities. There are two kinds of isolegs: some are lines of equal optimal behavior in the graph; others mark threshold combinations of densities past which sudden shifts in behavior should occur. A technique for determining whether isolegs exist is described and applied to hummingbird data. These data were collected experimentally in the field expressly to test one isoleg model. All three species of hummingbird exhibited at least one of the sudden-shift type of isoleg. Their behaviors map onto the density graph in the predicted portions of the graph with only one exception. The data also support the prediction that behavior in the field is disjunct, i.e. subject to substantial, abrupt, discontinuous changes produced by very small continuous changes in a control variable. Some evidence for continuous control was also found, but it is ambiguous. Theory predicts that the two forms of control should be found together in some optimal systems.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 1 (1987), S. 1-3 
    ISSN: 1573-8477
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-8477
    Keywords: Lag load ; Red Queen ; ESS ; coevolution ; evolutionary rate ; predator coevolution ; competitor coevolution ; stasis ; punctuated equilibrium ; evolutionary constraints ; White Queen's Constraint ; Alice's Constraint ; bauplan ; fitness-generating function ; versatility ; guilds ; adaptive zones ; constraint surface ; genostasis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Red Queen principle states that a set of interacting species reaches an evolutionary equilibrium at which all their rates of coevolution exactly balance each other. The lag-load model, which is one way of searching for Red Queens, has, by itself, previously predicted that they do not exist. But this model has assumed that infinite maladaptedness is possible. The lag-load model is improved by assuming that once the lag load of all but one species is determined, so is that of the final species. This assumption eliminates the possibility of infinite maladaptedness. Its result is to allow the lag-load model to yield Red Queen coevolution. It does this whether or not speciation and extinction rates are included. Thus the lag-load model is harmonized with the earlier Red Queen model derived from studies of predation. Because of the intercorrelation of phenotypic traits, the predatory model concluded that the eventual stable rate of coevolution must be zero (except for intermittent bursts after some correlation or compromise is successfully broken). Another model that predicts stable coevolutionary rates of zero is that of evolutionarily stable strategies (ESS). Red Queen assumes that the more extreme a phenotypic trait is, the better it is, and that there are no constraints on the growth of such a phenotypic trait value. Such traits are the key to the Red Queen prediction of progressive coevolution. ESS models make no such assumptions. Eliminating unbounded traits from the model of predator-victim evolution changed its prediction from progressive coevolution to stasis. Before this paper, no model had dealt simultaneously with both unbounded and constrained traits. To handle both sorts of phenotypic traits at the same time in the same model, we abandoned lag load as a measure of evolutionary rate (lag loads do not uniquely determine phenotype). Instead, we used the traditional assumption that rate is proportional to the slope of the adaptive landscape. A model, relying on continuous evolutionary game theory, was developed and simulated under various conditions in two or three species sets, with up to five independent traits coevolving simultaneously. The results were: (1) there was always a set of equilibrium densities eventually achieved by coevolution; if the population interaction represented by this stable coevolutionary state is also stable, then the system should persist whether it evolves further or not; (2) whenever traits were present which were unbounded and best at their most extreme values, then a Red Queen emerged; (3) whenever traits were present which were correlated with each other or constrained below infinity, then an ESS emerged; (4) if both types were present, both results occurred: Red Queen in the unbounded traits and ESS in the constrained ones. Because unbounded traits may not exist, the Red Queen may have no domain. But the domain of ESS is real. ESS should lead to the evolutionary pattern called punctuated equilibrium. The changes in design rules which punctuate stasis should lead to an ever-expanding independence of traits from each other, i.e. to more and more refined differentiation. A single set of design rules which governs a set of species is called a fitness-generating function. Such functions may help to define the concepts of adaptive zone and ecological guild.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 4 (1990), S. 276-276 
    ISSN: 1573-8477
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 1 (1987), S. 401-407 
    ISSN: 1573-8477
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 1 (1987), S. 315-330 
    ISSN: 1573-8477
    Keywords: Coevolution ; density-dependent fitnesses ; fitness sets ; habitat selection ; isolegs ; specialization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Question: What are the conditions required for natural selection to produce phenotypes specially adapted to the various habitats available in nature? Model: Assume there are two habitat types and one or two phenotypes of the same or different species. The phenotypes do not recognize any spatial differences among patches of the same habitat type. Possible evolutionary winners can do better in one habitat only by relinquishing some ability in the other. Results: If only one phenotype is present, it will be an intermediate (unless one of the two habitat types is so rare and unproductive that its effects can be ignored by natural selection). Even if two phenotypes are introduced, natural selection should generally restore monomorphism if habitat selection is not ever favored (e.g. if search costs are high). But if search costs and environmental variation are zero, dimorphism can be expected. And if they are small, then although monomorphism is stable, its basin of attraction is small, and invasion by a second form (such as a sibling species) can provide the discontinuous jump needed to put the system in the other basin of attraction. Once there, dimorphic extremism coevolves. Each successful morph is as specialized as possible on one of the habitats. Competition between the morphs is eliminated. Environmental variation may constrict the basin, but once a point is captured by it, the system approaches dimorphic extremism anyway. In general, whatever promotes the behavior of habitat selection also promotes the evolution of extreme morphologies and physiologies.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 1 (1987), S. 409-409 
    ISSN: 1573-8477
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 5 (1991), S. 219-219 
    ISSN: 1573-8477
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-8477
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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