130,802 research outputs found
Spontaneous Hybridization between Pinus sylvestris L. and P. mugo Turra in Slovakia
No full textAbstract
Molecular evidence for spontaneous hybridization between Pinus sylvestris L. and P. mugo Turra in the putative hybrid swarm populations of the species in Slovakia was provided based on PCR-RFLP analysis of the cpDNA trnV-trnH region. Species-specific restriction profiles generated by Hinf I digests of the cpDNA products reliably identified P. sylvestris and P. mugo haplotypes of the embryos from open pollination. Simultaneous analysis of the respective cpDNA region in megagametophytes and embryos of individual seeds along with needles of a given maternal tree has enabled to score either the P. sylvestris or P. mugo haplotypes in the embryos illustrating hybridization patterns between the two species. Data obtained in this way indicate a relatively extensive hybridization which takes place between P. sylvestris and P. mugo. The extent of hybridization varied among populations as evidenced by the 41.1-58.7% proportion of hybrid embryos registered on the locality Habovka, and by the 8.3% and 2.7% proportions of hybrid embryos on the localities Tisovnica and Sucha Hora, respectively. The approach itself is recommended as a convenient method for monitoring the hybridization patterns in sympatric zones of the studied pine species. </jats:p
Geographic patterns of nucleotide diversity and population differentiation in three closely related European pine species from the Pinus mugo complex
No full textNucleotide polymorphism at 12 nuclear loci and two mitochondrial gene fragments was studied in three closely related pine species from the Pinus mugo complex in populations across the species distributional range in Europe. Despite large differences in the census sizes of the populations, high and similar levels of nucleotide diversity (θsil = ∼0.013–0.017) were found at nuclear loci in the three pine species. More rapid decay of overall linkage disequilibrium (LD) and recombination to diversity ratio (ρ/θ) was observed across the species distributional range in P. mugo (ρ = 0.0369 ± 0.0028; ρ/θ = ∼2.2) than in P. uncinata (ρ = 0.0054 ± 0.0011; ρ/θ = ∼0.4) and P. uliginosa (ρ = 0.0051 ± 0.0010, ρ/θ = ∼0.4). However, regional groups of P. mugo showed similar levels of LD and ρ/θ ratio to the other species. An excess of rare nucleotide variants was found in P. mugo at four loci, but, overall, the allelic frequency spectrum in the three species did not deviate significantly from neutrality (multilocus Tajima's D = −0.681, D = −0.118 and D = −0.266, P > 0.05, respectively). Bayesian clustering methods showed no clear correspondence of clusters to species or geographical regions. Some differences between populations and species were found in a hierarchical analysis of molecular variance (AMOVA) and in the distribution of the mitochondrial DNA haplotypes, suggesting rather limited gene flow between the taxa and ongoing divergence. As all three pine taxa have similar genetic backgrounds, they form an excellent system for searching for loci involved in adaptive variation and speciation
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Pinus mugo Krummholz dynamics during concomitant change in pastoralism and climate in the central Apennines
No full textThe dynamics of Pinus
mugo krummholz during
concomitant change in
pastoral land use and
climate in central Italy
since the mid-20th century
was investigated.
Krummholz dynamics were
detected using sequential aerial photography and fitted to a
logistic regression model with elevation, grazing, proximity to
beech forest, and proximity to krummholz as explanatory
variables. Dendrochronological series were correlated with
temperature and precipitation and fitted to a linear model.
During this period krummholz doubled in extent and migrated
35–65 m upslope. Expansion was positively associated with krummholz proximity, residual pastoral grazing, and proximity to
beech forest beyond 10 m and negatively associated with
elevation and beech forest closer than 10 m. The logistic
regression model forecasts krummholz migration by an
additional 30 m upslope by 2060. During the 20th century,
winter and spring minimum temperatures increased but did not
result in increased radial stem growth of P. mugo. The
combined evidence suggests that krummholz dynamics can be
explained by the legacy of summer pastoralism and the
dispersal limitations of P. mugo, rather than by climate change.An Erasmus Mundus fellowship, the National
Natural Science Foundation of China (41271126 and 41361091), the Science
and Technology Foundation of Guizhou Province (J[2014]2126 and LH[2015]
7776), and a COST ECHOES (STSM-FP0703-6551) short scientific mission
grant.http://www.mrd-journal.org/default.aspam2017Geography, Geoinformatics and Meteorolog
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Long-Term Changes in Dwarf Pine (Pinus mugo Turra) Cover and Growth in the Orava Beskid Mountains, Slovakia
No full textDwarf pine (Pinus mugo Turra) thickets are a substantial land cover in high-elevation mountain ecosystems in Europe, where they fulfill important functions in soil conservation and as wildlife habitat. In many areas across Europe these thickets have rapidly expanded over the past decades because of changing climate and land use, highlighting the need to better understand how species spread relates to growth traits and changing environmental conditions. We quantified changes in dwarf pine cover by elevation on 2 mountains in the Western Carpathians (Central Europe) over 64 years (Babia hora) and 40 years (Pilsko), and we linked them to species growth responses to climate using archival photogrammetry and stem length measurements. We correlated mean growth chronologies with mean monthly temperature and precipitation to assess the main climatic factors driving growth. The total expansion of dwarf pine cover was substantial (28.6% in Babia hora and 57.1% in Pilsko), but the rate of expansion varied with elevation, site, and intra- and interspecific competition. The largest expansion occurred in the open stands of the high elevations (1550–1650 m). Statistically significant positive correlations between growth and temperature were recorded for the most recent growing season and for the preceding growing season. However, despite rising temperatures over time, mean species growth during the last 20 years decreased slightly. The correlation of growth with precipitation was mostly positive but not statistically significant. Thus, the impact of changing climate appeared too weak to overcome other influential factors (eg decline in grazing and intra- and interspecific competition)
Effect of storage on pollen viability in Pinus sylvestris L., Pinus mugo Turra and their hybrid swarms
No full textPollen storage is the only way how to overcome the differences in phenology of forest trees and
geographically determined reproductive barriers between them during controlled pollination. Pollen viability
of Scots pine (Pinus sylvestris L.), mountain dwarf pine (P. mugo Turra) and their hybrid swarms was evaluated
after 3-years storage at −20°C using in vitro germination test. One population of each P. sylvestris and P. mugo
were involved into study along with three hybrid swarms. Germination potential of the stored pollen grains
was reduced significantly in comparison with freshly collected pollen. Profound decrease in germination
rate was recorded in the two hybrid swarms (4.0–4.7%), less profound in the remaining three populations
(0.6–2.4%). Pollen tube length, as the second pollen viability trait was reduced in stored pollen grains in a
larger extend ranging between 51.4% and 54.3%. The pollen grains of the species P. mugo was exception in
this respect yielding pollen grains whose growth was retarded of 21.9% only. Analysis of variance confirmed
significant differences between fresh and stored pollen grains. Statistically significant were also the differenc-
es between compared populations and between tested individuals of the respective populations
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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