An Ecological Study of the Prairie and Sedge Meadow Communities of Richardson Wildlife Foundation

ID: 8259; Issue date not indicated on report.INHS Technical Report prepared for Terry Moyer, Richardson Wildlife Foundatio

The impact of population size on the evolution of asexual microbes on smooth versus rugged fitness landscapes

<p>Abstract</p> <p>Background</p> <p>It is commonly thought that large asexual populations evolve more rapidly than smaller ones, due to their increased rate of beneficial mutations. Less clear is how population size influences the level of fitness an asexual population can attain. Here, we simulate the evolution of bacteria in repeated serial passage experiments to explore how features such as fitness landscape ruggedness, the size of the mutational target under selection, and the mutation supply rate, interact to affect the evolution of microbial populations of different sizes.</p> <p>Results</p> <p>We find that if the fitness landscape has many local peaks, there can be a trade-off between the rate of adaptation and the potential to reach high fitness peaks. This result derives from the fact that whereas large populations evolve mostly deterministically and often become trapped on local fitness peaks, smaller populations can follow more stochastic evolutionary paths and thus locate higher fitness peaks. We also find that the target size of adaptation and the mutation rate interact with population size to influence the trade-off between rate of adaptation and final fitness.</p> <p>Conclusion</p> <p>Our study suggests that the optimal population size for adaptation depends on the details of the environment and on the importance of either the ability to evolve rapidly or to reach high fitness levels.</p

Correction: Meta-Analysis of the Relationship between Multiple Sclerosis and Migraine.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.PMCID: PMC3613438PMCID: PMC3613438PMCID: PMC3613438PMCID: PMC3613438[This corrects the article on p. e45295 in vol. 7.]

Quantum Fluctuations of Coulomb Potential as a Source of Flicker Noise. The Influence of External Electric Field

Fluctuations of the electromagnetic field produced by quantized matter in external electric field are investigated. A general expression for the power spectrum of fluctuations is derived within the long-range expansion. It is found that in the whole measured frequency band, the power spectrum of fluctuations exhibits an inverse frequency dependence. A general argument is given showing that for all practically relevant values of the electric field, the power spectrum of induced fluctuations is proportional to the field strength squared. As an illustration, the power spectrum is calculated explicitly using the kinetic model with the relaxation-type collision term. Finally, it is shown that the magnitude of fluctuations produced by a sample generally has a Gaussian distribution around its mean value, and its dependence on the sample geometry is determined. In particular, it is demonstrated that for geometrically similar samples, the power spectrum is inversely proportional to the sample volume. Application of the obtained results to the problem of flicker noise is discussed.Comment: 14 pages, 3 figure

Wayward Youth: Trans-Beringian Movement and Differential Southward Migration by Juvenile Sharp-tailed Sandpipers

The sharp-tailed sandpiper (Calidris acuminata) is a long-distance migrant that travels each year from breeding grounds in the Russian Arctic to nonbreeding areas in Australasia. Most adults migrate rapidly from breeding grounds along a largely inland route through Asia. Here we report on the highly unusual migratory strategy of this species in which some juveniles, but virtually no adults, take a pronounced detour to western Alaska before proceeding on southward migration. We analyzed data from our own studies in this region and published and unpublished observations and specimen records of sharptailed sandpipers from the entire Pacific Basin. Each autumn, sharp-tailed sandpipers began arriving on coastal graminoid meadows and intertidal habitats throughout western Alaska during the last half of August and the last sandpipers departed from southwestern Alaska during October and November. Body mass of birds banded or collected across multiple years and sites in western Alaska (n = 330) increased by an average of 0.57 ± 0.06 g per day between mid-August and late October. Records suggest a small, regular movement of juveniles (and a very few adults) along the Asiatic coast, but we estimate from surveys that a few tens of thousands of juveniles stage in western Alaska each autumn. The distribution of sight and specimen records from the Pacific Basin during autumn suggests strongly age-segregated migration routes, with the principal migration of juveniles crossing central and western Oceania in a possible nonstop trans-Pacific flight from Alaska. This is only the second well-documented case of differential migration among birds that involves different routes for adults and juveniles, and it raises intriguing questions about how and why this system has evolved.  Le bécasseau à queue pointue (Calidris acuminata) est un migrant de longue distance qui se déplace chaque année depuis les zones de reproduction de l’Arctique russe jusqu’aux zones de non-reproduction de l’Australasie. La plupart des adultes migrent rapidement à partir des zones de reproduction le long d’un corridor largement situé à l’intérieur qui traverse l’Asie. Ici, nous faisons état de la stratégie migratoire grandement inhabituelle de cette espèce dans le cadre de laquelle certains juvéniles, mais quasiment aucun adulte, font une déviation prononcée vers l’ouest de l’Alaska avant de migrer vers le Sud. Nous avons analysé les données dérivées de nos propres études dans la région de même que des observations publiées et inédites et des enregistrements de spécimens de bécasseaux à queue pointue de tout le bassin du Pacifique. Chaque automne, les bécasseaux à queue pointue commençaient à arriver sur les prés côtiers de graminoïdes et dans les habitats intertidaux de l’ouest de l’Alaska pendant la deuxième moitié du mois d’août. Les derniers bécasseaux quittaient le sud-ouest de l’Alaska aux mois d’octobre et de novembre. La masse corporelle des oiseaux en bandes ou recueillis au cours de plusieurs années et à plusieurs emplacements de l’ouest de l’Alaska (n = 330) a augmenté en moyenne de 0,57 ± 0,06 g par jour entre la mi-août et la fin octobre. Les données laissent voir la présence d’un petit mouvement régulier de juvéniles (et très peu d’adultes) le long de la côte asiatique, mais nous avons estimé d’après les dénombrements que quelques dizaines de milliers de juvéniles passent un certain temps dans l’ouest de l’Alaska chaque automne. La répartition d’enregistrements d’observations et de spécimens du bassin du Pacifique à l’automne laisse entrevoir des routes migratoires fortement ségrégées en fonction de l’âge et que la migration principale de juvéniles traversant le centre et l’ouest de l’Océanie dans le cadre d’un vol transpacifique est susceptible d’être sans escale depuis l’Alaska. Il s’agit seulement du deuxième cas bien répertorié de migration différentielle d’oiseaux dont les trajets diffèrent chez les adultes et les juvéniles, et cela soulève des questions à savoir comment et pourquoi ce système a évolué

Langevin Thermostat for Rigid Body Dynamics

We present a new method for isothermal rigid body simulations using the quaternion representation and Langevin dynamics. It can be combined with the traditional Langevin or gradient (Brownian) dynamics for the translational degrees of freedom to correctly sample the NVT distribution in a simulation of rigid molecules. We propose simple, quasi-symplectic second-order numerical integrators and test their performance on the TIP4P model of water. We also investigate the optimal choice of thermostat parameters.Comment: 15 pages, 13 figures, 1 tabl

Spatiotemporal complexity of the universe at subhorizon scales

This is a short note on the spatiotemporal complexity of the dynamical state(s) of the universe at subhorizon scales (up to 300 Mpc). There are reasons, based mainly on infrared radiative divergences, to believe that one can encounter a flicker noise in the time domain, while in the space domain, the scaling laws are reflected in the (multi)fractal distribution of galaxies and their clusters. There exist recent suggestions on a unifying treatment of these two aspects within the concept of spatiotemporal complexity of dynamical systems driven out of equilibrium. Spatiotemporal complexity of the subhorizon dynamical state(s) of the universe is a conceptually nice idea and may lead to progress in our understanding of the material structures at large scalesComment: references update

Deterministic Dicke state preparation with continuous measurement and control

We characterize the long-time projective behavior of the stochastic master equation describing a continuous, collective spin measurement of an atomic ensemble both analytically and numerically. By adding state based feedback, we show that it is possible to prepare highly entangled Dicke states deterministically.Comment: Additional information is available at http://minty.caltech.edu/Ensemble

Differential structural remodelling of heparan sulfate by chemokines: the role of chemokine oligomerization

Chemokines control the migration of cells in normal physiological processes and in the context of disease such as inflammation, autoimmunity and cancer. Two major interactions are involved: (i) binding of chemokines to chemokine receptors, which activates the cellular machinery required for movement; and (ii) binding of chemokines to glycosaminoglycans (GAGs), which facilitates the organization of chemokines into haptotactic gradients that direct cell movement. Chemokines can bind and activate their receptors as monomers; however, the ability to oligomerize is critical for the function of many chemokines in vivo. Chemokine oligomerization is thought to enhance their affinity for GAGs, and here we show that it significantly affects the ability of chemokines to accumulate on and be retained by heparan sulfate (HS). We also demonstrate that several chemokines differentially rigidify and cross-link HS, thereby affecting HS rigidity and mobility, and that HS cross-linking is significantly enhanced by chemokine oligomerization. These findings suggest that chemokine–GAG interactions may play more diverse biological roles than the traditional paradigms of physical immobilization and establishment of chemokine gradients; we hypothesize that they may promote receptor-independent events such as physical re-organization of the endothelial glycocalyx and extracellular matrix, as well as signalling through proteoglycans to facilitate leukocyte adhesion and transmigration