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Metapopulation capacity provides an analytic tool to quantify the impact of landscape configuration on metapopulation persistence, which has proven powerful in biological conservation. Yet surprisingly few efforts have been made to apply this approach to multispecies systems. Here, we extend metapopulation capacity theory to predict the persistence of trophically interacting species. Our results demonstrate that metapopulation capacity could be used to predict the persistence of trophic systems such as prey-predator pairs and food chains in fragmented landscapes. In particular, we derive explicit predictions for food chain length as a function of metapopulation capacity, top-down control, and population dynamical parameters. Under certain assumptions, we show that the fraction of empty patches for the basal species provides a useful indicator to predict the length of food chains that a fragmented landscape can support and confirm this prediction for a host-parasitoid interaction. We further show that the impact of habitat changes on biodiversity can be predicted from changes in metapopulation capacity or approximately by changes in the fraction of empty patches. Our study provides an important step toward a spatially explicit theory of trophic metacommunities and a useful tool for predicting their responses to habitat changes. [ABSTRACT FROM AUTHOR]

Neurotransmission at different synapses is highly variable, and cell-adhesion molecules like a-neurexins (α-Nrxn) and their extracellular binding partners determine synapse function. Although α-Nrxn affect transmission at excitatory and inhibitory synapses, the contribution of neurexophilin-1 (Nxph1), an α-Nrxn ligand with restricted expression in subpopulations of inhibitory neurons, is unclear. To reveal its role, we investigated mice that either lack or overexpress Nxph1. We found that genetic deletion of Nxph1 impaired GABAB receptor (GABABR)-dependent short-term depression of inhibitory synapses in the nucleus reticularis thalami, a region where Nxph1 is normally expressed at high levels. To test the conclusion that Nxph1 supports presynaptic GABABR, we expressed Nxph1 ectopically at excitatory terminals in the neocortex, which normally do not contain this molecule but can be modulated by GABABR. We generated Nxph1-GFP transgenic mice under control of the Thy1.2 promoter and observed a reduced short-term facilitation at these excitatory synapses, representing an inverse phenotype to the knockout. Consistently, the diminished facilitation could be reversed by pharmacologically blocking GABABR with CGP-55845. Moreover, a complete rescue was achieved by additional blocking of postsynaptic GABAAR with intracellular picrotoxin or gabazine, suggesting that Nxph1 is able to recruit or stabilize both presynaptic GABABR and postsynaptic GABAAR. In support, immunoelectron microscopy validated the localization of ectopic Nxph1 at the synaptic cleft of excitatory synapses in transgenic mice and revealed an enrichment of GABAAR and GABABR subunits compared with wild-type animals. Thus, our data propose that Nxph1 plays an instructive role in synaptic short-term plasticity and the configuration with GABA receptors. [ABSTRACT FROM AUTHOR]

Neutral models of species diversity predict patterns of abundance for communities in which all individuals are ecologically equivalent. These models were originally developed for Panamanian trees and successfully reproduce observed distributions of abundance. Neutral models also make macroevolutionary predictions that have rarely been evaluated or tested. Here we show that neutral models predict a humped or flat relationship between species age and population size. In contrast, ages and abundances of tree species in the Panamanian Canal watershed are found to be positively correlated, which falsifies the models. Speciation rates vary among phylogenetic lineages and are partially heritable from mother to daughter species. Variable speciation rates in an otherwise neutral model lead to a demographic advantage for species with low speciation rate. This demographic advantage results in a positive correlation between species age and abundance, as found in the Panamanian tropical forest community. [ABSTRACT FROM AUTHOR]

We report on label-free imaging, detection, and mass/size measurement of single viral particles in solution by high-resolution surface plasmon resonance microscopy. Diffraction of propagating plasmon waves along a metal surface by the viral particles creates images of the individual particles, which allow us to detect the binding of the viral particles to surfaces functionalized with and without antibodies. We show that the intensity of the particle image is related to the mass of the particle, from which we determine the mass and mass distribution of influenza viral particles with a mass detection limit of approximately 1 ag (or 0.2 fg/mm2). This work demonstrates a multiplexed method to measure the masses of individual viral particles and to study the binding activity of the viral particles. [ABSTRACT FROM AUTHOR]