Emergence of structural and dynamical properties of ecological mutualistic networks

Mutualistic networks are formed when the interactions between two classes of species are mutually beneficial. They are important examples of cooperation shaped by evolution. Mutualism between animals and plants plays a key role in the organization of ecological communities. Such networks in ecology have generically evolved a nested architecture independent of species composition and latitude - specialists interact with proper subsets of the nodes with whom generalists interact. Despite sustained efforts to explain observed network structure on the basis of community-level stability or persistence, such correlative studies have reached minimal consensus. Here we demonstrate that nested interaction networks could emerge as a consequence of an optimization principle aimed at maximizing the species abundance in mutualistic communities. Using analytical and numerical approaches, we show that because of the mutualistic interactions, an increase in abundance of a given species results in a corresponding increase in the total number of individuals in the community, as also the nestedness of the interaction matrix. Indeed, the species abundances and the nestedness of the interaction matrix are correlated by an amount that depends on the strength of the mutualistic interactions. Nestedness and the observed spontaneous emergence of generalist and specialist species occur for several dynamical implementations of the variational principle under stationary conditions. Optimized networks, while remaining stable, tend to be less resilient than their counterparts with randomly assigned interactions. In particular, we analytically show that the abundance of the rarest species is directly linked to the resilience of the community. Our work provides a unifying framework for studying the emergent structural and dynamical properties of ecological mutualistic networks.Comment: 10 pages, 4 figure

Acute reversible inactivation of the bed nucleus of stria terminalis induces antidepressant-like effect in the rat forced swimming test

<p>Abstract</p> <p>Background</p> <p>The bed nucleus of stria terminalis (BNST) is a limbic forebrain structure involved in hypothalamo-pituitary-adrenal axis regulation and stress adaptation. Inappropriate adaptation to stress is thought to compromise the organism's coping mechanisms, which have been implicated in the neurobiology of depression. However, the studies aimed at investigating BNST involvement in depression pathophysiology have yielded contradictory results. Therefore, the objective of the present study was to investigate the effects of temporary acute inactivation of synaptic transmission in the BNST by local microinjection of cobalt chloride (CoCl₂) in rats subjected to the forced swimming test (FST).</p> <p>Methods</p> <p>Rats implanted with cannulae aimed at the BNST were submitted to 15 min of forced swimming (pretest). Twenty-four hours later immobility time was registered in a new 5 min forced swimming session (test). Independent groups of rats received bilateral microinjections of CoCl₂(1 mM/100 nL) before or immediately after pretest or before the test session. Additional groups received the same treatment and were submitted to the open field test to control for unspecific effects on locomotor behavior.</p> <p>Results</p> <p>CoCl₂injection into the BNST before either the pretest or test sessions reduced immobility in the FST, suggesting an antidepressant-like effect. No significant effect of CoCl₂was observed when it was injected into the BNST immediately after pretest. In addition, no effect of BNST inactivation was observed in the open field test.</p> <p>Conclusion</p> <p>These results suggest that acute reversible inactivation of synaptic transmission in the BNST facilitates adaptation to stress and induces antidepressant-like effects.</p

Reconstructing the History of Energy Condition Violation from Observational Data

We study the likelihood of energy condition violations in the history of the Universe. Our method is based on a set of functions that characterize energy condition violation. FLRW cosmological models are built around these "indication functions". By computing the Fisher matrix of model parameters using type Ia supernova and Hubble parameter data, we extract the principal modes of these functions' redshift evolution. These modes allow us to obtain general reconstructions of energy condition violation history independent of the dark energy model. We find that the data suggest a history of strong energy condition violation, but the null and dominant energy conditions are likely to be fulfilled. Implications for dark energy models are discussed.Comment: v1: 6 pages, 7 figures, 1 table. Comments welcome; v2: 7 pages, expanded & corrected, accepted by Ap

Carvacrol, (-)-borneol and citral reduce convulsant activity in rodents

Carvacrol, a monoterpenic phenol present in essential oils of the Labiatae family, has been used through the ages as a source of flavor in food and for medicinal purposes. Borneol is a monoterpene found in several species of Artemisia and Dipterocarpaceae, used for anxiety, pain and anesthesia in traditional Chinese. Citral, a mixture of two geometrical isomers (neral and geranial), is one of the most important compounds in some citrus oils and has central nervous system (CNS) properties. The anticonvulsant effect of carvacrol (CARV), (-)-borneol (BOR) and citral (CIT) was investigated in two animal models of epilepsy. Mice were pretreated with CARV, BOR or CIT (50, 100, and 200 mg/kg, i.p.) 30 min before pentylenetetrazole (PTZ) or maximal electroshock (MES) tests, the two most important animal epilepsy tests. The latency for development of convulsions and protection percentage was recorded. In order to investigate the involvement of GABAergic system, flumazenil was utilized. These monoterpenes, CARV in a higher, but not in a lower dose (p &lt; 0.001), BOR and CIT in all doses (p &lt; 0.05 or p &lt; 0.001), were capable of promoting an increase of latency for the development of convulsions induced by PTZ. Additionally, these compounds were efficient in preventing the tonic convulsions (p &lt; 0.05) induced by MES. However, the GABAergic neurotransmitter system might be involved, at least in BOR effects. Henceforth, our results suggest that CARV, BOR and CIT possess anticonvulsant activity effect against PTZ-induced convulsions and MES.Key words: Carvacrol, (-)-borneol, citral, anticonvulsant activit

Fermentation of deproteinized cheese whey powder solutions to ethanol by engineered Saccharomyces cerevisiae : effect of supplementation with corn steep liquor and repeated-batch operation with biomass recycling by flocculation

The lactose in cheese whey is an interesting substrate for the production of bulk commodities such as bio-ethanol, due to the large amounts of whey surplus generated globally. In this work, we studied the performance of a recombinant Saccharomyces cerevisiae strain expressing the lactose permease and intracellular ß-galactosidase from Kluyveromyces lactis in fermentations of deproteinized concentrated cheese whey powder solutions. Supplementation with 10 g/l of corn steep liquor significantly enhanced whey fermentation, resulting in the production of 7.4% (v/v) ethanol from 150 g/l initial lactose in shake-flask fermentations, with a corresponding productivity of 1.2 g/l/h. The flocculation capacity of the yeast strain enabled stable operation of a repeated-batch process in a 5.5-l air-lift bioreactor, with simple biomass recycling by sedimentation of the yeast flocs. During five consecutive batches, the average ethanol productivity was 0.65 g/l/h and ethanol accumulated up to 8% (v/v) with lactose-toethanol conversion yields over 80% of theoretical. Yeast viability (>97%) and plasmid retention (>84%) remained high throughout the operation, demonstrating the stability and robustness of the strain. In addition, the easy and inexpensive recycle of the yeast biomass for repeated utilization makes this process economically attractive for industrial implementation.Fundação para a Ciência e a Tecnologia (FCT)LACTOGAL-Produtos Alimentares S.A.Companhia Portuguesa de Amidos, S.A