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PubMed2000

Competition and the Effect of Spatial Resource Heterogeneity on Evolutionary Diversification.

A model is presented to explore how the form of selection arising from competition for resources is affected by spatial resource heterogeneity. The model consists of a single species occupying two patches connected by migration, where the two patches can differ in the type of resources that they contain. The main goal is to determine the conditions under which competition for resources results in disruptive selection (i.e., selection favoring a polymorphism) since it is this form of selection that will give rise to the evolutionary diversification of resource exploitation strategies. In particular, comparing the conditions giving rise to disruptive selection when the two patches are identical to the conditions when they contain different resources reveals the effect of spatial resource heterogeneity. Results show that when the patches are identical, the conditions giving rise to disruptive selection are identical to those that give rise to character displacement in previous models. When the patches are different, the conditions giving rise to disruptive selection can be either more or less stringent depending upon demographic parameters such as the intrinsic rate of increase and the migration rate. Surprisingly, spatial resource heterogeneity can actually make forms of evolutionary diversification such as character displacement less likely. It is also found that results are dependent on how the resource exploitation strategies and the spatial resource heterogeneity affect the population dynamics. One robust conclusion however, is that spatial resource heterogeneity always has a disruptive effect when the migration rate between patches is low.

Lotka‐Volterra↗
PubMed2004

Resource partitioning through oceanic segregation of foraging juvenile southern elephant seals ( Mirounga leonina).

In highly dynamic and unpredictable environments such as the Southern Ocean, species that have evolved behaviors that reduce the effects of intra-specific competition may have a selective advantage. This is particularly true when juveniles face disadvantages when foraging due to morphological or physiological limitation, which is the case for many marine mammals. We tracked the at-sea movements of 48 juvenile southern elephant seals ( Mirounga leonina) between the ages of 1 and 4 years from the population at Macquarie Island using locations derived from recorded light levels. There were significant differences in the total amount of the Southern Ocean covered by the different age-groups. The younger seals used a smaller area than the older seals. On average, the younger individuals also made more trips to sea than the older seals and did not travel as far on each trip. Females spent more time at sea than males and there were no significant differences between the total areas used by male and females. In summary, younger seals remained closer to the island at all times, and they spent more time in more northerly regions that older seals. These differences in behavior created temporal and spatial segregation between juveniles of different ages. Therefore, we suggest that these temporal and spatial separations help to avoid intra-specific competition for resources on land, space on beaches, and at-sea foraging areas. Such modifications of haul-out timing and behavior enable them to exploit a patchy and unpredictable environment.

Age Factors↗
PubMed1997

Characterization of cellulase complex of Streptomyces albaduncus.

Exoglucanase and endoglucanase (glucanases) enzymes of S. albaduncus were found to be very stable, showing only 36% and 8% loss in activities respectively after 3 days of incubation at 50 degrees C. In contrast, beta-glucosidase was significantly less stable retaining only 22.30% activity after 30 min incubation at 40 degrees C. The glucanases manifested maximum stability in pH range of 5.5-6.0 whereas beta-glucosidase was completely stable over a broad pH range of 6.5-9.0. Both glucanases were enhanced by some cations whereas beta-glucosidase did not require any cation for activity. K(m) values for crude exoglucanase, endoglucanase and beta-glucosidase were 40.00 mg/ml, 92.30 mg/ml and 1.714 mM with maximum reaction velocities (Vmax) of 0.606, 33.330 and 0.109 IU/mg of protein, respectively. The enzymes were subject to end-product inhibition, with exo- and endo-glucanases decreasing by 20% and 70% respectively, in the presence of 0.3% glucose. However, beta-glucosidase showed marked resistance to glucose inhibition, retaining 59% of residual activity even in the presence of 30% glucose in the reaction mixture. This characteristic may be advantageous in the commercial exploitation of enzyme system. An activation of beta-glucosidase at lower concentrations of glucose suggests competitive inhibition.

Cations↗
PubMed2004

Recent advances in gene structure prediction.

De novo gene predictors are programs that predict the exon-intron structures of genes using the sequences of one or more genomes as their only input. In the past two years, dual-genome de novo predictors, which exploit local rates and patterns of mutation inferred from alignments between two genomes, have led to significant improvements in accuracy. Systems that exploit more than two genomes simultaneously have only recently begun to appear and are not yet competitive on practical tasks, but offer the greatest hope for near-term improvements. Dual-genome de novo prediction for compact eukaryotic genomes such as those of Arabidopsis thaliana and Caenorhabditis elegans is already quite accurate. Although mammalian gene prediction lags behind in accuracy, it is yielding ever more useful results. Coupled with significant improvements in pseudogene detection methods, which have eliminated many false positives, we have reached the point where de novo gene predictions are being used as hypotheses to drive experimental annotation via systematic RT-PCR and sequencing.

Animals↗
PubMedDate not supplied

Cross-linking exogenous bifunctional peptides into fibrin gels with factor XIIIa.

Bi-domain peptides with a factor XIIIa substrate in one domain and a bioactive peptide in another domain were covalently incorporated into fibrin gels during coagulation through the action of the transglutaminase factor XIIIa. The cross-linking characteristics were determined for two bi-domain peptides with factor XIIIa substrates based on fibrinogen, dYRGDTIGEGQQHHLGG-NH2, and dLRGDGAKDV-NH2, as well as one bi-domain peptide with a substrate sequence based on alpha2-plasmin inhibitor, dLNQEQVSPLRGD-NH2, and another with a nonbiological, oligolysine substrate, dLRGDKKKKG-NH2 (substrate domains in italic). Each of these peptides was able to cross-link into the fibrin gels during coagulation, with the peptide containing the factor XIIIa substrate based on alpha2-plasmin inhibitor being incorporated at levels in excess of 8 mol/mol fibrinogen. The structural characteristics of these peptide-modified gels proved to be the same as those for a native fibrin gel. The bioactivity of the incorporated active factors was tested in a neuronal culture model with day 8 chicken dorsal root ganglia using two bioactive sequences, RGD and DGEA, and one inactive control sequence, RDG. Each of these peptides influenced the extension of neurites from the ganglia as expected, indicating that the incorporated factors retained their activity. With the use of soluble competitive inhibitors, it was shown that this effect was due to the covalently incorporated peptides. Through exploiting the role of factor XIIIa in coagulation, we have developed a method by which to impart the character of nonfibrin proteins, such as extracellular matrix proteins, to fibrin, a biological material with many potential therapeutic and academic applications.

Amino Acid Sequence↗
PubMed1996

Affinity of fatty acid for (r)rat intestinal fatty acid binding protein:further examination.

The enhancement of the fluorescence quantum yield of 1,8-anilinonaphthalenesulfonic acid (ANS) upon binding to intestinal fatty acid protein (I-FABP) was exploited to devise an assay for free I-FABP. With this assay, we monitored the competition for free I-FABP between ANS and fatty acids and thereby extracted values for the dissociation constants (K(FA)) of fatty acids for I-FABP. We obtained these constants for the I-FABP ligands oleic acid, arachidonic acid, and palmitic acid. In addition, we measured the dependence of K(FA) for oleic acid upon temperature and at two pH values. From these data, we calculate the van't Hoff enthalpy of oleic acid binding. This enthalpy is compared with the enthalpies of binding obtained directly from titration calorimetry. Our experiments with the fluorescence-based assay generate values of K(FA) which disagree with older values obtained from calorimetry and other methods. Our own calorimetric data were analyzed with a view to improving the technique involved in subtraction of a "reference" dilution of the ligand into solution in the absence of the protein. By this maneuver, we obtained "corrected" titrations which could be fitted to values of K(FA) more in agreement with the values we determined via the fluorescence-based assay than wer the older literature values. Our new values for K(FA) also agree substantially with values derived using a complementary assay technique, one measuring the concentration of free fatty acid, that has recently been developed by Richiere et al [Richiere et al. (1995) J. Biol. Chem. 270, 15076-15084]. We compare the values of delta H degrees, delta S degrees, and delta C(p)degrees for fatty acid binding we have obtained in this work with those we found in earlier work with ANS binding to I-FABP [Kirk et al. (1996) Biophys. J. 70, 69-83]. Our interpretation of the origin of the thermodynamic changes for ANS binding in our earlier work is here substantiated and extended to include an evaluation in physical terms of the interaction of I-FABP with fatty acids.

Anilino Naphthalenesulfonates↗
PubMed1989

Competitive inhibitors of Klebsiella aerogenes urease. Mechanisms of interaction with the nickel active site.

We examined several compounds for their mechanisms of inhibition with the nickel-containing active site of homogeneous Klebsiella aerogenes urease. Thiolate anions competitively inhibit urease and directly interact with the metallocenter, as shown by the pH dependence of inhibition and by UV-visible absorbance spectroscopic studies. Cysteamine, which possesses a cationic beta-amino group, exhibited a high affinity for urease (Ki = 5 microM), whereas thiolates containing anionic carboxyl groups were uniformly poor inhibitors. Phosphate monoanion competitively inhibits a protonated form of urease with a pKa of less than 5. Both the thiolate and phosphate inhibition results are consistent with charge repulsion by an anionic group in the urease active site. Acetohydroxamic acid (AHA) was shown to be a slow-binding competitive inhibitor of urease. This compound forms an initial E.AHA complex which then undergoes a slow transformation to yield an E.AHA* complex; the overall dissociation constant of AHA is 2.6 microM. Phenylphosphorodiamidate, also shown to be a slow-binding competitive inhibitor, possesses an overall dissociation constant of 94 pM. The tight binding of phenylphosphorodiamidate was exploited to demonstrate the presence of two active sites per enzyme molecule. Urease contains 4 mol of nickel/mol enzyme, hence there are two nickel ions/catalytic unit. Each of the two slow-binding inhibitors are proposed to form complexes in which the inhibitor bridges the two active site nickel ions. The inhibition results obtained for K. aerogenes urease are compared with inhibition studies of other ureases and are interpreted in terms of a model for catalysis proposed for the jack bean enzyme (Dixon, N.E., Riddles, P.W., Gazzola, C., Blakely, R.L., and Zerner, B. (1980) Can. J. Biochem. 58, 1335-1344).

Binding Sites↗
PubMed2006

Ecological opportunity and phenotypic plasticity interact to promote character displacement and species coexistence.

We investigated the roles of resource availability and phenotypic plasticity in promoting ecological character displacement (i.e., trait evolution stemming from resource competition between species). Because ecological character displacement generates new populations that differ in resource use, this process should only occur when exploitable resources are available. We tested this hypothesis in two species of spadefoot toads (Spea bombifrons and S. multiplicata) whose tadpoles use phenotypic plasticity to develop into either an omnivore morph, which specializes on detritus, or a physically distinctive carnivore morph, which specializes on shrimp. Both species grow best on shrimp, but when reared together, S. bombifrons outcompetes S. multiplicata for shrimp and S. multiplicata outcompetes S. bombifrons for detritus. We found that when each species occurred alone in the field, they produced similar proportions of omnivores and carnivores. When the two species occurred together, however, they underwent ecological character displacement in larval development, with S. multiplicata producing mostly omnivores, and S. bombifrons producing mostly carnivores. We combined observations of natural populations with experiments to evaluate whether such character displacement was only possible when both shrimp and detritus were relatively abundant. Mixed-species ponds contained abundant detritus and shrimp, in contrast with nearby pure-species ponds, which were deficient in one resource. Experiments revealed that S. multiplicata competed poorly when detritus was rare and that S. bombifrons competed poorly when shrimp was rare. In nature, when one of these two resources was scarce, one species was missing, perhaps through competitive exclusion by the species that was the superior competitor for the remaining resource. Thus, ecological character displacement and, therefore, coexistence of close competitors, was only possible when diverse resources were available. Finally, even if exploitable resources are available, character displacement is not guaranteed to transpire if species cannot utilize such resources expeditiously. Phenotypic plasticity provides a general and important mechanism for facilitating resource partitioning. Thus, by facilitating shifts in resource use, phenotypic plasticity and ecological opportunity may often interact to promote divergence and coexistence of competitors.

Adaptation, Physiological↗
PubMed2006

Resource competition and social conflict in experimental populations of yeast.

Understanding the conditions that promote the maintenance of cooperation is a classic problem in evolutionary biology. The essence of this dilemma is captured by the 'tragedy of the commons': how can a group of individuals that exploit resources in a cooperative manner resist invasion by 'cheaters' who selfishly use common resources to maximize their individual reproduction at the expense of the group? Here, we investigate this conflict through experimental competitions between isogenic cheater and cooperator strains of yeast with alternative pathways of glucose metabolism, and by using mathematical models of microbial biochemistry. We show that both coexistence and competitive exclusion are possible outcomes of this conflict, depending on the spatial and temporal structure of the environment. Both of these outcomes are driven by trade-offs between the rate and efficiency of conversion of resources into offspring that are mediated by metabolic intermediates.

Biological Evolution↗
PubMed1996

Association of the anti-inflammatory activity of phosphodiesterase 4 (PDE4) inhibitors with either inhibition of PDE4 catalytic activity or competition for [3H]rolipram binding.

Phosphodiesterase 4 (PDE4) inhibitors are novel anti-inflammatory compounds. Unfortunately, the archetypal PDE4 inhibitor rolipram produces central nervous system and gastrointestinal side-effects. To exploit these agents, we need to identify PDE4 inhibitors that retain the anti-inflammatory activity with a reduced potential to elicit unwanted side-effects. PDE4 possesses both cyclic AMP catalytic activity that is inhibitable by rolipram and a high affinity binding site for rolipram. The function of this high affinity rolipram binding site is unclear; however, certain pharmacological effects of PDE4 inhibitors are associated with competition for this site. Since PDE4 inhibitors suppress both monocyte and neutrophil activation, the present experiments were carried out to establish a correlation between suppression of monocyte activation [tumor necrosis factor alpha (TNF alpha) formation] or suppression of neutrophil activation (degranulation) with inhibition of either PDE4 catalytic activity or [3H] rolipram binding. Suppression of TNF alpha formation demonstrated a strong correlation with inhibition of PDE4 catalytic activity (r=0.87; P<0.01; Spearman's Rho = 0.79, P<0.05), whereas there was no correlation with inhibition of [3H]rolipram binding(r=0.21, P>0.5; Spearman's Rho=0.16, P>0.5). Suppression of neutrophil degranulation was not associated with inhibition of PDE4 catalytic activity (r=0.25, P>0.4; Spearman's Rho=0.33, P>0.2), but was associated with inhibition of [3H]rolipram binding (r=0.68, P<0.05; Spearman's Rho=0.6, P=0.06). These results indicate that anti-inflammatory effects of PDE4 inhibitors can be associated with either inhibition of PDE4 catalytic activity or high affinity rolipram binding.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2000

Themes for mushroom exploitation in the 21st century: Sustainability, waste management, and conservation.

Because many natural resources are limited, sustainability becomes an important concept in maintaining the human population, health, and environment. Mushrooms are a group of saprotrophic fungi. Mushroom cultivation is a direct utilization of their ecological role in the bioconversion of solid wastes generated from industry and agriculture into edible biomass, which could also be regarded as a functional food or as a source of drugs and pharmaceuticals. To make the mushroom cultivation an environmentally friendly industry, the basic biology of mushrooms and the cultivation technology must be researched and developed. This is very true for Lentinula edodes, Volvariella volvacea, and Ganoderma lucidum, which are commonly consumed in Asian communities but are now gaining popularity worldwide. Besides the conventional method, strain improvement can also be exploited by protoplast fusion and transformation. Biodiversity is the key contribution to the genetic resource for breeding programs to fulfill different consumer demands. The conservation of these mushrooms becomes essential and is in immediate need not only because of the massive habitat loss as a result of human inhabitation and deforestation, but also because of the introduced competition by a cultivar with the wild germ plasm. Spent mushroom compost, a bulky solid waste generated from the mushroom industry, however, can be exploited as a soil fertilizer and as a prospective bioremediating agent.

Journal Article↗
PubMed1996

A neural model for generating and learning a rapid movement sequence.

In this article, a neural model for generating and learning a rapid ballistic movement sequence in two-dimensional (2D) space is presented and evaluated in the light of some considerations about handwriting generation. The model is based on a central nucleus (called a planning space) consisting of a fully connected grid of leaky integrators simulating neurons, and reading an input vector [symbol: see text] (t) which represents the external movement of the end effector. The movement sequencing results in a succession of motor strokes whose instantiation is controlled by the global activation of the planning space as defined by a competitive interaction between the neurons of the grid. Constraints such as spatial accuracy and movement time are exploited for the correct synchronization of the impulse commands. These commands are then fed into a neuromuscular synergy whose output is governed by a delta lognormal equation. Each movement sequence is memorized originally as a symbolic engram representing the sequence of the principal reference points of the 2D movement. These points, called virtual targets, correspond to the targets of each single rapid motor stroke composing the movement sequence. The task during the learning phase is to detect the engram corresponding to a new observed movement; the process is controlled by the dynamics of the neural grid.

Computer Simulation↗
PubMed2004

Extending the working range of immunoanalysis by exploitation of two monoclonal antibodies.

A newly established rat monoclonal antibody (mAb) for isoproturon, namely, IOC 10G7, is described. This mAb shows a standard curve for isoproturon in phosphate-buffered saline with a test midpoint of 5.5 +/- 1.8 microg/L (n = 15). In combination with the formerly developed mAb IOC 7E1, IOC 10G7 can be exploited to extend the working range for the analysis of isoproturon. Both antibodies were formatted into a competitive enzyme-linked immunosorbent assay (ELISA), using the same enzyme-tracer. MAb IOC 7E1 and mAb IOC 10G7 have different affinities for the target compound, but the signal-response curves of the single antibodies overlap. Cross-reactivity (CR) patterns of both antibodies are comparable, showing the highest CR for the metabolite 1-(4-isopropylphenyl)-3-methylurea (IOC 10G7, 9%; IOC 7E1, 19%). The system described here includes the combined, but individual, usage of both assays on one microtiter plate, as well as the strategy for mixing the two antibodies for the utilization in one assay. When standards are performed in Milli-Q water, the working range for isoproturon with the individual ELISAs using mAb IOC 7E1 is from 0.01 to 1 microg/L (test midpoint = 0.11 +/- 0.03 microg/L; n = 17) and with IOC 10G7, it is 1-100 microg/L (test midpoint = 10.3 +/- 1.6 microg/L; n = 32). The working range with mixed antibodies is usually on the order of 0.03-30 microg/L (test midpoint = 0.5 +/- 0.2 microg/L; n = 17). These strategies (mAbs individually and mixed) cover a range of 4 and 3 orders of magnitude, respectively. As a demonstration, water samples of different origins and an extract of mixed sediment were analyzed. The advantages of these strategies are discussed.

Animals↗
PubMed2002

Survival of, and competition between, oligodendrocytes expressing different alleles of the Plp gene.

Mutations in the X-linked Plp gene lead to dysmyelinating phenotypes and oligodendrocyte cell death. Here, we exploit the X inactivation phenomenon to show that a hierarchy exists in the influence of different mutant Plp alleles on oligodendrocyte survival. We used compound heterozygote mice to study the long-term fate of oligodendrocytes expressing either the jimpy or rumpshaker allele against a background of cells expressing a Plp-null allele. Although mutant and null oligodendrocytes were generated in equal numbers, the proportion expressing the mutant allele subsequently declined, but whereas those expressing the rumpshaker allele formed a reduced but stable population, the number of jimpy cells fell progressively. The age of decline in the jimpy cells in different regions of the CNS correlated with the temporal sequence of myelination. In compound heterozygotes expressing rumpshaker and jimpy alleles, oligodendrocytes expressing the former predominated and were more abundant than when the rumpshaker and null alleles were in competition. Thus, oligodendrocyte survival is not determined solely by cell intrinsic factors, such as the conformation of the misfolded PLP, but is influenced by neighboring cells, possibly competing for cell survival factors.

Alleles↗
PubMedDate not supplied

Market power and hospital pricing: are nonprofits different?

Dramatic changes in hospitals' operating environments are leading to major restructuring of hospital organizations. Hospital mergers and acquisitions are increasing each year, and conversions by hospitals to different forms of ownership also are continuing apace. Such changes require policymakers and regulators to develop and implement policies to ensure that consumers' interests are protected. An important consideration in this process is the impact on the price of hospital care following such transactions. This paper reviews empirical evidence that mergers that reduce competition will lead to price increases at both merging hospitals and their competitors, regardless of ownership status. We show that nonprofit and government hospitals have steadily become more willing to raise prices to exploit market power and discuss the implications for antitrust regulators and agencies that must approve nonprofit conversions.

Economic Competition↗
PubMed2004

Concepts in sperm heterogeneity, sperm selection and sperm competition as biological foundations for laboratory tests of semen quality.

Stringent selection mechanisms, in both internal and external fertilisation systems, reject all but a significant minority of the spermatozoa released at ejaculation. Sperm competition theory provides circumstantial evidence that the selection process involves mechanisms by which the quality of the fertilising spermatozoon is controlled, thereby ensuring that females and their offspring receive high quality genetic material. In this review we examine some of these selection processes to see whether they could be exploited for the improvement of laboratory tests of sperm quality. Such tests are not only required for clinical and agricultural purposes, but are increasingly needed in fields such as reproductive and environmental toxicology where the species requirement is much broader. Despite many years of research, sperm quality assessment methods continue to provide imprecise data about fertility; here we suggest that this may be a consequence of using tests that focus on the spermatozoa that would normally be unable to fertilise under natural conditions. To achieve fertilisation a spermatozoon must be capable of responding appropriately to external signalling stimuli; those involving protein kinase-regulated flagellar function seem especially influential in governing effects ranging from non-Mendelian inheritance in mammals to sperm chemotaxis in sea urchins. Examination of the elicited responses reveals considerable heterogeneity in all species. Here we propose that this level of heterogeneity is meaningful both in terms of understanding how spermatozoa from some individuals possess fertility advantages over spermatozoa from their rivals in sperm competition, and in that the heterogeneity should be exploitable in the development of more accurate laboratory tests.

Animals↗