Coral communities are regionally enriched along an oceanic biodiversity gradient

Ecological communities are influenced by processes operating at multiple scales. Thus, a better understanding of how broad- as well as local-scale processes affect species diversity and richness is increasingly becoming a central focus in modern community ecology. Here, in a study of unprecedented geographical scope, we show significant regional and local variation in the species richness of coral assemblages across an oceanic biodiversity gradient. The gradient that we sampled extends 10,000 km eastwards from the world's richest coral biodiversity hotspot in the central Indo-Pacific. Local richness and the size of regional species pools decline significantly across 15 islands spanning the gradient. In addition, richness declines across three adjacent habitats (reef slopes, crests and flats). In each habitat, a highly consistent linear relationship between local and regional species richness indicates strong regional enrichment. Thus, even on the most diverse coral reefs in the world, local coral assemblages are profoundly affected by regional-scale processes. Understanding these historical and biogeographical influences is essential for the effective management and preservation of these endangered communities.     

Export of dissolved organic carbon from peatlands under elevated carbon dioxide levels

Peatlands represent a vast store of global carbon. Observations of rapidly rising dissolved organic carbon concentrations in rivers draining peatlands have created concerns that those stores are beginning to destabilize. Three main factors have been put forward as potential causal mechanisms, but it appears that two alternatives--warming and increased river discharge--cannot offer satisfactory explanations. Here we show that the third proposed mechanism, namely shifting trends in the proportion of annual rainfall arriving in summer, is similarly unable to account for the trend. Instead we infer that a previously unrecognized mechanism--carbon dioxide mediated stimulation of primary productivity--is responsible. Under elevated carbon dioxide levels, the proportion of dissolved organic carbon derived from recently assimilated carbon dioxide was ten times higher than that of the control cases. Concentrations of dissolved organic carbon appear far more sensitive to environmental drivers that affect net primary productivity than those affecting decomposition alone.     

Ant parasite queens revert to mating singly

Multiple mating (polyandry) is widespread among animal groups, particularly insects. But the factors that maintain it and underlie its evolution are hard to verify because benefits and costs are not easily quantified and they tend to be similar in related species. Here we compare the mating strategies of the leaf-cutting ant Acromyrmex echinatior and its recently derived social parasite Acromyrmex insinuator, which is also its closest relative. We find that although the host queens mate with up to a dozen different males, the social parasite mates only singly. This rapid and surprising reversion to single mating in a socially parasitic ant indicates that the costs of polyandry are probably specific to a free-living lifestyle.     

Recombination signal sequences restrict chromosomal V(D)J recombination beyond the 12/23 rule

The genes encoding the variable regions of lymphocyte antigen receptors are assembled from variable (V), diversity (D) and joining (J) gene segments. V(D)J recombination is initiated by the recombinase activating gene (RAG)-1 and -2 proteins, which introduce DNA double-strand breaks between the V, D and J segments and their flanking recombination signal sequences (RSSs). Generally expressed DNA repair proteins then carry out the joining reaction. The conserved heptamer and nonamer sequences of the RSSs are separated by non-conserved spacers of 12 or 23 base pairs (forming 12-RSSs and 23-RSSs). The 12/23 rule, which is mediated at the level of RAG-1/2 recognition and cutting, specifies that V(D)J recombination occurs only between a gene segment flanked by a 12-RSS and one flanked by a 23-RSS. Vbeta segments are appended to DJbeta rearrangements, with little or no direct Vbeta to Jbeta joining, despite 12/23 compatibility of Vbeta 23-RSSs and Jbeta12-RSSs. Here we use embryonic stem cells and mice with a modified T-cell receptor (TCR)beta locus containing only one Dbeta (Dbeta1) gene segment and one Jbeta (Jbeta1) gene cluster to show that the 5' Dbeta1 12-RSS, but not the Jbeta1 12-RSSs, targets rearrangement of a diverse Vbeta repertoire. This targeting is precise and position-independent. This additional restriction on V(D)J recombination has important implications for the regulation of variable region gene assembly and repertoire development.     

Vanilloid receptor-1 is essential for inflammatory thermal hyperalgesia

The vanilloid receptor-1 (VR1) is a ligand-gated, non-selective cation channel expressed predominantly by sensory neurons. VR1 responds to noxious stimuli including capsaicin, the pungent component of chilli peppers, heat and extracellular acidification, and it is able to integrate simultaneous exposure to these stimuli. These findings and research linking capsaicin with nociceptive behaviours (that is, responses to painful stimuli in animals have led to VR1 being considered as important for pain sensation. Here we have disrupted the mouse VR1 gene using standard gene targeting techniques. Small diameter dorsal root ganglion neurons isolated from VR1-null mice lacked many of the capsaicin-, acid- and heat-gated responses that have been previously well characterized in small diameter dorsal root ganglion neurons from various species. Furthermore, although the VR1-null mice appeared normal in a wide range of behavioural tests, including responses to acute noxious thermal stimuli, their ability to develop carrageenan-induced thermal hyperalgesia was completely absent. We conclude that VR1 is required for inflammatory sensitization to noxious thermal stimuli but also that alternative mechanisms are sufficient for normal sensation of noxious heat.     

Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export

Diverse molecules, from small antibacterial drugs to large protein toxins, are exported directly across both cell membranes of gram-negative bacteria. This export is brought about by the reversible interaction of substrate-specific inner-membrane proteins with an outer-membrane protein of the TolC family, thus bypassing the intervening periplasm. Here we report the 2.1-A crystal structure of TolC from Escherichia coli, revealing a distinctive and previously unknown fold. Three TolC protomers assemble to form a continuous, solvent-accessible conduit--a 'channel-tunnel' over 140 A long that spans both the outer membrane and periplasmic space. The periplasmic or proximal end of the tunnel is sealed by sets of coiled helices. We suggest these could be untwisted by an allosteric mechanism, mediated by protein-protein interactions, to open the tunnel. The structure provides an explanation of how the cell cytosol is connected to the external environment during export, and suggests a general mechanism for the action of bacterial efflux pumps.