131 research outputs found
The critical role of ants in the extensive dispersal of Acacia seeds revealed by genetic parentage assignment
Ants are prominent seed dispersal agents in many ecosystems, and dispersal distances are small in comparison with vertebrate dispersal agents. However, the distance and distribution of ant-mediated dispersal in arid/semi-arid environments remains poorly explored. We used microsatellite markers and parentage assignment to quantify the distance and distribution of dispersed seeds of Acacia karina, retrieved from the middens of Iridomyrmex agilis and Melophorus turneri perthensis. From parentage assignment, we could not distinguish the maternal from each parent pair assigned to each seed, so we applied two approaches to estimate dispersal distances, one conservative (CONS), where the parent closest to the ant midden was considered to be maternal, and the second where both parents were deemed equally likely (EL) to be maternal, and used both distances. Parentage was assigned to 124 seeds from eight middens. Maximum seed dispersal distances detected were 417 m (CONS) and 423 m (EL), more than double the estimated global maximum. Mean seed dispersal distances of 40 m (±5.8 SE) (CONS) and 79 m (±6.4 SE) (EL) exceeded the published global average of 2.24 m (±7.19 SD) by at least one order of magnitude. For both approaches and both ant species, seed dispersal was predominantly (44–84 % of all seeds) within 50 m from the maternal source, with fewer dispersal events at longer distances. Ants in this semi-arid environment have demonstrated a greater capacity to disperse seeds than estimated elsewhere, which highlights their important role in this system, and suggests significant novel ecological and evolutionary consequences for myrmecochorous species in arid/semi-arid Australia
Historic and contemporary biogeographic perspectives on range‐wide spatial genetic structure in a widespread seagrass
Historical and contemporary processes drive spatial patterns of genetic diversity. These include climate-driven range shifts and gene flow mediated by biogeographical influences on dispersal. Assessments that integrate these drivers are uncommon, but critical for testing biogeographic hypotheses. Here, we characterize intraspecific genetic diversity and spatial structure across the entire distribution of a temperate seagrass to test marine biogeographic concepts for southern Australia. Predictive modeling was used to contrast the current Posidonia australis distribution to its historical distribution during the Last Glacial Maximum (LGM). Spatial genetic structure was estimated for 44 sampled meadows from across the geographical range of the species using nine microsatellite loci. Historical and contemporary distributions were similar, with the exception of the Bass Strait. Genetic clustering was consistent with the three currently recognized biogeographic provinces and largely consistent with the finer-scale IMCRA bioregions. Discrepancies were found within the Flindersian province and southwest IMCRA bioregion, while two regions of admixture coincided with transitional IMCRA bioregions. Clonal diversity was highly variable but positively associated with latitude. Genetic differentiation among meadows was significantly associated with oceanographic distance. Our approach suggests how shared seascape drivers have influenced the capacity of P. australis to effectively track sea level changes associated with natural climate cycles over millennia, and in particular, the recolonization of meadows across the Continental Shelf following the LGM. Genetic structure associated with IMCRA bioregions reflects the presence of stable biogeographic barriers, such as oceanic upwellings. This study highlights the importance of biogeography to infer the role of historical drivers in shaping extant diversity and structure.Elizabeth A. Sinclair, Renae K. Hovey, Siegfried L. Krauss, Janet M. Anthony, Michelle Waycott, Gary A. Kendric
Superconductors are topologically ordered
We revisit a venerable question: what is the nature of the ordering in a
superconductor? We find that the answer is properly that the superconducting
state exhibits topological order in the sense of Wen, i.e. that while it lacks
a local order parameter, it is sensitive to the global topology of the
underlying manifold and exhibits an associated fractionalization of quantum
numbers. We show that this perspective unifies a number of previous
observations on superconductors and their low lying excitations and that this
complex can be elegantly summarized in a purely topological action of the
``'' type and its elementary quantization. On manifolds with boundaries,
the action correctly predicts non-chiral edge states, gapped in general,
but crucial for fractionalization and establishing the ground state degeneracy.
In all of this the role of the physical electromagnetic fields is central. We
also observe that the action describes the topological order in several
other physically distinct systems thus providing an example of topological
universality
Quantum corrections to the ground state energy of a trapped Bose-Einstein condensate: A diffusion Monte Carlo calculation
The diffusion Monte Carlo method is applied to describe a trapped atomic
Bose-Einstein condensate at zero temperature, fully quantum mechanically and
nonperturbatively. For low densities, [n(0): peak
density, a: s-wave scattering length], our calculations confirm that the exact
ground state energy for a sum of two-body interactions depends on only the
atomic physics parameter a, and no other details of the two-body model
potential. Corrections to the mean-field Gross-Pitaevskii energy range from
being essentially negligible to about 20% for N=2-50 particles in the trap with
positive s-wave scattering length a=100-10000 a.u.. Our numerical calculations
confirm that inclusion of an additional effective potential term in the
mean-field equation, which accounts for quantum fluctuations [see e.g. E.
Braaten and A. Nieto, Phys. Rev. B 56}, 14745 (1997)], leads to a greatly
improved description of trapped Bose gases.Comment: 7 pages, 4 figure
Equatorial circular orbits in the Kerr-de Sitter spacetimes
Equatorial motion of test particles in the Kerr-de Sitter spacetimes is
considered. Circular orbits are determined, their properties are discussed for
both the black-hole and naked-singularity spacetimes, and their relevance for
thin accretion discs is established.Comment: 24 pages, 19 figures, REVTeX
Model-independent dark energy test with sigma_8 using results from the Wilkinson Microwave Anisotropy Probe
By combining the recent WMAP measurements of the cosmic microwave background
anisotropies and the results of the recent luminosity distance measurements to
type-Ia supernovae, we find that the normalization of the matter power spectrum
on cluster scales, sigma_8, can be used to discriminate between dynamical
models of dark energy (quintessence models) and a conventional cosmological
constant model (LCDM).Comment: 5 pages, 6 figures. Additional discussion and reference, matches PRD
accepted versio
Gravitationally violated U(1) symmetry and neutrino anomalies
The current searches for neutrino oscillations seem to suggest an approximate
L_e-L_\m-L_{\tau} flavor symmetry. This symmetry implies a pair of degenerate
neutrinos with mass and large leptonic mixing. We explore the possibility
that gravitational interactions break this global symmetry. The Planck scale
suppressed breaking of the L_e-L_\m-L_{\tau} symmetry is shown to lead to the
right amount of splitting among the degenerate neutrinos needed in order to
solve the solar neutrino problem. The common mass of the pair can be
identified with the atmospheric neutrino scale. A concrete model is proposed in
which smallness of and hierarchy in the solar and atmospheric neutrino
scales get linked to hierarchies in the weak, grand unification and the Planck
scales.Comment: 12 pages, LATE
Recommended from our members
Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity
Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements
Collider aspects of flavour physics at high Q
This review presents flavour related issues in the production and decays of
heavy states at LHC, both from the experimental side and from the theoretical
side. We review top quark physics and discuss flavour aspects of several
extensions of the Standard Model, such as supersymmetry, little Higgs model or
models with extra dimensions. This includes discovery aspects as well as
measurement of several properties of these heavy states. We also present public
available computational tools related to this topic.Comment: Report of Working Group 1 of the CERN Workshop ``Flavour in the era
of the LHC'', Geneva, Switzerland, November 2005 -- March 200
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