552 research outputs found
Molecular Phylogenetics of the Superfamily Curculionoidea (Insecta: Coleoptera)
This thesis examines higher-level evolutionary history within the superfamily Curculionoidea, the most speciose family-level taxon, which includes beetles commonly known as weevils. This is achieved using a phylogenetic approach incorporating the largest datamatrix yet employed for weevil molecular systematics, and includes an investigation into the prospect of obtaining short phylogenetically informative amplicons from archival museum specimens. Newly obtained DNA sequence data is analysed from a variety of mitochondrial and nuclear loci, including 92 mitogenomes assembled through the approach of next-generation sequencing of pooled genomic DNA. The resulting trees are used to test previous morphological- and molecular-based hypotheses of weevil relationships and classification schemes.
Mitogenomic-derived trees reveal topologies that are highly congruent with previous molecular studies, but that conflict with some morphological hypotheses. Strong nodal support strengthens inferences into the relationships amongst most weevil families and suggests that the largest family, the Curculionidae, is monophyletic, if the subfamily Platypodinae is excluded. Division of the Curculionidae into two large clades is well supported and the wood-boring habit adopted by three subfamilies is shown to have arisen multiple times, contradicting most morphological analyses.
Addition of several nuclear loci to the mitogenomic data is found to provide little additional value, in terms of improving nodal bootstrap support. A suggestion is made that future efforts to enhance understanding of relationships should focus on improving taxon sampling. Statistical tests of an augmented dataset, derived from public database sequences for single mitochondrial genes, wherein multiple tribes and subfamilies within the broad-nosed weevils are constrained as monophyletic, indicate that three entimine tribes, as currently defined, are each not consistent with the hypothesis for their monophyly.
Incongruences between molecular data and classical morphological taxonomy are suggestive that the current weevil classification system is misleading if used to interpret species richness, geographic distributions or ecological traits within currently recognised lineages
Bulk de novo mitogenome assembly from pooled total DNA elucidates the phylogeny of weevils (Coleoptera: Curculionoidea)
Complete mitochondrial genomes have been shown to be reliable markers for phylogeny reconstruction among diverse animal groups. However, the relative difficulty and high cost associated with obtaining de novo full mitogenomes have frequently led to conspicuously low taxon sampling in ensuing studies. Here, we report the successful use of an economical and accessible method for assembling complete or near-complete mitogenomes through shot-gun next-generation sequencing of a single library made from pooled total DNA extracts of numerous target species. To avoid the use of separate indexed libraries for each specimen, and an associated increase in cost, we incorporate standard polymerase chain reaction-based âbaitâ sequences to identify the assembled mitogenomes. The method was applied to study the higher level phylogenetic relationships in the weevils (Coleoptera: Curculionoidea), producing 92 newly assembled mitogenomes obtained in a single Illumina MiSeq run. The analysis supported a separate origin of wood-boring behavior by the subfamilies Scolytinae, Platypodinae, and Cossoninae. This finding contradicts morphological hypotheses proposing a close relationship between the first two of these but is congruent with previous molecular studies, reinforcing the utility of mitogenomes in phylogeny reconstruction. Our methodology provides a technically simple procedure for generating densely sampled trees from whole mitogenomes and is widely applicable to groups of animals for which bait sequences are the only required prior genome knowledge
Recent Southern Ocean warming and freshening driven by greenhouse gas emissions and ozone depletion
The brightest high-latitude 12-micron IRAS sources
The Infrared Astronomical Satellite (IRAS) Point Source catalog was searched for sources brighter than 28 Jy (0 mag) at 12 Όm with absolute galactic latitude greater than 30° excluding the Large Magellanic Cloud. The search resulted in 269 sources, two of which are the galaxies NGC 1068 and M82. The remaining 267 sources are identified with, or have infrared color indices consistent with late-type stars some of which show evidence of circumstellar dust shells. Seven sources are previously uncataloged stars. K and M stars without circumstellar dust shells, M stars with circumstellar dust shells, and carbon stars occupy well-defined regions of infrared color-color diagrams
Interplay between superconductivity and magnetism in K-doped EuFe2As2
Superconductivity is found in 50% K-doped EuFe2As2 sample below 33 K. Our
results of electrical resistivity, magnetic susceptibility and 57Fe and 151Eu
Mossbauer spectroscopy provide clear evidence that the ordering of the Fe
moments observed at 190 K in undoped EuFe2As2 is completely suppressed in our
50% K doped sample, thus there is no coexistence between the Fe magnetic order
and the superconducting state. However, short range ordering of the Eu moments
is coexisting with the superconducting state below 15 K. A bump in the
susceptibility well below Tc as well as a slight broadening of the Fe Mossbauer
line below 15 K evidence an interplay between the Eu magnetism and the
superconducting state.Comment: 7 pages, 6 figure
Evidence for Dirac nodes from quantum oscillations in SrFe2As2
We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe2As2 as the angle between the applied magnetic field and crystalline axes is varied. Our measurements were performed on high-quality single crystals in a superconducting magnet, and in pulsed magnetic fields up to 60 T, allowing us to observe orbits from several small Fermi-surface pockets. We extract the cyclotron effective mass mâ and frequency F for these orbits and track their values as the field is rotated away from the c axis. While a constant ratio of mâ/F is expected for a parabolic band, we observe deviations from this behavior. We conclude that this observation points to orbits derived from a band with Dirac dispersion near the Fermi level
Pressure effects on the electron-doped high Tc superconductor BaFe(2-x)Co(x)As(2)
Application of pressures or electron-doping through Co substitution into Fe
sites transforms the itinerant antiferromagnet BaFe(2)As(2) into a
superconductor with the Tc exceeding 20K. We carried out systematic transport
measurements of BaFe(2-x)Co(x)As(2) superconductors in pressures up to 2.5GPa,
and elucidate the interplay between the effects of electron-doping and
pressures. For the underdoped sample with nominal composition x = 0.08,
application of pressure strongly suppresses a magnetic instability while
enhancing Tc by nearly a factor of two from 11K to 21K. In contrast, the
optimally doped x=0.20 sample shows very little enhancement of Tc=22K under
applied pressure. Our results strongly suggest that the proximity to a magnetic
instability is the key to the mechanism of superconductivity in iron-pnictides.Comment: 5 figure
Obscured Activity: AGN, Quasars, Starbursts and ULIGs observed by the Infrared Space Observatory
Some of the most active galaxies in the Universe are obscured by large
quantities of dust and emit a substantial fraction of their bolometric
luminosity in the infrared. Observations of these infrared luminous galaxies
with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed
view to the sources fuelling this active emission. The improved sensitivity,
spatial resolution and spectroscopic capability of ISO over its predecessor
Infrared Astronomical Satellite (IRAS), has enabled significant advances in the
understanding of the infrared properties of active galaxies. ISO surveyed a
wide range of active galaxies which, in the context of this review, includes
those powered by intense bursts of star-formation as well as those containing a
dominant active galactic nucleus (AGN). Mid infrared imaging resolved for the
first time the dust enshrouded nuclei in many nearby galaxies, while a new era
in infrared spectroscopy was opened by probing a wealth of atomic, ionic and
molecular lines as well as broad band features in the mid and far infrared.
This was particularly useful since it resulted in the understanding of the
power production, excitation and fuelling mechanisms in the nuclei of active
galaxies including the intriguing but so far elusive ultraluminous infrared
galaxies. Detailed studies of various classes of AGN and quasars greatly
improved our understanding of the unification scenario. Far-infrared imaging
and photometry also revealed the presence of a new very cold dust component in
galaxies and furthered our knowledge of the far-infrared properties of faint
starbursts, ULIGs and quasars. We summarise almost nine years of key results
based upon ISO data spanning the full range of luminosity and type of active
galaxies.Comment: Accepted for publication in 'ISO science legacy - a compact review of
ISO major achievements', Space Science Reviews - dedicated ISO issue. To be
published by Springer in 2005. 62 pages (low resolution figures version).
Higher resolution PDFs available from
http://users.physics.uoc.gr/~vassilis/papers/VermaA.pdf or
http://www.iso.vilspa.esa.es/science/SSR/Verma.pd
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