18,959 research outputs found
Genomic variation in a widespread Neotropical bird (Xenops minutus) reveals divergence, population expansion, and gene flow
Elucidating the demographic and phylogeographic histories of species provides
insight into the processes responsible for generating biological diversity, and
genomic datasets are now permitting the estimation of histories and demographic
parameters with unprecedented accuracy. We used a genomic single nucleotide
polymorphism (SNP) dataset generated using a RAD-Seq method to investigate the
historical demography and phylogeography of a widespread lowland Neotropical
bird (Xenops minutus). As expected, we found that prominent landscape features
that act as dispersal barriers, such as Amazonian rivers and the Andes
Mountains, are associated with the deepest phylogeographic breaks, and also
that isolation by distance is limited in areas between these barriers. In
addition, we inferred positive population growth for most populations and
detected evidence of historical gene flow between populations that are now
physically isolated. Even with genomic estimates of historical demographic
parameters, we found the prominent diversification hypotheses to be untestable.
We conclude that investigations into the multifarious processes shaping species
histories, aided by genomic datasets, will provide greater resolution of
diversification in the Neotropics, but that future efforts should focus on
understanding the processes shaping the histories of lineages rather than
trying to reconcile these histories with landscape and climatic events in Earth
history.Comment: 61 pages, 4 figures (+3 supplemental), 3 tables (+6 supplemental
Theoretical Guidance on the Determinants of Success in Agricultural Marketing and Production Clubs
Institutional and Behavioral Economics, Marketing,
A phylogeny of birds based on over 1,500 loci collected by target enrichment and high-throughput sequencing
Evolutionary relationships among birds in Neoaves, the clade comprising the
vast majority of avian diversity, have vexed systematists due to the ancient,
rapid radiation of numerous lineages. We applied a new phylogenomic approach to
resolve relationships in Neoaves using target enrichment (sequence capture) and
high-throughput sequencing of ultraconserved elements (UCEs) in avian genomes.
We collected sequence data from UCE loci for 32 members of Neoaves and one
outgroup (chicken) and analyzed data sets that differed in their amount of
missing data. An alignment of 1,541 loci that allowed missing data was 87%
complete and resulted in a highly resolved phylogeny with broad agreement
between the Bayesian and maximum-likelihood (ML) trees. Although results from
the 100% complete matrix of 416 UCE loci were similar, the Bayesian and ML
trees differed to a greater extent in this analysis, suggesting that increasing
from 416 to 1,541 loci led to increased stability and resolution of the tree.
Novel results of our study include surprisingly close relationships between
phenotypically divergent bird families, such as tropicbirds (Phaethontidae) and
the sunbittern (Eurypygidae) as well as between bustards (Otididae) and turacos
(Musophagidae). This phylogeny bolsters support for monophyletic waterbird and
landbird clades and also strongly supports controversial results from previous
studies, including the sister relationship between passerines and parrots and
the non-monophyly of raptorial birds in the hawk and falcon families. Although
significant challenges remain to fully resolving some of the deep relationships
in Neoaves, especially among lineages outside the waterbirds and landbirds,
this study suggests that increased data will yield an increasingly resolved
avian phylogeny.Comment: 30 pages, 1 table, 4 figures, 1 supplementary table, 3 supplementary
figure
Anomaly mediated neutrino-photon interactions at finite baryon density
We propose new physical processes based on the axial vector anomaly and
described by the Wess-Zumino-Witten term that couples the photon, Z-boson, and
the omega-meson. The interaction takes the form of a pseudo-Chern-Simons term,
. This term
induces neutrino-photon interactions at finite baryon density via the coupling
of the Z-boson to neutrinos. These interactions may be detectable in various
laboratory and astrophysical arenas. The new interactions may account for the
MiniBooNE excess. They also produce a competitive contribution to neutron star
cooling at temperatures >10^9 K. These processes and related axion--photon
interactions at finite baryon density appear to be relevant in many
astrophysical regimes.Comment: 4 pages, 2 figures; references adde
On non-existence of static vacuum black holes with degenerate components of the event horizon
We present a simple proof of the non-existence of degenerate components of
the event horizon in static, vacuum, regular, four-dimensional black hole
spacetimes. We discuss the generalisation to higher dimensions and the
inclusion of a cosmological constant.Comment: latex2e, 9 pages in A
Four Dimensional Black Holes in String Theory
Exact solutions of heterotic string theory corresponding to four-dimensional
charge Q magnetic black holes are constructed as tensor products of an
SU(2)/Z(2Q+2) WZW orbifold with a (0,1) supersymmetric SU(1,1)/U(1) WZW coset
model. The spectrum is analyzed in some detail. ``Bad'' marginal operators are
found which are argued to deform these theories to asymptotically flat black
holes. Surprising behaviour is found for small values of Q, where low-energy
field theory is inapplicable. At the minimal value Q=1, the theory degenerates.
Renormalization group arguments are given that suggest the potential
gravitational singularity of the low-energy field theory is resolved by a
massive two-dimensional field theory. At Q=0, a stable, neutral ``remnant,'' of
potential relevance to the black hole information paradox, is found.Comment: 37 pages + 1 figure (tar compressed and uuencoded
On D-branes in the Nappi-Witten and GMM gauged WZW models
We construct D-branes in the Nappi-Witten (NW) and
Guadagnini-Martellini-Mintchev (GMM) gauged WZW models. For the NW and GMM models we present
the explicit equations describing the D-brane hypersurfaces in their target
spaces. In the latter case we show that the D-branes are classified according
to the Cardy theorem. We also present the semiclassical mass computation and
find its agreement with the CFT predictions.Comment: 16 pages, harvma
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