Network anatomy and in vivo physiology of visual cortical neurons

In the cerebral cortex, local circuits consist of tens of thousands of neurons, each of which makes thousands of synaptic connections. Perhaps the biggest impediment to understanding these networks is that we have no wiring diagrams of their interconnections. Even if we had a partial or complete wiring diagram, however, understanding the network would also require information about each neuron's function. Here we show that the relationship between structure and function can be studied in the cortex with a combination of in vivo physiology and network anatomy. We used two-photon calcium imaging to characterize a functional property--the preferred stimulus orientation--of a group of neurons in the mouse primary visual cortex. Large-scale electron microscopy of serial thin sections was then used to trace a portion of these neurons' local network. Consistent with a prediction from recent physiological experiments, inhibitory interneurons received convergent anatomical input from nearby excitatory neurons with a broad range of preferred orientations, although weak biases could not be rejected.     

The excitation of solar-like oscillations in a δSct star by efficient envelope convection

Delta Scuti (δSct) stars are opacity-driven pulsators with masses of 1.5-2.5 M⊙, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in δSct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δSct star HD187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.     

In defence of inclusive fitness theory

Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Arguably the defining characteristic of the scientific process is its capacity for self-criticism and correction. Nowak et al. challenge proposed connections between relatedness and the evolution of eusociality, suggest instead that defensible nests and "spring-loaded" traits are key, and present alternative modelling approaches. They then dismiss the utility of Hamilton's insight that relatedness has a profound evolutionary effect, formalized in his widely accepted inclusive fitness theory as Hamilton's rule ("Rise and fall of inclusive fitness theory"). However, we believe that Nowak et al. fail to make their case for logical, theoretical and empirical reasons.     

Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000

Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing. Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 1766, these floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at ￡1.3 billion (refs 5, 6). Although the flooding was deemed a 'wake-up call' to the impacts of climate change at the time, such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming, but fail to account fully for the complex hydrometeorology associated with flooding. Here we present a multi-step, physically based 'probabilistic event attribution' framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000. Using publicly volunteered distributed computing, we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather, both under realistic conditions, and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred. Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.     

Geographic patterns of ground-dwelling arthropods across an ecoregional transition in the North American Southwest

We examined the biogeographic patterns of ground-dwelling arthropod communities across a heterogeneous semiarid region of the Southern Rio Grande Rift Valley of New Mexico. Our 3 sites included portions of 5 ecoregions, with the middle site a transition area where all ecoregions converged. We addressed the following 3 questions: (1) Do the species assemblage patterns for ground arthropods across habitats and sites conform to recognized ecoregions? (2) Are arthropod assemblages in distinct vegetation-defined habitats within an ecoregion more similar to each other or to assemblages in similar vegetation-defined habitats in other ecoregions? (3) Is there a detectable edge effect with increased arthropod diversity in the area of converging ecoregions? We encountered 442 target arthropod species from pitfall traps operating continuously for 7 years over a series of different habitats at each of the 3 sites. We examined geographic distributions of spider and cricket/grasshopper species in detail, and they showed affinities for different ecoregions, respectively. Each habitat within a study site supported a unique overall arthropod assemblage; nevertheless, different habitats at the same site were more similar to each other than they were to similar habitats at other sites. Overall arthropod species richness was greatest in the area where all 5 ecoregions converged. Arthropod species and their geographic distributions are poorly known relative to vascular plants and vertebrate animals. Findings from this research indicate that ecoregional classification is a useful tool for understanding biogeographic patterns among arthropods.     

Vegetation and soil zonation associated with Juniperus pinchotii Sudw. trees

Herbaceous vegetation pattern and soil properties around individual Juniperus pinchotii Sudw. trees were studied on a grazed and a relict grassland in western Texas. Herb standing crop and soil samples were obtained under the canopy, at canopy edge, and beyond the canopy edge of three to five trees on each of four dates. Standing crop was lowest midway between the bole and canopy edge. Soil organic matter was highest under juniper canopies on both sites. Soil pH and P were not related to distance from tree bole on either site. Herbaceous pattern from under the canopy to canopy edge apparently depended primarily on individual tree size. However, trees had little influence on herbaceous vegetation pattern 3-5 m beyond canopy edge, a response attributed to distance-independent interaction between J. pinchotii and herbaceous vegetation. Given a shallow soil underlain by indurated caliche and tree densities ranging from 288 (relict size) to 2123 (grazed site) trees/ha, the interaction between J. pinchotii and herbaceous vegetation did not change over a distance of 3-5 m from tree canopy edge in our study area.     

Spruce beetle ( Dendroctonus rufipennis ) outbreak in Engelmann spruce ( Picea Engelmannii ) in central Utah, 1986-1998

Extensive Engelmann spruce ( Picea engelmannii Parry ex Engelm.) mortality caused by the spruce beetle ( Dendroctonus rufipennis Kirby) has been occurring at the southern end of the Wasatch Plateau in central Utah. This spruce beetle outbreak is the largest recorded in Utah history. An extensive ground survey was conducted in 1996 on the Manti-LaSal National Forest, Sanpete and Ferron Ranger Districts, to document mortality and impact of a major spruce beetle outbreak on post-outbreak forest composition. In 1998 the same sites were resurveyed. Survey results indicate Engelmann spruce basal area (BA) loss averaged 78% in trees ≥5 inches diameter breast height (DBH) in 1996. Ninety percent of BA ≥5 inches DBH was lost within the same sites by 1998. Tree mortality of spruce ≥5 inches DBH expressed in trees per acre (TPA) averaged 53% in 1996. In 1998 TPA ≥5 inches DBH mortality averaged 73%. Before the outbreak live Engelmann spruce BA ≥5 inches DBH averaged 99 square feet, and TPA ≥5 inches DBH averaged 97. In the sites surveyed in 1996 and resurveyed in 1998, Engelmann spruce BA ≥5 inches DBH averaged 21 and 9 square feet, and TPA ≥5 inches DBH averaged 43 and 25, respectively. Overstory tree species composition changed from stands dominated by spruce to subalpine fir. Stand ratings for potential spruce beetle outbreaks were high to mostly medium hazard pre-outbreak and medium to primarily low hazard by 1998, as a result of reduction in average spruce diameter, total basal area, and overstory spruce.     

A loose and separate certainty: Caves, Fuchs and Schack on quantum probability one

Carlton Caves, Fuchs, and Schack (2002) have recently appealed to an argument of mine (Stairs, 1983) to address a problem for their subjective Bayesian account of quantum probability. The difficulty is that on the face of it, quantum mechanical probabilities of one appear to be objective, but in that case, the Born Rule would yield a continuum of probabilities between zero and one. If so, we end up with objective probabilities strictly between zero and one. The authors claim that objective probabilities of one leads to a dilemma: give up locality or fall into contradiction. I argue that this conclusion depends on an overly strong interpretation of objectivism about quantum probabilities.     

Mechanisms controlling cellular suicide: role of Bcl-2 and caspases

Apoptosis is an essential and highly conserved mode of cell death that is important for normal development, host defense and suppression of oncogenesis. Faulty regulation of apoptosis has been implicated in degenerative conditions, vascular diseases, AIDS and cancer. Among the numerous proteins and genes involved, members of the Bcl-2 family play a central role to inhibit or promote apoptosis. In this article, we present up-to-date information and recent discoveries regarding biochemical functions of Bcl-2 family proteins, positive and negative interactions between these proteins, and their modification and regulation by either proteolytic cleavage or by cytosolic kinases, such as Raf-1 and stress-activated protein kinases. We have critically reviewed the functional role of caspases and the consequences of cleaving key substrates, including lamins, poly(ADP ribose) polymerase and the Rb protein. In addition, we have presented the latest Fas-induced signalling mechanism as a model for receptor-linked caspase regulation. Finally, the structural and functional interactions of Ced-4 and its partial mam malian homologue, apoptosis protease activating factor-1 (Apaf-1), are presented in a model which includes other Apafs. This model culminates in a caspase/Apaf regulatory cascade to activate the executioners of programmed cell death following cytochrome c release from the mitochondria of mammalian cells. The importance of these pathways in the treatment of disease is highly dependent on further characterization of genes and other regulatory molecules in mammals. Received 18 February 1998; accepted February 1998