Effects of Total Resources, Resource Ratios, and Species Richness on Algal Productivity and Evenness at Both Metacommunity and Local Scales

The study of the interrelationship between productivity and biodiversity is a major research field in ecology. Theory predicts that if essential resources are heterogeneously distributed across a metacommunity, single species may dominate productivity in individual metacommunity patches, but a mixture of species will maximize productivity across the whole metacommunity. It also predicts that a balanced supply of resources within local patches should favor species coexistence, whereas resource imbalance would favor the dominance of one species. We performed an experiment with five freshwater algal species to study the effects of total supply of resources, their ratios, and species richness on biovolume production and evenness at the scale of both local patches and metacommunities. Generally, algal biovolume increased, whereas algal resource use efficiency (RUE) and evenness decreased with increasing total supply of resources in mixed communities containing all five species. In contrast to predictions for biovolume production, the species mixtures did not outperform all monocultures at the scale of metacommunities. In other words, we observed no general transgressive overyielding. However, RUE was always higher in mixtures than predicted from monocultures, and analyses indicate that resource partitioning or facilitation in mixtures resulted in higher-than-expected productivity at high resource supply. Contrasting our predictions for the local scale, balanced supply of resources did not generally favor higher local evenness, however lowest evenness was confined to patches with the most imbalanced supply. Thus, our study provides mixed support for recent theoretical advancements to understand biodiversity-productivity relationships

Defects in Mitochondrial Dynamics and Metabolomic Signatures of Evolving Energetic Stress in Mouse Models of Familial Alzheimer's Disease

The identification of early mechanisms underlying Alzheimer's Disease (AD) and associated biomarkers could advance development of new therapies and improve monitoring and predicting of AD progression. Mitochondrial dysfunction has been suggested to underlie AD pathophysiology, however, no comprehensive study exists that evaluates the effect of different familial AD (FAD) mutations on mitochondrial function, dynamics, and brain energetics.We characterized early mitochondrial dysfunction and metabolomic signatures of energetic stress in three commonly used transgenic mouse models of FAD. Assessment of mitochondrial motility, distribution, dynamics, morphology, and metabolomic profiling revealed the specific effect of each FAD mutation on the development of mitochondrial stress and dysfunction. Inhibition of mitochondrial trafficking was characteristic for embryonic neurons from mice expressing mutant human presenilin 1, PS1(M146L) and the double mutation of human amyloid precursor protein APP(Tg2576) and PS1(M146L) contributing to the increased susceptibility of neurons to excitotoxic cell death. Significant changes in mitochondrial morphology were detected in APP and APP/PS1 mice. All three FAD models demonstrated a loss of the integrity of synaptic mitochondria and energy production. Metabolomic profiling revealed mutation-specific changes in the levels of metabolites reflecting altered energy metabolism and mitochondrial dysfunction in brains of FAD mice. Metabolic biomarkers adequately reflected gender differences similar to that reported for AD patients and correlated well with the biomarkers currently used for diagnosis in humans.Mutation-specific alterations in mitochondrial dynamics, morphology and function in FAD mice occurred prior to the onset of memory and neurological phenotype and before the formation of amyloid deposits. Metabolomic signatures of mitochondrial stress and altered energy metabolism indicated alterations in nucleotide, Krebs cycle, energy transfer, carbohydrate, neurotransmitter, and amino acid metabolic pathways. Mitochondrial dysfunction, therefore, is an underlying event in AD progression, and FAD mouse models provide valuable tools to study early molecular mechanisms implicated in AD

The financial structure of the Tunisian listed businesses: an application on panel data

Abstract This article aims at analyzing the financial structure of the Tunisian listed companies in the stock exchange of Tunis (SET). The study focuses on 26 companies observed over a period of 6 years (2005–2010). Three representations of the behavior of funding are tested: The first considers that the firms implement a policy of debt with an objective of debt ratio target, the second presupposes the existence of a hierarchy of funding and divides the existence of a target ratio, the third assumes that firms issuing shares when market conditions are favorable and redeemed in the opposite case. The statistical tests validate better the first approach. In fact, the choice of financing of Tunisian businesses confirms the greatest explanatory power of an analysis based on the existence of a debt ratio target

IPO anomalies and innovation capital

Innovation capital are typically expensed and/or unrecognized as assets under current generally accepted accounting principles. This results in accounting-related information asymmetry. This paper examines the association of innovation capital (as measured here by the proxies of R&D expenditures and granted patents) and initial public offerings (IPO) anomalies. These anomalies include initial IPO underpricing, duration of honeymoon (a distinct feature of the Taiwanese IPO environment), and long-term performance. The theoretical model underlying this research is a signaling model. The results indicate that more innovative firms are more likely to be underpriced, and have longer honeymoon periods than less innovative firms. Further, the more innovative firms have positive and growing long-term market-adjusted returns. This stands in contrast to the declining long-term stock performance of initial public offering firms that is evidenced in the literature. We conclude that pre-IPO research and development expenditures disclosed in the IPO prospectus, official monthly reports of newly developed patents released to the public, and the frequency of patent citations significantly signal both underpricing and future market performance of IPO firms in Taiwan. Copyright Springer Science + Business Media, LLC 2006Anomalies, Initial public offerings, Innovation capital, Patent, R&D, Signaling,