Tuning clathrate hydrates for hydrogen storage

The storage of large quantities of hydrogen at safe pressures is a key factor in establishing a hydrogen-based economy. Previous strategies--where hydrogen has been bound chemically, adsorbed in materials with permanent void space or stored in hybrid materials that combine these elements--have problems arising from either technical considerations or materials cost. A recently reported clathrate hydrate of hydrogen exhibiting two different-sized cages does seem to meet the necessary storage requirements; however, the extreme pressures (approximately 2 kbar) required to produce the material make it impractical. The synthesis pressure can be decreased by filling the larger cavity with tetrahydrofuran (THF) to stabilize the material, but the potential storage capacity of the material is compromised with this approach. Here we report that hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to approximately 4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability. The tuning mechanism is quite general and convenient, using water-soluble hydrate promoters and various small gaseous guests.     

Disruptive sexual selection for plumage coloration in a passerine bird

The theory of sexual selection was developed to explain the evolution of highly exaggerated sexual ornaments. Now supported by vast empirical evidence, sexual selection is generally considered to favour individuals with the most extreme trait expression. Here we describe disruptive selection on a sexual ornament, plumage coloration, in yearling male lazuli buntings (Passerina amoena). In habitats with limited good-quality nesting cover, the dullest and the brightest yearlings were more successful in obtaining high-quality territories, pairing with females and siring offspring, than yearlings with intermediate plumage. This pattern reflects the way that territorial adult males vary levels of aggression to influence the structure of their social neighbourhood. Adult males showed less aggression towards dull yearlings than intermediate and bright ones, permitting the dull yearlings to settle on good territories nearby. Fitness comparisons based on paternity analyses showed that both the adults and dull yearlings benefited genetically from this arrangement, revealing a rare example of sexually selected male-male cooperation.     

Multimodal warning signals for a multiple predator world

Aposematism is an anti-predator defence, dependent on a predator's ability to associate unprofitable prey with a prey-borne signal. Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated. Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats-predators with divergent sensory capacities. Many tiger moths advertise chemical defence using conspicuous colouration and/or ultrasonic clicks. During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.     

The tumour suppressor protein VHL targets hypoxia-inducible factors for oxygen-dependent proteolysis.

Hypoxia-inducible factor-1 (HIF-1) has a key role in cellular responses to hypoxia, including the regulation of genes involved in energy metabolism, angiogenesis and apoptosis. The alpha subunits of HIF are rapidly degraded by the proteasome under normal conditions, but are stabilized by hypoxia. Cobaltous ions or iron chelators mimic hypoxia, indicating that the stimuli may interact through effects on a ferroprotein oxygen sensor. Here we demonstrate a critical role for the von Hippel-Lindau (VHL) tumour suppressor gene product pVHL in HIF-1 regulation. In VHL-defective cells, HIF alpha-subunits are constitutively stabilized and HIF-1 is activated. Re-expression of pVHL restored oxygen-dependent instability. pVHL and HIF alpha-subunits co-immunoprecipitate, and pVHL is present in the hypoxic HIF-1 DNA-binding complex. In cells exposed to iron chelation or cobaltous ions, HIF-1 is dissociated from pVHL. These findings indicate that the interaction between HIF-1 and pVHL is iron dependent, and that it is necessary for the oxygen-dependent degradation of HIF alpha-subunits. Thus, constitutive HIF-1 activation may underlie the angiogenic phenotype of VHL-associated tumours. The pVHL/HIF-1 interaction provides a new focus for understanding cellular oxygen sensing.     

Prospects for NMR imaging in the study of biological morphogenesis

Small objects can be visualised with a spatial resolution that approaches microscopic dimensions using the technique of high resolution nuclear magnetic resonance (NMR) imaging. Some important features of the method are described and the prospects for using the technique to study morphogenesis are discussed. It is concluded that NMR imaging, in conjunction with the related method of localised spectroscopy, is capable of producing novel structural information.