Showing papers by "Université du Québec à Montréal published in 1998"

Accumulation of an Acidic Dehydrin in the Vicinity of the Plasma Membrane during Cold Acclimation of Wheat

Abstract: Expression of the acidic dehydrin gene wcor410 was found to be associated with the development of freezing tolerance in several Gramineae species. This gene is part of a family of three homologous members, wcor410 , wcor410b , and wcor410c , that have been mapped to the long arms of the homologous group 6 chromosomes of hexaploid wheat. To gain insight into the function of this gene family, antibodies were raised against the WCOR410 protein and affinity purified to eliminate cross-reactivity with the WCS120 dehydrin-like protein of wheat. Protein gel blot analyses showed that the accumulation of WCOR410 proteins correlates well with the capacity of each cultivar to cold acclimate and develop freezing tolerance. Immunoelectron microscope analyses revealed that these proteins accumulate in the vicinity of the plasma membrane of cells in the sensitive vascular transition area where freeze-induced dehydration is likely to be more severe. Biochemical fractionation experiments indicated that WCOR410 is a peripheral protein and not an integral membrane protein. These results provide direct evidence that a subtype of the dehydrin family accumulates near the plasma membrane. The properties, abundance, and localization of these proteins suggest that they are involved in the cryoprotection of the plasma membrane against freezing or dehydration stress. We propose that WCOR410 plays a role in preventing the destabilization of the plasma membrane that occurs during dehydrative conditions.

Canopy gap characteristics and tree replacement in the southeastern boreal forest

Abstract: This study identifies patterns in the gap disturbance regime along a succes- sional gradient in the southern boreal forest and uses this information to investigate canopy composition changes. Gaps were characterized in hardwood, mixed-forest, and conifer stands surrounding Lake Duparquet in northwestern Quebec. From 39 to 80 gaps were evaluated along transects established in each of these stands. The abundance of gap makers and gap fillers and total regeneration was evaluated by species, as well as the size of each gap encountered along the transects. The percentage of the forest in canopy gap was cal- culated directly from the proportion of the transect in gap and by using gap area and line- intercept techniques. Changes in composition were evaluated from gap-maker and gap- filler distributions and by using transition matrices based on species mortality and regen- eration in canopy gaps. The percentage of the forest in canopy gap ranges from 7.1% in a 50-yr-old forest dominated primarily by aspen to 40.4% in a 234-yr-old fir-dominated forest. Gap events are due to individual or small-group tree mortality in the early successional forest but become species-specific events controlled by spruce budworm outbreaks in the later stages of succession. Due to the high latitude, direct light only reaches the forest floor in the very largest gaps of the conifer-dominated stands. However, these gaps form slowly as budworm- caused mortality occurs over a number of years, whereas in aspen-dominated stands gaps are formed quickly by the snapping of tree stems. Balsam fir is the most abundant gap- filling species; however, its abundance is negatively correlated to gap size in all stand types. Markovian transition matrices suggest that in the young aspen-dominated forests small gaps lead to species replacment by more shade-tolerant conifers but that in the oldest forests the larger gaps will result in maintenance of the intolerant species and an increase in the abundance of cedar.

Effects of overstory and understory vegetation on the understory light environment in mixed boreal forests

Abstract: The percentage of above-canopy Photosynthetic Photon Flux Density (%PPFD) was measured at 0, 50 and 100 cm above the forest floor and above the main understory vegetation in stands of (1) pure Betula papyrifera (White birch), (2) pure Populus tremuloides (Trembling aspen), (3) mixed broad-leaf-conifer, (4) shade-tolerant conifer and (5) pure Pinus banksiana (Jack pine) occurring on both clay and till soil types. %PPFD was measured instantaneously under overcast sky conditions (nine locations within each of 29 stands) and continuously for a full day under clear sky conditions (five locations within each of eight stands). The percentage cover of the understory layer was estimated at the same locations as light measurements. Mean %PPFD varied from 2% at the forest floor under Populus forests to 15% above the understory vegetation cover under Betula forests. Percent PPFD above the understory vegetation cover was significantly higher under shade intolerant tree species such as Populus, Betula and Pinus than under shade tolerant conifers. No significant differences were found in %PPFD above the understory vegetation cover under similar tree species between clay and till soil types. The coefficient of variation in %PPFD measured in the nine locations within each stand was significantly lower under deciduous dominated forests (mean of 19%) than under coniferous dominated forests (mean of 40%). %PPFD measured at the forest floor was positively correlated with %PPFD measured above the understory vegetation and negatively correlated with cumulative total percent cover of the understory vegetation (R2 = 0.852). The proportion of sunflecks above 250 and 500 I¼mol m-2 s-1 was much lower and %PPFD in shade much higher under Populus and Betula forests than under the other forests. Differences in the mean, variability and nature of the light environment found among forest and soil types are discussed in relation to their possible influences on tree succession.

Future wildfire in circumboreal forests in relation to global warming

Abstract: Despite increasing temperatures since the end of the Little Ice Age (ca. 1850), wildfire frequency has decreased as shown in many field studies from North America and Europe. We believe that global warming since 1850 may have trig- gered decreases in fire frequency in some regions and future warming may even lead to further decreases in fire frequency. Simulations of present and future fire regimes, using daily outputs from the General Circulation Model (GCM), were in good agreement with recent trends observed in fire history studies. Daily data, rather than monthly data, were used be- cause the weather and, consequently, fire behavior can change dramatically over time periods much shorter than a month. The simulation and fire history results suggest that the impact of global warming on northern forests through forest fires may not be disastrous and that, contrary to the expectation of an overall increase in forest fires, there may be large regions of the Northern Hemisphere with a reduced fire frequency.

Intraguild predation among aphid predators : Characterization and influence of extraguild prey density

Abstract: Intraguild predation (IGP), a common interaction in invertebrates and vertebrates, affects the abundance and distribution of many species. Several parameters influence the magnitude and direction of IGP: feeding specificity, size, mobility, and aggressiveness of the protagonists, as well as extraguild prey density. Under laboratory conditions, we studied IGP among three species of aphid predators, Aphidoletes aphidimyza (Diptera: Cecidomyiidae), Chrysoperla rufilabris (Neuroptera: Chrysopidae), and Coleomegilla maculata lengi (Coleoptera: Coccinellidae), which commonly attack the potato aphid (extraguild prey) Macrosiphum euphorbiae (Homoptera: Aphididae). We characterized the levels and symmetry of IGP among the various stages of the predators in the absence of extraguild prey. The aphid specialist A. aphidimyza was more vulnerable to IGP than C. rufilabris and C. maculata, two generalist predators. The C. maculata/C. rufilabris interaction was symmetric (mutual IGP), whereas the C. maculata/A. aphidimyza and C. rufilabris/A. aphidimyza interactions were asymmetric, in favor of the coccinellid and the lacewing, respectively. Sessile and low mobility stages of all species were extremely vulnerable to IGP. Generally, the larger sized individual won confrontations. For similar sizes, lacewing larvae were superior to coccinellid larvae. We also tested whether IGP decreases when extraguild prey are introduced into the system. Data from five predator combinations revealed three types of responses: (1) an exponential decrease in IGP (lacewing instar I vs. coccinellid instar I); (2) a constant IGP (lacewing instar III vs. coccinellid instar I); (3) a constant IGP at low densities decreasing at high densities (lacewing instar III vs. gall midge old larva). Four theoretical scenarios are derived from these responses. Each is discussed according to the ecological attributes of the protagonists. This study shows that IGP is influenced by factors inherent to the predators and external factors such as extraguild prey density. The results are discussed further in the context of aphid biological control.

Effects of tree species, stand age and soil type on soil microbial biomass and its activity in a southern boreal forest

Abstract: Microbial C (Cmic) and N (Nmic), the Cmic-to-organic C (Corg) and Nmic-to-total N (Nt) ratios and the specific respiration of microbial biomass were investigated in a southern boreal mixed forest. The forest stands were 50 and 124 years old and consisted of trembling aspen, paper birch and mixed conifers comprising white spruce and balsam fir. Stands were growing on soils derived either from clay (89% average clay content) or till (46% average clay content) deposits in the clay belt region of northern Quebec. In the forest floors the relative concentrations of microbial C and N and the Cmic-to-Corg and Nmic-to-Nt ratios, regarded as measures of organic matter quality, declined with stand age whereas the specific microbial respiration increased, indicating decreasing C assimilation efficiency. In the mineral soils, in contrast, Cmic-to-Corg and Nmic-to-Nt ratios increased with stand age. The Cmic-to-Nmic ratio widened with stand age in both the forest floors and mineral soils, suggesting that the proportion of fungi had increased. Concentrations of microbial C and N were on average lower in forest floor beneath conifers (Cmic-to-Corg 1.9%, Nmic-to-Nt 7.5%) than beneath the deciduous species birch (Cmic-to-Corg 2.2%, Nmic-to-Nt 8.6%) and aspen (Cmic-to-Corg 2.4%, Nmic-to-Nt 9.2%). Average Cmic-to-Nmic ratios were only slightly different in the forest floors beneath the different tree species (Cmic-to-Nmic: conifers 8.9, birch 7.2, and aspen 8.3). In both forest floors and mineral soils, average concentrations of Cmic and Nmic were generally higher in the clay than in the till soils, but the Cmic-to-Corg ratios were similar in both soil types. The average Nmic-to-Nt ratios were lower in till than in clay soils only beneath conifers. The average specific microbial respiration (qCO2=μg CO2-C mg Cmic−1 d−1) in clay soils (22) was approximately half that in till soils (41). Since the microbial parameters measured were sensitive to the factors stand age, tree species and soil type, they may have the potential to be used as indicators of the influence of forest management on soil organic matter quality.

Dehn surgery on knots

Abstract: The Dehn surgery construction on knots in orientable 3-dimensional manifolds is introduced. We describe the parameters on which this construction depends, various situations in which it arises, and some of the main results and open research problems relating to it.

Correlates of Attachment at School Age: Maternal Reported Stress, Mother‐Child Interaction, and Behavior Problems

Abstract: The contribution of attachment, maternal reported stress, and mother-child interaction to the prediction of teacher-reported behavior problems was examined for a French-Canadian sample of 121 school-age children. Attachment classifications were assigned on the basis of reunion behavior with mother when the children were between 5 and 7 years of age. Maternal reported stress and mother-child interaction patterns were assessed concurrent to the attachment measure, whereas behavior problems were evaluated both at ages 5 to 7 and 7 to 9 years. Security of attachment significantly predicted the likelihood of school-age behavior problems: Controlling/other children were most at risk for both externalizing and internalizing problems across both age periods. Younger ambivalent children presented clinical cut-off levels of externalizing problems, and older avoidant boys had higher internalizing scores. Patterns of maternal-reported stress and mother-child interaction differed across attachment groups and contributed to prediction of school-age behavior problems, partially mediating the relation between attachment and adaptation. Results support the importance of attachment in explaining school-age adaptation and validity of attachment coding for children of this age.

Fish community structure in relation to environmental variation in floodplain lakes of the Araguaia River, Amazon Basin

Abstract: We examined the relationship between structure of fish communities and 11 environmental variables in floodplain lakes from the Middle Araguaia River, Brazil. Samples were collected at the beginning and at the end of the dry season in standardized surveys of six seasonally isolated lakes and six lakes permanently connected to the river mainstem. Canonical correspondence analysis revealed that among the environmental descriptors of lakes, only Secchi transparency and maximum depth were significantly related to fish community structure. Most of the patterned variation in community structure was associated with marked seasonal changes in lake transparency (means: early dry season=90.8 cm; late dry season = 33.2 cm) and depth (means: early dry season = 4.6 m; late dry season = 2.0 m). Visually oriented fishes had highest abundance in clear lakes, whereas fishes with adaptations to low visibility were most abundant in turbid lakes. The type of isolation of lakes from the river channel had no apparent effect on community structure. The results suggest that sensory adaptations for detection of prey under prevailing optical conditions play a major role in the organization of these communities, as predicted by a model of fish community organization originally developed for floodplain lakes of the Orinoco River, Venezuela.

Conifer seedling recruitment in a southeastern Canadian boreal forest: the importance of substrate

Abstract: In order to explain conifer species recruitment in Canada's southeastern boreal forest, we characterized conifer regeneration microsites and determined how these microsites vary in abundance during succession. Microsite abundance was evaluated in deciduous, mixed and coniferous stands along a 234-yr postfire chronosequence. Conifers were most often found in relatively well-illuminated microsites, devoid of litter, especially broad-leaf litter, and with a reduced cover of lower vegetation (< 50 cm tall). Although associated with moss-rich forest floor substrates, Abies balsamea was the most ubiquitously distributed species. Picea glauca and es- pecially Thuja occidentalis seedlings were frequently found on rotten logs. Light measurements did not show differences among seedling species nor between stand types. The per- centage cover of broad-leaf litter decreased significantly during succession. Also, rotten logs covered with moss occu- pied a significantly larger area in the mid-successionnal stands than in early successional deciduous or late succes- sional coniferous stands. The results suggest that the pres- ence of specific forest floor substrate types is a factor ex- plaining low conifer recruitment under deciduous stands, conifer codominance in the mid-successional stage, and de- layed Thuja recolonization after fire. Results also suggest that some facilitation mechanism is responsible for the ob- served directional succession.

Spruce budworm impact, abundance and parasitism rate in a patchy landscape.

Abstract: The hypothesis that vegetational diversity may lessen the impact of forest insect pests by favoring natural enemies is appealing to those who seek ecologically sound solutions to pest problems. We investigated the effect of forest diversity on the impact of the spruce budworm Choristoneurafumiferana following the last outbreak, as well as the budworm's current abundance and parasitism rate, in the boreal forest of northwestern Quebec. Mortality of balsam fir caused by the budworm was greater in extensive conifer stands than either in "habitat islands" of fir surrounded by deciduous forest or on true islands in the middle of a lake. Adult spruce budworm abundance, assessed by pheromone traps, did not differ significantly between the three types of sites. Larval and pupal parasitism rates were examined by transferring cohorts of laboratory-reared larvae and pupae to trees in the three site types and later collecting and rearing them. The tachinid Actiainterrupta, a parasitoid of fifth and sixth instar larvae, as well as the ichneumonid pupal parasitoids Itoplectesconquisitor, Ephialtesontario and Phaeogenesmaculicornis, caused higher mortality in the habitat islands than on true islands or in extensive stands. Exochusnigripalpistectulum, an ichneumonid that attacks the larvae and emerges from the pupae, caused greater mortality in the extensive stands of conifers.

Interrenal dysfunction in fish from contaminated sites: In vivo and in vitro assessment

Abstract: Cortisol, synthesized in the interrenal cells of teleost head kidney, has a major role in the physiologic response to physical and chemical stressors. Plasma levels of cortisol increase in physiologically competent fish acutely exposed to stressors such as cadmium or mercury. The effects of chronic low level exposures are less well understood. The author has diagnosed an endocrine impairment characterized by a reduced capacity to elevate plasma cortisol levels in response to an acute standardized capture stress in yellow perch (Perca flavescens) and in northern pike (Esox lucius) sampled at sites contaminated by mixtures of pollutants (heavy metals, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls), by heavy metals, or by bleached kraft mill effluent. The studies with fish, as well as with amphibians at contaminated sites, demonstrated that low level chronic exposures impair secretion of corticosteroids. The author has developed new tests for assessment of the functional integrity of teleost and amphibian interrenal tissue using an adrenocorticotropic hormone (ACTH) challenge, in vivo and in vitro. The reduced ability to respond to ACTH indicates that the normal neuroendocrine response to stressors may be disrupted and that the ability to cope with biotic and abiotic stressors in the environment may be significantly reducedmore » in the impaired animals.« less

Creole genesis and the acquisition of grammar : the case of Haitian creole

Abstract: Preface List of abbreviations 1. The problem of creole genesis and linguistic theory 2. Cognitive processes involved in creole genesis 3. The research methodology 4. Functional category lexical entries involved in nominal structure 5. The preverbal markers encoding relative tense, mood and aspect 6. Pronouns 7. Functional category lexical entries involved in the structure of the clause 8. The determiner and the structure of the clause 9. The syntactic properties of verbs 10. Are derivational affixes relexified? 11. The concatenation of words in compounds 12. Parameters 13. Evaluation of the hypothesis 14. Theoretical consequences Appendices Notes References Indexes.

Climate and climate change in western canada as simulated by the Canadian regional climate model

Abstract: A þrst climate simulation performed with the novel Canadian Regional Climate Model (CRCM) is presented. The CRCM is based on fully elastic non‐hydrostatic þeld equations, which are solved with an efþcient semi‐implicit semi‐Lagrangian (SISL) marching algorithm, and on the parametrization package of subgrid‐scale physical effects of the second‐generation Canadian Global Climate Model (GCMII). Two 5‐year integrations of the CRCM nested with GCMII simulated data as lateral boundary conditions are made for conditions corresponding to current and doubled CO2 scenarios. For these simulations the CRCM used a grid size of 45 km on a polar‐stereographic projection, 20 scaled‐height levels and a time step of 15 min; the nesting GCMII has a spectral truncation of T32, 10 hybrid‐pressure levels and a time step of 20 min. These simulations serve to document: (1) the suitability of the SISL numerical scheme for regional climate modelling, (2) the use of GCMII physics at much higher resolution than in the nesti...

Existence and Stochastic Structure of a Non‐negative Integer‐valued Autoregressive Process

Abstract: A simple criterion is given for the existence of a generalized integer-valued autoregressive (GINAR(p)) process. We show that the GINAR(p) process is nothing but an AR(p) process. The spectral density gives a good insight into the stochastic structure of a GINAR(p) model. The spectral representation of the process is explicitly given. The estimation of parameters of the process is also discussed and clarifies some results presented by Du and Li (The integer-valued autoregressive (INAR(p)) model. J. Times Ser. Anal., 12 (1991), 129--42). Finally, we describe the number of seizures of an epileptic patient using a model of this class.

Nitrate cycling in streams: using natural abundances of NO3--δ15N to measure in-situ denitrification

Abstract: Contamination of surface- and groundwaters as a result of anthropogenic nitrate loading is of concern in regions subjected to intense agricultural activities. The capacity of watersheds to absorb, process or release nitrate to outflow drainage waters, however, is poorly constrained. An investigation of in-stream denitrification was conducted in a small stream draining a heavily fertilized agricultural watershed by analyzing natural isotopic abundances of nitrate-nitrogen. Using δ15N isotopic signatures, we show that denitrification plays a large role in reducing nitrate levels during stream transport over a relatively short distance. We found in-situ nitrate losses of up to 50% and a corresponding shift in NO3--δ15N values of 10‰ over a 600 m distance downstream consistent with denitrification. Our results suggest that in-stream nitrate losses must be considered when examining nitrate cycling and contamination in watersheds. Not only should attempts to identify nitrate contamination sources using NO3--δ15N signatures be carried out with caution (as nitrate-N isotopic values can be altered during stream transport such that they no longer reflect the original nitrate source), but in-stream measures of nitrate concentrations aimed at monitoring contamination levels may underestimate nitrate inputs to surface waters due to denitrification during transport.

Design of class hierarchies based on concept (Galois) lattices

Abstract: Building and maintaining the class hierarchy has been recognized as an important but one of the most difficult activities of object-oriented design. Concept (or Galois) lattices and related structures are presented as a framework for dealing with the design and maintenance of class hierarchies. Because the design of class hierarchies is inherently an iterative and incremental process, we designed incremental algorithms that update existing Galois lattices as the result of adding, removing, or modifying class specifications. A prototype tool incorporating this and other algorithms has been developed as part of the IGLOO project, which is a large object-oriented software engineering joint research project involving academic and industrial partners. The tool can generate either the concept lattice or several variant structures incrementally by incorporating new classes one by one. The resulting hierarchies can be interactively explored and refined using a graphical browser. In addition, several metrics are computed to help evaluating the quality of the hierarchies. Experiments are presented to better assess the applicability of the approach.

Iron acquisition by photosynthetic marine phytoplankton from ingested bacteria

Abstract: Iron is unique among biologically essential trace metals in having a higher particulate than dissolved concentration in ocean surface waters1. Uptake of dissolved iron is generally considered to be the norm for phytoplankton, as even the smallest iron-bearing particles are unavailable for transport into cells2,3. But the oceanic dissolved fraction is so small, and the particulate fraction so inert2, that phytoplankton production is limited by a dearth of available iron in some regions4. Here we use incubation experiments to show that Ochromonas sp., a common photosynthetic flagellate from the Pacific Ocean, can obtain iron directly in particulate form, by ingesting bacteria. Iron acquisition is highly efficient; Ochromonas assimilates 30% of the ingested ration, acquiring a high intracellular iron concentration and maintaining a significantly faster growth rate than when iron is provided in the dissolved phase. Phytoplankton capable of such phagotrophy (so-called mixotrophic species) may thus be able to assimilate iron in both particulate and dissolved forms in the ocean. Moreover, when iron availability is limited, the iron ‘cost’ of growth is diminished because Ochromonas derives a greater fraction of its energy from the bacteria. Analysis of standing stocks and clearance rates of plankton in the equatorial Pacific shows that the iron flux through mixotrophic flagellates can amount to 35–58% of the total Fe uptake by the entire autotrophic community. Our results suggest that the phagotrophic ingestion of bacteria may be an effective adaptive strategy for photosynthetic organisms to obtain iron for growth in iron-limited regions of the sea.

Effects of subchronic exposure to cadmium chloride on endocrine and metabolic functions in rainbow trout Oncorhynchus mykiss.

Abstract: Adult and juvenile rainbow trout, Oncorhynchus mykiss, were exposed for 30 days to CdCl2 in water (10 and 25 μg Cd/L for adults, and 1 and 5 μg Cd/L for juveniles) to investigate effects of subchronic exposures to Cd on the hypothalamo-pituitary-interrenal and the hypothalamo-pituitary-thyroid axis, and on metabolic status Liver size and glycogen content and body mass gain were significantly reduced in the exposed adult fish and similar changes were detected in the juveniles Plasma cortisol levels increased after exposure to the lower dose but decreased at the higher dose Plasma T3 and T4 tended to decrease in the exposed adult fish No significant differences in plasma glucose or cholesterol levels were detected between the controls and the exposed fish, plasma calcium levels were lower in the exposed fish The results indicate that long-term exposures to Cd at sublethal doses have adverse effects on the physiological status of the fish and that these effects are mediated partly through alterations of endocrine function

Checking accounts and bank monitoring

Abstract: Do checking accounts help banks monitor borrowers? If they do, the rationale both for allowing regulated providers of liquidity to also make risky loans to commercial borrowers and for the government's providing deposit insurance becomes clearer. Using a unique set of data that includes monthly and annual information on small-business borrowers at an anonymous Canadian bank, we provide evidence that a bank has exclusive access to a continuous stream of borrower data that helps it to monitor the borrower, namely, the firm's checking account balances at the bank. In this paper, which to our knowledge is the first direct empirical test of the usefulness of checking account information in monitoring commercial borrowers, we provide "smoking gun" evidence that banks are special. We also provide detailed evidence of how a commercial bank uses this information to determine its credit ratings of borrowers and adjust the intensity of its monitoring activity.