402,424 research outputs found
Directional genetic differentiation and asymmetric migration
Understanding the population structure and patterns of gene flow within
species is of fundamental importance to the study of evolution. In the fields
of population and evolutionary genetics, measures of genetic differentiation
are commonly used to gather this information. One potential caveat is that
these measures assume gene flow to be symmetric. However, asymmetric gene flow
is common in nature, especially in systems driven by physical processes such as
wind or water currents. Since information about levels of asymmetric gene flow
among populations is essential for the correct interpretation of the
distribution of contemporary genetic diversity within species, this should not
be overlooked. To obtain information on asymmetric migration patterns from
genetic data, complex models based on maximum likelihood or Bayesian approaches
generally need to be employed, often at great computational cost. Here, a new
simpler and more efficient approach for understanding gene flow patterns is
presented. This approach allows the estimation of directional components of
genetic divergence between pairs of populations at low computational effort,
using any of the classical or modern measures of genetic differentiation. These
directional measures of genetic differentiation can further be used to
calculate directional relative migration and to detect asymmetries in gene flow
patterns. This can be done in a user-friendly web application called
divMigrate-online introduced in this paper. Using simulated data sets with
known gene flow regimes, we demonstrate that the method is capable of resolving
complex migration patterns under a range of study designs.Comment: 25 pages, 8 (+3) figures, 1 tabl
Muller's ratchet in random graphs and scale free networks
Muller's ratchet is an evolutionary process that has been implicated in the extinction of asexual species, the evolution of mitochondria, the degeneration of the Y chromosome, the evolution of sex and recombination and the evolution of microbes. Here we study the speed of Muller's ratchet in a population subdivided into many small subpopulations connected by migration, and distributed on a network. We compare the speed of the ratchet in two distinct types of topologies: scale free networks and random graphs. The difference between the topologies is noticeable when the average connectivity of the network and the migration rate is large. In this situation we observe that the ratchet clicks faster in scale free networks than in random graphs. So contrary to intuition, scale free networks are more prone to loss of genetic information than random graphs. On the other hand, we show that scale free networks are more robust to the random extinction than random graphs. Since these complex networks have been shown to describe well real-life systems, our results open a framework for studying the evolution of microbes and disease epidemics
The Evolution of Dispersal in Random Environments and The Principle of Partial Control
McNamara and Dall (2011) identified novel relationships between the abundance
of a species in different environments, the temporal properties of
environmental change, and selection for or against dispersal. Here, the
mathematics underlying these relationships in their two-environment model are
investigated for arbitrary numbers of environments. The effect they described
is quantified as the fitness-abundance covariance. The phase in the life cycle
where the population is censused is crucial for the implications of the
fitness-abundance covariance. These relationships are shown to connect to the
population genetics literature on the Reduction Principle for the evolution of
genetic systems and migration. Conditions that produce selection for increased
unconditional dispersal are found to be new instances of departures from
reduction described by the "Principle of Partial Control" proposed for the
evolution of modifier genes. According to this principle, variation that only
partially controls the processes that transform the transmitted information of
organisms may be selected to increase these processes. Mathematical methods of
Karlin, Friedland, and Elsner, Johnson, and Neumann, are central in
generalizing the analysis. Analysis of the adaptive landscape of the model
shows that the evolution of conditional dispersal is very sensitive to the
spectrum of genetic variation the population is capable of producing, and
suggests that empirical study of particular species will require an evaluation
of its variational properties.Comment: Dedicated to the memory of Professor Michael Neumann, one of whose
many elegant theorems provides for a result presented here. 28 pages, 1
table, 1 figur
Structural change and poverty reduction in Brazil : the impact of the Doha Round
Over the medium time horizon, skill upgrading, differentials in sectoral technological progress, and migration of labor out of farming activities are some of the major structural adjustment factors shaping the evolution of an economy and its connected poverty trends. The main focus of the authors is understanding, for the case of Brazil, how a trade shock interacts with these structural forces and ascertaining whether it enhances or hinders medium-term poverty reduction. In particular, they consider the interactions between the migration of labor out of agriculture, a potentially important poverty reduction factor, and trade liberalization, which increases the price incentives to stay in agriculture. A recursive-dynamic computable general equilibrium model simulates Doha scenarios and compares them against a business as usual scenario. The authors estimate the poverty effects using a microsimulation model that primarily takes into account individuals'labor supply decisions. Their analysis shows that trade liberalization does contribute to structural poverty reduction. But unless increased productivity and stronger growth rates are attributed to trade reform, its contribution to medium-term poverty reduction is rather small.Economic Theory&Research,Labor Markets,Rural Poverty Reduction,Achieving Shared Growth,Rural Development Knowledge&Information Systems
E-finance-lab at the House of Finance : about us
The financial services industry is believed to be on the verge of a dramatic [r]evolution. A substantial redesign of its value chains aimed at reducing costs, providing more efficient and flexible services and enabling new products and revenue streams is imminent. But there seems to be no clear migration path nor goal which can cast light on the question where the finance industry and its various players will be and should be in a decade from now. The mission of the E-Finance Lab is the development and application of research methodologies in the financial industry that promote and assess how business strategies and structures are shared and supported by strategies and structures of information systems. Important challenges include the design of smart production infrastructures, the development and evaluation of advantageous sourcing strategies and smart selling concepts to enable new revenue streams for financial service providers in the future. Overall, our goal is to contribute methods and views to the realignment of the E-Finance value chain. ..
Clumpy Disc and Bulge Formation
We present a set of hydrodynamical/Nbody controlled simulations of isolated
gas rich galaxies that self-consistently include SN feedback and a detailed
chemical evolution model, both tested in cosmological simulations. The initial
conditions are motivated by the observed star forming galaxies at z ~ 2-3. We
find that the presence of a multiphase interstellar media in our models
promotes the growth of disc instability favouring the formation of clumps which
in general, are not easily disrupted on timescales compared to the migration
time. We show that stellar clumps migrate towards the central region and
contribute to form a classical-like bulge with a Sersic index, n > 2. Our
physically-motivated Supernova feedback has a mild influence on clump survival
and evolution, partially limiting the mass growth of clumps as the energy
released per Supernova event is increased, with the consequent flattening of
the bulge profile. This regulation does not prevent the building of a
classical-like bulge even for the most energetic feedback tested. Our Supernova
feedback model is able to establish a self-regulated star formation, producing
mass-loaded outflows and stellar age spreads comparable to observations. We
find that the bulge formation by clumps may coexit with other channels of bulge
assembly such as bar and mergers. Our results suggest that galactic bulges
could be interpreted as composite systems with structural components and
stellar populations storing archaeological information of the dynamical history
of their galaxy.Comment: Accepted for publication in MNRAS - Aug. 20, 201
Modelling Circumbinary Planets: The case of Kepler-38
Recently, a number of planets orbiting binary stars have been discovered by
the Kepler space telescope. In a few systems the planets reside close to the
dynamical stability limit. Due to the difficulty of forming planets in such
close orbits, it is believed that they have formed further out in the disk and
migrated to their present locations. Our goal is to construct more realistic
models of planet migration in circumbinary disks, and to determine the final
position of these planets. In our work, we focus on the system Kepler-38. The
evolution of the circumbinary disk is studied using two-dimensional
hydrodynamical simulations. We study locally isothermal disks as well as more
realistic models with viscous heating, radiative cooling from the disk
surfaces, and radiative diffusion in the disk mid plane. After the disk has
been brought into equilibrium, a 115 Earth-mass planet is embedded and its
evolution is followed. In all cases the planets stop inward migration near the
inner edge of the disk. In isothermal disks with a typical disk scale height of
H/r = 0.05, the final outcome agrees very well with the observed location of
planet Kepler-38b. For the radiative models, the disk thickness and location of
the inner edge is determined by the mass in the system. For surface densities
in the order of 3000 g/cm^2 at 1 AU, the inner gap lies close to the binary and
planets stop in the region between the 5:1 and 4:1 mean-motion resonances with
the binary. A model with a disk with approximately a quarter of the mass yields
a final position very close to the observed one. For planets migrating in
circumbinary disks, the final position is dictated by the structure of the
disk. Knowing the observed orbits of circumbinary planets, radiative disk
simulations with embedded planets can provide important information on the
physical state of the system during the final stages of its evolution.Comment: 14 pages, accepted by Astronomy & Astrophysics, Animations available
under: http://www.tat.physik.uni-tuebingen.de/~kley/projects/kep38
Ten years tracking the migrations of small landbirds: Lessons learned in the golden age of bio-logging
In 2007, the first miniature light-level geolocators were deployed on small landbirds, revolutionizing the study of migration. In this paper, we review studies that have used geolocators to track small landbirds with the goal of summarizing research themes and identifying remaining important gaps in understanding. We also highlight research and opportunities using 2 recently developed tracking technologies: archival GPS tags and automated radio-telemetry systems. In our review, we found that most (54%) geolocator studies focused on quantifying natural history of migration, such as identifying migration routes, nonbreeding range, and migration timing. Studies of behavioral ecology (20%) uncovered proximate drivers of movements, including en route habitat quality; that migration routes, but not timing, may be flexible in some species; and different age and sex classes show significant differences in migration strategy. Studies of the evolution of migration (9%) have illustrated that migration is a potential barrier to hybridizing species or subspecies, and some work has correlated gene polymorphisms and methylation patterns with migration behavior. Studies of migratory connectivity (11%) have shown that a moderate level of connectivity is common, although variability across and within species exists. Studies of seasonal interactions (7%) have found mixed results: in some cases, carryover effects have been identified; in other cases, carryover effects are buffered during intervening stages of the annual cycle. Archival GPS tags provide unprecedented precision in locations of nonbreeding sites and migration routes, and will continue to improve understanding of migration across large spatial scales. Automated radio-telemetry systems are revolutionizing our knowledge of migratory stopover biology, and have led to discoveries of previously unknown stopover behaviors. Together, these tracking technologies will continue to provide insight into small migratory landbird movements and contribute important information for conservation of this rapidly declining group
Ten years tracking the migrations of small landbirds: Lessons learned in the golden age of bio-logging
In 2007, the first miniature light-level geolocators were deployed on small landbirds, revolutionizing the study of migration. In this paper, we review studies that have used geolocators to track small landbirds with the goal of summarizing research themes and identifying remaining important gaps in understanding. We also highlight research and opportunities using 2 recently developed tracking technologies: archival GPS tags and automated radio-telemetry systems. In our review, we found that most (54%) geolocator studies focused on quantifying natural history of migration, such as identifying migration routes, nonbreeding range, and migration timing. Studies of behavioral ecology (20%) uncovered proximate drivers of movements, including en route habitat quality; that migration routes, but not timing, may be flexible in some species; and different age and sex classes show significant differences in migration strategy. Studies of the evolution of migration (9%) have illustrated that migration is a potential barrier to hybridizing species or subspecies, and some work has correlated gene polymorphisms and methylation patterns with migration behavior. Studies of migratory connectivity (11%) have shown that a moderate level of connectivity is common, although variability across and within species exists. Studies of seasonal interactions (7%) have found mixed results: in some cases, carryover effects have been identified; in other cases, carryover effects are buffered during intervening stages of the annual cycle. Archival GPS tags provide unprecedented precision in locations of nonbreeding sites and migration routes, and will continue to improve understanding of migration across large spatial scales. Automated radio-telemetry systems are revolutionizing our knowledge of migratory stopover biology, and have led to discoveries of previously unknown stopover behaviors. Together, these tracking technologies will continue to provide insight into small migratory landbird movements and contribute important information for conservation of this rapidly declining group
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