Isolation and characterization of a protochordate histocompatibility locus

Histocompatibility--the ability of an organism to distinguish its own cells and tissue from those of another--is a universal phenomenon in the Metazoa. In vertebrates, histocompatibility is a function of the immune system controlled by a highly polymorphic major histocompatibility complex (MHC), which encodes proteins that target foreign molecules for immune cell recognition. The association of the MHC and immune function suggests an evolutionary relationship between metazoan histocompatibility and the origins of vertebrate immunity. However, the MHC of vertebrates is the only functionally characterized histocompatibility system; the mechanisms underlying this process in non-vertebrates are unknown. A primitive chordate, the ascidian Botryllus schlosseri, also undergoes a histocompatibility reaction controlled by a highly polymorphic locus. Here we describe the isolation of a candidate gene encoding an immunoglobulin superfamily member that, by itself, predicts the outcome of histocompatibility reactions. This is the first non-vertebrate histocompatibility gene described, and may provide insights into the evolution of vertebrate adaptive immunity.     

Mutual phase-locking of microwave spin torque nano-oscillators

The spin torque effect that occurs in nanometre-scale magnetic multilayer devices can be used to generate steady-state microwave signals in response to a d.c. electrical current. This establishes a new functionality for magneto-electronic structures that are more commonly used as magnetic field sensors and magnetic memory elements. The microwave power emitted from a single spin torque nano-oscillator (STNO) is at present typically less than 1 nW. To achieve a more useful power level (on the order of microwatts), a device could consist of an array of phase coherent STNOs, in a manner analogous to arrays of Josephson junctions and larger semiconductor oscillators. Here we show that two STNOs in close proximity mutually phase-lock-that is, they synchronize, which is a general tendency of interacting nonlinear oscillator systems. The phase-locked state is distinct, characterized by a sudden narrowing of signal linewidth and an increase in power due to the coherence of the individual oscillators. Arrays of phase-locked STNOs could be used as nanometre-scale reference oscillators. Furthermore, phase control of array elements (phased array) could lead to nanometre-scale directional transmitters and receivers for wireless communications.     

Botany: specialized bird perch aids cross-pollination

Birds may hover over or perch on flowers when feeding on nectar, and this assists cross-pollination if they then visit other plants. Here we investigate the curious sterile inflorescence axis of the South African Cape endemic 'rat's tail' plant (Babiana ringens, Iridaceae), whose function--unlike in other bird-pollinated plants--is exclusively to provide a perch for foraging birds. We find that this structure promotes the plant's mating success by causing the malachite sunbird (Nectarinia famosa), its main pollinator, to adopt a position ideal for the cross-pollination of its unusual ground-level flowers.     

Secondary craters on Europa and implications for cratered surfaces

For several decades, most planetary researchers have regarded the impact crater populations on solid-surfaced planets and smaller bodies as predominantly reflecting the direct ('primary') impacts of asteroids and comets. Estimates of the relative and absolute ages of geological units on these objects have been based on this assumption. Here we present an analysis of the comparatively sparse crater population on Jupiter's icy moon Europa and suggest that this assumption is incorrect for small craters. We find that 'secondaries' (craters formed by material ejected from large primary impact craters) comprise about 95 per cent of the small craters (diameters less than 1 km) on Europa. We therefore conclude that large primary impacts into a solid surface (for example, ice or rock) produce far more secondaries than previously believed, implying that the small crater populations on the Moon, Mars and other large bodies must be dominated by secondaries. Moreover, our results indicate that there have been few small comets (less than 100 m diameter) passing through the jovian system in recent times, consistent with dynamical simulations.     

Ancient co-speciation of simian foamy viruses and primates

Although parasite-host co-speciation is a long-held hypothesis, convincing evidence for long-term co-speciation remains elusive, largely because of small numbers of hosts and parasites studied and uncertainty over rates of evolutionary change. Co-speciation is especially rare in RNA viruses, in which cross-species transfer is the dominant mode of evolution. Simian foamy viruses (SFVs) are ubiquitous, non-pathogenic retroviruses that infect all primates. Here we test the co-speciation hypothesis in SFVs and their primate hosts by comparing the phylogenies of SFV polymerase and mitochondrial cytochrome oxidase subunit II from African and Asian monkeys and apes. The phylogenetic trees were remarkably congruent in both branching order and divergence times, strongly supporting co-speciation. Molecular clock calibrations revealed an extremely low rate of SFV evolution, 1.7 x 10(-8) substitutions per site per year, making it the slowest-evolving RNA virus documented so far. These results indicate that SFVs might have co-speciated with Old World primates for at least 30 million years, making them the oldest known vertebrate RNA viruses.     

Dance reveals symmetry especially in young men

Dance is believed to be important in the courtship of a variety of species, including humans, but nothing is known about what dance reveals about the underlying phenotypic--or genotypic--quality of the dancer. One measure of quality in evolutionary studies is the degree of bodily symmetry (fluctuating asymmetry, FA), because it measures developmental stability. Does dance quality reveal FA to the observer and is the effect stronger for male dancers than female? To answer these questions, we chose a population that has been measured twice for FA since 1996 (ref. 9) in a society (Jamaican) in which dancing is important in the lives of both sexes. Motion-capture cameras created controlled stimuli (in the form of videos) that isolated dance movements from all other aspects of visual appearance (including FA), and the same population evaluated these videos for dancing ability. Here we report that there are strong positive associations between symmetry and dancing ability, and these associations were stronger in men than in women. In addition, women rate dances by symmetrical men relatively more positively than do men, and more-symmetrical men value symmetry in women dancers more than do less-symmetrical men. In summary, dance in Jamaica seems to show evidence of sexual selection and to reveal important information about the dancer.     

Genomic sequence of the pathogenic and allergenic filamentous fungus Aspergillus fumigatus

Aspergillus fumigatus is exceptional among microorganisms in being both a primary and opportunistic pathogen as well as a major allergen. Its conidia production is prolific, and so human respiratory tract exposure is almost constant. A. fumigatus is isolated from human habitats and vegetable compost heaps. In immunocompromised individuals, the incidence of invasive infection can be as high as 50% and the mortality rate is often about 50% (ref. 2). The interaction of A. fumigatus and other airborne fungi with the immune system is increasingly linked to severe asthma and sinusitis. Although the burden of invasive disease caused by A. fumigatus is substantial, the basic biology of the organism is mostly obscure. Here we show the complete 29.4-megabase genome sequence of the clinical isolate Af293, which consists of eight chromosomes containing 9,926 predicted genes. Microarray analysis revealed temperature-dependent expression of distinct sets of genes, as well as 700 A. fumigatus genes not present or significantly diverged in the closely related sexual species Neosartorya fischeri, many of which may have roles in the pathogenicity phenotype. The Af293 genome sequence provides an unparalleled resource for the future understanding of this remarkable fungus.