Clonogenicity, gene expression and phenotype during neutrophil versus erythroid differentiation of cytokine-stimulated CD34 human marrow cells in vitro.

With the objective to correlate clonogenicity, gene expression and phenotype during differentiation, human bone marrow CD34+ cells were cultured in vitro to stimulate erythroid or neutrophil development, and sorted into five subpopulations according to their surface expression of CD15/CD33 and blood group antigen A/CD117 respectively. Sorted cells were cultured in methylcellulose and analysed by real-time reverse transcription polymerase chain reaction for expression of neutrophil and erythroid marker genes. Surface expression of CD15 coincided with restriction to neutrophil/monocyte differentiation and A antigen with restriction to erythroid differentiation. GATA-2 mRNA was down-regulated during both neutrophil and erythroid maturation, whereas GATA-1, SCL, ABO, erythropoietin receptor, Kell, glycophorin A, β-globin and α-haemoglobin stabilizing protein were up-regulated during erythroid differentiation and silenced during neutrophil differentiation. CCAAT/enhancer-binding protein (C/EBP)-α, PU.1, granulocyte colony-stimulating factor receptor, PR3, C/EBP-e and lactoferrin were sequentially expressed during neutrophil differentiation but rapidly down-regulated during the early erythroid stages. Nuclear factor erythroid-derived 2 (NF-E2) and glycophorin C were expressed both during neutrophil and erythroid differentiation. Our data support the notion of early expression of several lineage-associated genes prior to actual lineage commitment, defined by surface expression of CD15 and A antigen as markers for definitive neutrophil/monocyte and erythroid differentiation respectively. Previous findings, primarily from cell lines and mouse models, have been extended to adult human haematopoiesis

Why do male Callosobruchus maculatus harm their mates?

Males of the bruchid beetle Callosobruchus maculatus have spines on their intromittent organs that puncture the female reproductive tract during mating. Females kick their mates during copulation. If females are prevented from kicking the males, copulations last longer and the injuries females sustain are more severe. We tested whether or not these injuries represent real fitness costs that can be mitigated by kicking and also what males gain by inflicting them. Our results show that females do indeed suffer lowered lifetime fecundity if they are prevented from kicking. However, we could find no evidence that males gain benefits through harming their mates. It has been suggested that the way females respond to the harm may benefit the male causing it. Injured females may be less willing to remate to avoid sustaining further injuries, or they may respond by increasing their rate of oviposition if they perceive the injuries as a threat to their survival. In our study, however, females that were prevented from kicking did not respond by delaying remating or increasing their rate of oviposition. Furthermore, preventing females from kicking during their second copulation did not make their second mates more successful in sperm competition. This suggests that the spines have evolved for other reasons than harming the females, such as serving as an anchor during copulation, and that the harm they cause is a side effect of a male adaptation and is not itself adaptive for either sex

Chemical abundances in 43 metal-poor stars

We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni and Ba for 43 metal-poor field stars in the solar neighbourhood with iron abundances [Fe/H] ranging from -0.4 to -3.0. Total abundance errors are estimated to about 0.1-0.2 dex for most elements, while relative abundances are most probably more accurate. We have made an extensive comparison with other similar studies and traced the reasons for the, in most cases, relatively small differences. Among the results we note the following: We find [O/Fe] from the O I IR- triplet lines to possibly increase beyond [Fe/H]=-1.0, though considerably less than obtained by others from abundances based on OH lines. We find correlations among the deviations for individual stars from the trends of individual alpha elements relative to Fe. This may support the idea that the formation of the Halo stars occurred in smaller systems with different star formation rates. We verify the finding by Gratton et al. (2003b) that stars that do not participate in the rotation of the galactic disk show a lower mean and larger spread in [alpha/Fe] than stars participating in the general rotation. The latter stars also seem to show some correlation between [alpha/Fe] and rotation speed. We finally advocate that a spectroscopic study of a larger sample of halo stars with well-defined selection criteria is very important, in addition to the very considerable efforts that various groups have already made. (Abridged)Comment: A&A LaTeX, 24 pages, 18 b/w figures. Astronomy & Astrophysics, accepte

Lithium in Blanco1: Implications for Stellar Mixing

We obtain lithium abundances for G and K stars in Blanco 1, an open cluster with an age similar to, or slightly younger than, the Pleiades. We critically examine previous spectroscopic abundance analyses of Blanco 1 and conclude that while there were flaws in earlier work, it is likely that Blanco 1 is close in overall metallicity to the older Hyades cluster and more metal-rich than the Pleiades. However, we find Blanco 1 has Li abundances and rotation rates similar to the Pleiades, contradicting predictions from standard stellar evolution models, in which convective pre-main sequence (PMS) Li depletion should increase rapidly with metallicity. If the high metallicity of Blanco 1 is subsequently confirmed, our observations imply (1) that a currently unknown mechanism severely inhibits PMS Li depletion, (2) that additional non-standard mixing modes, such as those driven by rotation and angular momentum loss, are then responsible for main sequence Li depletion between the ages of Blanco 1 and the Hyades, and (3) that in clusters younger than the Hyades, metallicity plays only a minor role in determining the amount of Li depletion among G and K stars. These conclusions suggest that Li abundance remains a useful age indicator among young (less than 700 Myr) stars even when metallicities are unknown. If non-standard mixing is effective in Population I stars, the primordial Li abundance could be significantly larger than present day Population II Li abundances, due to prior Li depletion.Comment: 18 pages, 3 figs. To appear in ApJ Vol. 511 (Jan 20 1999

The evolution of harm: effect of sexual conflicts and population size

Conflicts of interest between mates can lead to the evolution of male traits reducing female fitness and to coevolution between the sexes. The rate of adaptation and counter-adaptation is constrained by the intensity of selection and its efficiency, which depends on drift and genetic variability. This leads to the largely untested prediction that coevolutionary adaptations such as those driven by sexual conflict should evolve faster in large populations where the response to selection is stronger and sexual selection is more intense. We test this using the bruchid beetle Callosobruchus maculatus, a species with well documented male harm. Whilst most experimental evolution studies remove sexual conflicts, we reintroduce sexual conflict in populations where it has been experimentally removed. Both population size and standing genetic variability were manipulated in a factorial experimental design. After 90 generations of relaxed conflict (monogamy), the reintroduction of sexual conflicts for 30 generations favoured males that harmed females and females more resistant to the genital damage inflicted by males. Large population size rather than high initial genetic variation allowed males to evolve faster and become more harmful. Sexual selection thus creates conditions where males benefit from harming females and this selection is more effective in larger populations

Genetic examination of historical North Atlantic right whale (Eubalaena glacialis) bone specimens from the eastern North Atlantic: Insights into species history, transoceanic population structure, and genetic diversity

Species monitoring and conservation is increasingly challenging under current climate change scenarios. For the North Atlantic right whale (Eubalaena glacialis) this challenge is heightened by the added effects of complicated and uncertain past species demography. Right whales once had a much wider distribution across the North Atlantic Ocean, although the degree to which right whales in the western and eastern North Atlantic were genetically isolated remains unknown. We analyzed DNA from 24 4th–20th century (CE) right whale bone specimens that were collected from 10 historical and archaeological sites in Iceland, the Faroe Islands, and Scotland. Following mtDNA species identification, we obtained 15-locus nuclear microsatellite profiles from a subset of eight specimens and compared these to contemporary data from animals remaining in the western North Atlantic population. While some specimens share mtDNA haplotypes with the contemporary population, several new haplotypes were found. Moderate mtDNA and nuclear differentiation between the two regions was identified (mtDNA: FST = 0.0423, ΦST = 0.041; nuclear DNA: FST = 0.024). Interpretation of the relationships between animals in the two regions is not simple, and this research highlights the difficulty in conducting such assessments in species with complex histories of unknown structure prior to extensive exploitation.publishedVersio

A New Association of Post-T Tauri Stars Near The Sun

Observing ROSAT sources in 20 x 25 deg centered at the high latitude active star ER Eri, we found evidences for a new young nearby association (~30Myr at~60pc), the Horologium Association (HorA), formed by at least 10 probable and 6 possible members, some being Post-T Tauri stars. We examine several requirements that characterize a young association and they, together, create a strong evidence for the reality of the HorA. In fact, the Li line intensities are between those of the oldest classical T Tauri stars and the ones of the Local Association stars. The space velocities of the HorA relative to the Sun, U= -9.5+/-1.0, V = -20.9 +/- 1.1, W = -2.1 +/- 1.9, are not far from those of the Local Association. We suggest that some hotter and non-X-ray active stars, with similar space velocities, could be massive members of the HorA, among them, the nearby Be star Achernar. The maximum of the mass distribution function of the HorA is around 0.8 solar masses. At its distance, the projected size of the HorA, ~50 pc, would be larger than our surveyed area and many other members could have been missed. We also observed 3 control regions, two at northern and southern galactic latitudes and a third one in the known TW Hya Association (TWA), and the properties and distribution of their young stars strengthen the reality of the HorA. Contrary to the TWA, the only known binaries in the HorA are 2 very wide systems. The HorA is much more isolated from clouds and older than the TWA and could give some clues about the lifetime of the disks around T Tauri stars. Actually, none of the proposed members is an IRAS source indicating an advanced stage of the evolution of their accreting disks. ER Eri itself was found to be a RS CVn-like system.Comment: 25 pages, 5 eps figures, to appear in Astron.

A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood

Full space velocities are computed for a sample of 130 nearby RR Lyrae variables using both ground-based and Hipparcos proper motions. In many cases proper motions from multiple sources have been averaged to produce a significant improvement in the transverse space velocity errors. In most cases, this exceeds the accuracy of Hipparcos proper motions alone. The velocity ellipsoids computed for halo and thick disk samples are in agreement with previous studies. No distinct sample of thin disk RR Lyraes has been isolated but there is kinematic evidence for some thin disk stars in our thick disk samples. A sample of 21 stars with [Fe/H] < -1.0 and disk-like kinematics have been isolated. It is concluded from their kinematics and spatial distribution that these stars represent a sample of RR Lyraes in the metal weak tail of the thick disk. In the halo samples the distribution of V velocities is not gaussian, even when the metal weak thick disk stars are removed. Also, a plot of U and W velocities as a function of V velocity for the kinematically unbiased halo sample shows some curious structure. The cause of these kinematic anomalies is not clear. In addition, systematic changes to the distance scale within the range of currently accepted values of Mv(RR) are shown to significantly change the calculated halo kinematics. Fainter values of Mv(RR), such as those obtained by statistical parallax (~ 0.60 to 0.70 at [Fe/H]=-1.9), result in local halo kinematics similar to those reported in independent studies of halo kinematics, while brighter values of Mv(RR), such as those obtained through recent analysis of Hipparcos subdwarf parallaxes (~ 0.30 to 0.40 at [Fe/H]=-1.9), result in a halo with retrograde rotation and significantly enlarged velocity dispersions.Comment: 40 pages (including tables), 7 PostScript figures, accepted for publication in the Astronomical Journa

The Top Ten solar analogs in the ELODIE library

Several solar analogs have been identified in the library of high resolution stellar spectra taken with the echelle spectrograph ELODIE. A purely differential method has been used, based on the chi2 comparison of a large number of G dwarf spectra to 8 spectra of the Sun, taken on the Moon and Ceres. HD 146233 keeps its status of closest ever solar twin (Porto de Mello & da Silva 1997). Some other spectroscopic analogs have never been studied before, while the two planet-host stars HD095128 and HD186427 are also part of the selection. The fundamental parameters found in the literature for these stars show a surprising dispersion, partly due to the uncertainties which affect them. We discuss the advantages and drawbacks of photometric and spectroscopic methods to search for solar analogs and conclude that they have to be used jointly to find real solar twins.Comment: 12 pages, accepted in A&

Probing the peak of the star formation rate density with the extragalactic background light

The extragalactic background light (EBL), i.e., the diffuse meta-galactic photon field in the ultraviolet to infrared, is dominated by the emission from stars in galaxies. It is, therefore, intimately connected with the integrated star formation rate density (SFRD). In this paper, the SFRD is constrained using recent limits on the EBL density derived from observations of distant sources of high and very-high energy gamma-rays. The stellar EBL contribution is modeled utilizing simple stellar population spectra including dust attenuation and emission. For modeling the SFRD up to z=4 a broken power law function in z+1 is assumed. A wide range of values for the different model parameters (SFRD(z), metallicity, dust absorption) is investigated and their impact on the resulting EBL is studied. The calculated EBL densities are compared with the specific EBL density limits and constraints on the SFRD are derived. For the fiducial model, adopting a Chabrier initial mass function (IMF) and a second power law index for the SFRD of beta=0.3, the SFRD is constrained to <~ 0.1 M_solar yr^-1 Mpc^-3 and < 0.2 M_solar yr^-1 Mpc^-3 for a redshift of z~1 and z~2, respectively. The limits for a redshift of z~1 are in tension with SFRD measurements derived from instantaneous star formation tracers. While the tension for the conservative fiducial model in this study is not yet overly strong, the tension increases when applying plausible changes to the model parameters, e.g., using a Salpeter instead of a Chabrier IMF or a adopting a sub-solar metallicity.Comment: 10 pages, 12 figure, accepted for publication in MNRAS, v3: clarifications following referee's comments, conclusions unchange