Foraging as sampling without replacement: A Bayesian statistical model for estimating biases in target selection

Foraging entails finding multiple targets sequentially. In humans and other animals, a key observation has been a tendency to forage in ‘runs’ of the same target type. This tendency is context-sensitive, and in humans, it is strongest when the targets are difficult to distinguish from the distractors. Many important questions have yet to be addressed about this and other tendencies in human foraging, and a key limitation is a lack of precise measures of foraging behaviour. The standard measures tend to be run statistics, such as the maximum run length and the number of runs. But these measures are not only interdependent, they are also constrained by the number and distribution of targets, making it difficult to make inferences about the effects of these aspects of the environment on foraging. Moreover, run statistics are underspecified about the underlying cognitive processes determining foraging behaviour. We present an alternative approach: modelling foraging as a procedure of generative sampling without replacement, implemented in a Bayesian multilevel model. This allows us to break behaviour down into a number of biases that influence target selection, such as the proximity of targets and a bias for selecting targets in runs, in a way that is not dependent on the number of targets present. Our method thereby facilitates direct comparison of specific foraging tendencies between search environments that differ in theoretically important dimensions. We demonstrate the use of our model with simulation examples and re-analysis of existing data. We believe our model will provide deeper insights into visual foraging and provide a foundation for further modelling work in this area.     

Diacylglycerols interact with the L2 lipidation site in TRPC3 to induce a sensitized channel state

Coordination of lipids within transient receptor potential canonical channels (TRPCs) is essential for their Ca²⁺ signaling function. Single particle cryo‐EM studies identified two lipid interaction sites, designated L1 and L2, which are proposed to accommodate diacylglycerols (DAGs). To explore the role of L1 and L2 in TRPC3 function, we combined structure‐guided mutagenesis and electrophysiological recording with molecular dynamics (MD) simulations. MD simulations indicate rapid DAG accumulation within both L1 and L2 upon its availability within the plasma membrane. Electrophysiological experiments using a photoswitchable DAG‐probe reveal potentiation of TRPC3 currents during repetitive activation by DAG. Importantly, initial DAG exposure generates a subsequently sensitized channel state that is associated with significantly faster activation kinetics. TRPC3 sensitization is specifically promoted by mutations within L2, with G652A exhibiting sensitization at very low levels of active DAG. We demonstrate the ability of TRPC3 to adopt a closed state conformation that features partial lipidation of L2 sites by DAG and enables fast activation of the channel by the phospholipase C‐DAG pathway.     

The hepatic galactosyl receptor system: two different ligand dissociation pathways are mediated by distinct receptor populations

After internalization of 125I-asialo-orosomucoid (ASOR) by isolated rat hepatocytes, ligand dissociates by two kinetically distinct pathways (Oka and Weigel, J. Biol. Chem. 257, 10,253, 1983). These slow and fast dissociation pathways correspond to two functionally different subpopulations of cell surface galactosyl receptors designated, respectively, State 1 and State 2 receptors. Freshly isolated cells or cells equilibrated below 24 degrees C express only State 1 receptors. Cells equilibrated at 37 degrees C express both State 1 and State 2 receptors. Ligand dissociation after internalization of surface-bound 125I-ASOR was measured using the permeabilizing detergent, digitonin. The slow dissociation pathway was mediated by State 1 receptors and was the only pathway expressed by cells which were freshly isolated or had been equilibrated at 24 degrees C. State 2 receptors are expressed at temperatures above about 20 degrees C, and both the fast and slow dissociation pathways occurred in cells equilibrated at 37 degrees C. State 2 receptors therefore mediate the rapid dissociation pathway. Dissociation and subsequent degradation of specifically bound ligand routed in either pathway were complete, respectively, within 3 and 6 hrs.     

The anti-sickling drug lawsone (2-OH-1,4-naphthoquinone) protects sickled cells against membrane damage

The ability of an anti-sickling drug lawsone, 2-OH-1,4-naphthoquinone, and two related compounds to inhibit the haematoporphyrin-sensitised photohaemolysis of normal and sickle cell erythrocytes has been investigated. The compounds appear to protect the erythrocyte membranes by reaction with transient oxidative species. Differential effects between normal and sickle cells are shown and these are attributed to the different membrane composition of irreversibly sickled erythrocytes. This report describes a possible basis for the decreased formation of irreversibly sickled cells in the presence of lawsone.     

Expression of the cloned subunits of Escherichia coli transhydrogenase from separate replicons

The pntA and pntB genes of Escherichia coli, encoding the alpha- and beta-subunits of the pyridine nucleotide transhydrogenase, were cloned individually in two different compatible plasmids into Escherichia coli mutants lacking transhydrogenase activity. Energy-linked and non-energy-linked transhydrogenase activities were produced only in cells carrying both plasmids thus showing that the products of both genes are required for the formation of an active enzyme. ATP-energized transhydrogenase activity was not increased in cells containing amplified levels of the transhydrogenase when the cell membrane ATPase was also amplified. It is suggested that the excess transhydrogenase is effectively uncoupled from the ATPase by compartmentalization in the cell.     

Dissecting the immune response to the entomopathogen Photorhabdus

Bacterial pathogens either hide from or modulate the host's immune response to ensure their survival. Photorhabdus is a potent insect pathogenic bacterium that uses entomopathogenic nematodes as vectors in a system that represents a useful tool for probing the molecular basis of immunity. During the course of infection, Photorhabdus multiplies rapidly within the insect, producing a range of toxins that inhibit phagocytosis of the invading bacteria and eventually kill the insect host. Photorhabdus bacteria have recently been established as a tool for investigating immune recognition and defense mechanisms in model hosts such as Manduca and Drosophila. Such studies pave the way for investigations of gene interactions between pathogen virulence factors and host immune genes, which ultimately could lead to an understanding of how some Photorhabdus species have made the leap to becoming human pathogens.     

Determination of reactor biomass by acoustic resonance densitometry

Acoustic resonance densitometry (ARD) is reported as a method suitable not only for precise investigations into changes of specific gravity in bioreactor media but also as a technique able to provide an accurate wide range and direct determination of cellular mass in fermentation processes. It is further shown that this method can replace present optical procedures, minimizing dilution errors and operator involvement and is suitable for development as an on-line biomass monitoring system.     

Clarireedia: A new fungal genus comprising four pathogenic species responsible for dollar spot disease of turfgrass

Dollar spot is one of the most destructive and economically important fungal diseases of amenity turfgrasses. The causal agent was first described in 1937 as the ascomycete Sclerotinia homoeocarpa. However, the genus-level taxonomic placement of this fungus has been the subject of an ongoing debate for over 75 y. Existing morphological and rDNA sequence evidence indicates that this organism is more appropriately placed in the family Rutstroemiaceae rather than the Sclerotiniaceae. Here we use DNA sequence data from samples of the dollar spot fungus and other members of the Rutstroemiaceae (e.g. Rutstroemia, Lanzia, Lambertella) collected throughout the world to determine the generic identity of the turfgrass dollar spot pathogen. Phylogenetic evidence from three nucleotide sequence markers (CaM, ITS and Mcm7; 1810-bp) confirmed that S. homoeocarpa is not a species of Sclerotinia; nor is it a member of any known genus in the Rutstroemiaceae. These data support the establishment of a new genus, which we describe here as Clarireedia gen. nov. The type species for the genus, Clarireedia homoeocarpa comb. nov., is described to accommodate the dollar spot fungus, and a neotype is designated. Three new species in this clade, Clarireedia bennettii sp. nov., Clarireedia jacksonii sp. nov., and Clarireedia monteithiana sp. nov. that also cause dollar spot disease are described. Clarireedia homoeocarpa and C. bennettii occur primarily on Festuca rubra (C3 grass) hosts and appear to be restricted to the United Kingdom. Clarireedia jacksonii and C. monteithiana occur on a variety of C3 and C4 grass hosts, respectively, and appear to be globally distributed. This resolved taxonomy puts to rest a major controversy amongst plant pathologists and provides a foundation for better understanding the nature and biology of these destructive pathogens.