Population dynamics: limits of predictability

Problems pertaining to the complex character of ecological system dynamics are discussed. Examples of the complex dynamics of plankton populations in a heterogeneous environment and agricultural ecosystems under invasion of pests resistant to Bt toxins produced by genetically modified insecticidal crops are given.     

Rigidity,Secondary Structure,and the Universality of the Boson Peak in Proteins

Complementary neutron- and light-scattering results on nine proteins and amino acids reveal the role of rigidity and secondary structure in determining the time- and lengthscales of low-frequency collective vibrational dynamics in proteins. These dynamics manifest in a spectral feature, known as the boson peak (BP), which is common to all disordered materials. We demonstrate that BP position scales systematically with structural motifs, reflecting local rigidity: disordered proteins appear softer than α-helical proteins; which are softer than β-sheet proteins. Our analysis also reveals a universal spectral shape of the BP in proteins and amino acid mixtures; superimposable on the shape observed in typical glasses. Uniformity in the underlying physical mechanism, independent of the specific chemical composition, connects the BP vibrations to nanometer-scale heterogeneities, providing an experimental benchmark for coarse-grained simulations, structure/rigidity relationships, and engineering of proteins for novel applications.     

Rigidity,Secondary Structure,and the Universality of the Boson Peak in Proteins

Complementary neutron- and light-scattering results on nine proteins and amino acids reveal the role of rigidity and secondary structure in determining the time- and lengthscales of low-frequency collective vibrational dynamics in proteins. These dynamics manifest in a spectral feature, known as the boson peak (BP), which is common to all disordered materials. We demonstrate that BP position scales systematically with structural motifs, reflecting local rigidity: disordered proteins appear softer than α-helical proteins; which are softer than β-sheet proteins. Our analysis also reveals a universal spectral shape of the BP in proteins and amino acid mixtures; superimposable on the shape observed in typical glasses. Uniformity in the underlying physical mechanism, independent of the specific chemical composition, connects the BP vibrations to nanometer-scale heterogeneities, providing an experimental benchmark for coarse-grained simulations, structure/rigidity relationships, and engineering of proteins for novel applications.     

Universality and structure of the N-end rule

Our previous work has shown that, in the yeast Saccharomyces cerevisiae, any of the eight stabilizing amino-terminal residues confers a long (greater than 20 h) half-life on a test protein beta-galactosidase (beta gal), whereas 12 destabilizing amino-terminal residues confer on beta gal half-lives from less than 3 min to 30 min. We now show that an analogous single-residue code (the N-end rule) operates in an in vitro system derived from mammalian reticulocytes. We also show that the N-end rule has a hierarchical structure. Specifically, amino-terminal Glu and Asp (and also Cys in reticulocytes) are secondary destabilizing residues in that they are destabilizing through their ability to be conjugated to primary destabilizing residues such as Arg. Amino-terminal Gln and Asn are tertiary destabilizing residues in that they are destabilizing through their ability to be converted, via selective deamidation, into secondary destabilizing residues Glu and Asp. Furthermore, in reticulocytes, distinct types of the N-end-recognizing activity are shown to be specific for three classes of primary destabilizing residues: basic (Arg, Lys, His), bulky hydrophobic (Phe, Leu, Trp, Tyr), and small uncharged (Ala, Ser, Thr). Features of the N-end rule in reticulocytes suggest that the exact form of the N-end rule may depend on the cell's physiological state, thereby providing a mechanism for selective destruction of preexisting proteins upon cell differentiation.     

Cerebellum,temporal predictability and the updating of a mental model

We live in a dynamic and changing environment, which necessitates that we adapt to and efficiently respond to changes of stimulus form (‘what’) and stimulus occurrence (‘when’). Consequently, behaviour is optimal when we can anticipate both the ‘what’ and ‘when’ dimensions of a stimulus. For example, to perceive a temporally expected stimulus, a listener needs to establish a fairly precise internal representation of its external temporal structure, a function ascribed to classical sensorimotor areas such as the cerebellum. Here we investigated how patients with cerebellar lesions and healthy matched controls exploit temporal regularity during auditory deviance processing. We expected modulations of the N2b and P3b components of the event-related potential in response to deviant tones, and also a stronger P3b response when deviant tones are embedded in temporally regular compared to irregular tone sequences. We further tested to what degree structural damage to the cerebellar temporal processing system affects the N2b and P3b responses associated with voluntary attention to change detection and the predictive adaptation of a mental model of the environment, respectively. Results revealed that healthy controls and cerebellar patients display an increased N2b response to deviant tones independent of temporal context. However, while healthy controls showed the expected enhanced P3b response to deviant tones in temporally regular sequences, the P3b response in cerebellar patients was significantly smaller in these sequences. The current data provide evidence that structural damage to the cerebellum affects the predictive adaptation to the temporal structure of events and the updating of a mental model of the environment under voluntary attention.     

Record performances at the Boston Marathon: Biometeorological factors

Air temperature and relative humidity have long been suspected of affecting the performance of marathon runners. Though these factors are important in their extremes, we show that other factors are even more indicative of race performances. Performances of the top 3 finishers in the last 30 Boston Marathons were correlated with hourly meteorological data for each race day. These 90 individual performances were classified as: record breaking performances (31), average performances (35), and unusually slow performances (24). The factors that help predict record breaking and unusually slow performances are: (i) wet bulb temperature, (ii) percent sky cover, and (iii) presence or absence of a light precipitation. Record breaking performances are characterized by a wet bulb temperature of <7.8°C, and 100% sky cover. A light drizzle is also conducive to better performances. On the other hand, unusually low performances are accompanied by a wet bulb temperature of >7.8°C, and a sky cover of 50% or less. No light, precipitation was recorded on any of the unusually slow race days. A graphic analysis clearly shows these relationships to exist. In addition, a multiple regression analysis confirms the importance of these variables. The authors advise that these are reliable predictors; however, when considering marathon races held in various geographical regions and differing climatic regimes, the exact numerical thresholds used here may not apply.     

Analytical methods for the determination of aflatoxins in various food matrices at concentrations regarding the limits set in european regulations: development, characteristics, limits

Methods for the determination of aflatoxins in paprika, peanut butter, pistachio paste, fig paste and baby food were developed. The methods employ an immunoaffinity cleanup step and reversed-phase liquid chromatography. All steps of the analysis were tested for their suitability for all matrices with focus on method robustness, simplicity, toxicology, environment, and user friendliness. Extraction procedures, chromatographic separation and post column derivatisation techniques were elaborated for this purpose. The methods were statistically validated in collaborative trials at currently established legal limits for aflatoxins and are in the process for adoption as official methods by CEN and AOAC.     

Hawks, doves, and mixed-symmetry games

The hawk-dove game has proved to be an important tool for understanding the role of aggression in social interactions. Here, the game is presented in a more general form (GHD) to facilitate analyses of interactions between individuals that may differ in "size", where size is interpreted as a surrogate for resource holding power. Three different situations are considered, based on the availability and use of information that interacting individuals have about their sizes: the classical symmetric case, in which no information about sizes is used, the asymmetric case, in which the individuals know their relative sizes and thus their chances of prevailing in combat, and a mixed-symmetry case, in which each individual only knows its own size (or only knows its opponent's size). I describe and use some recently developed methods for multitype games-evolutionary games involving two or more categories of players. With these methods and others, the evolutionarily stable strategies (ESSs) that emerge for the three different cases are identified and compared. A proof of the form and uniqueness of the ESS for the mixed-symmetry case is presented. In this situation, one size category at most can play a mixed strategy; larger individuals are aggressive and smaller individuals are not. As the number of size categories approaches infinity and the size distribution becomes continuous, there is a threshold size, above which all individuals are aggressive, and below which they are not.     

The auxiliary substrate concept — an approach for overcoming limits of microbial performances

In biotechnological processes, fundamental performances of microorganisms are used. The economy of these processes is essentially determined by the efficiency, velocity (productivity) and quality of the products. Therefore it is a permanent task and challenge for basic and biotechnological research to seek out measures for improving the actually attained parameters. The auxiliary substrate concept supplics an approach. It is based on the fact that chemo-organo-heterotrophic substrates differ in the carbon: energy ratio, thus, growth yield is limited in energy and/or reducing power. It says that, by simultaneous utilization of physiologically similar substrates (mixed substrates), the growth yield increases. The substrates are to combine in such a way that with their simultaneous utilization a minimum of carbon is dissimilated merely for the purpose of the generation of biologically useful energy and/or reducing power. Since all chemo-organo-heterotrophic substrates are more or less energy-deficient, an increase in growth efficiency can be expected if the individual substrates of the mixture are assimilated more efficiently than the respective substrates alone. This may result, for instance, from an immediate assimilation of a substrate (according to the “manner of finished part construction”). An increased growth rate is rather the rule than the exception in mixed substrate utilization. In product syntheses the substrates are, depending on the concrete product and metabolic pathway, either energy-excess or energy-excess or energy-deficient. or, in other words, the processes are energy-generating or energy-consuming, respectively. If this is responsible for discrepancies between the possible yields determined by the carbon metabolism and the experimentally obtained yields, the discrepancies should be able to be decreased and the yields increased by mixing substrates. The substrates are to choose and combine so that, due to simultaneous utilization, the product formation process becomes energy neutral. As a rule, the enhanced efficiency is accompanied by an increased velocity. This does not only apply to syntheses, but also to degradation (and detoxification) reactions. Even supposedly inert compounds or persistent substances can be activated by simultaneous (co-)metabolization of another (an auxiliary substrate, victim substrate or co-substrate) and converted at a considerable rate. It is of interest for syntheses of products but in particular for degradation and decontamination of harmful and waste products in the environment that the residual concentrations of the substrates are smaller than those achieved if the compounds of a mixture are metabolized separately. The auxiliary substrate concept has proven to be fruitful, both for theoretical and practical questions. It was practically already being used before it was formulated (mixed substrate utilization, cometabolism). However, an abundance of regulatory and energetic aspects are waiting to be investigated in more detail.     

Automata,repeated games and noise

We consider two-state automata playing repeatedly the Prisoner's Dilemma (or any other 2 × 2-game). The 16 × 16-payoff matrix is computed for the limiting case of a vanishingly small noise term affecting the interaction. Some results concerning the evolution of populations of automata under the action of selection are obtained. The special role of win-stay, lose-shift-strategies is examined.     

Spatial predictability and resource specialization of bees (Hymenoptera: Apoidea) at a superabundant, widespread resource

For reciprocal specialization (coevolution) to occur among floral visitors and their host plants the interactions must be temporally and spatially persistent. However, studies repeatedly have shown that species composition and relative abundance of floral visitors vary dramatically at all spatial and temporal scales. We test the hypothesis that, on average, pollen specialist bee species occur more predictably at their floral hosts than pollen generalist bee species. Taxonomic floral specialization reaches its extreme among species of solitary, pollen-collecting bees, yet few studies have considered how pollen specialization by floral visitors influences their spatial constancy. We test this hypothesis using an unusually diverse bee guild that visits creosote bush (Larrea tridentatd), the most widespread, dominant plant of the warm deserts of North America. Twenty-two strict pollen specialist and 80 + generalist bee species visit Larrea for its floral resources. The sites we sampled were separated by 0.5 to > 1450 km, and spanned three distinct deserts and four vegetation zones. We found that species of Larrea pollen specialist bees occurred at more sites and tended to be more abundant than generalists. Surprisingly, spatial turnover was high for both pollen specialist and generalist bee species at all distances, and species composition of samples from sites 1–5 km apart varied as much as repeat samples made at single sites. Nevertheless, the pattern of bee species turnover was not haphazard. As distance among sites increased faunal similarity of sites decreased. Faunal similarities among sites within 250 km of each other were generally greater than if randomly distributed over all sites (the null model). No single ecological category of species (widespread, localized, Larrea pollen specialist, floral generalist) accounted for this spatial predictability. Evidently, concordant local distribution patterns of many ecologically diverse species contribute to the non-random spatial pattern. The ecological dominance of creosote bush does not confer obvious ecological advantages to its specialist floral visitors. Spatial turnover is comparable to that found for bee guilds from other biogeographic regions of the world and is not therefore limited to those bee species that inhabit highly seasonal climates, such as deserts. Philopatry and differences in bloom predictability among sites are probably more important causes for spatial turnover of bee species than are interspecific competition for nest sites or floral resources.