1,721,060 research outputs found
Quantitative genetic approach for assessing invasiveness: geographic and genetic variation in life-history traits
No full textPredicting the spread of invasive species is a challenge for modern
ecology. Although many invasive species undergo genetic bottlenecks
during introduction to new areas resulting in a loss of genetic
diversity, successful invaders manage to flourish in novel environments
either because of pre-adaptations or because important traits contain
adaptive variation enabling rapid adaptation to changing conditions. To
predict and understand invasion success, it is crucial to analyse these
features. We assessed the potential of a well-known invader, the
Colorado potato beetle (Leptinotarsa decemlineata), to expand north of
its current range in Europe. A short growing season and harsh
overwintering conditions are apparent limiting factors for this species'
range. By rearing full-sib families from four geographically distinct
populations (Russia, Estonia, Poland, Italy) at two fluctuating
temperature regimes, we investigated (a) possible differences in
survival, development time, and body size among populations and (b) the
amount of adaptive variation within populations in these traits. All
populations were able to complete their development in cooler conditions
than in their current range. A significant genotype-environment
interaction for development time and body size suggests the presence of
adaptive genetic variation, indicating potential to adapt to cooler
conditions. The northernmost population had the highest survival rates
and fastest development times on both temperature regimes, suggesting
pre-adaptation to cooler temperatures. Other populations had minor
differences in development times. Interestingly, this species lacks the
classical trade-off between body size and development time which could
have contributed to its invasion potential. This study demonstrates the
importance of considering both ecological and evolutionary aspects when
assessing invasion risk
Cold tolerance during larval development: effects on the thermal distribution limits of Leptinotarsa decemlineata
No full textInsects' cold tolerance during their development is a surprisingly
understudied subject in ecology, despite the fact that subzero
temperatures during the growing season are common at high altitudes and
latitudes. Subzero temperatures can have detrimental effects on
organisms, restricting a species' range. This study addresses the
question whether night frosts during the growing season have an instant
or delayed negative impact on larval mortality of the Colorado potato
beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). We
also tested whether populations from the centre (Poland) and margins
(Russia) of the distribution range of L. decemlineata differ in their
responses to subzero exposure and a low rearing temperature. Larvae of
three ages were subjected to a subzero temperature (-4 degrees C for 3 h
simulating night frost) twice, after which they were reared on a
fluctuating temperature regime of 10-15 degrees C. These rearing
conditions imitated cool summer temperatures beyond the beetles' current
range, such as in Finland. Individuals of both populations were highly
cold tolerant, as only 3.1% of larvae died immediately following the
subzero treatment. Nonetheless, the low rearing temperature was harmful
to beetles of both populations. It caused high larval (ca. 90%) and
overwintering (ca. 80%) mortality. As beetle performance was affected
solely by rearing temperature, low temperatures during the growing
season rather than night frosts apparently retard the beetle's northern
expansion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
The voyage of an invasive species across continents: genetic diversity of North American and European Colorado potato beetle populations
No full textThe paradox of successful invading species is that they are likely to be
genetically depauperate compared to their source population. This study
on Colorado potato beetles is one of the few studies of the genetic
consequences of continent-scale invasion in an insect pest.
Understanding gene flow, population structure and the potential for
rapid evolution in native and invasive populations offers insights both
into the dynamics of small populations that become successful invaders
and for their management as pests. We used this approach to investigate
the invasion of the Colorado potato beetle (Leptinotarsa decemlineata)
from North America to Europe. The beetles invaded Europe at the
beginning of the 20th century and expanded almost throughout the
continent in about 30 years. From the analysis of mitochondrial DNA
(mtDNA) and amplified fragment length polymorphism (AFLP) markers, we
found the highest genetic diversity in beetle populations from the
central United States. The European populations clearly contained only a
fraction of the genetic variability observed in North American
populations. European populations show a significant reduction at
nuclear markers (AFLPs) and are fixed for one mitochondrial haplotype,
suggesting a single successful founder event. Despite the high vagility
of the species and the reduction of genetic diversity in Europe, we
found a similar, high level of population structure and low gene flow
among populations on both continents. Founder events during range
expansion, agricultural management with crop rotation, and selection due
to insecticide applications are most likely the causes partitioning
genetic diversity in this species
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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