Pleiotropy as a mechanism to stabilize cooperation

Most genes affect many traits. This phenomenon, known as pleiotropy, is a major constraint on evolution because adaptive change in one trait may be prevented because it would compromise other traits affected by the same genes. Here we show that pleiotropy can have an unexpected effect and benefit one of the most enigmatic of adaptations--cooperation. A spectacular act of cooperation occurs in the social amoeba Dictyostelium discoideum, in which some cells die to form a stalk that holds the other cells aloft as reproductive spores. We have identified a gene, dimA, in D. discoideum that has two contrasting effects. It is required to receive the signalling molecule DIF-1 that causes differentiation into prestalk cells. Ignoring DIF-1 and not becoming prestalk should allow cells to cheat by avoiding the stalk. However, we find that in aggregations containing the wild-type cells, lack of the dimA gene results in exclusion from spores. This pleiotropic linkage of stalk and spore formation limits the potential for cheating in D. discoideum because defecting on prestalk cell production results in an even greater reduction in spores. We propose that the evolution of pleiotropic links between cheating and personal costs can stabilize cooperative adaptations.     

Discovery of a new population of high-energy gamma-ray sources in the Milky Way

One of the great mysteries of the high-energy gamma-ray sky is the group of approximately 170 unidentified point sources found along the Galactic plane. They are more numerous than all other high-energy gamma-ray sources combined and, despite 20 years of effort, no clear counterparts have been found at other wavelengths. Here we report a new population of such objects. A cluster of approximately 20 faint sources appears north of the Galactic Centre, which is part of a broader class of faint objects at mid-latitudes. In addition, we show in a model-independent way that the mid-latitude sources are distinct from the population of bright unidentified sources along the Galactic plane. The distribution on the sky indicates that the faint mid-latitude sources are associated with the Gould belt of massive stars and gas clouds at approximately 600 light years distance, as has been previously suggested.     

Natural occurrence of 2-5A in interferon-treated EMC virus-infected L cells.

Until now the interferon-mediated 2'-5' adenine oligonucleotide inhibitors (2-5A) of cell-free protein synthesis have not been detected in intact cells. Here we report their natural occurrence in interferon-treated, EMC virus-infected mouse L cells in amounts consistent with the idea that they play a part in the inhibition of virus growth.     

New evidence for enhanced cosmogenic isotope production rate in the atmosphere ≈37 kaBP from the Guliya ice core

A³⁶Cl peak was found in the predicted section of Guliya ice core, from the Qinghai-Tibetan Plateau, at about 37 kaBP. This cannot be interpreted by means of changes in the accumulation rate, but by the enhanced cosmogenic isotope production rate in the atmosphere. Compared with the records of¹⁰Be and³⁶Cl in the other regions, the peaks of the cosmogenic isotopes are global and can be considered as time marks. An intriguing fact is that the peaks coincided with cold periods.     

Plutonium-based superconductivity with a transition temperature above 18 K

Plutonium is a metal of both technological relevance and fundamental scientific interest. Nevertheless, the electronic structure of plutonium, which directly influences its metallurgical properties, is poorly understood. For example, plutonium's 5f electrons are poised on the border between localized and itinerant, and their theoretical treatment pushes the limits of current electronic structure calculations. Here we extend the range of complexity exhibited by plutonium with the discovery of superconductivity in PuCoGa5. We argue that the observed superconductivity results directly from plutonium's anomalous electronic properties and as such serves as a bridge between two classes of spin-fluctuation-mediated superconductors: the known heavy-fermion superconductors and the high-T(c) copper oxides. We suggest that the mechanism of superconductivity is unconventional; seen in that context, the fact that the transition temperature, T(c) approximately 18.5 K, is an order of magnitude greater than the maximum seen in the U- and Ce-based heavy-fermion systems may be natural. The large critical current displayed by PuCoGa5, which comes from radiation-induced self damage that creates pinning centres, would be of technological importance for applied superconductivity if the hazardous material plutonium were not a constituent.