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Québec, Canada

Giraudo M.,CNRS Sophia Agrobiotech Institute | Giraudo M.,French National Center for Scientific Research | Giraudo M.,University of Nice Sophia Antipolis | Giraudo M.,Center Saint Laurent | And 9 more authors.
Journal of Insect Physiology

The fall armyworm Spodoptera frugiperda is. a major polyphagous pest in agriculture and little is known on how this insect can adapt to the diverse and potentially toxic plant allelochemicals that they ingest or to insecticides. To investigate the involvement of nuclear receptors in the response of S. frugiperda to its chemical environment, we cloned SfHR96, a nuclear receptor orthologous to the mammalian xenobiotic receptors, pregnane X receptor (PXR) and constitutive androstane receptor (CAR). We also cloned ultraspiracle (USP), the ortholog of retinoid X receptor (RXR) that serves as partner of dimerization of PXR and CAR. Cloning of SfUSP revealed the presence of two isoforms, SfUSP-1 and SfUSP-2 in this species, that differ in their N-terminal region. The expression of these receptors as well as the ecdysone receptor was studied during specific steps of development in different tissues. SfHR96 was constitutively expressed in larval midgut, fat body and Malpighian tubules throughout the last two instars and pupal stage, as well as in Sf9 cells. EcR and SfUSP-2 showed peaks of expression before larval moults and during metamorphosis, whereas SfUSP-1 was mainly expressed in the pre-pupal stage. Receptor induction was followed after exposure of larvae or cells to 11 chemical compounds. SfHR96 was not inducible by the tested compounds. EcR was significantly induced by the 20-hydroxyecdysone agonist, methoxyfenozide, and SfUSP showed an increase expression when exposed to the juvenile hormone analog, methoprene. The cloning of these nuclear receptors is a first step in understanding the important capacities of adaptation of this insect pest. © 2013 Elsevier Ltd. Source

Marty C.,Center Saint Laurent | Lamaze T.,University Paul Sabatier | Pornon A.,CNRS Biological Evolution and Diversity Laboratory
New Phytologist

Owing to nitrogen (N) translocation towards new leaves, the shedding of old leaves can increase the whole-plant carbon gain. It occurs when their photosynthetic nitrogen use efficiency (PNUE) declines below a given threshold. Here, we investigated variations in net photosynthetic capacity (A max), N resorption and PNUE in populations of Rhododendron ferrugineum presenting different mean leaf life spans (LLS). Both populations had comparable annual leaf surface area production and A max across leaf-age cohorts. Branch photosynthetic capacity was up to 95% higher in the population with the longer LLS mainly because of the high contribution of old leaves to the total leaf area. Despite lower N concentrations, old leaves maintained relatively high A max and consequently PNUE that were higher than or similar to the values found in current-year leaves. As the ratio of PNUE in old to PNUE in new leaves was always higher than the fraction of leaf N resorbed during leaf shedding, we concluded that leaf shedding did not improve plant photosynthetic capacity. We suggest that in R. ferrugineum, leaf shedding is mainly controlled by the leaf storage function and, therefore, that models aiming to explain LLS should not only consider the leaf carbon assimilation function, particularly in nutrient-poor habitats. No claim to original French government works. Journal compilation © New Phytologist Trust (2010). Source

Houde M.,Center Saint Laurent | Douville M.,Center Saint Laurent | Gagnon P.,Center Saint Laurent | Sproull J.,Prairie and Northern Laboratory for Environmental Testing | Cloutier F.,Environmental Operations
Ecotoxicology and Environmental Safety

Trichloroethylene (TCE) is a ubiquitous contaminant classified as a human carcinogen. Vinyl chloride (VC) is primarily used to manufacture polyvinyl chloride and can also be a degradation product of TCE. Very few data exist on the toxicity of TCE and VC in aquatic organisms particularly at environmentally relevant concentrations. The aim of this study was to evaluate the sub-lethal effects (10. day exposure; 0.1; 1; 10. μg/L) of TCE and VC in Daphnia magna at the gene, cellular, and life-history levels. Results indicated impacts of VC on the regulation of genes related to glutathione-. S-transferase (. GST), juvenile hormone esterase (. JHE), and the vitelline outer layer membrane protein (. VMO1). On the cellular level, exposure to 0.1, 1, and 10. μg/L of VC significantly increased the activity of JHE in D. magna and TCE increased the activity of chitinase (at 1 and 10. μg/L). Results for life-history parameters indicated a possible tendency of TCE to affect the number of molts at the individual level in D. magna (. p=0.051). Measurement of VG-like proteins using the alkali-labile phosphates (ALP) assay did not show differences between TCE treated organisms and controls. However, semi-quantitative measurement using gradient gel electrophoresis (213-218. kDa) indicated significant decrease in VG-like protein levels following exposure to TCE at all three concentrations. Overall, results indicate effects of TCE and VC on genes and proteins related to metabolism, reproduction, and growth in D. magna. © 2015. Source

Beauregard S.L.,McGill University | Cote B.,McGill University | Houle D.,Direction de la recherche forestiere | Houle D.,Center Saint Laurent

The maple-dominated forest of eastern Canada and northeastern United States has experienced forest decline that can be linked to changes in soil fertility and soil acidification. In this study, we used a new dendrochemical approach to trace back changes in nutrients (Ca, K, Mg, and Mn) and Al availability. Compositional Nutrient Diagnosis (CND) was applied on the residual fraction of wood obtained after acid-leaching of the mobile fraction. Sites (Saint-Lawrence Lowlands; Lower Laurentians; and Appalachian Highlands) and tree species (American beech (Fagus grandifolia Ehrh.; sugar maple (Acer saccharum Marsh.; red maple (Acer rubrum L.) were chosen to represent a gradient of decreasing resilience to increasing soil acidity. The tree ring chronologies covered the period of 1940-1999. The acid-sensitive Appalachians region had the highest Mn and the greatest increase in Al, the likely result of a Mn-rich bedrock and poorly-buffered soils, respectively. The acid-resilient American beech had decreasing Al and constant Ca and Mn in contrast to sugar and red maple that had increasing Al and decreasing Ca and Mn. Red maple was high in Mn particularly in terms of CND, which could be linked to its preference for wetter sites that are more conducive to reducing conditions. The patterns of change over time in ring chemistry were often altered around 1960-1970. These patterns appear to be driven by the resilience of the region or species to increased acidity. The detection of these regional and species differences in resiliency were facilitated by the use of CND. © 2009 Elsevier GmbH. All rights reserved. Source

Massicotte P.,University of Quebec at Trois - Rivieres | Bertolo A.,University of Quebec at Trois - Rivieres | Brodeur P.,Direction Regionale Of La Mauricie Et Du Center Du Quebec | Hudon C.,Center Saint Laurent | And 2 more authors.
Journal of Great Lakes Research

Aquatic vegetation (AV) is an important component of aquatic system, affecting habitat carrying capacity and fish productivity. By modulating habitat complexity, AV has the potential to influence the early ontogenetic stages of many fish species. However, understanding how variations in AV abundance influence fish distribution and abundance at the landscape scale of freshwater ecosystems is a considerable challenge due to the difficulty of collecting the high-resolution data needed for such analyses. We used yellow perch (Perca flavescens) as a biological model to test the hypothesis that larval fish abundance is positively related to a AV-rich landscape. Combining seven years of extensive larval sampling and satellite imagery, our results suggest that fish larvae tend to be associated with AV habitats after hatching. Based on zero-inflated binomial models, the probability of observing perch larvae increased from approximately 20% in low AV habitats to nearly 100% in dense AV habitats (pseudo-R 2 =0.54). Our results also show that the probability of observing yellow perch larvae was lower during years of low water level and low AV biomass, likely limiting the availability of proper spawning or nursery habitats for fish. Furthermore, we demonstrate that larvae use both new AV as well as vegetative debris from the previous year that persisted through the winter. In agreement with a growing literature, our study gives additional support to the idea that AV plays a key role in freshwater fish recruitment. © 2015 International Association for Great Lakes Research. Source

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