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Search Results: 1 - 10 of 462045 matches for " A. Letourneau "
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Plant Fitness Assessment for Wild Relatives of Insect Resistant Bt-Crops
D. K. Letourneau,J. A. Hagen
Journal of Botany , 2012, DOI: 10.1155/2012/389247
Abstract: When field tests of transgenic plants are precluded by practical containment concerns, manipulative experiments can detect potential consequences of crop-wild gene flow. Using topical sprays of bacterial Bacillus thuringiensislarvicide (Bt) and larval additions, we measured fitness effects of reduced herbivory on Brassica rapa (wild mustard) and Raphanus sativus (wild radish). These species represent different life histories among the potential recipients of Bt transgenes from Bt cole crops in the US and Asia, for which rare spontaneous crosses are expected under high exposure. Protected wild radish and wild mustard seedlings had approximately half the herbivore damage of exposed plants and 55% lower seedling mortality, resulting in 27% greater reproductive success, 14-day longer life-spans, and 118% more seeds, on average. Seed addition experiments in microcosms and in situ indicated that wild radish was more likely to spread than wild mustard in coastal grasslands. 1. Introduction Commercialized transgenic, insect resistant (IR) crops currently grown in the United States have virtually no wild relatives near production sites, thus ensuring that novel crop traits are unlikely to move into local wild gene pools. However, an assessment of the consequences of gene flow will be necessary in future deregulation decisions because most of the major and minor crops in the world either exist in the wild themselves or hybridize with wild relatives somewhere in their range [1–5]. Wild relatives of transformed plants that obtain IR traits through gene flow and introgression may be released from the pressure exerted by susceptible herbivores [6–14]. However, scant knowledge about the ecological factors that regulate the abundance, competitive ability, or geographic range of weeds limits our ability to predict whether novel plant defenses are likely to increase the weediness of wild crop relatives [14] or even whether herbivory has a negative or positive effect on plant growth and fitness [15–20]. Surprisingly, few tests have been conducted on the effects of herbivory on the spread of invasive plants [21, 22] or to quantify the effects of herbivory on plant vital rates [23]. Identifying and quantifying environmental risks associated with gene flow from transgenic crops is subject to methodological tradeoffs because of containment restrictions, especially for plant fitness effects, which require pollen production. Field tests with pollen-producing transgenic plants must be contained physically in cages or greenhouses or established at sites where wild relatives do
Can Climate Change Trigger Massive Diversity Cascades in Terrestrial Ecosystems?
Lee A. Dyer,Deborah K. Letourneau
Diversity , 2013, DOI: 10.3390/d5030479
Abstract: We summarize research on diversity and trophic interactions under a trophic cascades model that is reframed and expanded from the traditional biomass- or abundance- based indirect effects and discuss the response of such “diversity cascades” to climate change and other global change parameters. The studies we summarize encompass dynamic processes in which species richness or evenness in one trophic level indirectly affects or is affected by changes in a non-adjacent level. The diversity cascade concept explicitly links trophic cascades models to the debates about biodiversity loss, exotic species gain, ecosystem services and biological control. First, we summarize the idea that the trophic cascades model includes different currencies and alternative processes. Second, we question the paradigm that trophic cascades weaken as the complexity of the community increases. Third, we illustrate the mechanisms by which diversity cascades may follow indirect bottom-up and top-down pathways. Fourth, we show how this diversity cascades model has been applied successfully to frame questions in conservation, agriculture and infectious disease. Finally, we examine the implications of diversity cascades for our understanding of how climate change affects biodiversity and call for an increase in the scope of experiments and focused hypotheses on indirect trophic effects and how these processes may lead to very large changes in biodiversity.
Huygens-Fresnel wavefront tracing in non-uniform media
F. A. Volpe,P. -D. Letourneau,A. Zhao
Physics , 2015,
Abstract: We present preliminary results on a novel numerical method describing wave propagation in non-uniform media. Following Huygens-Fresnel' principle, we model the wavefront as an array of point sources that emit wavelets, which interfere. We then identify a set of new points where the electric field has equal phase. In fact, without losing generality, we find zeros of the electric field, by means of the bisection method. This obviously corresponds to a specific phase-advance, but is easily generalized, e.g. by phase-shifting all sources. The points found form the new wavefront. One of the advantages of the method is that it includes diffraction. Two examples provided are diffraction around an obstacle and the finite waist of a focused Gaussian beam. Refraction is also successfully modeled, both in slowly-varying media as well as in the presence of discontinuities. The calculations were performed in two dimensions, but can be easily extended to three dimensions. We also discuss the extension to anisotropic, birefringent, absorbing media.
Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards
Julie A. Jedlicka, Russell Greenberg, Deborah K. Letourneau
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0027347
Abstract: Insectivorous Western Bluebirds (Sialia mexicana) occupy vineyard nest boxes established by California winegrape growers who want to encourage avian conservation. Experimentally, the provision of available nest sites serves as an alternative to exclosure methods for isolating the potential ecosystem services provided by foraging birds. We compared the abundance and species richness of avian foragers and removal rates of sentinel prey in treatments with songbird nest boxes and controls without nest boxes. The average species richness of avian insectivores increased by over 50 percent compared to controls. Insectivorous bird density nearly quadrupled, primarily due to a tenfold increase in Western Bluebird abundance. In contrast, there was no significant difference in the abundance of omnivorous or granivorous bird species some of which opportunistically forage on grapes. In a sentinel prey experiment, 2.4 times more live beet armyworms (Spodoptera exigua) were removed in the nest box treatment than in the control. As an estimate of the maximum foraging services provided by insectivorous birds, we found that larval removal rates measured immediately below occupied boxes averaged 3.5 times greater than in the control. Consequently the presence of Western Bluebirds in vineyard nest boxes strengthened ecosystem services to winegrape growers, illustrating a benefit of agroecological conservation practices. Predator addition and sentinel prey experiments lack some disadvantages of predator exclusion experiments and were robust methodologies for detecting ecosystem services.
Efecto del Compost de Biosólidos en la producción de plantines de Austrocedrus Chilensis (ciprés de la cordillera)
Basil,Gustavo; Mazzarino,María Julia; Roselli,Lucía; Letourneau,Federico;
Ciencia del suelo , 2009,
Abstract: using composts of urban waste, including biosolids, as substrates for containerized plant production is a sound economic and environmental alternative, since it could reduce the use of peat- and ?black earth?-based media, and the disposal of organic wastes in landfills. the objectives of this work were to study the effect of 0, 30 and 50% biosolids compost on the initial growth (first year) of cypress (austrocedrus chilensis d. don), and the effect during the subsequent two years of a unique treatment with 50% compost on the posterior growth and nutritional status of the seedlings. diameter and height were measured after 18, 25 and 37 months, shoot and root biomass after 25 and 37 months, and the foliar concentrations of c, n, p, k, ca and mg after 37 months. although all initial treatments were treated with 50% compost after one year, significant differences of diameter, height, and biomass of shoots and roots were found among the original treatments in all analyzed dates, values being higher in the compost treatments. at the end of the experiment, foliar nutrient concentrations were similar, except for mg that was higher in the original treatment with 50% compost. results show the importance of the initial growth on the posterior development of cypress seedlings, and the potential value of biosolids compost as a substrate for the containerized production of this species.
Progenitor cells as remote
Peter A Walker,Phillip A Letourneau,Supinder Bedi,Shinil K Shah
World Journal of Stem Cells , 2011,
Abstract: Acute central nervous system (CNS) injuries such as spinal cord injury, traumatic brain injury, autoimmune encephalomyelitis, and ischemic stroke are associated with significant morbidity, mortality, and health care costs worldwide. Preliminary research has shown potential neuroprotection associated with adult tissue derived stem/progenitor cell based therapies. While initial research indicated that engraftment and transdifferentiation into neural cells could explain the observed benefit, the exact mechanism remains controversial. A second hypothesis details localized stem/progenitor cell engraftment with alteration of the loco-regional milieu; however, the limited rate of cell engraftment makes this theory less likely. There is a growing amount of preclinical data supporting the idea that, after intravenous injection, stem/progenitor cells interact with immunologic cells located in organ systems distant to the CNS, thereby altering the systemic immunologic/inflammatory response. Such distant cell “bioreactors” could modulate the observed post-injury pro-inflammatory environment and lead to neuroprotection. In this review, we discuss the current literature detailing the above mechanisms of action for adult stem/progenitor cell based therapies in the CNS.
Efecto del Compost de Biosólidos en la producción de plantines de Austrocedrus Chilensis (ciprés de la cordillera) Effect of Biosolids Compost on seedling production of Austrocedrus Chilensis (ciprés de la cordillera)
Gustavo Basil,María Julia Mazzarino,Lucía Roselli,Federico Letourneau
Ciencia del Suelo , 2009,
Abstract: La utilización de compost de residuos urbanos como sustrato en contenedores es una alternativa interesante a nivel económico y ambiental, dado que reduciría el uso de turba y tierra negra en la producción de plantines, y la disposición de residuos en vertederos. En el presente trabajo se estudió el efecto de 0, 30 y 50% de compost de biosólidos en el crecimiento inicial (primer a o) de ciprés de la cordillera, y el efecto durante los dos a os siguientes de un tratamiento único con 50% de compost en el crecimiento posterior y el estado nutricional de los plantines. Se determinó diámetro y altura a 18, 25 y 37 meses, biomasa aérea y radicular a 25 y 37 meses, y concentración foliar de C, N, P, K, Ca y Mg a 37 meses. A pesar de que los tres tratamientos iniciales fueron homogeneizados al a o en un único tratamiento con 50% de compost, se encontraron diferencias significativas de diámetro, altura y biomasa aérea y radicular entre los tratamientos originales en todas las fechas analizadas, correspondiendo los mayores valores a los tratamientos con compost. Al finalizar el ensayo, las concentraciones foliares de nutrientes fueron muy similares en todos los plantines, excepto Mg que fue mayor en el tratamiento original con 50% de compost. Los resultados muestran la importancia de los primeros meses de crecimiento en el desarrollo posterior de los plantines de ciprés y el valor potencial de los compost de biosólidos como sustrato para la producción de esta especie en contenedores. Using composts of urban waste, including biosolids, as substrates for containerized plant production is a sound economic and environmental alternative, since it could reduce the use of peat- and black earth -based media, and the disposal of organic wastes in landfills. The objectives of this work were to study the effect of 0, 30 and 50% biosolids compost on the initial growth (first year) of cypress (Austrocedrus chilensis D. Don), and the effect during the subsequent two years of a unique treatment with 50% compost on the posterior growth and nutritional status of the seedlings. Diameter and height were measured after 18, 25 and 37 months, shoot and root biomass after 25 and 37 months, and the foliar concentrations of C, N, P, K, Ca and Mg after 37 months. Although all initial treatments were treated with 50% compost after one year, significant differences of diameter, height, and biomass of shoots and roots were found among the original treatments in all analyzed dates, values being higher in the compost treatments. At the end of the experiment, foliar nutrient concentrations we
The Reactor Antineutrino Anomaly
G. Mention,M. Fechner,Th. Lasserre,Th. A. Mueller,D. Lhuillier,M. Cribier,A. Letourneau
Physics , 2011, DOI: 10.1103/PhysRevD.83.073006
Abstract: Recently new reactor antineutrino spectra have been provided for 235U, 239Pu, 241Pu and 238U, increasing the mean flux by about 3 percent. To good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances <100 m leads to a ratio of observed event rate to predicted rate of 0.976(0.024). With our new flux evaluation, this ratio shifts to 0.943(0.023), leading to a deviation from unity at 98.6% C.L. which we call the reactor antineutrino anomaly. The compatibility of our results with the existence of a fourth non-standard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNE-neutrino data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that |Delta m_{new}^2|>1.5 eV^2 (95%) and sin^2(2\theta_{new})=0.14(0.08) (95%). Constraints on the theta13 neutrino mixing angle are revised.
Coping and Suicidal Ideations in Women with Symptoms of Postpartum Depression
S. Doucet and N. Letourneau
Clinical Medicine Insights: Reproductive Health , 2012,
Abstract: Objective: To explore the relationship between coping mechanisms and suicidal ideations among women who experience symptoms of postpartum depression. Design: This exploratory descriptive study used secondary data from a study of women who experienced symptoms of postpartum depression. Participants: Convenience and purposive sampling were used to obtain the community sample of 40 women who experienced symptoms of postpartum depression. Methods: Binary logistic regression was employed to explore emotion-focused coping, avoidance-focused coping, problem-focused coping, and religious coping as predictors of suicidal ideations. Results: Approximately 27% of the sample reported suicidal ideations within the past seven days. The results showed that lower levels of emotion-focused coping and higher levels of avoidance-focused and religious coping predicted suicidal ideations in participants. Problem-focused coping did not predict suicidal ideations. Conclusion: Overall, our findings provide support for the importance of coping mechanisms as predictors of suicidal ideations among women who experience symptoms of postpartum depression. The results illustrate the need for health professionals to conduct routine assessments on coping strategies and thoughts of suicide when caring for postpartum women, as well as the need to integrate coping approaches in the prevention and treatment of suicidal ideations.
Strategies for modulating the inflammatory response after decompression from abdominal compartment syndrome
Shinil K Shah, Fernando Jimenez, Phillip A Letourneau, Peter A Walker, Stacey D Moore-Olufemi, Randolph H Stewart, Glen A Laine, Charles S Cox
Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine , 2012, DOI: 10.1186/1757-7241-20-25
Abstract: A review of the relevant English language literature was conducted. Priority was placed on articles published within the last 5 years.Recent data from our group and others have begun to lay the foundation for the concept of TAC as a method to modulate the local and/or systemic inflammatory response in patients with an open abdomen resulting from ACS.Management of the open abdomen is an increasingly common part of modern surgical practice. Common clinical situations that mandate the use of temporary abdominal closure (TAC) include intra-abdominal hypertension (IAH) with new organ dysfunction (abdominal compartment syndrome (ACS)), intra-abdominal sepsis without adequate source control, damage control in trauma, and mesenteric ischemia [1]. While it is difficult to estimate the prevalence or economic impact of the open abdomen, it is associated with significant issues contributing to morbidity and mortality, including development of ventral hernias, enteroatmospheric fistulas, and un-intentional protein loss [2].The focus of this review is to detail current thoughts on the use of TAC in the management of the open abdomen, with particular attention to decompression after ACS. We review the relevant intra-abdominal related pathophysiology involved with ACS (with emphasis on the gut), the different types of TAC and evidence to support various choices. Recent data from our group and others have begun to lay the foundation for the concept of TAC as a method to modulate the local and/or systemic inflammatory response after ACS.As defined by the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome (World Society of the Abdominal Compartment Syndrome, http://www.wsacs.org webcite), ACS is defined as IAH (increased intra-abdominal pressure (IAP) (> 20 mmHg)) leading to new organ dysfunction/failure [3,4]. In general, there is improvement in organ function after decompressive laparotomy. ACS can be subdivided into primary, secon
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