Colonisation européenne des Amériques

Résumé

Le début de la colonisation européenne des Amériques (la Conquista, menée par les Conquistadors) est habituellement daté à 1492, même si les premiers Européens à avoir atteint les Amériques et à y établir des colonies sont les Vikings au Vinland. Racines médiévales Selon l'historien Jérôme Baschet, cette conquête européenne a des racines médiévales. La société au Moyen Âge est en effet articulée autour de l'expansionnisme féodal et de l'Église catholique au message universaliste et à la mentalité missionnaire. Stimulée par l'essor démographique et productif entre le et le , l'Europe occidentale se constitue peu à peu en une économie-monde à l'origine de la mondialisation au . L'universalisme chrétien, relayé par la puissance croissante des monarchies européennes monarchiques . Explorations de l'Amérique Découverte et exploration de l'Amérique En 1492, Christophe Colomb accoste aux Amériques, après quoi l'exploration et la colonisation avanceront rapidement.

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As one of the most commonly utilized organisms in the study of local adaptation, an accurate characterization of the demographic history of Drosophila melanogaster remains as an important research question. This owes both to the inherent interest in characterizing the population history of this model organism, as well as to the well-established importance of an accurate null demographic model for increasing power and decreasing false positive rates in genomic scans for positive selection. Although considerable attention has been afforded to this issue in non-African populations, less is known about the demographic history of African populations, including from the ancestral range of the species. While qualitative predictions and hypotheses have previously been forwarded, we here present a quantitative model fitting of the population history characterizing both the ancestral Zambian population range as well as the subsequently colonized west African populations, which themselves served as the source of multiple non-African colonization events. We here report the split time of the West African population at 72 kya, a date corresponding to human migration into this region as well as a period of climatic changes in the African continent. Furthermore, we have estimated population sizes at this split time. These parameter estimates thus represent an important null model for future investigations in to African and non-African D. melanogaster populations alike.

OXFORD UNIV PRESS2018

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Molecular ecological analysis of the succession and diversity of sulfate-reducing bacteria in the mouse gastrointestinal tract

Bart Deplancke

Intestinal sulfate-reducing bacteria (SRB) growth and resultant hydrogen sulfide production may damage the gastrointestinal epithelium and thereby contribute to chronic intestinal disorders. However, the ecology and phylogenetic diversity of intestinal dissimilatory SRB populations are poorly understood, and endogenous or exogenous sources of available sulfate are not well defined. The succession of intestinal SRB was therefore compared in inbred C57BL/6J mice using a PCR-based metabolic molecular ecology (MME) approach that targets a conserved region of subunit A of the adenosine-5'-phosphosulfate (APS) reductase gene. The APS reductase-based MME strategy revealed intestinal SRB in the stomach and small intestine of 1-, 4-, and 7-day-old mice and throughout the gastrointestinal tract of 14-, 21-, 30-, 60-, and 90-day-old mice. Phylogenetic analysis of APS reductase amplicons obtained from the stomach, middle small intestine, and cecum of neonatal mice revealed that Desulfotomaculum spp. may be a predominant SRB group in the neonatal mouse intestine. Dot blot hybridizations with SRB-specific 16S ribosomal DNA (rDNA) probes demonstrated SRB colonization of the cecum and colon pre- and postweaning and colonization of the stomach and small intestine of mature mice only. The 16S rDNA hybridization data further demonstrated that SRB populations were most numerous in intestinal regions harboring sulfomucin-containing goblet cells, regardless of age. Reverse transcriptase PCR analysis demonstrated APS reductase mRNA expression in all intestinal segments of 30-day-old mice, including the stomach. These results demonstrate for the first time widespread colonization of the mouse intestine by dissimilatory SRB and evidence of spatial-specific SRB populations and sulfomucin patterns along the gastrointestinal tract.

2000

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