Gene Flow and Hybridization between Numerically Imbalanced Populations of Two Duck Species in the Falkland Islands

Interspecific hybridization is common in plants and animals, particularly in waterfowl (Anatidae). One factor shown to contribute to hybridization is restricted mate choice, which can occur when two species occur in sympatry but one is rare. The Hubbs principle, or “desperation hypothesis,” states that under such circumstances the rarer species is more likely to mate with heterospecifics. Here we report interspecific hybridization between two waterfowl species that coexist in broad sympatry and mixed flocks throughout southern South America. Speckled teal (Anas flavirostris) and yellow-billed pintails (Anas georgica) are abundant in continental South America, but in the Falkland Islands speckled teal outnumber yellow-billed pintails approximately ten to one. Using eight genetic loci (mtDNA and 7 nuclear introns) coupled with Bayesian assignment tests and relatedness analysis, we identified a speckled teal x yellow-billed pintail F1 hybrid female and her duckling sired by a male speckled teal. Although our sample in the Falkland Islands was small, we failed to identify unequivocal evidence of hybridization or introgression in a much larger sample from Argentina using a three-population “isolation with migration” coalescent analysis. While additional data are needed to determine if this event in the Falkland Islands was a rare singular occurrence, our results provide further support for the “desperation hypothesis,” which states that scarcity in one population and abundance of another will often lead to hybridization

The peroxisome: still a mysterious organelle

More than half a century of research on peroxisomes has revealed unique features of this ubiquitous subcellular organelle, which have often been in disagreement with existing dogmas in cell biology. About 50 peroxisomal enzymes have so far been identified, which contribute to several crucial metabolic processes such as β-oxidation of fatty acids, biosynthesis of ether phospholipids and metabolism of reactive oxygen species, and render peroxisomes indispensable for human health and development. It became obvious that peroxisomes are highly dynamic organelles that rapidly assemble, multiply and degrade in response to metabolic needs. However, many aspects of peroxisome biology are still mysterious. This review addresses recent exciting discoveries on the biogenesis, formation and degradation of peroxisomes, on peroxisomal dynamics and division, as well as on the interaction and cross talk of peroxisomes with other subcellular compartments. Furthermore, recent advances on the role of peroxisomes in medicine and in the identification of novel peroxisomal proteins are discussed

Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts

We present constraints on cosmological parameters using number counts as a function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ (PSZ) catalogue. The PSZ is selected through the signature of the Sunyaev--Zeldovich (SZ) effect, and the sub-sample used here has a signal-to-noise threshold of seven, with each object confirmed as a cluster and all but one with a redshift estimate. We discuss the completeness of the sample and our construction of a likelihood analysis. Using a relation between mass $M$ and SZ signal $Y$ calibrated to X-ray measurements, we derive constraints on the power spectrum amplitude $\sigma_8$ and matter density parameter $\Omega_{\mathrm{m}}$ in a flat $\Lambda$CDM model. We test the robustness of our estimates and find that possible biases in the $Y$--$M$ relation and the halo mass function are larger than the statistical uncertainties from the cluster sample. Assuming the X-ray determined mass to be biased low relative to the true mass by between zero and 30%, motivated by comparison of the observed mass scaling relations to those from a set of numerical simulations, we find that $\sigma_8=0.75\pm 0.03$, $\Omega_{\mathrm{m}}=0.29\pm 0.02$, and $\sigma_8(\Omega_{\mathrm{m}}/0.27)^{0.3} = 0.764 \pm 0.025$. The value of $\sigma_8$ is degenerate with the mass bias; if the latter is fixed to a value of 20% we find $\sigma_8(\Omega_{\mathrm{m}}/0.27)^{0.3}=0.78\pm 0.01$ and a tighter one-dimensional range $\sigma_8=0.77\pm 0.02$. We find that the larger values of $\sigma_8$ and $\Omega_{\mathrm{m}}$ preferred by Planck's measurements of the primary CMB anisotropies can be accommodated by a mass bias of about 40%. Alternatively, consistency with the primary CMB constraints can be achieved by inclusion of processes that suppress power on small scales relative to the $\Lambda$CDM model, such as a component of massive neutrinos (abridged).Comment: 20 pages, accepted for publication by A&

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Failure to demonstrate anti-lymphocytic antibody in serum of patients with AIDS.

Several studies have produced evidence for anti-lymphocytic antibodies (ALA) in AIDS. We attempted to demonstrate ALA by immunofluorescent flow cytometry. Normal human peripheral blood lymphocytes (PBL) and the T-cell line, CEM, were incubated with sera from patients with AIDS, patients with chronic HIV infection and HIV-seronegative blood donors. ALA were not detected in the AIDS sera with fluorescein isothiocyanate (FITC)-labelled rabbit anti-mu, anti-alpha or the F(ab)2 fragment of anti-human gamma. A small number of CEM cells (2%) fluoresced with either AIDS or normal serum. A larger proportion of PBL were immunofluorescent after serum treatment but there was no difference between normal and AIDS serum. We were able to detect ALA in the serum of patients with systemic lupus erythematosus with both CEM and PBL. In contrast, incubation of either CEM or PBL with some AIDS sera, and to a lesser degree normal sera, enhanced the binding of intact FITC-rabbit anti-gamma. Anti-gamma was not bound by CEM cells unexposed to human serum. The binding was blocked by rabbit immunoglobulin, demonstrable with CEM fixed in 1% formalin, and unrelated to the density of CD4 on CEM cells

Human immunodeficiency virus (HIV) infection in the regular sexual partners of homosexual men with AIDS and persistent generalised lymphadenopathy.

Thirty-five homosexual men who had been the regular sexual partners (for at least 6 months) of anti-HIV-positive patients with AIDS (N = 18) or PGL (N = 17) were studied. Twenty-one (60%) were seropositive, but 14 (40%) were consistently anti-HIV-negative. The duration of relationship with the index case was not statistically different in seropositive compared to seronegative partners; median 26 months (range 7-60) vs 30 months (range 7-60). However, seropositive partners had a significantly higher monthly number of other sexual partners and sexually transmitted diseases and a higher frequency of insertive and receptive anal intercourse in the preceding five years. The risk of acquiring HIV infection was significantly increased by frequent receptive anal intercourse when the frequency of insertive was controlled for but not the converse. Seronegative partners had undetectable antibodies by live and fixed cell immunofluorescence and by radioimmunoprecipitation and were repeatedly negative by competitive enzyme immunoassay. Furthermore, the sera of seronegative partners lacked HIV neutralising activity. Peripheral blood mononuclear cells (PBMCs) from seronegative partners, stained with monoclonal antibodies to seven different CD4 epitopes, revealed no differences when compared to those from heterosexual controls and no qualitative differences from cells from seropositive individuals. In addition, PBMCs from seronegative partners could be productively infected by HIV in vitro. If resistance to infection in seronegative partners exists, then it is likely that mechanisms other than a specific humoral immunity or CD4 polymorphisms are involved

Immunization with recombinant p17/p24:Ty virus-like particles in human immunodeficiency virus-infected persons.

In studies of the natural history of human immunodeficiency virus type 1 (HIV-1) infection, it has been repeatedly shown that higher-titer antibody responses to the HIV gag p24 protein correlate with less rapid disease progression. In HIV-negative persons, immunization with HIV-1 p17/p24:Ty virus-like particles (p24-VLP) induced humoral and cellular immune responses to p24. This construct was therefore studied as a potential immunotherapeutic agent with the objective of augmenting the immune response to p24 in a double-blind placebo-controlled trial involving 74 p24 antibody-positive, asymptomatic HIV-1-infected subjects with CD4 cell counts > 350/mm3. Immunization with p24-VLP was generally well tolerated. Immunization with p24-VLP did not increase p24 antibody levels and had no effect on CD4 cell counts or virus load. The failure to increase p24 antibody titers cannot entirely be explained by the subjects' immunodeficiency because most generated an antibody response to Ty, a yeast component of the immunogen