The hyperbolic formal affine Demazure algebra

In the present paper we extend the construction of the formal (affine) Demazure algebra due to Hoffnung, Malag\'on-L\'opez, Savage and Zainoulline in two directions. First, we introduce and study the notion of an extendable weight lattice in the Kac-Moody setting and show that all the definitions and properties of the formal (affine) Demazure operators and algebras hold for such lattices. Second, we show that for the hyperbolic formal group law the formal Demazure algebra is isomorphic (after extending the coefficients) to the Hecke algebra.Comment: Final version. Accepted for publication in Algebras and Representation Theory. ALGE-D-15-0016

Immigration factors and potentially avoidable hospitalizations in Canada

Objective Estimate the effect of immigration characteristics on the risk of a hospitalization for an ambulatory care sensitive condition (ACSC). Research design We analyzed data on the Canadian resident adult population aged 18 to 74 years who responded to the 2006 long form Census. The Census data were linked to the Canadian Institute for Health Information (CIHI)’s Discharge Abstract Database (DAD) for fiscal years 2006–2007, 2007–2008, and 2008–2009. We conducted a logistic regression on the binary variable we created for an ACSC admission. Measures The CIHI definition of ACSC hospitalizations was used to identify potentially avoidable hospitalizations in the DAD. Immigration factors analyzed included years in Canada, ethnic origin, and ability to speak one of the official languages. Results There were 3,342,450 respondents aged between 18 and 74. Using the Canadian at birth as our reference population, recent immigrants (up to five years in Canada) had lower odds of an ACSC hospitalization, regardless of their ethnic origins, with the exception of immigrants from Oceania and from other North American countries for whom the effect was not significant. The protective effect was still present in children of immigrants (AOR=0.89). Immigrants from the Caribbean, from Southern, Eastern, and Western Europe, as well as those from East Asia had lower odds across categories of time spent in Canada. The protective effect was stronger in immigrants from East Asia and lower in those of Oceanic and other North American countries. Conclusions Our results suggest that the healthy immigrant effect dissipates with time in Canada but remains even in children of immigrants. The protective effect differs depending on the ethnic origin of the immigrant

Photodemethylation of methylmercury in Eastern Canadian Arctic thaw pond and lake ecosystems

Permafrost thaw ponds of the warming Eastern Canadian Arctic are major landscape constituents and often display high levels of methylmercury (MeHg). We examined photodegradation potentials in high-dissolved organic matter (DOC) thaw ponds on Bylot Island (BYL) and a low-DOC oligotrophic lake on Cornwallis Island (Char Lake). In BYL, the ambient MeHg photodemethylation (PD) rate over 48 h of solar exposure was 6.1 × 10–3 m2 E–1, and the rate in MeHg amended samples was 9.3 × 10–3 m2 E–1. In contrast, in low-DOC Char Lake, PD was only observed in the first 12 h, which suggests that PD may not be an important loss process in polar desert lakes. Thioglycolic acid addition slowed PD, while glutathione and chlorides did not impact northern PD rates. During an ecosystem-wide experiment conducted in a covered BYL pond, there was neither net MeHg increase in the dark nor loss attributable to PD following re-exposure to sunlight. We propose that high-DOC Arctic thaw ponds are more prone to MeHg PD than nearby oligotrophic lakes, likely through photoproduction of reactive species rather than via thiol complexation. However, at the ecosystem level, these ponds, which are widespread through the Arctic, remain likely sources of MeHg for neighboring systems

Holocene reconstruction of spruce budworm-fire interactions in the mixed boreal forest of Québec (Canada) / Chronologie Holocène de l’interaction entre la tordeuse des bourgeons de l’épinette et les feux dans la forêt mixte du Québec (Canada)

Within the context of a changing climate, multi-millennial reconstructions are fundamental to our understanding of the range of variability in key ecosystem processes such as insect outbreaks and wildfires. Reconstructions spanning the Holocene allow us to observe how natural disturbances have behaved, and interacted in different climate phases and may provide a sustainable forest management framework going forward. However, for our understanding at vast temporal scales to be robust and accurate, we require the use of adequate proxies that have been validated and calibrated. I use the eastern Canadian mixed boreal forest as a model system to validate, and calibrate the use of a novel paleo-proxy, lepidopteran scales, to detect spruce budworm outbreaks in recent history, and then reconstruct spruce budworm, and wildfire events over the course of the Holocene. I demonstrated that lepidopteran scale accumulations in lake surface sediment are able to detect local spruce budworm outbreaks as these achieved high agreement with aerial surveys conducted in the late 20th century (1967-1986; 2010-present). Using the same surface sediment cores, I then assessed whether annually interpolated lepidopteran scale accumulations and tree-ring records both detected local spruce budworm impacts, and if the recorded impacts were synchronous. I demonstrated that each proxy individually identified local spruce budworm impacts at a periodicity of approximately 16 to 32 years coinciding with known outbreak return intervals, and that, when compared to each other, both proxies detected similar outbreak periodicities. Further, I demonstrated that the proxy record signals were relatively synchronous, and that the relationship between the two records suggests that large lepidopteran scale accumulations translate to a greater percentage of affected trees in a stand, and to greater recorded growth suppression i.e., narrower ring-widths. The validation and calibration of this novel proxy therefore provided a more robust and accurate foundation to interpret lepidopteran scale accumulations at multimillennial time scales. Finally, I reconstructed spruce budworm and wildfire events in the mixed boreal forest at lake Buire throughout the Holocene. The frequency of spruce budworm and wildfire events exhibited a negative correlation for the majority of the Holocene suggesting a linked interaction at the millennial and local/extra-local scales where one disturbance inhibits the presence of the other. Further, disturbance event frequencies oscillated during the Holocene following the postglacial establishment ofbalsam fir, and the switch in the dominant disturbance tended to coincide with rapid significant climate change events. The present study advanced our understanding of the long-term range of variability of the main disturbances of the mixed boreal and their interactions. The results of this thesis contribute to the body of knowledge of forest ecology, and disturbance interactions and provide insight into potential frameworks that could be utilized in sustainable forest management. Dans le contexte des changements climatiques, les reconstructions plurimillénaires sont fondamentales à notre compréhension de la variabilité des processus écosystémiques tels que les épidémies d'insectes et les feux de forêt. Les reconstitutions couvrant l'Holocène nous permettent d'observer comment ces perturbations naturelles se sont comportées et ont interagi au cours de différentes phases climatiques et ont le potentiel de fournir un cadre pour la gestion durable des forêts. Cependant, pour que notre compréhension à de vastes échelles temporelles soit robuste et précise, nous devons utiliser des proxys adéquats qui ont été validés et calibrés. J'utilise la forêt boréale mixte de l'est du Canada comme système modèle pour valider et calibrer l'utilisation d'un nouveau paléo-proxy, les écailles de papillon, afin de détecter les épidémies de tordeuse des bourgeons de l'épinette dans l’histoire récente et ensuite de reconstruire les événements liés à la tordeuse et aux feux de forêt au cours de l'Holocène. J'ai démontré que les accumulations d'écailles de papillon dans les sédiments de surface des lacs sont capables de détecter les épidémies locales de la tordeuse, car elles concordent bien avec les relevés aériens effectués à la fin du XXe siècle (1967-1986; 2010-présent). En utilisant les mêmes carottes de sédiments de surface, j'ai ensuite évalué si les accumulations d'écailles de papillon interpolées annuellement et les cernes de croissance détectaient aussi bien les impacts locaux de la tordeuse des bourgeons de l'épinette, et si ces impacts enregistrés étaient synchrones. J'ai démontré que chaque proxy identifiait individuellement les impacts locaux de la tordeuse, coïncidant avec les intervalles des épidémies connues, et que, comparées l'une à l'autre, les deux approximations détectaient des périodicités d'épidémies similaires. De plus, j'ai démontré que les signaux enregistrés par les proxys étaient relativement synchrones. La relation entre les deux proxys suggère que les grandes accumulations d'écailles se traduisent par un plus grand pourcentage d'arbres affectés dans un peuplement, et par des cernes plus étroits. La validation et l'étalonnage de ce nouvel indicateur ont donc fourni une base plus solide et précise pour interpréter les accumulations d’écailles à des échelles de temps plurimillénaires. Enfin, j'ai reconstitué les événements liés à la tordeuse des bourgeons de l'épinette et aux feux de forêt dans la forêt boréale mixte au lac Buire tout au long de l'Holocène. J’ai observé une corrélation négative entre la fréquence des épidémies de la tordeuse et des feux de forêt pendant la majeure partie de l'Holocène, ce qui suggère une interaction liée aux échelles millénaire et locale/extra-locale, où une perturbation inhibe la présence de l'autre. Aussi, la fréquence des perturbations a oscillé au cours de l'Holocène suite à l'établissement postglaciaire du sapin baumier, et que la perturbation dominante semblait être déterminé par des évènements de changements climatique rapides et significatifs. Cette étude a permis de mieux comprendre la variabilité à long terme des principales perturbations de la forêt boréale mixte et leurs interactions. Les résultats de cette thèse contribuent à l’ensemble des connaissances sur l’écologie forestière et les interactions entre les perturbations et donnent un aperçu de cadres potentiels qui pourraient être utilisés dans la gestion durable des forêts

Response of wild bee communities to beekeeping, urbanization, and flower availability

Wild bees provide pollination services and are currently declining at the global scale. A potential cause for this decline is competitive interactions with domestic honey bees. Urban beekeeping, a fairly new activity, is rapidly gaining popularity. In contrast with agricultural and natural areas, the extent of competition between honey bees and wild bees in urban areas is unclear. The objectives of this study were to quantify the impact of honey bees, urbanization, and the availability of floral resources on wild bee communities. We hypothesized that honey bees exert negative impacts on wild bees, that floral resources favor wild bee communities and mitigate the negative impacts of competition with honey bees, and that the influence of heat islands, used as a proxy for urbanization, varies between wild bees with their functional traits (nesting behavior). We tested these hypotheses with a data set of 19,077 wild bee specimens collected using colored pan-traps at 25 urban sites in 2012 and 2013. We investigated community and population patterns after accounting for imperfect detection probability. We found no evidence of competition between wild and domesticated bees. Our analyses indicate mixed effects of urban heat islands across species and positive effects of floral resources. We conclude that cities can allow the coexistence of urban beekeeping and wild bees under moderate hive densities. However, it will remain crucial to further investigate the competitive interactions between wild and honey bees to determine the threshold of hive densities beyond which competition could occur

Cooking and co-ingested polyphenols reduce in vitro methylmercury bioaccessibility from fish and may alter exposure in humans

Fish consumption is a major pathway for mercury exposure in humans. Current guidelines and risk assessments assume that 100% of methylmercury (MeHg) in fish is absorbed by the human body after ingestion. However, a growing body of literature suggests that this absorption rate may be overestimated. We used an in vitro digestion method to measure MeHg bioaccessibility in commercially-purchased fish, and investigated the effects of dietary practices on MeHg bioaccessibility. Cooking had the greatest effect, decreasing bioaccessibility on average to 12.5 ± 5.6%. Polyphenol-rich beverages also significantly reduced bioaccessibility to 22.7 ± 3.8% and 28.6 ± 13.9%, for green and black tea respectively. We confirmed the suspected role of polyphenols in tea as being a driver of MeHg's reduced bioaccessibility, and found that epicatechin, epigallocatechin gallate, rutin and cafeic acid could individually decrease MeHg bioaccessibility by up to 55%. When both cooking and polyphenol-rich beverage treatments were combined, only 1% of MeHg remained bioaccessible. These results call for in vivo validation, and suggest that dietary practices should be considered when setting consumer guidelines for MeHg. More realistic risk assessments could promote consumption of fish as a source of fatty acids, which can play a protective role against cardiovascular disease

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis

<p>Abstract</p> <p>Background</p> <p>Various histone acetylases (HATs) play a critical role in the regulation of gene expression, but the precise functions of many of those HATs are still unknown. Here we provide evidence that MYST4, a known HAT, may be involved in early mammalian gametogenesis.</p> <p>Results</p> <p>Although <it>MYST4 </it>mRNA transcripts are ubiquitous, protein expression was restricted to select extracts (including ovary and testis). Immunohistochemistry experiments performed on ovary sections revealed that the MYST4 protein is confined to oocytes, granulosa and theca cells, as well as to cells composing the blood vessels. The transcripts for <it>MYST4 </it>and all-<it>MYST4</it>-isoforms were present in oocytes and in <it>in vitro </it>produced embryos. In oocytes and embryos the MYST4 protein was localized in both the cytoplasm and nucleus. Within testis sections, the MYST4 protein was specific to only one cell type, the elongating spermatids, where it was exclusively nuclear.</p> <p>Conclusion</p> <p>We established that MYST4 is localized into specialized cells of the ovary and testis. Because the majority of these cells are involved in male and female gametogenesis, MYST4 may contribute to important and specific acetylation events occurring during gametes and embryo development.</p

Antagonistic control of muscle cell size by AMPK and mTORC1.

7 pages (2640-2646)International audienceNutrition and physical activity have profound effects on skeletal muscle metabolism and growth. Regulation of muscle mass depends on a thin balance between growth-promoting and growth-suppressing factors. Over the past decade, the mammalian target of rapamycin (mTOR) kinase has emerged as an essential factor for muscle growth by mediating the anabolic response to nutrients, insulin, insulin-like growth factors and resistance exercise. As opposed to the mTOR signaling pathway, the AMP-activated protein kinase (AMPK) is switched on during starvation and endurance exercise to upregulate energy-conserving processes. Recent evidence indicates that mTORC1 (mTOR Complex 1) and AMPK represent two antagonistic forces governing muscle adaption to nutrition, starvation and growth stimulation. Animal knockout models with impaired mTORC1 signaling showed decreased muscle mass correlated with increased AMPK activation. Interestingly, AMPK inhibition in p70S6K-deficient muscle cells restores cell growth and sensitivity to nutrients. Conversely, muscle cells lacking AMPK have increased mTORC1 activation with increased cell size and protein synthesis rate. We also demonstrated that the hypertrophic action of MyrAkt is enhanced in AMPK-deficient muscle, indicating that AMPK acts as a negative feedback control to restrain muscle hypertrophy. Our recent results extend this notion by showing that AMPKα1, but not AMPKα2, regulates muscle cell size through the control of mTORC1 signaling. These results reveal the diverse functions of the two catalytic isoforms of AMPK, with AMPKα1 playing a predominant role in the control of muscle cell size and AMPKα2 mediating muscle metabolic adaptation. Thus, the crosstalk between AMPK and mTORC1 signaling is a highly regulated way to control changes in muscle growth and metabolic rate imposed by external cues

Understanding food web mercury accumulation through trophic transfer and carbon processing along a river affected by recent run-of-river dams

Unlike large dams which favor methylation of Hg in flooded soils over long periods, run-of-river dams are designed to flood a limited area of soils and are therefore not expected to significantly affect mercury (Hg) cycling or carbon processing. We studied the Hg and carbon cycles within food webs from several sectors along the Saint-Maurice River, Quebec, Canada, that differ in how they are influenced by two run-of-river dams and other watershed disturbances. We observed peak Hg concentrations in fish five-year postimpoundment, but these levels were reduced three years after this peak. Methylmercury concentrations in low trophic level fish and invertebrates were related to their carbon source (δ13C) rather than their trophic positions (δ15N). Biomagnification, measured by trophic magnification slopes, was driven mainly by methylmercury concentrations in low-trophic level organisms and environmental factors related to organic matter degradation and Hg-methylation. River sectors, δ13C and δ15N, predicted up to 80% of the variability in food web methylmercury concentrations. The installation of run-of-river dams and the related pondages, in association with other watershed disturbances, altered carbon processing, promoted Hg-methylation and its accumulation at the base of the food web, and led to a temporary increase in Hg levels in fish