Do Food Web Models Reproduce the Structure of Mutualistic Networks?

Background

Simple models inspired by processes shaping consumer-resource interactions have helped to establish the primary processes underlying the organization of food webs, networks of trophic interactions among species. Because other ecological interactions such as mutualisms between plants and their pollinators and seed dispersers are inherently based in consumer-resource relationships we hypothesize that processes shaping food webs should organize mutualistic relationships as well.

Methodology/Principal Findings

We used a likelihood-based model selection approach to compare the performance of food web models and that of a model designed for mutualisms, in reproducing the structure of networks depicting mutualistic relationships. Our results show that these food web models are able to reproduce the structure of most of the mutualistic networks and even the simplest among the food web models, the cascade model, often reproduce overall structural properties of real mutualistic networks.

Conclusions/Significance

Based on our results we hypothesize that processes leading to feeding hierarchy, which is a characteristic shared by all food web models, might be a fundamental aspect in the assembly of mutualisms. These findings suggest that similar underlying ecological processes might be important in organizing different types of interactions.     

Population dynamics of Aceodromus convolvuli (Acari: Mesostigmata: Blattisociidae) on spontaneous plants associated with Jatropha curcas in central Brazil

Spontaneously growing plants are commonly considered competitors of cultivated plants. Owing to the lack of specificity of many arthropods, spontaneous plants may be attacked by the same arthropods that attack cultivated plants and they may also harbor natural enemies of organisms harmful to cultivated plants. Aceodromus convolvuli Muma (Blattisociidae) has been reported recently in relatively large numbers in Tocantins state, central Brazil, mostly on Helicteres guazumifolia Kunth (Malvaceae). Very little has been reported about the population dynamics of blattisociid mites under field conditions. The objective of this work was to study the population dynamics of A. convolvuli in Gurupi, Tocantins state, to evaluate its possible interaction with associated mites. Monthly samples were taken from leaves of the 11 most abundant and frequent spontaneous plants in a Jatropha curcas L. (Euphorbiaceae) plantation. About 96.5 % of the specimens of A. convolvuli were collected in the rainy season. The patterns of variation of the population of A. convolvuli and of predators belonging to the family Phytoseiidae were similar, but A. convolvuli was much more numerous than all phytoseiid specimens combined. Highly significant correlations were observed between A. convolvuli densities and relative humidity or diversity of spontaneous plants. When only mites on H. guazumifolia were considered, highly significant correlation was also observed between densities of A. convolvuli and of mites of the family Tetranychidae. The results suggested that A. convolvuli could be a predator of tenuipalpid and/or tetranychid mites. Studies about its biology are needed to determine its preferred food sources and potential as biological control agent.     

Sperm quality of Colossoma macropomum after room‐temperature and cold storage

The objective of this study was to evaluate the effects of cold and room‐temperature storage on the quality of Colossoma macropomum sperm. The experiment was carried out in December (end of Spring), in Nova Mutum‐MT, Brazil, involving nine C. macropomum males (4 years old; 6.4 ± 1.5 kg average weight). The fish were selected and transferred to masonry tanks (4 m³) in a laboratory (water renewal rate: 10 L/s; average water temperature: 28°C). Subsequently, reproduction was induced using 2.5 mg of crude carp pituitary extract/kg and the semen was harvested 240 degree hours after hormonal induction. The following sperm characteristics were analyzed every 5 hr using Image J/casa software: total motility (MOT), curvilinear velocity (VCL), average path velocity (VAP), straight‐line velocity (VSL), straightness of sperm path (STR), wobble (WOB), progressive motility (PROG), beat cross frequency (BCF) and total number of spermatozoa (NSPZ). A fresh sample of semen from each animal was kept at room temperature (25.3 ± 1.2°C). For analysis of cooled semen, syringes were kept in cooling boxes at an average temperature of 16.9 ± 2.1°C. The reduction (p < 0.05) of MOT in semen kept at room temperature occurred at 10 hr (13.95%); in cooled semen, however, MOT declined at 15 hr (76.87%). At 15 hr, there was practically no MOT in the semen kept at room temperature (0.20%), whereas in the cooled semen this situation was observed only at 35 hr (2.91%) The MOT of cooled sperm was higher (p < 0.05) at all times (except zero time), compared with the semen maintained at room temperature. At 15 hr, the cooled spermatozoa showed higher (p < 0.05) VCL (142.18 μm/s) and BCF (29.72 Hz) than those maintained at room temperature (VCL: 51.18 μm/s; BCF: 19.57 Hz). After 15 hr, only the cooled sperm showed quality. In conclusion, semen cooling allows for extending the viability of C. macropomum spermatozoa from 5 to 10 hr without compromising their quality in most characteristics. At 15 and 25 hr of cooling, sperm viability is still observed, though with decreased quality.     

MODULAR: software for the autonomous computation of modularity in large network sets

Many ecological systems can be represented as networks of interactions. A key feature in these networks is their organization into modules, which are subsets of tightly connected elements. We introduce MODULAR to perform rapid and autonomous calculation of modularity in network sets. MODULAR reads a set of files representing unipartite or bipartite networks, and identifies modules using two different modularity metrics widely used in the ecological networks literature. To estimate modularity, the software offers five optimization methods to the user. The software also includes two null models commonly used in studies of ecological networks to verify how the degree of modularity differs from two distinct theoretical benchmarks.     

Synthetic inhibitors of the processing of pretransfer RNA by the ribonuclease P ribozyme: enzyme inhibitors which act by binding to substrate

2,2'-p-Phenylene bis[6-(4-methyl-1-piperazinyl)]benzimidazole, 2,2'-bis(3,5-dihydroxyphenyl)-6,6'-bis benzimidazole, and 2,2'-bis(4-hydroxyphenyl)-6,6'-bis benzimidazole are shown by UV-visible and fluorescence spectrophotometry to be strong ligands for tRNA, giving simple, hyperbolic binding isotherms with apparent dissociation constants in the micromolar range. Hydroxyl radical footprinting indicates that they may bind in the D and T loops. On the basis of this tRNA recognition as a rationale, they were tested as inhibitors of the processing of precursor tRNAs by the RNA subunit of Escherichia coli RNase P (M1 RNA). Preliminary studies show that inhibition of the processing of Drosophila tRNA precursor molecules by phosphodiester bond cleavage, releasing the extraneous 5'-portion of RNA and the mature tRNA molecule, was dependent on both the structure of the inhibitor and the structure of the particular tRNA precursor substrate for tRNA(Ala), tRNA(Val), and tRNA(His). In more detailed followup using the tRNA(His) precursor as the substrate, experiments to determine the concentration dependence of the reaction showed that inhibition took time to reach its maximum extent. I(50) values (concentrations for 50% inhibition) were between 5.3 and 20.8 microM, making these compounds among the strongest known inhibitors of this ribozyme, and the first inhibitors of it not based on natural products. These compounds effect their inhibition by binding to the substrate of the enzyme reaction, making them examples of an unusual class of enzyme inhibitors. They provide novel, small-molecule, inhibitor frameworks for this endoribonuclease ribozyme.     

Complete Chloroplast Genome of the Wollemi Pine (Wollemia nobilis): Structure and Evolution

The Wollemi pine (Wollemia nobilis) is a rare Southern conifer with striking morphological similarity to fossil pines. A small population of W. nobilis was discovered in 1994 in a remote canyon system in the Wollemi National Park (near Sydney, Australia). This population contains fewer than 100 individuals and is critically endangered. Previous genetic studies of the Wollemi pine have investigated its evolutionary relationship with other pines in the family Araucariaceae, and have suggested that the Wollemi pine genome contains little or no variation. However, these studies were performed prior to the widespread use of genome sequencing, and their conclusions were based on a limited fraction of the Wollemi pine genome. In this study, we address this problem by determining the entire sequence of the W. nobilis chloroplast genome. A detailed analysis of the structure of the genome is presented, and the evolution of the genome is inferred by comparison with the chloroplast sequences of other members of the Araucariaceae and the related family Podocarpaceae. Pairwise alignments of whole genome sequences, and the presence of unique pseudogenes, gene duplications and insertions in W. nobilis and Araucariaceae, indicate that the W. nobilis chloroplast genome is most similar to that of its sister taxon Agathis. However, the W. nobilis genome contains an unusually high number of repetitive sequences, and these could be used in future studies to investigate and conserve any remnant genetic diversity in the Wollemi pine.     

Physical Anthropology and the dental and medical specialties

The rise of two sub-specialties in Physical Anthropology traces back to the Anatomy Departments of Schools of Medicine in Germany and France during the nineteenth century. The study of human diversity in bones and bodies was largely by medically-trained anatomists. There developed Medical Anthropology and Dental Anthropology, employing osteometry and craniometry on the skeleton, somatometry and cephalometry on the living body. As a result cross-sectional studies gave way to longitudinal studies and X-ray techniques were added to purely mensurational procedures. In Medical Anthropology the specialties most directly concerned are pediatrics, plastic surgery, endocrinology, and orthopaedics. In Dental Anthropology the specialties most directly concerned are pedodontics, orthodontics, oral surgery, and prosthodontics. The contributions of Physical Anthropology to each is discussed.     

An analytical model for the ergometer rowing: inverse multibody dynamics analysis

A model for the ergometer rowing exercise is presented in this paper. From the quantitative observations of a particular trajectory (motion), the model is used to determine the moment of the forces produced by the muscles about each joint. These forces are evaluated according to the continuous system of equations of motion. An inverse dynamics analysis is performed in order to predict the joint torques developed by the muscles during the execution of the task. An elementary multibody mechanical system is used as an example to discuss the assumptions and procedures adopted.     

The threat of emerging and re-emerging pathogenic Sporothrix species

Mycopathologia - Sporotrichosis is a neglected subcutaneous mycosis of humans and animals acquired by traumatic inoculation of soil and plant material (classical route) contaminated with infectious...