576 research outputs found
Reconstructing the evolutionary history of the radiation of the land snail genus Xerocrassa on Crete based on mitochondrial sequences and AFLP markers
No full textSauer J, Hausdorf B. Reconstructing the evolutionary history of the radiation of the land snail genus Xerocrassa on Crete based on mitochondrial sequences and AFLP markers. BMC Evolutionary Biology. 2010;10(1): 299.Background: A non-adaptive radiation triggered by sexual selection resulted in ten endemic land snail species of the genus Xerocrassa on Crete. Only five of these species and a more widespread species are monophyletic in a mitochondrial gene tree. The reconstruction of the evolutionary history of such closely related species can be complicated by incomplete lineage sorting, introgression or inadequate taxonomy. To distinguish between the reasons for the nonmonophyly of several species in the mitochondrial gene tree we analysed nuclear AFLP markers. Results: Whereas six of the eleven morphologically delimited Xerocrassa species from Crete are monophyletic in the mitochondrial gene tree, nine of these species are monophyletic in the tree based on AFLP markers. Only two morphologically delimited species could not be distinguished with the multilocus data and might have diverged very recently or might represent extreme forms of a single species. The nonmonophyly of X. rhithymna with respect to X. kydonia is probably the result of incomplete lineage sorting, because there is no evidence for admixture in the AFLP data and the mitochondrial haplotype groups of these species coalesce deeply. The same is true for the main haplotype groups of X. mesostena. The nonmonophyly of X. franciscoi might be the result of mitochondrial introgression, because the coalescences of the haplotypes of this species with some X. mesostena haplotypes are shallow and there is admixture with neighbouring X. mesostena. Conclusion: The most likely causes for the nonmonophyly of species in the mitochondrial gene tree of the Xerocrassa radiation on Crete could be inferred using AFLP data by a combination of several criteria, namely the depth of the coalescences in the gene tree, the geographical distribution of shared genetic markers, and concordance with results of admixture analyses of nuclear multilocus markers. The strongly subdivided population structure increases the effective population size of land snail species and, thus, the likelihood of a long persistence of ancestral polymorphisms. Our study suggests that ancestral polymorphisms are a frequent cause for nonmonophyly of species with a strongly subdivided population structure in gene trees
Continuing Fragmentation of a Widespread Species by Geographical Barriers as Initial Step in a Land Snail Radiation on Crete
No full textSauer J, Oldeland J, Hausdorf B. Continuing Fragmentation of a Widespread Species by Geographical Barriers as Initial Step in a Land Snail Radiation on Crete. PLoS ONE. 2013;8(5): e62569.The phylogeographic structure of the land snail Xerocrassa mesostena on Crete inferred from AFLP markers and mitochondrial cox1 sequences can be explained by three mechanisms: gene flow restriction, population expansion and leptokurtic dispersal. Gene flow restriction by geographic barriers caused subdivision of the gene pool into distinct clusters. Population expansion was probably facilitated by deforestation of Crete in the postglacial. Newly available areas were colonized by leptokurtic dispersal, i.e. slow active expansion resulting in isolation by distance within the clusters and occasional long distance dispersal events that resulted in departures from the isolation by distance model. Less than one percent of the AFLP markers show correlations with environmental variables. Random phylogeographic breaks in the distribution of the mitochondrial haplotype groups indicate that single locus markers, especially mitochondrial DNA, might result in a misleading picture of the phylogeographic structure of a species. Restriction of gene flow between metapopulations caused by geographical barriers can interact with sexual selection resulting in the differentiation of these metapopulations into separate species without noticeable ecological differentiation. Evidence for gene flow between parapatrically distributed evolutionary units representing different stages of the speciation process suggests that the ongoing process of fragmentation of the X. mesostena complex might be an example for parapatric speciation. The lack of ecological differentiation between these units confirms theoretical predictions that divergent selection for local adaptation is not required for rapid speciation
Introducción a la geografía histórica
No full textSauer\u27s work opens the way for the formation of environmental knowledge of our time and contribute to its development in Latin America. The article continues a series of topics in depth by the author, and concludes by reminding us that the terrifying impact of modern Western world, does not cancel the truth that human history has been remarkably pluralistic, and there are no general laws of society, but only cultural agreements.La obra de Sauer abre paso a la formación del saber ambiental de nuestro tiempo y contribuye a su desarrollo en América Latina. El artículo sigue una serie de temas profundizados por el autor, y concluye recordándonos que el aterrador impacto del moderno mundo Occidental, no cancela la verdad de que el la historia del hombre ha sido marcadamente pluralista, y que no existen leyes generales de la sociedad, sino únicamente acuerdos culturales
Romance
No full textA review of the works written about Romance in 2012.Kate Ash, Elizabeth Elliott, Mary C. Flannery, Hollie Morgan, Holly Moyer, Michelle M. Sauer, Greg Walker, and Will Youngman</p
Romance
No full textA review of the works written about Romance in 2012.Kate Ash, Elizabeth Elliott, Mary C. Flannery, Hollie Morgan, Holly Moyer, Michelle M. Sauer, Greg Walker, and Will Youngman</p
Introducción a la geografía histórica
No full textLa obra de Sauer abre paso a la formación del saber ambiental de nuestro tiempo y contribuye a su desarrollo en América Latina. El artículo sigue una serie de temas profundizados por el autor, y concluye recordándonos que el aterrador impacto del moderno mundo Occidental, no cancela la verdad de que el la historia del hombre ha sido marcadamente pluralista, y que no existen leyes generales de la sociedad, sino únicamente acuerdos culturales.L’œuvre de Sauer ouvre la voie à la formation d’un savoir environnemental de notre temps et contribue à son développement en Amérique latine. L’article poursuit une série de thèmes approfondis par l’auteur, et conclut en nous rappelant que l’épouvantable impact du monde moderne Occidental, n’annule point la vérité que l’histoire de l’homme a toujours été pluraliste, et qu’il n’existe point de lois générales de la société mais uniquement des accords culturels.Sauer's work opens the way for the formation of environmental knowledge of our time and contribute to its development in Latin America. The article continues a series of topics in depth by the author, and concludes by reminding us that the terrifying impact of modern Western world, does not cancel the truth that human history has been remarkably pluralistic, and there are no general laws of society, but only cultural agreements
The Fall of Nebuchadnezzar
No full textThis paper examines the relationship of verbal expression, political engagement, and historical progress in a poem which has traditionally been labelled undramatic and read as an allegory of Milton\u27s post-revolutionary resignation to quietism. While "Paradise Regained" consists primarily of a debate between two speakers and thus appears hostile to multivocality, the verbal combat, E. Sauer contends, transforms the poem into a historically engaged, politically charged text in which the Son challenges the oppressive homogeneity of Satan\u27s opposing discourse and reemplots the events of his master-narrative. In part 2, the author argues that Satan\u27s fall from the temple pinnacle-Nebuchadnezzar\u27s reconstructed tower of Babel, the site of contending voices and contested identities in "Paradise Regained"-represents the silencing of the monological, negating voice and the symbolic collapse of monarchy (Prose, 3: 405)
Introducción a la geografía histórica
No full textLa obra de Sauer abre paso a la formación del saber ambiental de nuestro tiempo y contribuye a su desarrollo en América Latina. El artículo sigue una serie de temas profundizados por el autor, y concluye recordándonos que el aterrador impacto del moderno mundo Occidental, no cancela la verdad de que el la historia del hombre ha sido marcadamente pluralista, y que no existen leyes generales de la sociedad, sino únicamente acuerdos culturales.L’œuvre de Sauer ouvre la voie à la formation d’un savoir environnemental de notre temps et contribue à son développement en Amérique latine. L’article poursuit une série de thèmes approfondis par l’auteur, et conclut en nous rappelant que l’épouvantable impact du monde moderne Occidental, n’annule point la vérité que l’histoire de l’homme a toujours été pluraliste, et qu’il n’existe point de lois générales de la société mais uniquement des accords culturels.Sauer's work opens the way for the formation of environmental knowledge of our time and contribute to its development in Latin America. The article continues a series of topics in depth by the author, and concludes by reminding us that the terrifying impact of modern Western world, does not cancel the truth that human history has been remarkably pluralistic, and there are no general laws of society, but only cultural agreements
US tactical nuclear weapons: a European perspective
No full textAbstract: The debate over the removal of tacticalweapons is not a simple one; linked with it are the debates over the utility ofNATO and how to reach a global consensus on nuclear disarmament. Advocates of withdrawal view inaction regarding tactical nuclear weapons as just one example of general inertiawithin the alliance; the lack of a serious political discussion inside NATO, they argue, is a cause of concern for the true value of NATO. Belgian author Tom Sauer writes that such a debate has only stalled action, resulting in missed opportunities to remove the weapons from Europe. Looking at the arguments for and against the removal of tactical nuclear weapons in Europe, the author writes that the answers to this debate are to be found in the capitals ofNATOmember states. The time is ripe to withdraw all U.S. nuclear weapons from Europe; the arguments of the few opponents do not outweigh the benefits of withdrawal. The political climate
1with a U.S. president who is personally committed to the nuclear weapons threat
1is also ideal. The question is not if but rather how NATO will change its policy
Player agency in interactive narrative: audience, actor & author
No full textThe question motivating this review paper is, how can
computer-based interactive narrative be used as a constructivist learn-
ing activity? The paper proposes that player agency can be used to
link interactive narrative to learner agency in constructivist theory,
and to classify approaches to interactive narrative. The traditional
question driving research in interactive narrative is, ‘how can an in-
teractive narrative deal with a high degree of player agency, while
maintaining a coherent and well-formed narrative?’ This question
derives from an Aristotelian approach to interactive narrative that,
as the question shows, is inherently antagonistic to player agency.
Within this approach, player agency must be restricted and manip-
ulated to maintain the narrative. Two alternative approaches based
on Brecht’s Epic Theatre and Boal’s Theatre of the Oppressed are
reviewed. If a Boalian approach to interactive narrative is taken the
conflict between narrative and player agency dissolves. The question
that emerges from this approach is quite different from the traditional
question above, and presents a more useful approach to applying in-
teractive narrative as a constructivist learning activity
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