1,643 research outputs found
Reserve Size And Fragmentation Alter Community Assembly, Diversity, And Dynamics
Researchers have disputed whether a single large habitat reserve will support more species than many small reserves. However, relatively little is known from a theoretical perspective about how reserve size affects competitive communities structured by spatial abiotic gradients. We investigate how reserve size affects theoretical communities whose assembly is governed by dispersal limitation, abiotic niche differentiation, and source-sink dynamics. Simulations were conducted with varying scales of dispersal across landscapes with variable environmental spatial autocorrelation. Landscapes were inhabited by simulated trees with seedling and adult stages. For a fixed total area in reserves, we found that small reserve systems increased the distance between environments dominated by different species, diminishing the effects of source-sink dynamics. As reserve size decreased, environmental limitations to community assembly became stronger, species richness decreased, and richness increased. When dispersal occurred across short distances, a large reserve strategy caused greater stochastic community variation, greater richness, and lower richness than in small reserve systems. We found that reserve size variation trades off between preserving different aspects of natural communities, including diversity versus diversity. Optimal reserve size will depend on the importance of source-sink dynamics and the value placed on different characteristics of natural communities. Anthropogenic changes to the size and separation of remnant habitats can have far-reaching effects on community structure and assembly.Integrative Biolog
The effect of noise artefacts on gravitational-wave searches for neutron star post-merger remnants
Gravitational waves from binary neutron star post-merger remnants have the
potential to uncover the physics of the hot nuclear equation of state. These
gravitational-wave signals are high frequency ( kHz) and short lived
(), which introduces potential problems for
data-analysis algorithms due to the presence of non-stationary and non-Gaussian
noise artefacts in gravitational-wave observatories. We quantify the degree to
which these noise features in LIGO data may affect our confidence in
identifying post-merger gravitational-wave signals. We show that the
combination of vetoing data with non-stationary glitches and the application of
the Allen veto (usually reserved for long-lived lower-frequency
gravitational-wave signals), allows one to confidently detect post-merger
signals with signal-to-noise ratio . We discuss the need to
incorporate the data-quality checks and vetos into realistic post-merger
gravitational-wave searches, and describe how one can incorporate them to
calculate realistic false-alarm and false-dismissal rates.Comment: 6 pages, 4 figures, submitted for publication in Monthly Notices of
the Royal Astronomical Societ
Natural variation in abiotic stress responsive gene expression and local adaptation to climate in Arabidopsis thaliana.
Gene expression varies widely in natural populations, yet the proximate and ultimate causes of this variation are poorly known. Understanding how variation in gene expression affects abiotic stress tolerance, fitness, and adaptation is central to the field of evolutionary genetics. We tested the hypothesis that genes with natural genetic variation in their expression responses to abiotic stress are likely to be involved in local adaptation to climate in Arabidopsis thaliana. Specifically, we compared genes with consistent expression responses to environmental stress (expression stress responsive, "eSR") to genes with genetically variable responses to abiotic stress (expression genotype-by-environment interaction, "eGEI"). We found that on average genes that exhibited eGEI in response to drought or cold had greater polymorphism in promoter regions and stronger associations with climate than those of eSR genes or genomic controls. We also found that transcription factor binding sites known to respond to environmental stressors, especially abscisic acid responsive elements, showed significantly higher polymorphism in drought eGEI genes in comparison to eSR genes. By contrast, eSR genes tended to exhibit relatively greater pairwise haplotype sharing, lower promoter diversity, and fewer nonsynonymous polymorphisms, suggesting purifying selection or selective sweeps. Our results indicate that cis-regulatory evolution and genetic variation in stress responsive gene expression may be important mechanisms of local adaptation to climatic selective gradients
Pleiotropy of FRIGIDA enhances the potential for multivariate adaptation.
An evolutionary response to selection requires genetic variation; however, even if it exists, then the genetic details of the variation can constrain adaptation. In the simplest case, unlinked loci and uncorrelated phenotypes respond directly to multivariate selection and permit unrestricted paths to adaptive peaks. By contrast, 'antagonistic' pleiotropic loci may constrain adaptation by affecting variation of many traits and limiting the direction of trait correlations to vectors that are not favoured by selection. However, certain pleiotropic configurations may improve the conditions for adaptive evolution. Here, we present evidence that the Arabidopsis thaliana gene FRI (FRIGIDA) exhibits 'adaptive' pleiotropy, producing trait correlations along an axis that results in two adaptive strategies. Derived, low expression FRI alleles confer a 'drought escape' strategy owing to fast growth, low water use efficiency and early flowering. By contrast, a dehydration avoidance strategy is conferred by the ancestral phenotype of late flowering, slow growth and efficient water use during photosynthesis. The dehydration avoidant phenotype was recovered when genotypes with null FRI alleles were transformed with functional alleles. Our findings indicate that the well-documented effects of FRI on phenology result from differences in physiology, not only a simple developmental switch
Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ( Hz). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from (25 Hz) to (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.Comment: 33 pages, 11 figure
Structure of Neutron Stars in Tensor-Vector-Scalar Theory
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success
in explaining various phenomena without the need for dark matter. However, it
is difficult to observationally discern the differences between TeVeS and
predictions made within the Lambda-cold dark matter concordance model. This
implies that alternative tests are required that independently verify which
theory is correct. For this we turn to the strong-field regime of TeVeS. In
particular, we solve the spherically symmetric equations of hydrostatic
equilibrium for a perfect fluid with a realistic equation of state to build
models of neutron stars in TeVeS. We show that causality within the neutron
star is only maintained for certain cosmological values of the scalar field,
which allows us to put constraints on this value independently of cosmological
observations. We also discuss in detail the internal structure of neutron stars
and how each of the free parameters in the theory effects the overall size and
mass of the neutron stars. In particular, the radii of neutron stars in TeVeS
can significantly differ from those in General Relativity for certain values of
the vector field coupling, which allows us to also place extra constraints on
this parameter. Finally, we discuss future observations of neutron stars using
both the electromagnetic and gravitational wave spectrums that will allow for
tests of the appropriate theory of gravity.Comment: Accepted for publication in Phys. Rev.
Linking the rates of neutron star binaries and short gamma-ray bursts
Short gamma-ray bursts are believed to be produced by both binary neutron
star (BNS) and neutron star-black hole (NSBH) mergers. We use current estimates
for the BNS and NSBH merger rates to calculate the fraction of observable short
gamma-ray bursts produced through each channel. This allows us to constrain
merger rates of BNS to ( credible interval), a decrease in the rate
uncertainties from the second LIGO--Virgo Gravitational-Wave Transient Catalog,
GWTC-2. Assuming a top-hat emission profile with a large Lorentz factor, we
constrain the average opening angle of gamma-ray burst jets produced in BNS
mergers to . We also measure the fraction of BNS and NSBH
mergers that produce an observable short gamma-ray burst to be
and , respectively and find that of BNS mergers launch jets (90\% confidence). We forecast constraints for
future gravitational-wave detections given different modelling assumptions,
including the possibility that BNS and NSBH jets are different. With BNS
and NSBH observations, expected within six months of the LIGO-Virgo-KAGRA
network operating at design sensitivity, it will be possible to constrain the
fraction of BNS and NSBH mergers that launch jets with precision. Within
a year of observations, we can determine whether the jets launched in NSBH
mergers have a different structure than those launched in BNS mergers and rule
out whether of binary neutron star mergers launch jets. We
discuss the implications of future constraints on understanding the physics of
short gamma-ray bursts and binary evolution.Comment: Accepted in Physical Review D: 13 pages, 5 figure
Identification of a protein encoded in the EB-viral open reading frame BMRF2
Using monospecific rabbit sera against a peptide derived from a potential antigenic region of the Epstein-Barr viral amino acid sequence encoded in the open reading frame BMRF2 we could identify a protein-complex of 53/55 kDa in chemically induced B95-8, P3HR1 and Raji cell lines. This protein could be shown to be membrane-associated, as predicted by previous computer analysis of the secondary structure and hydrophilicity pattern, and may be a member of EBV-induced membrane proteins in lytically infected cells
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