JOURNAL OF PHYCOLOGY, Issue 6 2004
Akira F. Peters
The emergence of model organisms that permit the application of a powerful combination of genomic and genetic approaches has been a major factor underlying the advances that have been made in the past decade in dissecting the molecular basis of a wide range of biological processes. However, the phylogenetic distance separating marine macroalgae from these model organisms, which are mostly from the animal, fungi, and higher plant lineages, limits the latters' applicability to problems specific to macroalgal biology. There is therefore a pressing need to develop similar models for the macroalgae. Here we describe a survey of potential model brown algae in which particular attention was paid to characteristics associated with a strong potential for genomic and genetic analysis, such as a small nuclear genome size, sexuality, and a short life cycle. Flow cytometry of nuclei isolated from zoids showed that species from the Ectocarpales possess smaller haploid genomes (127,290 Mbp) than current models among the Laminariales (580,720 Mbp) and Fucales (1095,1271 Mbp). Species of the Ectocarpales may complete their life histories in as little as 6 weeks in laboratory culture and are amenable to genetic analyses. Based on this study, we propose Ectocarpus siliculosus (Dillwyn) Lyngbye as an optimal choice for a general model organism for the molecular genetics of the brown algae. [source]

NITROGEN LIMITATION EFFECTS OF DIFFERENT NITROGEN SOURCES ON NUTRITIONAL QUALITY OF TWO FRESHWATER ORGANISMS, SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE) AND SYNECHOCOCCUS SP. (CYANOPHYCEAE)

JOURNAL OF PHYCOLOGY, Issue 5 2003
Gunnel Ahlgren
Food quality for grazers has been related to mineral (nitrogen, phosphorus) and biochemical (amino acids, fatty acids) constituents. The aim of the study was to examine the influence of different nitrogen sources on these constituents in two organisms, the green alga Scenedesmus quadricauda Turp. and the cyanobacterium Synechococcus sp., commonly used in feeding experiments. The two organisms were grown in continuous cultures at different growth rates. Nitrate or ammonium salts were used as nitrogen sources under both replete and limited conditions. Carbon content (mg·g,1 dry weight) was stable in both organisms independent of nitrogen source, nitrogen limitation, and growth rate. Nitrogen content decreased with limitation and growth rate in Scenedesmus and to a lesser degree in Synechococcus, whereas changes in phosphorus content were not statistically significant. The relative proportions of amino acids (% of total amino acids) were relatively stable in both organisms, whereas the proportions of fatty acids varied with growth rate and limitation. Fatty acid content was much lower in Synechococcus than in Scenedesmus. At N limitation, polyunsaturated fatty acids (PUFAs) showed lower levels in both organisms. The change occurred in the ,3 PUFA (linolenic acid) of the green alga and in the ,6 PUFA (linoleic acid) of the cyanobacterium. The difference in the response of N limitation in the two organisms may be traced to the different composition of the chloroplast membranes (the prokaryotic way) and the microsomal membranes (the eukaryotic way) where the desaturation takes place. [source]

Listeria: A Practical Approach to the Organism and its Control in Foods.

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2008
Ioannis S. Arvanitoyannis (Dr, Ph.D.)
No abstract is available for this article. [source]

Clostridium botulinum: a Practical Approach to the Organism and its Control in Foods

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 7 2003
Roy Betts
No abstract is available for this article. [source]

Occurrence of the Enigmatic, Unicellular Psorospermium Organism in Several Cultured, Sympatric Populations of the Freshwater Crayfishes Procambarus clarkii and Procambarus zonangulus

JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 2 2000
David P. Klarberg
The parasitic Psorospermium organism was studied in cultured sympatric populations of mature Procambarus clarkii and Procambarus zonangulus during four consecutive annual crayfish seasons from 1991,1992 through 1994,1995. Most P. clarkii were infected while fewer than half of the P. zonangulus were infected throughout the study period. The numbers of Psorospermium were four to eight times greater in P. clarkii and showed annual changes not seen in P. zonangulus. Both crayfishes demonstrate 1yr life cycles in Louisiana and this seemed to explain the variations seen in Psorospermium dynamics in the two hosts. In general, there was no consistent association between crayfish size and the number of parasites found in them for either crayfish species. There was some indication of an association between the presence of infection and the number of parasites found in P. zonangulus. [source]

Soil Organism and Plant Introductions in Restoration of Species-Rich Grassland Communities

RESTORATION ECOLOGY, Issue 2 2009
Paul Kardol
Abstract Soil organisms can strongly affect competitive interactions and successional replacements of grassland plant species. However, introduction of whole soil communities as management strategy in grassland restoration has received little experimental testing. In a 5-year field experiment at a topsoil-removed ex-arable site (receptor site), we tested effects of (1) spreading hay and soil, independently or combined, and (2) transplanting intact turfs on plant and soil nematode community development. Material for the treatments was obtained from later successional, species-rich grassland (donor site). Spreading hay affected plant community composition, whereas spreading soil did not have additional effects. Plant species composition of transplanted turfs became less similar to that in the donor site. Moreover, most plants did not expand into the receiving plots. Soil spreading and turf transplantation did not affect soil nematode community composition. Unfavorable soil conditions (e.g., low organic matter content and seasonal fluctuations in water level) at the receptor site may have limited plant and nematode survival in the turfs and may have precluded successful establishment outside the turfs. We conclude that introduction of later successional soil organisms into a topsoil-removed soil did not facilitate the establishment of later successional plants, probably because of the "mismatch" in abiotic soil conditions between the donor and the receptor site. Further research should focus on the required conditions for establishment of soil organisms at restoration sites in order to make use of their contribution to grassland restoration. We propose that introduction of organisms from "intermediate" stages will be more effective as management strategy than introduction of organisms from "target" stages. [source]

A Diatomic Molecule Receptor That Removes CO in a Living Organism,

ANGEWANDTE CHEMIE, Issue 7 2010
Hiroaki Kitagishi Dr.
Ein CO-Fänger: Ein supramolekularer Eisen(II)porphyrin-Cyclodextrin-Komplex (hemoCD) mit gebundenem O2, der in eine Rattenvene injiziert wird, reagiert unter Ligandenaustausch mit internem CO, und das hemoCD mit gebundenem CO wird sofort in den Urin ausgeschieden (siehe Bild). Diese Wirkungsweise von hemoCD als CO-Rezeptor ermöglichte die quantitative Bestimmung von endogenem CO in einem lebenden Organismus. [source]

The Flexible and the Pliant: Disturbed Organisms of Soviet Modernity

CULTURAL ANTHROPOLOGY, Issue 3 2004
Serguei Alex.
In the texts of prominent Soviet figures such as writer Maxim Gorky, the agrobiologist Trofim Lysenko, and the educator Anton Makarenko, the uncertainty of social norms in early Soviet society became equated with an instability of environment in general and nature in particular. A powerful and vivid rhetoric of a "second nature," to use Gorky's phrase, overcame the absence of clearly articulated models for subjectivity. A series of disciplining routines and activities capable of producing the new Soviet subject compensated in the 1930s for the dissolution of the daily order of things and all the structuring effects, social networks, and reciprocal obligations that were associated with it. [source]

Coaxial Aerodynamically Assisted Bio-jets: A Versatile Paradigm for Directly Engineering Living Primary Organisms

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 6 2007
S. Irvine
Abstract In this paper, a coaxial jetting methodology is demonstrated as a first example (non-electric field driven) completely run by aerodynamic forces which are brought about by the application of a differential pressure for the safe handling of primary living organisms by means of jets as encapsulated droplets. Previously this jetting technique in this configuration has only been investigated for processing combinations of liquid-liquid and liquid-gas systems. These developmental studies into aerodynamically assisted jets (AAJ) have unearthed a versatile bio-jetting approach referred to here as coaxial aerodynamically assisted bio-jetting (CAABJ). In the current work, this flexible approach is demonstrated to handle two primary cell types for drop-and-placing onto several different substrates. Furthermore, the study assesses cellular viability of the post-treated cells in comparison to controls by way of flow cytometry. These first steps demonstrate the promise this protocol has in exploring the creation of biologically viable structures to form encapsulations of cells which would be useful as a direct tissue engineering to the immuno-hinding methodology in bio-repair and therapeutics. Therefore, these investigations place CAABJ into the cell jetting pursuit together with bio-electrosprays, which will undergo an explosive developmental research. [source]

Whole-body sodium concentration in larval fathead minnows (Pimephales promelas) during and following copper exposure

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2006
Holly M. Zahner
Abstract This research used whole-body sodium concentration to characterize exposure and recovery of larval fathead minnows (Pimephales promelas) from acute pulsed copper exposures. Whole-body sodium was chosen because the acute mechanism of copper toxicity to fishes is putative disruption of ion regulation, resulting in a loss of sodium and eventually leading to mortality. Whole-body sodium response in larval fathead minnows exposed to copper was both concentration and duration dependent. The loss of sodium to approximately 70% of control levels occurred within 12 h of exposure. Organisms demonstrated an ability to recover whole-body sodium within 48 h after exposure to concentrations below 0.47 ,M Cu2+ for 3, 6, or 9 h. However, at higher concentrations, organisms required more than 48 h to recover. Whole-body sodium concentrations and mortality for all continuous exposures were strongly correlated. These results may facilitate development of a physiologically based model to predict the response of organisms to copper in receiving streams. [source]

Interactions between metabolism of trace metals and xenobiotic agonists of the aryl hydrocarbon receptor in the antarctic fish Trematomus bernacchii: Environmental perspectives

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2005
Francesco Regoli
Abstract Although Antarctica is a pristine environment, organisms are challenged with contaminants either released locally or transported from industrialized regions through atmospheric circulation and marine food webs. Organisms from Terra Nova Bay also are exposed to a natural enrichment of cadmium, but to our knowledge, whether such environmental conditions influence biological responses to anthropogenic pollutants has never been considered. In the present study, the Antarctic rock cod (Trematomus bernacchii) was exposed to model chemicals, including polycyclic aromatic hydrocarbons (benzo[a]pyrene), persistent organic pollutants (2,3,7,8-tetrachlorodibenzo- p -dioxin [TCDD]), cadmium, and a combination of cadmium and TCDD. Analyzed parameters included chemical bioaccumulation, activity, and levels of biotransformation enzymes (cytochrome P4501A); metallothioneins and the efficiency of the antioxidant system measured as individual defenses (catalase, glutathione, glutathione reductase, glutathione S -transferases, and glutathione peroxidases); and total scavenging capacity toward peroxyl and hydroxyl radicals. Reciprocal interactions between metabolism of inorganic and organic pollutants were demonstrated. Dioxin enhanced the accumulation of cadmium, probably stored within proliferating endoplasmic reticulum, and cadmium suppressed the inducibility of cytochrome P4501A, allowing us to hypothesize a posttranscriptional mechanism as the depletion of heme group availability. Clear evidence of oxidative perturbation was provided by the inhibition of antioxidants and enhanced sensitivity to oxyradical toxicity in fish exposed to organic chemicals. Exposure to cadmium revealed counteracting responses of glutathione metabolism; however, these responses did not prevent a certain loss of antioxidant capacity toward peroxyl radicals. The pattern of antioxidant responses exhibited by fish coexposed to cadmium and TCDD was more similar to that observed for cadmium than to that observed for TCDD. The overall results suggest that elevated natural levels of cadmium in Antarctic organisms from Terra Nova Bay can limit biotransformation capability of polycyclic (halogenated) hydrocarbons, thus influencing the bioaccumulation and biological effects of these chemicals in key sentinel species. [source]

Effect of culture water hardness on the sensitivity of Ceriodaphnia dubia to copper toxicity

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2003
Rami B. Naddy
Abstract We examined whether the sensitivity of Ceriodaphnia dubia to copper toxicity was influenced by the hardness of the water in which they were reared or in which they were exposed. Organisms cultured in very hard water were 1.5-fold less sensitive to copper than those in moderately hard water. However, the hardness of the exposure water had a greater (2.5-fold) effect on copper median effective concentration (EC50s). [source]

Response of Daphnia magna to pulsed exposures of chlorpyrifos,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2000
Rami B. Naddy
Abstract Because aquatic organisms can be exposed to contaminants in an episodic manner, it is necessary to determine whether standard toxicity tests adequately simulate the toxicity of short-lived compounds, such as the organophosphate insecticide chlorpyrifos (CPF). We conducted experiments to evaluate the effect of binary combinations of concentration, duration, and interval of CPF exposures to Daphnia magna. Organisms were monitored for changes in survival and/or reproduction after pulsed exposure to CPF at 0.12, 0.25, 0.5, or 1.0 ,g/L. The exposure duration resulting in a 50% response in survival was 6.5 h at 1.0 ,g/L, 12.2 h at 0.5 ,g/L, and 48 h at 0.25 ,g/L. Daphnids exposed to two 12-h pulses of CPF at 0.5 ,g/L responded similarly (,85% mortality) regardless of the pulse interval (0, 3, 7, 14 d). However, daphnids were able to survive a 12-h exposure of CPF at 0.5 ,g/L if the exposure regime was separated into two 6-h pulses with a minimum interval of 3 d. Further experiments suggested that the interval studies may have been potentially confounded, because organisms exposed on day 3, 7, or 14 seemed more sensitive than those exposed as neonates. Additionally, no latent effects were measured for daphnids that survived the initial exposure. [source]

Enemy Recognition of Reed Warblers (Acrocephalus scirpaceus): Threats and Reproductive Value Act Independently in Nest Defence Modulation

ETHOLOGY, Issue 6 2010
Daniela Campobello
Organisms should respond more aggressively towards species perceived as a danger to their offspring, but intensity of defence may be gauged by the value of current offspring weighed against the value of future reproductive opportunities. We tested whether defensive responses of nesting reed warblers (Acrocephalus scirpaceus) are the result of an interaction effect between the type of stimulus confronted and the value of the warbler's nesting attempt. We quantified the ability of reed warblers to discriminate among brood parasites, nestling predators and non-threatening species at different stages of the breeding cycle. We also determined whether variables that influence the value of offspring, such as time of season, size and age of clutch or brood, and time of day and number of visits to the nest, explain variation in the intensity of defence recorded during the egg and nestling stages. Responses to the three stimuli differed significantly, as reed warblers consistently directed their mobbing calls and attacks towards parasites, whereas they were less conspicuous when confronted with models of predators. Reed warblers modulated their responses towards each stimulus in accordance with the threat each posed at a specific nesting stage, whereas they were not affected by other variables relative to their reproductive potential. The churr call, however, was uttered independently of the stimulus, as it was triggered by the mere presence of nestlings in the nest. [source]

DEFINED ORDER OF EVOLUTIONARY ADAPTATIONS: EXPERIMENTAL EVIDENCE

EVOLUTION, Issue 7 2008
Erez Oxman
Organisms often adapt to new conditions by means of beneficial mutations that become fixed in the population. Often, full adaptation requires several different mutations in the same cell, each of which may affect a different aspect of the behavior. Can one predict order in which these mutations become fixed? To address this, we experimentally studied evolution of Escherichia coli in a growth medium in which the effects of different adaptations can be easily classified as affecting growth rate or the lag-phase duration. We find that adaptations are fixed in a defined and reproducible order: first reduction of lag phase, and then an increase of the exponential growth rate. A population genetics theory explains this order, and suggests growth conditions in which the order of adaptations is reversed. We experimentally find this order reversal under the predicted conditions. This study supports a view in which the evolutionary path to adaptation in a new environment can be captured by theory and experiment. [source]

Doin' what comes natur'lly

EVOLUTIONARY ANTHROPOLOGY, Issue 2 2004
Article first published online: 8 APR 200, Kenneth Weiss
Behavior affects evolution in many ways. Organisms are adapted for what they do, but they also do what they are adapted for. [source]

Living Yeast Cells as a Controllable Biosynthesizer for Fluorescent Quantum Dots

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Ran Cui
Abstract There are currently some problems in the field of chemical synthesis, such as environmental impact, energy loss, and safety, that need to be tackled urgently. An interdisciplinary approach, based on different backgrounds, may succeed in solving these problems. Organisms can be chosen as potential platforms for materials fabrication, since biosystems are natural and highly efficient. Here, an example of how to solve some of these chemical problems through biology, namely, through a novel biological strategy of coupling intracellular irrelated biochemical reactions for controllable synthesis of multicolor CdSe quantum dots (QDs) using living yeast cells as a biosynthesizer, is demonstrated. The unique fluorescence properties of CdSe QDs can be utilized to directly and visually judge the biosynthesis phase to fully demonstrate this strategy. By such a method, CdSe QDs, emitting at a variety of single fluorescence wavelengths, can be intracellularly, controllably synthesized at just 30°C instead of at 300°C with combustible, explosive, and toxic organic reagents. This green biosynthetic route is a novel strategy of coupling, with biochemical reactions taking place irrelatedly, both in time and space. It involves a remarkable decrease in reaction temperature, from around 300 °C to 30 °C and excellent color controllability of CdSe photoluminescence. It is well known that to control the size of nanocrystals is a mojor challenge in the biosynthesis of high-quality nanomaterials. The present work demonstrates clearly that biological systems can be creatively utilized to realize controllable unnatural biosynthesis that normally does not exist, offering new insights for sustainable chemistry. [source]

Food Safety Objective (FSO) and Performance Objective/Heat Resistance of Pathogenic Organisms

INTERNATIONAL JOURNAL OF DAIRY TECHNOLOGY, Issue 1 2006
Alan G Williams
No abstract is available for this article. [source]

Testing of Genetically Modified Organisms in Food

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2005
Article first published online: 16 FEB 200
No abstract is available for this article. [source]

Fermentation of Reconstituted Skim Milk Supplemented with Soy Protein Isolate by Probiotic Organisms

JOURNAL OF FOOD SCIENCE, Issue 2 2008
T.T. Pham
ABSTRACT:, Utilization of lactose and production of organic acid were determined in reconstituted skim milk (RSM) and RSM supplemented with soy protein isolate (SPI) (RSMS) by 6 probiotic organisms, including L. acidophilus 4461, L. acidophilus 4962, L. casei 290, L. casei 2607, B. animalis subsp. lactis bb12, and B. longum 20099. The viable counts of probiotic organisms of RSM and RSMS were enumerated and pH measured during fermentation. Our results showed that 3% to 10% more lactose was utilized by all the 6 probiotic microorganisms from RSMS than RSM. All 6 probiotic organisms produced significantly more acetic acid in RSMS than RSM. However, the viable microbial populations in RSMS were lower than those in RSM due to lower pH of the former. It appears that addition of SPI enhanced lactose utilization and acetic acid production but slightly reduced the lactic acid production and the growth of probiotic microorganisms. [source]

Hypothalamic-pituitary-adrenal axis activation by experimental periodontal disease in rats

JOURNAL OF PERIODONTAL RESEARCH, Issue 5 2001
T. Breivik
Organisms respond to inflammatory conditions by mounting a co-ordinated complex series of adaptive responses involving the immune, nervous and endocrine systems that are aimed at restoring the homeostatic balance. We have recently shown in a rat model that inappropriate hypothalamic-pituitary-adrenal (HPA) axis regulation and a subsequent inability to mount a suitable glucocorticoid response to gingival inflammation may influence susceptibility to periodontal disease. This study was designed to investigate whether ligature- and bacterial lipopolysaccharide (LPS)-induced inflammation in the gingival connective tissues may activate this physiological axis, and to further explore the significance of HPA regulation in periodontal disease. Experimental periodontal disease was induced in major histocompability complex (MHC)-identical but HPA low (LEW) and high (F344) responding rat strains. We tested (1) whether ongoing periodontal disease activates the HPA axis as measured by corticosterone levels, and (2) whether genetic differences in HPA regulation modulate periodontal disease progression. In the F344 strain, the periodontal tissue destruction was more severe. This observation was associated with a significant increase of corticosterone levels in F344 rats only. Addition of LPS at the gingival inflammatory site led to a further increase of corticosterone levels and disease severity in F344 rats. These findings illustrate a positive feedback loop between the HPA axis and periodontal disease: the disease activates the HPA axis, and a genetically determined high HPA responsitivity further increases disease susceptibility. [source]

THE CYANOTOXINS-BIOACTIVE METABOLITES OF CYANOBACTERIA: OCCURRENCE, ECOLOGICAL ROLE, TAXONOMIC CONCERNS AND EFFECTS ON HUMANS

JOURNAL OF PHYCOLOGY, Issue 2001
Article first published online: 24 SEP 200
Carmichael, W. W. Department of Biological Sciences, Wright State University, Dayton, Ohio 45435 USA Cyanobacteria toxins (cyanotoxins) include cytotoxins and biotoxins with cytotoxins including about 60 compounds ranging from phytoalexins to animicrobials to enzyme inhibitors to compounds that can reverse multidrug resistance. Producer organisms include marine/brackish water Cystoseira, Hormothamnin, Lyngbya, Nodularia and Synechocystis, and the freshwater/terrestrial genera Anabaena, Dichotrix, Fischerella, Hapalosiphon, Lyngbya, Microcystis, Nostoc, Oscillatoria, Planktothrix, Phormidium, Schizothrix, Scytonema, Spirulina, Stigonema and Symploca. Since many of these compounds have been identified, not during ecological studies, but during drug discovery investigations, their ecological role is only speculative. Biotoxins are responsible for acute lethal, acute, chronic and sub-chronic poisonings of wild/domestic animals and humans. They include the neurotoxins; anatoxin-a, anatoxin-a(s) and saxitoxins plus the hepatotoxins; microcystins, nodularins and cylindrospermopsin. These compounds are included when referencing harmful algal blooms (HAB's) such as the more predominate marine PSP (paralytic shellfish poisoning), DSP (diarrhetic shellfish poisoning), NSP (neurotoxic shellfish poisoning), ASP (amnesic shellfish poisoning) and EAS (estuary associated syndrome). The CTP (cyanobacteria toxin poisoning) organisms occur in freshwater lakes, ponds, rivers and reservoirs throughout the world. Organisms responsible for CTP's are Anabaena, Aphanizomenon, Cylindrosperm- opsis, Microcystis, Nodularia, Nostoc Oscillatoria (Planktothrix), Trichodesmium and certain picoplanktic genera. Concern for animal and human health impairments arises from animal poisonings, associated with cyanobacteria waterblooms, beginning with the later part of the 1800's. It was not until the 1950's that we began to understand that cyanobacteria could indeed produce highly toxic compounds. A recent 1998 compilation of all available information on toxic cyanobacteria was published by the World Health Organization. This increasing focus on the role of cyanobacteria metabolites in chemical ecology, drug discovery and toxinology has placed new importance on using correct taxonomy for communication of responsible organisms. [source]

Solar disinfection of poliovirus and Acanthamoeba polyphaga cysts in water , a laboratory study using simulated sunlight

LETTERS IN APPLIED MICROBIOLOGY, Issue 2 2006
W. Heaselgrave
Abstract Aims:, To determine the efficacy of solar disinfection (SODIS) in disinfecting water contaminated with poliovirus and Acanthamoeba polyphaga cysts. Methods and Results:, Organisms were subjected to a simulated global solar irradiance of 850 Wm,2 in water temperatures between 25 and 55°C. SODIS at 25°C totally inactivated poliovirus after 6-h exposure (reduction of 4·4 log units). No SODIS-induced reduction in A. polyphaga cyst viability was observed for sample temperatures below 45°C. Total cyst inactivation was only observed after 6-h SODIS exposure at 50°C (3·6 log unit reduction) and after 4 h at 55°C (3·3 log unit reduction). Conclusions:, SODIS is an effective means of disinfecting water contaminated with poliovirus and A. polyphaga cysts, provided water temperatures of 50,55°C are attained in the latter case. Significance and Impact of the Study:, This research presents the first SODIS inactivation curve for poliovirus and provides further evidence that batch SODIS provides effective protection against waterborne protozoan cysts. [source]

The influence of bite size on foraging at larger spatial and temporal scales by mammalian herbivores

OIKOS, Issue 12 2007
Lisa A. Shipley
Organisms respond to their heterogeneous environment in complex ways at many temporal and spatial scales. Here, I examine how the smallest scale process in foraging by mammalian herbivores, taking a bite, influences plants and herbivores over larger scales. First, because cropping bites competes with chewing them, bite size influences short-term intake rate of herbivores within plant patches. On the other hand, herbivores can chew bites while searching for new ones, thus influencing the time spent vigilant and intake rate as animals move among food patches. Therefore, bite size affects how much time herbivores must spend foraging each day. Because acquiring energy is necessary for fitness, herbivores recognize the importance of bite size and select bites, patches and diets based on tradeoffs between harvesting rates, digestion, and sheering forces. In turn, induced structural defenses of plants, such as thorns, allow plants to respond immediately to herbivory by reducing bite size and thus tissue loss. Over evolutionary time, herbivores have adapted mouth morphology that allows them to maximize bite size on their primary forage plant, whereas plants faced with large mammalian herbivores have adapted structures such as divarication that minimize bite size and protect themselves from herbivory. Finally, bite size available among plant communities can drive habitat segregation and migration of larger herbivores across landscapes. [source]

The Flask model: emergence of nutrient-recycling microbial ecosystems and their disruption by environment-altering ,rebel' organisms

OIKOS, Issue 7 2007
Hywel T. P. Williams
Here we introduce a new model of life,environment interaction, which simulates an evolving microbial community in a ,Fask' of liquid with prescribed inputs of nutrients. The flask is seeded with a clonal population of ,microbes' that are subject to mutation on genetic loci that determine their nutrient uptake patterns, release patterns, and their effects on, and response to, other environmental variables. In contrast to existing models of life-environment interaction, notably Daisyworld, what benefits the individual organisms is decoupled from their ,global' (system-level) effects. A robust property of the model is the emergence of ecosystems that tend toward a state where nutrients are efficiently utilised and differentially recycled, with a correlated increase in total population. Organisms alter the environment as a free ,by-product' of their growth, and their growth is constrained by adverse environmental effects. This introduces environmental feedback, which can disrupt the model ecosystems, even though there are no constraints on the conditions to which the organisms can theoretically adapt. ,Rebel' organisms can appear that grow rapidly by exploiting an under-utilised resource, but in doing so shift the environment away from the state to which the majority of the community are adapted. The result can be a population crash with lossof recycling, followed by later recovery, or in extreme cases, a total extinction of the system. Numerous runs of these ,flask' ecosystems show that tighter environmental constraints on growth make the system more vulnerable to internally generated ecosystem extinction. [source]

HOW DID LIFE BECOME SO DIVERSE?

PALAEONTOLOGY, Issue 1 2007
THE DYNAMICS OF DIVERSIFICATION ACCORDING TO THE FOSSIL RECORD AND MOLECULAR PHYLOGENETICS
Abstract:, The long-term diversification of life probably cannot be modelled as a simple equilibrial process: the time scales are too long, the potential for exploring new ecospace is too large and it is unlikely that ecological controls can act at global scales. The sum of many clade expansions and reductions, each of which happens according to its own dynamic, probably approximates more a damped exponential curve when translated into a global-scale species diversification curve. Unfortunately, it is not possible to plot such a meaningful global-scale species diversification curve through time, but curves at higher taxonomic levels have been produced. These curves are subject to the vagaries of the fossil record, but it is unlikely that the sources of error entirely overwhelm the biological signal. Clades radiate when the external and internal conditions are right: a new territory or ecospace becomes available, and the lineage has acquired a number of characters that open up a new diet or mode of life. Modern high levels of diversity in certain speciose clades may depend on such ancient opportunities taken. Dramatic climatic changes through the Quaternary must have driven extinctions and originations, but many species responded simply by moving to more favourable locations. Ecological communities appear to be no more than merely chance associations of species, but there may be real interactions among species. Ironically, high species diversity may lead to more speciation, not, as had been assumed, less: more species create more opportunities and selective pressures for other species to respond to, rather than capping diversity at a fixed equilibrium level. Studies from the scale of modern ecosystems to global long-term patterns in the fossil record support a model for the exponential diversification of life, and one explanation for a pattern of exponential diversification is that as diversity increases, new forms become ever more refinements of existing forms. In a sense the world becomes increasingly divided into finer niche space. Organisms have a propensity to speciate freely, species richness within ecosystems appears to generate opportunities for more speciation, clades show all kinds of patterns from sluggish speciation rates and constant diversity through time to apparently explosive speciation, and there is no evidence that rapidly speciating clades have reached a limit, nor that they are driving other clades to extinction. A corollary of this view is that current biodiversity must be higher than it has ever been. Limits to infinite growth are clearly local, regional, and global turnover and extinction events, when climate change and physical catastrophes knock out species and whole clades, and push the rising exponential curve down a notch or two. [source]

Long-term impact of respiratory viral infection after pediatric lung transplantation

PEDIATRIC TRANSPLANTATION, Issue 3 2010
M. Liu
Liu M, Mallory GB, Schecter MG, Worley S, Arrigain S, Robertson J, Elidemir O, Danziger-Isakov LA. Long-term impact of respiratory viral infection after pediatric lung transplantation. Pediatr Transplantation 2010: 14:431,436. © 2010 John Wiley & Sons A/S. Abstract:, To evaluate the epidemiology and to investigate the impact of RVI on chronic allograft rejection after pediatric lung transplantation, a retrospective study of pediatric lung transplant recipients from 2002 to 2007 was conducted. Association between RVI and continuous and categorical risk factors was assessed using Wilcoxon rank-sum tests and Fisher's exact tests, respectively. Association between risk factors and outcomes were assessed using Cox proportional hazards models. Fifty-five subjects were followed for a mean of 674 days (range 14,1790). Twenty-eight (51%) developed 51 RVI at a median of 144 days post-transplant (mean 246; range 1,1276); 41% of infections were diagnosed within 90 days. Twenty-five subjects developed 39 LRI, and eight subjects had 11 URI. Organisms recovered included rhinovirus (n = 14), adenovirus (n = 10), parainfluenza (n = 10), influenza (n = 5), and RSV (n = 4). Three subjects expired secondary to their RVI (two adenovirus, one RSV). Younger age and prior CMV infection were risks for RVI (HR 2.4 95% CI 1.1,5.3 and 17.0; 3.0,96.2, respectively). RVI was not associated with the development of chronic allograft rejection (p = 0.25) or death during the study period. RVI occurs in the majority of pediatric lung transplant recipients, but was not associated with mortality or chronic allograft rejection. [source]

The Occurrence of the psbS Gene Product in Chlamydomonas reinhardtii and in Other Photosynthetic Organisms and Its Correlation with Energy Quenching,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2008
Giulia Bonente
To avoid photodamage, photosynthetic organisms have developed mechanisms to evade or dissipate excess energy. Lumen overacidification caused by light-induced electron transport triggers quenching of excited chlorophylls and dissipation of excess energy into heat. In higher plants participation of the PsbS protein as the sensor of low lumenal pH was clearly demonstrated. Although light-dependent energy quenching is a property of all photosynthetic organisms, large differences in amplitude and kinetics can be observed thus raising the question whether a single common mechanism is in action. We performed a detailed study of PsbS expression/accumulation in Chlamydomonas reinhardtii and investigated its accumulation in other algae and plants. We showed that PsbS cannot be detected in Chlamydomonas under a wide range of growth conditions. Overexpression of the endogenous psbs gene showed that the corresponding protein could not be addressed to the thylakoid membranes. Survey of different unicellular green algae showed no accumulation of anti-PsbS reactive proteins differently from multicellular species. Nevertheless, some unicellular species exhibit high energy quenching activity, suggesting that a PsbS-independent mechanism is activated. By correlating growth habitat and PsbS accumulation in different species, we suggest that during the evolution the light environment has been a determinant factor for the conservation/loss of the PsbS function. [source]

Effects of Mycorrhizae and Nontarget Organisms on Restoration of a Seasonal Tropical Forest in Quintana Roo, Mexico: Factors Limiting Tree Establishment

RESTORATION ECOLOGY, Issue 2 2005
Michael F. Allen
Abstract We initiated a study of the effects of mycorrhizal fungal community composition on the restoration of tropical dry seasonal forest trees. Tree seedlings were planted in a severely burned experimental site (1995 fire) during the growing season of 1998 at the El Edén Ecological Reserve, in north Quintana Roo, Mexico. Seedlings of Leucaena leucocephala, Guazuma ulmifolia, Caesalpinia violacea, Piscidia piscipula, Gliricidia sepium, and Cochlospermum vitifolium were germinated in steam-sterilized soil and either remained uninoculated (nonmycorrhizal at transplanting) or were inoculated with mycorrhizal fungi in soils from early-seral (recently burned) or late-seral (mature forest) inoculum. Inoculum from the early-seral soil was largely Glomus spp., whereas a diverse community of arbuscular mycorrhizal fungi were reintroduced from the mature forest including species of Scutellospora, Gigaspora, Glomus, Sclerocystis, and Acaulospora. Plants grew better when associated with the mature forest inoculum, unlike a previous experiment in which plants grew taller with the early-seral inoculum. Reasons for the different responses include a less-intense burn resulting in more residual organic matter. In addition to mycorrhizal responses, plants were severely affected by deer browsing. One tree species, C. vitifolium found in the region but not in the reserve, was eliminated by a resident fungal facultative pathogen. Several practical conclusions for restoration can be made. The common nursery practice of soil sterilization may be detrimental because it eliminates beneficial mycorrhizal fungi; species not native to the site may not survive because they may not be adapted to the local pathogens; and herbivory can be severe depending on the landscape context of the restoration. [source]

Optimization of Volumetric Computed Tomography for Skeletal Analysis of Model Genetic Organisms

THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 5 2008
Sergio X. Vasquez
Abstract Forward and reverse genetics now allow researchers to understand embryonic and postnatal gene function in a broad range of species. Although some genetic mutations cause obvious morphological change, other mutations can be more subtle and, without adequate observation and quantification, might be overlooked. For the increasing number of genetic model organisms examined by the growing field of phenomics, standardized but sensitive methods for quantitative analysis need to be incorporated into routine practice to effectively acquire and analyze ever-increasing quantities of phenotypic data. In this study, we present platform-independent parameters for the use of microscopic x-ray computed tomography (microCT) for phenotyping species-specific skeletal morphology of a variety of different genetic model organisms. We show that microCT is suitable for phenotypic characterization for prenatal and postnatal specimens across multiple species. Anat Rec, 291:475,487, 2008. © 2008 Wiley-Liss, Inc. [source]