Plant-disperser mutualisms in a semi-arid habitat invaded by <Emphasis Type="Italic">Lantana camara</Emphasis> L.

Dispersal is an important ecological process that affects plant population structure and community composition. Invasive plants with fleshy fruits rapidly form associations with native and invasive dispersers, and may affect existing native plant-disperser associations. We asked whether frugivore visitation rate and fruit removal was associated with plant characteristics in a community of fleshy-fruited plants and whether an invasive plant receives more visitation and greater fruit removal than native plants in a semi-arid habitat of Andhra Pradesh, India. Tree-watches were undertaken at individuals of nine native and one invasive shrub species to assess the identity, number and fruit removal by avian frugivores. Network analyses and generalised linear mixed-effects models were used to understand species and community-level patterns. All plants received most number of visits from abundant, generalist avian frugivores. Number of frugivore visits and time spent by frugivores at individual plants was positively associated with fruit crop size, while fruit removal was positively associated with number of frugivore visits and their mean foraging time at individual plants. The invasive shrub, Lantana camara L. (Lantana), had lower average frugivore visit rate than the community of fleshy-fruited plants and received similar average frugivore visits but greater average per-hour fruit removal than two other concurrently fruiting native species. Based on the results of our study, we infer that there is little evidence of competition between native plants and Lantana for the dispersal services of native frugivores and that more data are required to assess the nature of these interactions over the long term. We speculate that plant associations with generalist frugivores may increase the functional redundancy of this frugivory network, buffering it against loss of participating species.     

Structural and functional changes in the olfactory pathway of adult Drosophila take place at a critical age

The olfactory system of several holometabolous insect species undergoes anatomical changes after eclosion of the imago, following those occurring during metamorphosis. In parallel, odor experience and learning performance also evolve with age. Here, we analyze the case of adult Drosophila females. Synaptogenesis in the antennal lobe (AL) starts in late pupa and continues during the first days of adult life, at the same time as the behavioral response to odors matures. Individual olfactory glomeruli (DM6, DM2, and V) display specific growth patterns between days 1 and 12 of adult life. Experience can modify the olfactory pathway both structurally and functionally as shown by adaptation experiments. The modifications associated with this form of nonassociative learning seem to take place at a critical age. Exposure to benzaldehyde at days 2-5 of adult life, but not at 8-11, causes behavioral adaptation as well as structural changes in DM2 and V glomeruli. Altered levels in intracellular cAMP, caused by dunce and rutabaga mutants, do not affect the normal changes in glomerular size, at least at day 6 of development, but they prevent those elicited by experience, establishing a molecular difference between glomerular changes of intrinsic versus environmental origin. Taken together, these data demonstrate an imprinting-like phenomenon in the olfactory pathway of young Drosophila adults, and illustrate its glomerulus-specific dynamics.     

Retrograde regulation in the CNS; neuron-specific interpretations of TGF-beta signaling

Retrograde signals influence neuronal survival, differentiation, synaptogenesis, and plasticity. Several recent papers describe novel roles for the well-studied TGF-beta pathway in retrograde synaptic signaling. While each dissects spatial and molecular aspects of TGF-beta signaling in a specific synaptic context, together these studies demonstrate that a specific retrograde signal may be interpreted in diverse, neuron-specific ways. Thus, a neuron's intrinsic properties and its other extrinsic signaling inputs determine its cellular and genomic response to TGF-beta.     

Modeling virus self-assembly pathways: avoiding dynamics using geometric constraint decomposition.

We develop a model for elucidating the assembly pathways by which an icosahedral viral shell forms from 60 identical constituent protein monomers. This poorly understood process a remarkable example of macromolecular self-assembly occuring in nature and possesses many features that are desirable while engineering self-assembly at the nanoscale. The model uses static geometric and tensegrity constraints to represent the driving (weak) forces that cause a viral shell to assemble and hold it together. The goal is to answer focused questions about the structural properties of a successful assembly pathway. Pathways and their properties are carefully defined and computed using computational algebra and geometry, specifically state-of-art concepts in geometric constraint decomposition. The model is analyzable and refinable and avoids expensive dynamics. We show that it has a provably tractable and accurate computational simulation and that its predictions are roughly consistent with known information about viral shell assembly. Justifications for mathematical and biochemical assumptions are provided, and comparisons are drawn with other virus assembly models. A method for more conclusive experimental validation involving specific viruses is sketched. Overall, the paper indicates a strong and direct, mutually beneficial interplay between (a) the concepts underlying macromolecular assembly; and (b) a wide variety of established as well as novel concepts from combinatorial and computational algebra, geometry and algebraic complexity.     

Drosophila endosomal proteins hook and deep orange regulate synapse size but not synaptic vesicle recycling

To study the function of endosomes at synapses we analyzed the localization and function of two Drosophila endosomal proteins, Hook and Deep orange (Dor), at the larval neuromuscular junction. Hook, a negative regulator of endocytic trafficking, and Dor, a positive regulator of endocytic trafficking, are highly enriched at synapses, especially close to postsynaptic membranes. Mutations in hook (hk) and dor do not affect synaptic vesicle recycling, as assessed by electrophysiological analysis of synaptic transmission and behavioral studies of double mutants with shi(ts) mutations that alter vesicle recycling. However, hk and dor mutations alter the number of presynaptic varicosities (synapse size) in opposing ways. Synapse size is increased in hk(11) mutants and is decreased in dor(4) mutants. Double mutants for dor and hk show a dor-like phenotype. These effects on synapse size parallel known functions of Hook and Dor in endocytosis and strongly indicate a role for endocytic trafficking in the regulation of synapse size in vivo. Our observations suggest a model in which Hook and Dor function in later stages of endocytosis is essential for regulating synaptic plasma membrane composition but not synaptic vesicle recycling.     

Sampling methodologies and dosage assessment techniques for submicrometre and ultrafine virus aerosol particles

AIMS: The aerosolization and collection of submicrometre and ultrafine virus particles were studied with the objective of developing robust and accurate methodologies to study airborne viruses. METHODS AND RESULTS: The collection efficiencies of three sampling devices used to sample airborne biological particles - the All Glass Impinger 30, the SKC BioSampler and a frit bubbler - were evaluated for submicrometre and ultrafine virus particles. Test virus aerosol particles were produced by atomizing suspensions of single-stranded RNA and double-stranded DNA bacteriophages. Size distribution results show that the fraction of viruses present in typical aqueous virus suspensions is extremely low such that the presence of viruses has little effect on the particle size distribution of atomized suspensions. It has been found that none of the tested samplers are adequate in collecting submicrometre and ultrafine virus particles, with collection efficiencies for all samplers below 10% in the 30-100 nm size range. Plaque assays and particle counting measurements showed that all tested samplers have time-varying virus particle collection efficiencies. A method to determine the size distribution function of viable virus containing particles utilizing differential mobility selection was also developed. CONCLUSIONS: A combination of differential mobility analysis and traditional plaque assay techniques can be used to fully characterize airborne viruses. SIGNIFICANCE AND IMPACT OF THE STUDY: The data and methods presented here provide a fundamental basis for future studies of submicrometre and ultrafine airborne virus particles.