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The stable isotopic compositions of nitrogen and carbon in animal tissues reflect diet. However, factors other than diet can also affect these stable isotope ratios, leading to misinterpretations of diet composition. To test the hypothesis that variation in metabolic rate alters the isotopic compositions of tissues, deer mice (Peromyscus maniculatus (Wagner, 1845)) were kept at three temperatures (thermoneutral (23°C), cool (5°C), and cold (-10°C)) and fed ad libitum. The changes in carbon and nitrogen isotope compositions of liver associated with the thermoneutral versus cool and cold conditions were very small in comparison with those arising from differences in diet. We conclude that temperature-induced variations in metabolic rate are insufficient to produce differences in the stable carbon or nitrogen isotope compositions that could be mistaken for changes in diet. Les compositions d'isotopes stables d'azote et de carbone dans les tissus animaux refletent le regime alimentaire. Cependant, des facteurs autres que le regime peuvent affecter ces rapports d'isotopes stables, ce qui entraine des interpretations erronees de la composition du regime alimentaire. Afin de tester l'hypothese qui veut que la variation du taux metabolique affecte la composition isotopique des tissus, nous avons garde des souris du crepuscule (Peromyscus maniculatus (Wagner, 1845)) a trois temperatures differentes, soit des regimes thermiques neutre (23°C), frais (5°C) et froid (-10°C), et les avons nourries a volonte. Les modifications dans les compositions d'isotopes de carbone et d'azote dans le foie associees au regime thermique neutre par rapport a ceux des regimes frais et froids sont tres petites par comparaison a celles qui proviennent de differences de regime alimentaire. Nous en concluons que les variations du taux metabolique causees par la temperature ne sont pas assez importantes pour produire des differences de composition des isotopes stables de carbone et d'azote qui pourraient etre interpretees par erreur comme des changements de regime alimentaire. [Traduit par la Redaction], Introduction Measurement of stable carbon ([sup.13]C/[sup.12]C) and nitrogen ([sup.15]N/[sup.14]N) isotope ratios is commonly undertaken in ecological studies because the compositions of tissues reflect the composition of the diet (Kelly 2000). [...]

Berry crops in the southwestern Yukon were quantified from 1997 to 2008 at 10 locations along 210 km of the Alaska and Haines highways. We tested the hypothesis that the size of berry crops could be predicted from spring and summer temperature and rainfall of years t, t-1 (1 year prior), and t-2 (2 years prior). Six common species were studied in the boreal forest of the Kluane region: Arctostaphylos rubra (Rehd. & Wils.) Fern., Arctostaphylos uva-ursi (L.) Spreng. s.l., Empetrum nigrum L., Vaccinium vitis-idaea L., Geocaulon lividum (Richards) Fern, and Shepherdia canadensis (L.) Nutt.. For the first five species we counted berries on fixed 40 cm x 40 cm quadrats to obtain an index of berry production for the Kluane region for each of the 12 years, and for S. canadensis we counted berries on two tagged branches of 10 bushes at each location. Stepwise multiple regressions were utilized to predict the size of berry crops for each species. For all species, predictive equations could explain statistically 80%-96% of the variation in berry crops. Different weather variables characterized each plant species, and there was no common weather regression that could explain the variation in berry crops in all species. Rainfall and temperature from years t-1 and t-2 were typically the significant predictors. There was no indication of a periodicity in berry production, and 43%-60% of the quadrats counted had large berry crops at one year intervals, while other quadrats never had a high crop during the study interval. Key words: berry production, Yukon, climate, Kluane, dwarf shrubs. Les auteurs ont quantifie les recoltes de baies dans le sud-ouest du Yukon de 1997 a 2008, a 10 endroits sur 210 km le long des autoroutes d'Alaska et de Haines. Its ont verifie l'hypothese qu'on pourrait predire l'importance des recoltes de petits fruits a partir des temperatures estivales des annees t, t-1 et t-2. Its ont etudie six especes communes de la foret boreale dans la region de Kluane: Arctostaphylos rubra (Rehd. & Wils.) Fern., Arctostaphylos uva-ursi (L.) Spreng. s.l., Empetrum nigrum L., Vaccinium vitis-idaea L., Geocaulon lividum (Richards) Fern et Shepherdia canadensis (L.) Nutt. Chez les 5 premieres especes, on a compte les baies sur des quadrats fixes de 40 cm x 40 cm afin d'obtenir un index de la production des baies dans la region de Kluane pour chacune des 12 annees, et pour le S. canadensis on a compte les baies sur deux branches marquees chez 10 bosquets sur chaque site. Les auteurs ont utilise la regression multiple progressive pour predire la dimension des recoltes de petits fruits pour chaque espece. Chez toutes les especes, les equations predictives peuvent expliquer statistiquement 80-96 % de la variation des recoltes de petits fruits. Differentes variables climatiques caracterisent chaque espece de plante, et on n'observe pas de regression commune qui pent expliquer la variation des recoltes de baies chez toutes les especes. La precipitation et la temperature des annees t-1 et t-2 constituent des pronostiques significatifs. Il n'y a pas d'indication qu'il existerait une periodicity dans la production des baies, et 43-60 % des quadrats enumeres montrent de fortes productions de baies a un an d'intervalles, alors que les autres quadrats n'ont jam ais montre de fortes recoltes tout an long de l'etude. Mots-cles : production de baies, Yukon, climat, Kluane, arbustes nains. [Traduit par la Redaction], Introduction Berry crops in the boreal forest region vary dramatically from year to year. A combination of soil factors and climatic events are usually put forward to explain these variations [...]

Epigeous mushroom production in the boreal forest ecosystem varies dramatically from year to year. We tested the hypothesis that the aboveground production of epigeous mushrooms in the Kluane region, Yukon, could be predicted by summer rainfall. There is a single crop in this part of the boreal zone with maximum production during the first 2 weeks of August. We measured standing crops from 1993 to 2007 at 13 areas along 210 km of the Alaska Highway and Haines Road in the southwestern Yukon. Aboveground mushroom crops averaged 24 kg/ha wet weight but varied from 0.0 to 117 kg/ha over the 15 years of study, with a coefficient of variation among years of 143%. Epigeous mushroom production could be predicted from June rainfall of the current year and May rainfall of the year previous with [R.sup.2] = 0.85. Part of the lack of a perfect fit to rainfall was due to the constraint that years of high mushroom crops could not be followed by another high year, no matter what the rainfall pattern. We were not able to identify the species of mushrooms in this study but we confirm from natural history observations that mushrooms are a critical food for several of the small mammal species in the Yukon boreal forest. Key words: epigeous mushrooms, biomass prediction, boreal forest, Kluane Lake, Yukon, rainfall. La production de champignons epiges des ecosystemes de la foret boreale varie fortement d'une annee a l'autre. Les auteurs ont verifie l'hypothese a savoir que la production, au-dessus du sol, des champignons epiges dans la region de Kluane au Yukon, pourrait etre predite a l'aide de la precipitation estivale. Dans cette partie de la foret boreale, il y a une seule poussee avec un maximum de production au cours des deux premieres semaines d'aout. Ils ont mesure la ressource produite annuellement de 1993 a 2007 sur 13 sites etales sur 210 km de l'autoroute de l'Alaska et de la route Haines, dans le sud-ouest du Yukon. La productivite epigee en champignons atteint une moyenne de 24 kg/ha en poids frais, mais a varie de 0,0 a 117 kg/ha au cours des 15 annees de l'etude, avec un coefficient de variation au cours des annees de 143 %. On peut predire la production des champignons epiges a partir de la precipitation en juin de l'annee en cours et celle de mai de l'annee precedente avec [R.sup.2] = 0,85. On constate que les annees de fortes productions de champignons ne peuvent pas etre suivies par une autre annee de forte production, quel que soit le patron de precipitation; ceci constitue une contrainte qui empeche d'obtenir une correlation parfaite. Les auteurs n'ont pas ete en mesure d'identifier les especes de champignons dans cette etude, mais les observations de naturaliste confirment que les champignons y constituent une nourriture critique pour plusieurs des petits mammiferes qui vivent dans la foret boreale du Yukon. Mots-cles : champignons epiges, prediction de la biomasse, foret boreale, lac Kluane, Yukon, pluie. [Traduit par la Redaction], Introduction Aboveground mushroom crops in the boreal forest are known to fluctuate dramatically from year to year, and these crops are used as food both by small mammals and the [...]

Abstract: The hormonal stress response is adapted to deal with acute (short-term) stressors; however, chronic (long-term) stressors have negative effects on survival and fitness. Field and laboratory evidence suggest that [...]

Biological invasions erode ecosystem functioning and occur more frequently in freshwater ecosystems than in terrestrial environments. Nonphysical deterrents may be used to limit invasive fish dispersal, without altering the streamflow or connectivity of a watershed. Little is currently known about how behavioral variation among individuals may affect the efficacy of a deterrent, although such variation has been shown to affect fish dispersal in other contexts, such as range expansion. Furthermore, deterrent effectiveness is rarely tested when fish are motivated to disperse. Across a control, CO2, and CO2 + deterrent treatment, we quantified the avoidance response of invasive Common Carp Cyprinus carpio to a combined acoustic‐stroboscopic deterrent. In the CO2 treatment, we motivated individuals to enter a novel environment by degrading the home chamber of a choice arena with a continuous infusion of CO2. In the CO2 + deterrent treatment we introduced acoustic and stroboscopic stimuli to delay the departure of the fish and evaluate the efficacy of the deterrent. Finally, we tested a subset of the fish multiple times to determine whether they consistently responded to the same concentration of CO2. We found that the acoustic and stroboscopic deterrent could detain the fish in an increasingly unfavorable environment. Common Carp took only 195 and 131 s, respectively, to swim between the chambers during the control and CO2 treatment but took an average of 596 s in the CO2 + deterrent treatment. High CO2 concentrations in the CO2 + deterrent treatment led to most fish eventually dispersing toward the deterrent stimuli. Avoidance behavior varied widely within the CO2 + deterrent treatment, and Common Carp expressed repeatable differences in the tank‐inflow CO2 concentrations that were observed during chamber departure. Such interindividual variation in deterrent avoidance indicates that some individuals within a given species are more likely to move past a deterrent than others. [ABSTRACT FROM AUTHOR]

The understory plants of the boreal forests have evolved divergent strategies to succeed under low nitrogen conditions, with their ability to respond to nitrogen addition varying greatly. We examined the response of 5 key understory North American boreal forest species in the Yukon (4 shrubs and a herb) to low levels of nitrogen that could occur from natural pulses and to high levels that could occur because of anthropogenic deposition from either atmospheric deposition or as a management strategy to increase tree growth. We fertilized 240 one m 2 plots for the three dwarf shrubs and one herb and 60 three m 2 plots for one tall shrub at 0, 0.5, 1.0, 2.0, 4.0, and 17.5 g nitrogen/m 2 in June 2004 and May 2005. We measured changes in cover, growth, leaf metrics, and berry production in three dwarf shrubs ( Arctostaphylos rubra [deciduous] and A. uva-ursi and Empetrum nigrum [both evergreen]), one herb ( Geocaulon lividum ), and one tall shrub ( Shepherdia canadensis ) . We predicted the first three would be strongly affected by variation in nitrogen levels but that neither Geocaulon (a hemi-parasite) nor Shepherdia (a nitrogen fixer) would be. To examine for long-term effects of nitrogen application, we also fertilized four 2.8 ha plots in 2004 and 2005 with 1.0 and 2.0 g/m 2 and then measured berry production in 2006 and 2007 on the two Arctostaphylos species. Nitrogen addition at all levels had no effect on either Geocaulon or Shepherdia . There were general positive effects at low nitrogen levels and negative ones at high levels on the other 3 dwarf shrub species in a species-specific manner. There were marked year effects in some plant growth metrics and in berry production, emphasizing the role of climate, but also clear evidence that individual species tradeoff somatic growth for reproduction. There was a pronounced long-term negative effect of low nitrogen addition on the large plots, causing marked reductions in berry production in both Arctostaphylos species. We conclude that these dwarf shrubs are constrained to function optimally within a narrow range of nitrogen levels normally encountered, but are unable to cope with higher levels. Both Geocaulon and Shepherdia function independently of nitrogen limitation. Thus the life history adaptations of these understory plants to variation in nitrogen levels are species-specific and understanding their individual responses is key in predicting their fate and the biodiversity and organization of boreal forest ecosystem when challenged with higher anthropogenic levels of nitrogen. [ABSTRACT FROM AUTHOR]

The risk of predation can cause strong antipredator behaviors and marked stress-induced changes in physiology. In mothers, predator-induced stress can reduce reproductive fitness and alter offspring phenotypes. Acting via these generational, maternal stress effects, predation risk may continue to influence the demography of prey populations even when the predators are no longer present. The 10-year snowshoe hare cycle is the classic top-down predator-driven example in nature and is caused both by direct mortality and by indirect risk effects. During the decline phase, virtually, all hares die because they are killed and simultaneously hares exhibit pronounced stress effects caused by high predation risk. However, the rapidity of the decline phase varies among cycles. When the decline is extremely rapid, we expect that the risk experienced by hares is much greater than when the decline is prolonged. The enigma of these cycles is the low phase following the decline, when there is little or no population growth in spite of the absence of predators and ample food. Previously, we have shown that predator-induced maternal stress decreases reproduction and compromises the offspring stress axis. Here, we examine how the severity of predation risk during six separate population declines is related to the length of the subsequent low phase. We show that the more severe the decline, as indicated by the greater rate of loss of hares, the longer the subsequent low phase. These results support the hypothesis that the greater the degree of risk, the longer the generational impact on population demography (the longer the low phase of the hare population). Our findings have broad applicability to conservation and management efforts; even when a stressor (predator, human disturbance) is removed or when exposure may be short term (drought, fire or translocation), the signature of the stressor may be evident over several future generations. [ABSTRACT FROM AUTHOR]

We examined growth, immune response, and basal corticosterone (CORT) levels in tree swallow (Tachycineta bicolor) nestlings over two years (2004 and 2005), and at two sites differing historically in insect abundance. We adjusted all broods to a common size of 6 nestlings. To assess the cell-mediated immune response, we injected phytohaemagglutinin (PHA) into the wing webs of two nestling per nest, followed by measurement of the swelling response 24 hours later. Humoral immune response was studied by vaccinating two nestlings per nest with either sheep red blood cells (SRBC; 2004), or with Newcastle Disease Virus (NDV; 2005). Blood samples were collected 7 days later to measure either anti-SRBC or anti-NDV titres. The remaining two nestlings per nest were blood sampled for determination of basal CORT levels. Nestling growth rates were significantly higher at the breeding site with historically higher insect abundance. Nonetheless, neither CORT levels nor the PHA swelling response differed between the two breeding sites, suggesting little evidence of a trade-off between growth rates and cell-mediated immunity. No antibodies to either SRBCs or NDV were detected in plasma of nestlings, likely as a result of their immature immune system. We suggest that natural variation in insect abundance has minimal effects on cell-mediated or humoral immunity in tree swallow nestlings.

Making babies and raising them successfully is difficult even in the best environments. When birds and mammals are confronted by this imperative in the arctic, the difficulties are magnified enormously. The summer days are long, but the growing season is short and climatic unpredictability and severity is potentially great. When faced with these challenges, these animals may suspend physiological adaptations which are the norm in more moderate environments or at other times in their life cycle in order to permit reproduction. The hypothalamic-pituitary-adrenal axis is key to coordinating the stress response to environmental challenges. Usually activation of this axis causes an inhibition other hormonal axes, such as the reproductive axis: However this inhibition may not occur in arctic animals Detailed physiological studies of migratory birds in the arctic indicate that they modulate the sensitivity of the stress response. Their stress axis fails to activate when challenged during the breeding season. Male arctic ground squirrels have evolved a different strategy. During the period of intense intrasexual conflict (2-3 weeks), their stress axis is strongly activated, resulting in inhibition of immune function, but not of reproductive function. The benefits are obvious, but many trade off survival for reproduction. Bird species may adapt more readily to warming of the arctic then mammals, as there appears to be pronounce population variation in the stress response and thus there is within species plasticity to permit change. In mammals, we do not know the degree of plasticity in these hormonal axes and thus their capacity for change. In addition, changes in other environmental conditions (snow cover in winter, food quality in summer, etc.) may have unknown consequences.

Live-capture is a necessary component for the scientific study and management of most mammals, but it may negatively affect their health and physiology. We compared blood parameters related to the stress response (nominal base levels) from red squirrels Tamiasciurus hudsonicus after capture of up to 4.5 h in five different live trap models ( Hava-hart, Sherman, Tomahawk 102, Tomahawk 103 and ' Special Squirrel' trap) with true base levels (obtained in less than three minutes). In addition, we evaluated the capture rate in the five trap models. We found that (1) prolonged time in live traps altered stress hormone concentrations compared with true base levels, but maximum corticosteroid-binding capacity was unaffected; (2) squirrels captured in a trap model with reduced visibility (a roof cover - Hava-hart) had significantly lower ( c. 50%) mean free cortisol levels compared with those captured in a trap model with full visibility ( Tomahawk 102), but all other blood parameters were similar; (3) cortisol levels and white blood cell counts (mainly neutrophil counts) were positively related to duration of capture; (4) a non-covered trap ( Tomahawk 102) was most effective and fully covered trap ( Sherman) was least effective at capturing squirrels. We discuss the use of effective, yet less stress-inducing trap models to mitigate the stress caused by live-capture on these animals. We conclude that covered traps such as the Hava-hart may reduce trap-induced stress in red squirrels, but at the same time also reduces their capture rates. [ABSTRACT FROM AUTHOR]

Environmental variation in mountainous regions can impose major differences in demography and physiology on animal populations that occupy a large elevation range. This variation can be both predictable and unpredictable. In the south-western Yukon, arctic ground squirrel ( AGS) populations occur all the way from the forested valley bottoms to the alpine meadows and, in so doing, experience a wide range of predation risk, forage quality and exposure to weather variables. To assess how AGS integrate these factors and respond to them, we measured fecal glucocorticoid metabolites ( FCM) as an index of the stress axis on four sites at different elevations. We first validated the enzyme immunoassay with a hormonal challenge protocol and a simulated predator stressor. AGS show a strong diurnal pattern in FCM levels, with peaks at mid-day and a marked increase in response to adrenocorticotropic hormone and the simulated predator and a decline in response to dexamethasone. The lag time between the challenge and its reflection in the feces was 4-12 h. Using this method in our field studies, we found that FCM levels decreased as the active season progressed; however, specific patterns differed among sites. We hypothesized that the early season peak in FCM levels followed by the general decline was due to brief, intense early season breeding, followed by the necessity of AGS to increase mass in preparation for hibernation. Although we found no clear, single explanation for the different FCM patterns among sites, we hypothesized that differences in seasonal climate and adverse weather may be major factors affecting FCM levels. The environment was markedly different between years, with 2008 being colder and wetter than 2009 and this was associated with AGS in 2008 having much higher FCM levels in general than 2009. We found that population density and visibility may also contribute. In conclusion, AGS live in a mosaic of habitats and each population is faced with a variety of environmental stressors; how they cope and respond to these stressors may not depend on a single factor but the complete aggregate of these stressors. [ABSTRACT FROM AUTHOR]

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The reproductive periodicity of blacknose sharks Carcharhinus acronotus in the northern Gulf of Mexico was determined by examining reproductive tissues from specimens collected monthly from 2002 to 2005. Monthly changes in shell gland mass, right ovary mass and ovarian follicle diameter were assessed for 74 mature females. Temporal changes in testes mass, testes width and proportion of mature spermatocysts were examined for 64 mature males. Trends in female reproductive tissues suggested an annual peak in reproductive activity during June and July, while trends in male variables suggested an annual reproductive peak during May and June. Although male and female reproductive activity peaked in different months, a strong synchronicity existed between the proportion of mature spermatocysts and the diameter of the largest ovarian follicle. Based on these results, the mating season of blacknose sharks lasts from mid-May to July in the Gulf of Mexico. Maximum embryo sizes were observed in May, which suggested that partition occurs during late May or early June. Results indicate that blacknose sharks have a clearly defined annual cycle in the Gulf of Mexico. This conclusion is further supported by the complete absence of gravid females without vitellogenic ovarian follicles among all mature females examined. [ABSTRACT FROM AUTHOR]

In physiological research on natural populations, it is essential to understand the impact of capture-induced stress because of its numerous effects on many physiological processes. Our objective was to determine the extent to which the stress levels of meadow voles Microtus pennsylvanicus were affected by short-term responses to live trapping and how these were influenced by the amount of time spent in live traps. Baseline levels were obtained from a snap-trapped sample and stress levels were determined from voles that had spent variable amounts of time in live traps (up to 16.5 h). Stress levels were inferred from corticosterone and glucose concentrations and haematocrit levels. In the live-trapped sample, corticosterone concentrations reflect only the stress of trap confinement whereas glucose concentrations and haematocrit reflect both the effects of trap confinement and handling. Live trapping caused corticosterone concentrations to increase by 108% (from 390.3 to 810.6 ng mL−1), glucose concentrations to increase by 58% (from 55.4 to 87.4 mg dL−1) and haematocrit levels to increase by 10% (from 49 to 54%) from baseline levels. The length of time a vole spent in a live trap did not affect corticosterone and glucose concentrations; however, haematocrit levels increased slightly over time (0.21% h−1). We conclude that live trapping induced a stress response in voles, but that longer times in traps did not increase the stress levels. [ABSTRACT FROM AUTHOR]

The aim of this study was to find factors that could explain the accumulation difference of mitoxantrone in the BCRP1-negative GLC4-MITO cell line compared to GLC4. Comparative genomic hybridisation (CGH) was applied to determine chromosomal differences between GLC4 and GLC4-MITO. Comparative genomic hybridisation analysis revealed gain of 2q, 6p, 9q, 13q, 14q, 15q, 19q and Xp and loss of 1p, 2q, 3p, 3q, 4q, 6q, 8q, 11p, 16p, 17q, 18p, 20p and Xq. In the over-represented chromosomal areas, seven transporter genes were identified: ABCB6, ABCB2 (TAP1), ABCB3 (TAP2), ABCF1 (ABC50), ABCC10 (MRP7), ABCA2 (ABC2) and ABCC4 (MRP4). No RNA or protein upregulation was observed for ABCB6, ABCF1, ABCC10, ABCC4, ABCB2 and ABCB3, but an increased expression was detected for ABCA2 mRNA in GLC4-MITO. ABCA2 is known to be involved in resistance to estramustine. In the MTT assay, GLC4-MITO was two-fold resistant to estramustine compared to GLC4. Coincubation with estramustine and mitoxantrone increased mitoxantrone accumulation in GLC4-MITO, while this was not affected in GLC4. This suggests that estramustine is able to block mitoxantrone efflux in GLC4-MITO cells. These data reveal that cellular reduction of mitoxantrone in a mitoxantrone-resistant cell line is associated with overexpression of ABCA2. [ABSTRACT FROM AUTHOR]

The dogma that the adult brain produces no new neurons has been overturned, but the critics are still asking, so what? Is adult neurogenesis a biologically relevant phenomenon, or is it perhaps harmful because it disrupts the existing neuronal circuitry? Considering that the phenomenon is evolutionarily conserved in all mammalian species examined to date and that its relevance has been well documented in non-mammalian species, it seems self-evident that neurogenesis in adult mammals must have a role. In birds, it has been established that neurogenesis varies dramatically with seasonal changes in song production. In chickadees, the learning behaviour related to finding stored food is also correlated with seasonal adult neurogenesis. Such studies are still nonexistent in mammals, but the related evidence suggests that neurogenesis does vary seasonally in hamsters and shows sexual differences in meadow voles. To promote studies on natural populations asking fundamental questions of the purpose and function of neurogenesis, we organized a Workshop on "Hippocampal Neurogenesis in Natural Populations" in Toronto in May 2000. The Workshop highlighted recent discoveries in neurogenesis from the lab, and focused on its functional consequences. The consensus at the Workshop was that demonstration of a role for neurogenesis in natural behaviours will ultimately be essential if we are to understand the purpose and function of neurogenesis in humans.Key words: neurogenesis, hippocampus, dentate gyrus, learning, memory, wild population.Le dogme selon lequel le cerveau adulte ne produit pas de nouveaux neurones ne tient plus, mais les critiques continuent à dire, et alors ? La neurogenèse chez l'adulte est-elle un phénomène biologiquement pertinent, ou peut-elle être dommageable parce qu'elle perturbe le circuit neuronal existant ? Compte tenu du fait que le phénomène a été bien conservé au cours de l'évolution chez tous les mammifères examinés à ce jour et que sa pertinence a été bien documentée chez d'autres espèces, il semble aller de soi que la neurogenèse doit avoir un rôle chez les mammifères adultes. Chez les oiseaux, il est bien établi que la neurogenèse varie considérablement avec les variations saisonnières de la production de chants. Chez les mésanges, le comportement d'apprentissage lié à la découverte de la nourriture entreposée est aussi corrélé avec une neurogenèse saisonnière chez l'adulte. Il n'existe toujours pas d'études de ce genre chez les mammifères, mais les données connexes donnent à penser que la neurogenèse varie effectivement de façon saisonnière et montre des différences sexuelles chez les campagnols des champs et dans les variations du rythme circadien chez les hamsters. Pour encourager les études sur les populations naturelles abordant les questions fondamentales du but et de la fonction de la neurogenèse, nous avons organisé un colloque intitulé " Hippocampal Neurogenesis in Natural Populations ", à Toronto, au mois de mai 2000. Le Colloque a donné un aperçu des récentes découvertes sur la neurogenèse en laboratoire et mis l'accent sur ses conséquences fonctionnelles.. Selon le consensus établi lors du Colloque, il faudra nécessairement démontrer le rôle de la neurogenèse dans les comportements naturels si nous voulons comprendre le but et la fonction de la neurogenèse chez les humains.Mots clés : neurogenèse, hippocampe, corps godronné, apprentissage, mémoire, population sauvage.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Purpose: To compare clinical and radiographic outcomes after treatment with standardized high-energy extracorporeal shock wave therapy (ESWT) and ultrasound-guided needling (UGN) in patients with symptomatic calcific tendinitis of the rotator cuff who were nonresponsive to conservative treatment.Methods: The study was designed as a randomized controlled trial. The ESWT group received ESWT (2000 pulses, energy flux density 0.35 mJ/mm2) in 4 sessions with 1-week intervals. UGN was combined with a corticosteroid ultrasound-guided subacromial bursa injection. Shoulder function was assessed at standardized follow-up intervals (6 weeks and 3, 6, and 12 months) using the Constant Murley Score (CMS), the Disabilities of the Arm, Shoulder, and Hand questionnaire, and visual analog scale for pain and satisfaction. The size, location, and morphology of the deposits were evaluated on radiographs. The a priori sample size calculation computed that 44 participants randomized in each treatment group was required to achieve a power of 80%.Results: Eighty-two patients were treated (56 female, 65%; mean age 52.1 ± 9 years) with a mean baseline CMS of 66.8 ± 12 and mean calcification size of 15.1 ± 4.7 mm. One patient was lost to follow-up. At 1-year follow-up, the UGN group showed similar results as the ESWT group with regard to the change from baseline CMS (20.9 vs 15.7; P = .23), Disabilities of the Arm, Shoulder, and Hand questionnaire (-20.1 vs -20.7; P = .78), and visual analog scale for pain (-3.9 and -2.6; P = .12). The mean calcification size decreased by 13 ± 3.9 mm in the UGN group and 6.7 ± 8.2 mm in the ESWT group (Conclusions: This RCT compares the clinical and radiographic results of UGN and high-energy ESWT in the treatment of calcific tendinitis of the rotator cuff. Both techniques are successful in improving function and pain, with high satisfaction rates after 1-year follow-up. However, UGN is more effective in eliminating the calcific deposit, and the amount of additional treatments was greater in the ESWT group.Level Of Evidence: II, randomized controlled trial. [ABSTRACT FROM AUTHOR]

We examined patterns of inheritance of size, growth and behavioural traits of collared lemmings (Dicrostonyx groenlandicus). Work was conducted on field-caught parents from the Canadian Arctic and their lab-born progeny. We partitioned inherited variance in traits into additive genetic and maternal effects components by using a half-sib breeding experiment in which each sire was mated to two dams. We found no evidence of statistically significant amounts of additive genetic variance in any of the traits measured. However, significant maternal effects were detected for several size- and growth-related traits. Three behavioural traits involving aggression, dispersal and activity showed no statistically significant inheritance of any kind. The presence of maternal effects may have consequences for population dynamics by causing 'lags' resulting in inappropriate phenotypes being producedunder regimes of fluctuating selection pressure. We recommend that maternal effects should be investigated as a potential general cause of population cycles in small mammals. [ABSTRACT FROM AUTHOR]

1. We examined the relative importance of food and predators in limiting Arctic ground squirrel (Spermophilus parryii plesius Richardson)populations in the boreal forest of the southwestern Yukon during the peak and early decline of a snowshoe hare cycle (Lepus americanus Erxleben). 2. Squirrels were live-trapped from 1990 to 1992 on two control grids and three experimental treatments (food addition, mammalian and avian predator exclosure, and food addition plus mammalian predator exclosure). Adult squirrels were radio-collared on all areas in 1992. 3. Food addition increased densities 3--8 times, generally increased reproductive traits (increased proportion of females lactating,doubled recruited litter sizes, resulted in earlier emergence of juveniles), increased immigration rates (but only in 1992), resulted in heavier females though not males at emergence in spring, and resultedin more rapid growth rates of juvenile males, but not of juvenile females. It had no effect on active season or overwinter survival rates. 4. Exclusion of predators had virtually no effect on any demographic variable measured, except for population densities in 1991 when they were approximately double those of the control populations. 5. Foodaddition plus exclusion of mammalian predators resulted in demographic changes that were comparable to those of food addition alone. 6. Thus, it appeared that food, not predators, limited ground squirrel populations at this stage of the hare cycle. However, independent of experimental treatment, active season survival of adult squirrels declined markedly from 1990 (high hare numbers) to 1992 (low hare numbers). Most of the radio-collared squirrels disappearing in 1992 were killed by predators and this was coincident with high densities of predators. In the predator exclosures, all predation mortalities resulted from avian predators which we could not exclude. 7. We conclude that both food and predators interact to limit Arctic ground squirrel populatio [ABSTRACT FROM AUTHOR]