Preliminary geoarchaeological data from a Senegambian megalithic world heritage site (Wanar, Senegal)

The Senegambian megalithic complex spread over a territory of 250 km from east to west and 120 to 150km from north to south. It consists of various monumental forms, especially erected stones circles. At the regional Senegambian scale the excavated sites suggest dates between 7th and 16th century AD, maby older. The exceptional concentration of the alignments and the originality of the forms (“lyre” stones, bifid stones, disc decorations, associated with other monuments, e.g. burial mounds) motivated  he inscription of four sites of Senegal and Gambia as World Heritage by UNESCO, like the site of Wanar in Senegal, in the watershed of the Bao Bolon, a tributary of the Gambia River (whc.unesco.org/en/list/1226). However, very little is known about the natural environment of these spectacular monumental manifestations, nor about the socio-economic context of their edification and the surrounding landscapes. Since 2005, archaeological excavations are carried out every year on the necropolis of Wanar. Such research contributes to enrich the socio-cultural knowledge of the Senegambian megalithism, phenomenon associated with the Protohistory (wanar-excavations.jimdo.com). Geoarchaeological studies (geomorphological and palaeo-biogeographical) currently in progress atWanar aim to reconstruct palaeoenvironments and landscapes contemporary of the monument construction, in order to answer a series of questions: In which landscape context have these populations developed? What were their relations with their environment? How did they fit into their territory, and how did they adapt to environmental changes? The dated material from two cores shows that the sedimentary records cover an extended timespan which include the Senegalese protohistory and previous periods (up to 5000 cal. BP). First sedimentological results describe the hydrosedimentary functioning of the Wanar watershed during the period contemporary with the megalithic phenomenon. Palaeoclimatic signals and anthropogenic impacts must be deciphered in order to better understand the fluctuating environmental dynamics of this era. The processing of grain size parameters, CM patterns (one-percentile/median) according to the method of Passega (1964), makes possible to well characterize the fluvial functioning and the depositional environments (ponds/stagnant water, flood plain or channel with low and intermittent current). These wetlands are very good recorders of palaeoenvironmental dynamics. Paleobiological multiproxies analysis (pollens, diatoms, dendrology, palynofacies and fire signal) are currently in progress and should allow the reconstruction of the history of vegetal landscapes and natural environments. Particular attention will be given to the dynamic factors linked to human activities (fires, vegetation clearing, agro-pastoral practices) and their imprint on the landscape

Le projet "Dahomey Gap": une contribution à l'histoire de la végétation au Sud-Bénin et Sud-ouest du Nigéria

La coupure que l'on constate dans les forêts denses africaines au niveau du Togo et du Bénin soulève de nombreuses questions sur les rapports forêt/savane au cours des derniers millénaires. Le projet Dahomey Gap vise à y répondre, par une approche pluridisciplinaire intégrant botanique et histoire de la végétation dans le Sud-Bénin et le Sud-Ouest du Nigéria. A partir de travaux déjà avancés sur la végétation du Bénin et des premières prospections palynologiques, quelques aspects du projet sont exposés ici: tels la caractérisation des différentes formations forestières du Bénin, les premiers résultats sur l'histoire holocène de la végétation du Sud-Bénin (mangroves, forêts, savanes) enregistrée depuis près de 7000 ans dans les lagunes

Ounjougou (Mali): A history of holocene settlement at the southern edge of the Sahara

The area of Ounjougou consists of a series of gullies cut through Upper Pleistocene and Holocene formations on the Dogon Plateau in the Sahel at the south edge of the Sahara Desert. Here the authors have chronicled a stratified sequence of human occupation from the tenth to the second millennium BC, recording natural and anthropogenic strata containing artefacts and micro- and macro- palaeoecological remains, mostly in an excellent state of preservation. They present a first synthesis of the archaeological and environmental sequence for the Holocene period, define five main occupation phases for Ounjougou, and attempt to place them within the context of West African prehistor

Enjeux et impacts des barrages de Diama (Mauritanie) et Arzal (France) : des contextes socio-économiques et environnementaux différents pour de mêmes conséquences

The similar dams of Arzal (Vilaine, France) and Diama (Mauritania-Senegal frontier) have same strategic functions for the regions and countries where they are built as fresh waters storage. They also had similar consequences over the ecosystems and local and regional activities. The imperfect results of the belated remediations also had as disastrous induced effects and leave the populations and ecosystems in a fragile and vulnerable situation if confronted with any environmental (drought, flood…), socio-economical or political (relations between Mauritania and Senegal) crisis

The emergence of pottery in Africa during the tenth millennium cal BC: new evidence from Ounjougou (Mali)

New excavations in ravines at Ounjougou in Mali have brought to light a lithic and ceramic assemblage that dates from before 9400 cal BC. The authors show that this first use of pottery coincides with a warm wet period in the Sahara. As in East Asia, where very early ceramics are also known, the pottery and small bifacial arrowheads were the components of a new subsistence strategy exploiting an ecology associated with abundant wild grasses. In Africa, however, the seeds were probably boiled (then as now) rather than made into brea

The emergence of pottery in Africa during the tenth millennium cal BC: new evidence from Ounjougou (Mali)

New excavations in ravines at Ounjougou in Mali have brought to light a lithic and ceramic assemblage that dates from before 9400 cal BC. The authors show that this first use of pottery coincides with a warm wet period in the Sahara. As in East Asia, where very early ceramics are also known, the pottery and small bifacial arrowheads were the components of a new subsistence strategy exploiting an ecology associated with abundant wild grasses. In Africa, however, the seeds were probably boiled (then as now) rather than made into bread

Asymmetric response of forest and grassy biomes to climate variability across the African Humid Period : influenced by anthropogenic disturbance?

A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental‐scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE‐21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental‐scale vegetation change

Enterobactin-Mediated Delivery of β-Lactam Antibiotics Enhances Antibacterial Activity against Pathogenic Escherichia coli

The design, synthesis, and characterization of enterobactin–antibiotic conjugates, hereafter Ent-Amp/Amx, where the β-lactam antibiotics ampicillin (Amp) and amoxicillin (Amx) are linked to a monofunctionalized enterobactin scaffold via a stable poly(ethylene glycol) linker are reported. Under conditions of iron limitation, these siderophore-modified antibiotics provide enhanced antibacterial activity against Escherichia coli strains, including uropathogenic E. coli CFT073 and UTI89, enterohemorrhagic E. coli O157:H7, and enterotoxigenic E. coli O78:H11, compared to the parent β-lactams. Studies with E. coli K-12 derivatives defective in ferric enterobactin transport reveal that the enhanced antibacterial activity observed for this strain requires the outer membrane ferric enterobactin transporter FepA. A remarkable 1000-fold decrease in minimum inhibitory concentration (MIC) value is observed for uropathogenic E. coli CFT073 relative to Amp/Amx, and time-kill kinetic studies demonstrate that Ent-Amp/Amx kill this strain more rapidly at 10-fold lower concentrations than the parent antibiotics. Moreover, Ent-Amp and Ent-Amx selectively kill E. coli CFT073 co-cultured with other bacterial species such as Staphylococcus aureus, and Ent-Amp exhibits low cytotoxicity against human T84 intestinal cells in both the apo and iron-bound forms. These studies demonstrate that the native enterobactin platform provides a means to effectively deliver antibacterial cargo across the outer membrane permeability barrier of Gram-negative pathogens utilizing enterobactin for iron acquisition.Pacific Southwest Regional Center of Excellence for Biodefense and Emerging Infectious DiseaseKinship Foundation. Searle Scholars ProgramMassachusetts Institute of Technology. Department of Chemistr