Major Burst Research Articles

Reconstructing the evolutionary history of gypsy retrotransposons in the Périgord black truffle (Tuber melanosporum Vittad.).

Truffles are ascomycete fungi belonging to genus Tuber, and they form ectomycorrhizal associations with trees and shrubs. Transposable elements constitute more than 50% of the black Périgord truffle (Tuber melanosporum) genome, which are mainly class 1 gypsy retrotransposons, but their impact on its genome is unknown. The aims of this study are to investigate the diversity of gypsy retrotransposons in this species and their evolutionary history by analysing the reference genome and six resequenced genomes of different geographic accessions. Using the reverse transcriptase sequences, six different gypsy retrotransposon clades were identified. Tmt1 and Tmt6 are the most abundant transposable elements, representing 14 and 13% of the T. melanosporum genome, respectively. Tmt6 showed a major burst of proliferation between 1 and 4 million years ago, but evidence of more recent transposition was observed. Except for Tmt2, the other clades tend to aggregate, and their mode of transposition excluded the master copy model. This suggests that each new copy has the same probability of transposing as other copies. This study provides a better view of the diversity and dynamic nature of gypsy retrotransposons in T. melanosporum. Even if the major gypsy retrotransposon bursts are old, some elements seem to have transposed recently, suggesting that they may continue to model the truffle genomes.

Observation of 2.45 MeV neutrons correlated with natural atmospheric lightning discharges by Lead‐Free Gulmarg Neutron Monitor

AbstractThe first experimental evidence of detecting the neutrons correlated with the natural atmospheric lightning discharges (NALD) was obtained with Lead‐Free Gulmarg Neutron Monitor (LFGNM) operating at High Altitude Research Laboratory, Gulmarg, Kashmir, India, and was reported in the year 1985. The neutron observations still continue with LFGNM. However, the current configuration of LFGNM is the upgraded version of the system used earlier to record neutron bursts (in the recording period of 320 μs in four successive electronic gates of 80 μs each) supposedly originating from an NALD. In the current system the neutron recording time period/interval has been extended to 1260 μs with 63 successive gates of 20 μs each. The system also simultaneously records the differential times—maximum up to 14—between the consecutive strokes of a multistroke lightning flash. The distance between an NALD channel and LFGNM setup is determined empirically by making use of the time delay (td)/time of flight (TOF) measurement of the first detected neutron subsequent to the sensing of the electrostatic field variation caused by the initiation of an NALD in the ambient atmosphere of the LFGNM setup. Assuming a priori incident energy as 2.45 MeV of the detected neutrons supposedly generated due to the fusion of deuterium ions in the lightning discharge channel leads to quantifying the neutron emission flux if the NALD channel distance with respect to the LFGNM setup is established. In this paper we discuss the experiment and the time profiles of several of a large number of the major neutron burst events recorded with LFGNM in association with NALDs. Moreover, a rare and an extraordinary neutron burst event, in terms of its associated “td/TOF” of first detected neutron after triggering, recorded by this system is specifically discussed. In this event, the recorded TOF of 14 μs of the escaping neutron detected by the system immediately after getting triggered by the NALD that struck a nearby tree found located just around 300 m (physically measured) away from the detector position indicates the energy of the detected neutron ϵn ≈2.45 MeV. In the light of this only event, we, therefore, cautiously suggest deuteron‐deuteron fusion reaction, 2H(2H,n)3He, as one of the possible mechanisms of the neutron generation correlated with an NALD. Nonetheless, the observations so far have reconfirmed production of neutrons in an NALD.

The coelacanth: Can a "living fossil" have active transposable elements in its genome?

The coelacanth has long been regarded as a "living fossil," with extant specimens looking very similar to fossils dating back to the Cretaceous period. The hypothesis of a slowly or even not evolving genome has been proposed to account for this apparent morphological stasis. While this assumption seems to be sustained by different evolutionary analyses on protein-coding genes, recent studies on transposable elements have provided more conflicting results. Indeed, the coelacanth genome contains many transposable elements and has been shaped by several major bursts of transposition during evolution. In addition, comparison of orthologous genomic regions from the genomes of the 2 extant coelacanth species L. chalumnae and L. menadoensis revealed multiple species-specific insertions, indicating transposable element recent activity and contribution to post-speciation genome divergence. These observations, which do not support the genome stasis hypothesis, challenge either the impact of transposable elements on organismal evolution or the status of the coelacanth as a "living fossil." Closer inspection of fossil and molecular data indicate that, even if coelacanths might evolve more slowly than some other lineages due to demographic and/or ecological factors, this variation is still in the range of a "non-fossil" vertebrate species.

Survey of Saturn auroral storms observed by the Hubble Space Telescope: Implications for storm time scales

AbstractWe examine the ultraviolet images of Saturn obtained by the Hubble Space Telescope (HST) between 1997 and 2013 for the presence of auroral storm signatures, consisting of 2060 individual images over 74.4 h of exposure time. We find 12 storm intervals in these data, identified by bright high‐latitude auroras spanning the dawn sector, which previous studies have shown are excited by strong magnetospheric compressions by the solar wind. While most of these events have previously been discussed individually, here we consider what may be deduced about the lifetime of storms, yet unobserved directly for a given event, by examining the ensemble. Specifically, we examine the presence or absence of storm signatures in successive HST observing “visits” separated by varying intervals of time. We show that the observations are consistent with a typical lifetime of ~1.5 Saturn rotations (~16 h), within a likely range between ~1 and ~2 rotations. We suggest that this time scale and the storm evolution morphology relate to the time for hot plasma subcorotation around the planet, following injection postmidnight after a major burst of tail reconnection excited by the solar wind compression. From the overall observed ~12% occurrence frequency of storm signatures, we further infer an averaged storm recurrence time of ~5.5 days (~4‐7 days), although this averaged value could be shortened by the occurrence of successive storm activations within few‐day disturbed solar wind intervals as observed directly in two cases.

Regional and global variations in the temporal clustering of tectonic tremor activity

The temporal distribution of tremor activity exhibits a highly non-Poissonian behavior, and its maximum period of non-Poissonian clustering statistically describes the recurrence interval of major tremor bursts. Here, we examine variations in the temporal clustering properties of tremor activity by assessing their characteristic times, which are determined by the maximum period of the non-Poissonian distribution. By applying a two-point correlation integral to some of the world's major tremor zones, including Shikoku, Kii-Tokai, and Kyushu in Japan; Cascadia, Jalisco, and Guerrero in Mexico; southern Chile; Taiwan; and Manawatu in New Zealand, we reveal local spatial variations in the temporal clustering properties in each tremor zone and show global-scale variations in tremor activity. The spatial variation in local tremor activity is characterized by a gradual transition in the along-dip direction and shorter-wavelength heterogeneities in the along-strike direction, possibly associated with a spatial change in frictional conditions at the plate interface and rheological conditions in the surrounding materials. The characteristic time correlates positively with locally measured median tremor duration, implying an inherent correlation between the moment release rate and the recurrence interval of tremors.

ALMA resolves turbulent, rotating [CII] emission in a young starburst galaxy atz= 4.8

We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) [CII] observations of the z=4.7555 submillimetre galaxy, ALESS 73.1. Our 0.5" FWHM map resolves the [CII] emitting gas which is centred close to the active galactic nucleus (AGN). The gas kinematics are dominated by rotation but with high turbulence, v_rot/sigma_int~3.1, and a Toomre Q parameter <1 throughout the disk. By fitting three independent thin rotating disk models to our data, we derive a total dynamical mass of 3+-2x10^10 M_sol. This is close to the molecular gas mass derived from previous CO(2-1) observations, and implies a CO to H_2 conversion factor alpha_CO<2.3M_sol(K km/s/pc^2)^-1. The mass budget also constrains the stellar mass to <3.1x10^10 M_sol, and entails a gas fraction of f_gas>~0.4. The diameter of the dust continuum emission is <2 kpc, while the star-formation rate is as high as 1000 M_sol/yr. Combined with our stellar mass constraint, this implies an extreme specific star formation rate >80 Gyr^{-1}, especially since there are no clear indications of recent merger activity. Finally, our high signal-to-noise [CII] measurement revises the observed [NII]/[CII] ratio, which suggests a close to solar metallicity, unless the [CII] flux contains significant contributions from HII regions. Our observations suggest that ALESS73.1 is a nascent galaxy undergoing its first major burst of star formation, embedded within an unstable but metal-rich gas disk.

Elastic-Plastic Deformation of KDP Crystals under Nanoindentation

This paper investigates the mechanical properties of potassium dihydrogen phosphate (KDP) crystals with the aid of nanoindentation using a conical diamond indenter. It was found that when unloading is after the first pop-in, the common method of obtaining elastic modulus from the unloading curve of nanoindentation is no longer applicable, because the unloading is inelastic. The study revealed that the pop-in could be due to dislocation nucleation and propagation, and that the first pop-in occurs under a stress below that of the major dislocation burst. Hence, the macroscopic yielding point, which is usually regarded as the onset of plasticity of a material, is nanoscopically not a critical point of the first dislocation in KDP. The study found that the elastic modulus of KDP indenting on its (001) plane is 52.8±3.8GPa. The hardness of the material is 1.89±0.05GPa.

Activation of group I metabotropic glutamate receptors enhances persistent sodium current and rhythmic bursting in main olfactory bulb external tufted cells

Rhythmically bursting olfactory bulb external tufted (ET) cells are thought to play a key role in synchronizing glomerular network activity to respiratory-driven sensory input. Whereas spontaneous bursting in these cells is intrinsically generated by interplay of several voltage-dependent currents, bursting strength and frequency can be modified by local intrinsic and centrifugal synaptic input. Activation of metabotropic glutamate receptors (mGluRs) engages a calcium-dependent cation current (I(CAN)) that increases rhythmic bursting, but mGluRs may also modulate intrinsic mechanisms involved in bursting. Here, we used patch-clamp electrophysiology in rat olfactory bulb slices to investigate whether mGluRs modulate two key intrinsic currents involved in ET cell burst initiation: persistent sodium (I(NaP)) and hyperpolarization-activated cation (Ih) currents. Using a BAPTA-based internal solution to block I(CAN), we found that the mGluR1/5 agonist DHPG enhanced I(NaP) but did not alter Ih. I(NaP) enhancement consisted of increased current at membrane potentials between -60 and -50 mV and a hyperpolarizing shift in activation threshold. Both effects would be predicted to shorten the interburst interval. In agreement, DHPG modestly depolarized (∼3.5 mV) ET cells and increased burst frequency without effect on other major burst parameters. This increase was inversely proportional to the basal burst rate such that slower ET cells exhibited the largest increases. This may enable ET cells with slow intrinsic burst rates to pace with faster sniff rates. Taken with other findings, these results indicate that multiple neurotransmitter mechanisms are engaged to fine-tune rhythmic ET cell bursting to context- and state-dependent changes in sniffing frequency.

Editorial

Editorial

Evolutionary active transposable elements in the genome of the coelacanth

The apparent morphological stasis in the lineage of the coelacanth, which has been called a "living fossil" by many, has been suggested to be causally related to a slow evolution of its genome, with strongly reduced activity of transposable elements (TEs). Analysis of the African coelacanth showed that at least 25% of its genome is constituted of transposable elements including retrotransposons, endogenous retroviruses and DNA transposons, with a strong predominance of non-Long Terminal Repeat (non-LTR) retrotransposons. The coelacanth genome has been shaped by four major general bursts of transposition during evolution, with major contributions of LINE1, LINE2, CR1, and Deu non-LTR retrotransposons. Many transposable elements are expressed in different tissues and might be active. The number of TE families in coelacanth, but also in lungfish, is lower than in teleost fish, but is higher than in chicken and human. This observation is in agreement with the hypothesis of a sequential elimination of many TE families in the sarcopterygian lineage during evolution. Taken together, our analysis indicates that the coelacanth contains more TE families than birds and mammals, and that these elements have been active during the evolution of the coelacanth lineage. Hence, at the level of transposable element activity, the coelacanth genome does not appear to evolve particularly slowly.

Leader neurons drive spontaneous and evoked activation patterns in cortical networks

Recent studies about the generation and propagation of coordinated activity in cultured neuronal networks reported the existence of privileged neurons that consistently fire earlier than others at the onset of synchronized bursting events (or network bursts, NB), which have been termed major burst leaders (MBL) [1]. At the same time, by stimulating the network from different channels one can obtain very different responses, not only in size and delay but also in the activation order of the responding neurons [2]. We electrically stimulated rat cortical networks cultured on micro-electrode arrays from different locations, either MBL or non-MBL. We evaluated the intensity and the delay of responses from either MBL or non-MBL and we also compared the spontaneous and the evoked activation patterns. By comparing the responses obtained by stimulating either MBL or non-MBL, we found that the stimulation from MBL induces on average earlier responses. By comparing the responses of MBL and non-MBL, we found that MBL respond better and more rapidly to the stimulation coming from any other site in the network. Some networks showed different spontaneous propagation patterns within synchronized bursts depending on the identity of the corresponding MBL (Figure ​(Figure1).1). In these cases the evoked propagation patterns correlate with the spontaneous ones and also depend on the spatial location of the stimulating site with respect to MBL. Figure 1 A. Similarity matrix of activation order for 1000 spontaneous NB, ranked according to the MBL (indicated by numbers). Two distinct propagation patterns are visible. B. Color maps of average delays of followers with respect to either MBL spontaneous activation ... To summarize, we demonstrated that MBLs do not only drive the propagation of coordinated spontaneous activations, but also play a special role in coordinating and driving the evoked bursts of activity.

Burst fractures of the lumbar spine in frontal crashes

BackgroundIn the United States, major compression and burst type fractures (>20% height loss) of the lumbar spine occur as a result of motor vehicle crashes, despite the improvements in restraint technologies. Lumbar burst fractures typically require an axial compressive load and have been known to occur during a non-horizontal crash event that involve high vertical components of loading. Recently these fracture patterns have also been observed in pure horizontal frontal crashes. This study sought to examine the contributing factors that would induce an axial compressive force to the lumbar spine in frontal motor vehicle crashes. MethodsWe searched the National Automotive Sampling System (NASS, 1993–2011) and Crash Injury Research and Engineering Network (CIREN, 1996–2012) databases to identify all patients with major compression lumbar spine (MCLS) fractures and then specifically examined those involved in frontal crashes. National trends were assessed based on weighted NASS estimates. Using a case–control study design, NASS and CIREN cases were utilized and a conditional logistic regression was performed to assess driver and vehicle characteristics. CIREN case studies and biomechanical data were used to illustrate the kinematics and define the mechanism of injury. ResultsDuring the study period 132 NASS cases involved major compression lumbar spine fractures for all crash directions. Nationally weighted, this accounted for 800 cases annually with 44% of these in horizontal frontal crashes. The proportion of frontal crashes resulting in MCLS fractures was 2.5 times greater in late model vehicles (since 2000) as compared to 1990s models. Belted occupants in frontal crashes had a 5 times greater odds of a MCLS fracture than those not belted, and an increase in age also greatly increased the odds. In CIREN, 19 cases were isolated as horizontal frontal crashes and 12 of these involved a major compression lumbar burst fracture primarily at L1. All were belted and almost all occurred in late model vehicles with belt pretensioners and buckets seats. ConclusionMajor compression burst fractures of the lumbar spine in frontal crashes were induced via a dynamic axial force transmitted to the pelvis/buttocks into the seat cushion/pan involving belted occupants in late model vehicles with increasing age as a significant factor.

Molecular phylogenetics of ponerine ants (Hymenoptera: Formicidae: Ponerinae).

Recent molecular phylogenetic studies of ants (Hymenoptera: Formicidae) have revolutionized our understanding of how these ecologically dominant organisms diversified, but detailed phylogenies are lacking for most major ant subfamilies. I report the results of the first detailed phylogenetic study of the ant subfamily Ponerinae, a diverse cosmopolitan lineage whose properties make it an attractive model system for investigating social and ecological evolution in ants. Molecular sequence data were obtained from four nuclear genes (wingless, long-wavelength rhodopsin, rudimentary [CAD], 28S rDNA; total of ~3.3 kb) for 86 ponerine taxa, representing all three ponerine tribes, 22 of the 28 currently recognized genera, and 14 of the 18 informal subgenera of Pachycondyla, a heterogeneous grouping whose monophyly is doubtful on morphological grounds. Phylogenetic reconstructions using maximum likelihood and Bayesian inference support the monophyly of Ponerinae and tribe Platythyreini, but fail to support the monophyly of the large tribe Ponerini due to its inclusion of the unusual genus Thaumatomyrmex. Pachycondyla is inferred to be broadly non-monophyletic. Numerous novel generic and suprageneric relationships are inferred within Ponerini, which was found to consist of four major multi-generic clades (the Ponera, Pachycondyla, Plectroctena and Odontomachus genus groups) plus the single genera Hypoponera and Harpegnathos. Uncertainty remains in some regions of the phylogeny, including at the base of Ponerini, possibly reflecting rapid radiation. Divergence dating using a Bayesian relaxed clock method estimates an origin for stem Ponerinae in the upper Cretaceous, a major burst of diversification near the K/T boundary, and a rich and continual history of diversification during the Cenozoic. These results fail to support the predictions of the "dynastic-succession hypothesis" previously developed to explain the high species diversity of Ponerinae. Though model-based reconstructions of historical biogeography and trait evolution were not attempted in this study, the phylogeny suggests that ponerine evolution was marked by regionalized radiations and frequent faunal exchange between major biogeographic provinces. The reported results also imply multiple origins of cryptobiotic foraging, mass raiding behavior, and gamergate reproduction within Ponerinae, highlighting the value of the subfamily as a model for studying the incipient evolution of these and other ecological and behavioral traits.

Exorcism

<i>Exorcism</i>

Mechanical Behavior and Fabrication of One-dimensional Nanomaterials

For centuries, improvements in structural materials relied heavily on processing, which in turn, dictated resulting microstructure and properties. Materials sciences are entering a revolutionary era, where specific material properties are attained through not only materials but also architecture control of its constituents, often with sub-micron and nanoscale dimensions. One-dimensional homogeneous or heterogeneous micro/nanoscale materials often show the unusual mechanical strength and physical features in electric and optical spectra, and they have broad potential applications in future nano devices. Thus, the study of the structure and properties of micro/nanoscale materials is becoming a burgeoning scientific research field. In parallel, synthesizing such controllable one-dimensional nanoscale materials has attracted extensive attention. In this regard, five articles are included in this issue, three related to mechanical deformation and two to the synthesis. Regarding mechanical deformation in micro/nanoscale materials, Zhiwei Shan at Xi’an Jaiotong University reviews their recent progress on revealing the novel properties of micro/ nanoscaled metal pillars by using in situ transmission electron microscopy (TEM), including facecentered cubic (fcc) single-crystal Ni, body-centered cubic (bcc) single-crystal Mo alloy, hexagonal-closepacked (hcp) a-Ti alloy, and metallic glasses. For instance, ‘‘mechanical annealing’’ was demonstrated in submicron-sized fcc single-crystal nickel pillars fabricated through focused ion beam (FIB). But, mechanical annealing occurs in a bcc single crystal as the dimension is below 200 nm, which was attributed to the high flow stress enhanced by size effect. Strong size effect is also observed in hcp structured Ti alloy. The critical sample size ( 1 lm) below which the plastic flow becomes quite continuous without any major strain burst and the maximum flow stress is observed to saturate at close to the ideal strength of Ti. The second article focuses on deformation mechanism (twinning/slip) dependence on sample size in hcp metals. Quian Yu at the University of California, Berkeley has conducted in situ and ex situ small-scale testing for hcp metals, Mg, Ti, and their alloys. The effect of size on deformation twinning in these systems is remarkable, resulting in a significant change in corresponding mechanical properties. They found that deformation twinning can be restricted by the size effect in certain dimension regimes and materials but also can be promoted by the presence of surfaces at extremely small scales. The third article reviews deformation mechanisms in one-dimensional nanostructures containing homogeneous (i.e., grain and twin boundaries) and heterogeneous (i.e., phase and precipitate-matrix boundaries) interfaces. Julia Greer at the California Institute of Technology has been devoted to investigating mechanical behavior and microstructural evolution in small-scale metallic systems, whose deformation is governed by intricate interactions of defects with interfaces as well as free surfaces, including multiple grain boundaries spanning the sample volume; periodic in-grown twin boundaries; and bi-material samples. This overview sheds light on the relative role of intrinsic versus extrinsic dimension limitations on the deformation mechanisms in nanostructured metals. Although testing one-dimensional samples is usually fabricated by the FIB technique, defects associated with one-dimensional growth are also closely related with the materials mechanical properties. Hanchen Huang at the University of Connecticut has been devoted to developing a solid framework for the growth of one-dimensional crystalline nanostructures. The framework derives from three scientific advancements in crystal growth, with a focus on multiple-layer surface steps: the diffusion barrier of adatoms down multiple-layer surface steps, the formation and stability of multiple-layer surface steps, and the dimension of surface facets that are bounded by competing monolayer and multiple-layer surface steps. As an example of impact, this framework predicts that growth of Al nanorods is not feasible using physical vapor depoJOM, Vol. 64, No. 10, 2012

Time analysis of above-threshold ionization in extreme-ultraviolet laser pulses: a three-dimensional study

The ab&#xA0;initio investigation of ionization shows the strong regularization of the Coulomb potential by a high-frequency laser field in the stabilization regime, which is characterized with a large energy shift in the first dressed state. The decreasing of the second major ionization burst at the lowering edge of the laser pulse indicates another aspect of three-dimensional effect. Moreover, the modulation in the ionization time profile, previously attributed to the classical drift [Phys. Rev. A83, 063418 (2011)], is illustrated by a superposition of the two free-electron wave-packets, which have arisen via ionization from the two different Kramers&#x2013;Henneberger states. This finding is in excellent agreement with the time profile of the current density.

Culture-based study of endophytes associated with rubber trees in Peru reveals a new class of Pezizomycotina: Xylonomycetes

Through a culture-based survey of living sapwood and leaves of rubber trees (Hevea spp.) in remote forests of Peru, we discovered a new major lineage of Ascomycota, equivalent to a class rank. Multilocus phylogenetic analyses reveal that this new lineage originated during the radiation of the ‘Leotiomyceta’, which resulted not only in the evolution of the Arthoniomycetes, Dothideomycetes, Eurotiomycetes, Geoglossomycetes, Lecanoromycetes, Leotiomycetes, Lichinomycetes, and Sordariomycetes, but also of the majority of hyperdiverse foliar endophytes. Because its origin is nested within this major burst of fungal diversification, we could not recover strong support for its phylogenetic relationship within the ‘Leotiomyceta’. Congruent with their long phylogenetic history and distinctive preference for growing in sapwood, this new lineage displays unique morphological, physiological, and ecological traits relative to known endophytes and currently described members of the ‘Leotiomyceta’. In marked contrast to many foliar endophytes, the strains we isolated fail to degrade cellulose and lignin in vitro. Discovery of the new class, herein named Xylonomycetes and originally mis-identified by ITSrDNA sequencing alone, highlights the importance of inventorying tropical endophytes from unexplored regions, using multilocus data sets to infer the phylogenetic placement of unknown strains, and the need to sample diverse plant tissues using traditional methods to enhance efforts to discover the evolutionary, taxonomic, and functional diversity of symbiotrophic fungi.

Unusual Emissions at Various Energies Prior to the Impulsive Phase of the Large Solar Flare and Coronal Mass Ejection of 4 November 2003

The GOES X28 flare of 4 November 2003 was the largest ever recorded in its class. It produced the first evidence for two spectrally separated emission components, one at microwaves and the other in the THz range of frequencies. We analyzed the pre-flare phase of this large flare, twenty minutes before the onset of the major impulsive burst. This period is characterized by unusual activity in X-rays, sub-THz frequencies, Hα, and microwaves. The CME onset occurred before the onset of the large burst by about 6 min. It was preceded by pulsations of 3 – 5 s periods at sub-THz frequencies together with X-ray and microwave enhancements. The sub-THz pulsations faded out as impulsive bursts were detected at 100 – 300 keV and 7 GHz, close to the time of the first Hα brightening and the CME onset. The activities detected prior to and at the CME onset were located nearly 2 arcmin south of the following large flare, suggesting they were separate events. This unusual activity brings new clues to understanding the complex energy buildup mechanisms prior to the CME onset, occurring at a distinct location and well before the major flare that exploded afterwards.

Expansion of CORE-SINEs in the genome of the Tasmanian devil

BackgroundThe genome of the carnivorous marsupial, the Tasmanian devil (Sarcophilus harrisii, Order: Dasyuromorphia), was sequenced in the hopes of finding a cure for or gaining a better understanding of the contagious devil facial tumor disease that is threatening the species’ survival. To better understand the Tasmanian devil genome, we screened it for transposable elements and investigated the dynamics of short interspersed element (SINE) retroposons.ResultsThe temporal history of Tasmanian devil SINEs, elucidated using a transposition in transposition analysis, indicates that WSINE1, a CORE-SINE present in around 200,000 copies, is the most recently active element. Moreover, we discovered a new subtype of WSINE1 (WSINE1b) that comprises at least 90% of all Tasmanian devil WSINE1s. The frequencies of WSINE1 subtypes differ in the genomes of two of the other Australian marsupial orders. A co-segregation analysis indicated that at least 66 subfamilies of WSINE1 evolved during the evolution of Dasyuromorphia. Using a substitution rate derived from WSINE1 insertions, the ages of the subfamilies were estimated and correlated with a newly established phylogeny of Dasyuromorphia. Phylogenetic analyses and divergence time estimates of mitochondrial genome data indicate a rapid radiation of the Tasmanian devil and the closest relative the quolls (Dasyurus) around 14 million years ago.ConclusionsThe radiation and abundance of CORE-SINEs in marsupial genomes indicates that they may be a major player in the evolution of marsupials. It is evident that the early phases of evolution of the carnivorous marsupial order Dasyuromorphia was characterized by a burst of SINE activity. A correlation between a speciation event and a major burst of retroposon activity is for the first time shown in a marsupial genome.

NGC 4656UV: A UV-SELECTED TIDAL DWARF GALAXY CANDIDATE

We report the discovery of a UV-bright tidal dwarf galaxy candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet we investigate the gas kinematics and stellar properties of this system. The HI morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M_sun yr^-1 from the FUV flux and measure a total HI mass of 3.8x10^8 M_sun for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low metallicity system whose only major burst of star formation occurred within the last ~260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object--whether it is tidal or pre-existing in origin--in the context of its metallicity being a factor of ten lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates.