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121.
Early setting of grammatical processing in the bilingual brain 总被引:27,自引:0,他引:27
The existence of a "critical period" for language acquisition is controversial. Bilingual subjects with variable age of acquisition (AOA) and proficiency level (PL) constitute a suitable model to study this issue. We used functional magnetic resonance imaging to investigate the effects of AOA and PL on neural correlates of grammatical and semantic judgments in Italian-German bilinguals who learned the second language at different ages and had different proficiency levels. While the pattern of brain activity for semantic judgment was largely dependent on PL, AOA mainly affected the cortical representation of grammatical processes. These findings support the view that both AOA and PL affect the neural substrates of second language processing, with a differential effect on grammar and semantics. 相似文献
122.
Over the last 20 years, the species assemblage of the species-rich dry grassland communities of central Germany has changed due to the ongoing abandonment of traditional land-use practices. In our study we wanted to investigate the germination biology and the plant-plant interaction of the low-growing and declining forb Alyssum montanum and the increasingly dominant grass Festuca rupicola. To investigate the germination behaviour we simulated cold (8/4°C), warm (20/10°C) and hot (32/20°C) conditions under a light-dark regime (12/12 hours) as well as in constant darkness. Germination of both species was similar with almost all non-dormant seeds germinating under intermediate temperature conditions (20/10°C). Whereas F. rupicola (F) germinated equally well under light changing conditions and constant darkness, the germination of A. montanum (A) was clearly reduced in darkness, which implies a strong competitive advantage of F. rupicola in dense vegetation cover. However, A. montanum germinated early under all temperatures regimes and better under 20/10°C as well as with light changing conditions. The interactions between the two species were tested in a pod-experiment with a replacement design, within which the composition of individuals was changed in the following way: 4A/1F, 3A/2F, 2A/3F, 1A/4F (eight replications per each). To evaluate any influence of intraspecific competition we created monocultures in an additive design (1A, 2A, 3A, 4A, 5A, 1F, 5F; eight replications per each). Despite that A. montanum developed faster and flowered after only four months in the replacement design experiment, the herb responded negatively to the presence of F. rupicola in several parameters (number of flowers, number of fruits and biomass per individual). The calculation of the Relative Neighbour Effect (RNE) indicated facilitation for F. rupicola and competition on A. montanum, which increased with increasing number of individuals of the other species. Our data suggest that A. montanum seedling recruitment, growth and fitness are negatively affected by increasing vegetation density of the expanding grass species F. rupicola. 相似文献
123.
Background
Soil biota effects are increasingly accepted as an important driver of the abundance and distribution of plants. While biogeographical studies on alien invasive plant species have indicated coevolution with soil biota in their native distribution range, it is unknown whether adaptation to soil biota varies among populations within the native distribution range. The question of local adaptation between plants and their soil biota has important implications for conservation of biodiversity and may justify the use of seed material from local provenances in restoration campaigns.Methodology/Principal Findings
We studied soil biota effects in ten populations of the steppe grass Stipa capillata from two distinct regions, Europe and Asia. We tested for local adaptation at two different scales, both within (ca. 10–80 km) and between (ca. 3300 km) regions, using a reciprocal inoculation experiment in the greenhouse for nine months. Generally, negative soil biota effects were consistent. However, we did not find evidence for local adaptation: both within and between regions, growth of plants in their ‘home soil’ was not significantly larger relative to that in soil from other, more distant, populations.Conclusions/Significance
Our study suggests that negative soil biota effects can prevail in different parts of a plant species'' range. Absence of local adaptation points to the possibility of similar rhizosphere biota composition across populations and regions, sufficient gene flow to prevent coevolution, selection in favor of plasticity, or functional redundancy among different soil biota. From the point of view of plant - soil biota interactions, our findings indicate that the current practice of using seeds exclusively from local provenances in ecosystem restoration campaigns may not be justified. 相似文献124.
Isabell Hensen Arne Cierjacks Heidi Hirsch Michael Kessler Katya Romoleroux Daniel Renison Karsten Wesche 《Global Ecology and Biogeography》2012,21(4):455-464
Aim To assess the effects of altitude and historic and recent forest fragmentation on the genetic diversity and structure of the wind‐pollinated tropical tree line species Polylepis incana. Location One of the highest mountain forest regions of the world, located in the Eastern Cordillera of the Ecuadorian Andes. Methods We compared genetic diversity and structure of adult trees with those of seedlings (n= 118 in both cases) in nine forest stands spanning an altitudinal gradient from 3500 to 4100 m a.s.l. using amplified fragment length polymorphisms (AFLPs). Genetic diversity was calculated as percentage of polymorphic bands (P) and Nei's expected heterozygosity (He); genetic differentiation was assessed using analysis of molecular variance, ΦST statistics and Bayesian cluster analysis. Results Estimates of genetic diversity at the population level were significantly lower in seedlings than in adults. Genetic diversity (He‐value) was, in both cases, negatively correlated to altitude and positively correlated to population size in the seedlings. Genetic differentiation of the seedlings was approximately as high (φST= 0.298) as that of the adults (φST= 0.307), and geographical differentiation was clearly reflected in both AFLP profiles, with mountain ridges acting as barriers to gene flow. Main conclusions Our study provides evidence of a historic upslope migration of P. incana in central Ecuador. In addition, it highlights the detrimental effects of unexpectedly strong genetic isolation, both recent and historical, particularly for our wind‐pollinated species where the distance between forest stands was less than 25 km. We therefore additionally propose that in habitats with pronounced high‐mountain landscape structures, gene flow may be hampered to such an extent that species have a more pronounced sensitivity to habitat fragmentation, even among populations of wind‐pollinated trees. 相似文献
125.
C Chanvillard JM Millward M Lozano I Hamann F Paul F Zipp J Dörr C Infante-Duarte 《PloS one》2012,7(6):e39625
Mitoxantrone is one of the few drugs approved for the treatment of progressive multiple sclerosis (MS). However, the prolonged use of this potent immunosuppressive agent is limited by the appearance of severe side effects. Apart from its general cytotoxic effect, the mode of action of mitoxantrone on the immune system is poorly understood. Thus, to develop safe therapeutic approaches for patients with progressive MS, it is essential to elucidate how mitoxantrone exerts it benefits. Accordingly, we initiated a prospective single-arm open-label study with 19 secondary progressive MS patients. We investigated long-term effects of mitoxantrone on patient peripheral immune subsets using flow cytometry. While we corroborate that mitoxantrone persistently suppresses B cells in vivo, we show for the first time that treatment led to an enrichment of neutrophils and immunomodulatory CD8(low) T cells. Moreover, sustained mitoxantrone applications promoted not only persistent NK cell enrichment but also NK cell maturation. Importantly, this mitoxantrone-induced NK cell maturation was seen only in patients that showed a clinical response to treatment. Our data emphasize the complex immunomodulatory role of mitoxantrone, which may account for its benefit in MS. In particular, these results highlight the contribution of NK cells to mitoxantrone efficacy in progressive MS. 相似文献
126.
127.
Maria Rostovskaya Jun Fu Mandy Obst Isabell Baer Stefanie Weidlich Hailong Wang Andrew J. H. Smith Konstantinos Anastassiadis A. Francis Stewart 《Nucleic acids research》2012,40(19):e150
Transgenesis is a cornerstone of molecular biology. The ability to integrate a specifically engineered piece of DNA into the genome of a living system is fundamental to our efforts to understand life and exploit its implications for medicine, nanotechnology and bioprospecting. However, transgenesis has been hampered by position effects and multi-copy integration problems, which are mainly due to the use of small, plasmid-based transgenes. Large transgenes based on native genomic regions cloned into bacterial artificial chromosomes (BACs) circumvent these problems but are prone to fragmentation. Herein, we report that contrary to widely held notions, large BAC-sized constructs do not prohibit transposition. We also report the first reliable method for BAC transgenesis in human embryonic stem cells (hESCs). The PiggyBac or Sleeping Beauty transposon inverted repeats were integrated into BAC vectors by recombineering, followed by co-lipofection with the corresponding transposase in hESCs to generate robust fluorescent protein reporter lines for OCT4, NANOG, GATA4 and PAX6. BAC transposition delivers several advantages, including increased frequencies of single-copy, full-length integration, which will be useful in all transgenic systems but especially in difficult venues like hESCs. 相似文献
128.
Megan Landes Monique van Lettow Adrienne K. Chan Isabell Mayuni Erik J. Schouten Richard A. Bedell 《PloS one》2012,7(10)
Background
Mortality and morbidity among HIV-exposed children are thought to be high in Malawi. We sought to determine mortality and health outcomes of HIV-exposed and unexposed infants within a PMTCT program.Method
Data were collected as part of a retrospective cohort study in Zomba District, Malawi. HIV-infected mothers were identified via antenatal, delivery and postpartum records with a delivery date 18–20 months prior; the next registered HIV-uninfected mother was identified as a control. By interview and health record review, data on socio-demographic characteristics, service uptake, and health outcomes were collected. HIV-testing was offered to all exposed children.Results
173 HIV-infected and 214 uninfected mothers were included. 4 stillbirths (1.0%) occurred; among the 383 livebirths, 41 (10.7%) children died by 20 months (32 (18.7%) HIV-exposed and 9 unexposed children (4.3%; p<0.0001)). Risk factors for child death included: HIV-exposure [adjOR2.9(95%CI 1.1–7.2)], low birthweight [adjOR2.5(1.0–6.3)], previous child death (adjOR25.1(6.5–97.5)] and maternal death [adjOR5.3(11.4–20.5)]. At 20 months, HIV-infected children had significantly poorer health outcomes than HIV-unexposed children and HIV-exposed but uninfected children (HIV-EU), including: hospital admissions, delayed development, undernutrition and restrictions in function (Lansky scale); no significant differences were seen between HIV-EU and HIV-unexposed children. Overall, no difference was seen at 20 months among HIV-infected, HIV-EU and HIV-unexposed groups in Z-scores (%<−2.0) for weight, height and BMI. Risk factors for poor functional health status at 20 months included: HIV-infection [adjOR8.9(2.4–32.6)], maternal illness [adjOR2.8(1.5–5.0)] and low birthweight [adjOR2.0(1.0–4.1)].Conclusion
Child mortality remains high within this context and could be reduced through more effective PMTCT including prioritizing the treatment of maternal HIV infection to address the effect of maternal health and survival on infant health and survival. HIV-infected children demonstrated developmental delays, functional health and nutritional deficits that underscore the need for increased uptake of early infant diagnosis and institution of ART for all infected infants. 相似文献129.
Ma. Laura Suarez Daniel Renison Paula Marcora Isabell Hensen 《Biodiversity and Conservation》2008,17(11):2617-2625
Assessing tree ages is important for the understanding of forest recruitment patterns and tree growth. However, little experience
exists in the subtropics and accurate aging usually involves potentially damaging techniques such as tree coring or even the
use of entire cross sections, which is not recommendable in endangered species or ecosystems. We provide an example of how
age may be predicted on the basis of tree size and site conditions, using Polylepis australis of Central Argentina. Our study was conducted in two entire river basins where 96 independent trees were successfully cored
for age analysis. Site and tree characteristics were registered and tree age determined through standard dendrochronological
techniques. The multiple regression procedure selected tree circumference and proportion of rock under the tree canopy as
significant variables explaining 48% of the variation in number of growth rings. Trees surrounded by rock clearly grew slower
than those surrounded by a higher proportion of soil and vegetation. A comparison with a one site study shows that the ability
to predict P. australis age is clearly reduced when geographical range is extended but the explanatory power of our model is still high enough for
certain applications and within the range of other one site studies. We suggest that tree size and site characteristics may
be used to predict age in other subtropical mountain forests with a well marked growth season. 相似文献
130.