1,721,149 research outputs found
Unveiling an ancient biological invasion: molecular analysis of an old European alien, the crested porcupine (<it>Hystrix cristata</it>)
Full text linkAbstract Background Biological invasions can be considered one of the main threats to biodiversity, and the recognition of common ecological and evolutionary features among invaders can help developing a predictive framework to control further invasions. In particular, the analysis of successful invasive species and of their autochthonous source populations by means of genetic, phylogeographic and demographic tools can provide novel insights into the study of biological invasion patterns. Today, long-term dynamics of biological invasions are still poorly understood and need further investigations. Moreover, distribution and molecular data on native populations could contribute to the recognition of common evolutionary features of successful aliens. Results We analyzed 2,195 mitochondrial base pairs, including Cytochrome b, Control Region and rRNA 12S, in 161 Italian and 27 African specimens and assessed the ancient invasive origin of Italian crested porcupine (Hystrix cristata) populations from Tunisia. Molecular coalescent-based Bayesian analyses proposed the Roman Age as a putative timeframe of introduction and suggested a retention of genetic diversity during the early phases of colonization. The characterization of the native African genetic background revealed the existence of two differentiated clades: a Mediterranean group and a Sub-Saharan one. Both standard population genetic and advanced molecular demography tools (Bayesian Skyline Plot) did not evidence a clear genetic signature of the expected increase in population size after introduction. Along with the genetic diversity retention during the bottlenecked steps of introduction, this finding could be better described by hypothesizing a multi-invasion event. Conclusion Evidences of the ancient anthropogenic invasive origin of the Italian Hystrix cristata populations were clearly shown and the native African genetic background was preliminary described. A more complex pattern than a simple demographic exponential growth from a single propagule seems to have characterized this long-term invasion.</p
Tempo and mode of species diversification in Dolichopoda cave crickets (Orthoptera, Rhaphidophoridae)
No full textThis study focuses on the phylogenetic relationships among ninety percent of known Dolichopoda species (44 out of 49); primarily a Mediterranean genus, distributed from eastern Pyrenees to Caucasus. A total of 2490 base pairs were sequenced corresponding to partial sequences of one nuclear (28SrRNA) and three mitochondrial genes (12S, 16S and COI). A relaxed molecular clock, inferred from Bayesian analysis was applied to estimate the divergence times between the lineages using well dated palaeoevents of the study areas. Molecular substitution rates per lineage per million years were also obtained for each analyzed gene. Based on the nearly complete species phylogeny, temporal patterns of diversification were analyzed using Lineage-Through-Time plots and diversification statistics. Alternative hypotheses about the colonization of present range by Dolichopoda species were tested by means of Approximate Bayesian Computation analysis. Results from this analysis carried out on the 90% of known Dolichopoda species confirmed the previous ones based on subgroups of species, suggesting the ABC analysis as a remarkable tool in biogeographic studies. Based on these results, the distribution of Dolichopoda species appears to have been shaped by the palaeogeographic and climatic events that occurred from Late Miocene up to the Plio-Pleistocene. Both vicariance and dispersal events appear to have influenced Dolichopoda species distributions, with many processes occurring in ancestral epigean populations before the invasion of the subterranean environment
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
Struttura genetica di popolazioni e variazione geografica nell'isopode terrestre Androniscus dentiger dell'Italia Centrale (Isopoda, Oniscidea, Trichoniscidae).
No full textVariabilità genetica a livello del DNA mitocondriale nei Cayapa dell'Ecuador e confronto con altre popolazioni indiane americane.
No full textMOLECULAR SYSTEMATICS AND THE MULTIDIMENSIONAL CONCEPT OF SPECIES
No full textFollowing a critical review of the species concepts and stressing the need for a single, general classification system to serve both systematists and evolutionary biologists, the author seeks to identify a conceptual framework where matching of taxonomic characters to the biological properties of species is maximized. Sympatric and synchronic populations of amphigonic organisms can almost unequivocally be identified as species when reproductive gaps occur between them. In such situations species are recognized by appropriate descriptors (characters) as genetic units and ecological units. Multivariate statistical methods provide a powerful tool to analyse more complex situations where non-amphigonic organisms and/or allopatric populations are investigated, on condition that appropriate character sets are considered. The increasing availability of molecular data for analysis certainly enhances the recognition of species as genetic unities, whilst much of the ecological role of an organism may be read from a careful choice of morphometric and ethological descriptors. On these premises it is suggested that species can be defined as groups of individuals (populations) which are discretely separated from other such groups in the character space. This definition is phenetical in its form but biological in its meaning since character sifting and weighting are considered essential features at the operational level
Struttura genotipica e fenotipica di Tapes decussatus e Tapes philippinarum (Bivalvia, Veneridae).
No full textStrength and Limitations of DNA Barcode under the Multidimensional Species Perspective.
Full text linkDNA barcoding aims at providing an efficient method for specieslevel separation using a partial sequence of the mitochondrial COI gene. The efficiency of the barcode in separating species is based on the amount
of genetic distance among samples. While in many taxa the species can be efficiently identified through the barcode, other situations cannot be treated by this approach. The causes for such discrepancy appear to be mostly related to the nature of speciation events and to the different roles of the genetic system, natural selection and evolutionary time. Thus, DNA barcode represent just one important descriptor in the framework of the multidimensional species
approach
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
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