Végétation et climat dans les forêts du sud-ouest Cameroun depuis 4770 ans BP : analyse pollinique des sédiments du lac Ossa

L'analyse palynologique détaillée d'une carotte prélevée dans le lac Ossa, situé au coeur de la forêt littorale atlantique du SW Cameroun, apporte de nouvelles informations sur l'histoire botanique et climatique de cette région depuis 4 770 ans BP. La microflore pollinique inventoriée, riche et très diversifiée, indique la permanence de l'environnement forestier durant toute cette période. De 4 770 à 2 730 BP, les forêts Biafréenne et afromontagnarde sont bien représentées dans les spectres polliniques. Puis vers 2 730 BP (âge estimé), une modification majeure du paysage apparaît. La forêt de type primaire est remplacée par une forêt perturbée riche en arbres pionniers (#Alchornea, #Macaranga). Ultérieurement on note l'extension du palmier à huile (#Elaeis guineensis$) qui culmine vers 1 600 BP. (Résumé d'auteur

Interaction of Cupidin/Homer2 with two actin cytoskeletal regulators, Cdc42 small GTPase and Drebrin, in dendritic spines

<p>Abstract</p> <p>Background</p> <p>Homer is a postsynaptic scaffold protein that links various synaptic signaling proteins, including the type I metabotropic glutamate receptor subunits 1α and 5, the inositol 1,4,5-trisphosphate receptor, Shank and Cdc42 small GTPase. Overexpression of Homer induces changes in dendritic spine morphology in cultured hippocampal neurons. However, the molecular basis underpinning Homer-mediated spine morphogenesis remains unclear. In this study, we aimed to elucidate the structural and functional properties of the interaction between Cupidin/Homer2 and two actin-cytoskeletal regulators, Cdc42 small GTPase and Drebrin.</p> <p>Results</p> <p>Cupidin/Homer2 interacted with activated Cdc42 small GTPase via the Cdc42-binding domain that resides around amino acid residues 191–283, within the C-terminal coiled-coil domain. We generated a Cupidin deletion mutant lacking amino acids 191–230 (CPDΔ191–230), which showed decrease Cdc42-binding ability but maintained self-multimerization ability. Cupidin suppressed Cdc42-induced filopodia-like protrusion formation in HeLa cells, whereas CPDΔ191–230 failed to do so. In cultured hippocampal neurons, Cupidin was targeted to dendritic spines, whereas CPDΔ191–230 was distributed in dendritic shafts as well as spines. Overexpression of CPDΔ191–230 decreased the number of synapses and reduced the amplitudes of miniature excitatory postsynaptic currents in hippocampal neurons. Cupidin interacted with a dendritic spine F-actin-binding protein, Drebrin, which possesses two Homer ligand motifs, via the N-terminal EVH-1 domain. CPDΔ191–230 overexpression decreased Drebrin clustering in the dendritic spines of hippocampal neurons.</p> <p>Conclusion</p> <p>These results indicate that Cupidin/Homer2 interacts with the dendritic spine actin regulators Cdc42 and Drebrin via its C-terminal and N-terminal domains, respectively, and that it may be involved in spine morphology and synaptic properties.</p

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

Climatic and cultural changes in the west Congo Basin forests over the past 5000 years

Central Africa includes the world's second largest rainforest block. The ecology of the region remains poorly understood, as does its vegetation and archaeological history. However, over the past 20 years, multidisciplinary scientific programmes have enhanced knowledge of old human presence and palaeoenvironments in the forestry block of Central Africa. This first regional synthesis documents significant cultural changes over the past five millennia and describes how they are linked to climate. It is now well documented that climatic conditions in the African tropics underwent significant changes throughout this period and here we demonstrate that corresponding shifts in human demography have had a strong influence on the forests. The most influential event was the decline of the strong African monsoon in the Late Holocene, resulting in serious disturbance of the forest block around 3500 BP. During the same period, populations from the north settled in the forest zone; they mastered new technologies such as pottery and fabrication of polished stone tools, and seem to have practised agriculture. The opening up of forests from 2500 BP favoured the arrival of metallurgist populations that impacted the forest. During this long period (2500–1400 BP), a remarkable increase of archaeological sites is an indication of a demographic explosion of metallurgist populations. Paradoxically, we have found evidence of pearl millet (Pennisetum glaucum) cultivation in the forest around 2200 BP, implying a more arid context. While Early Iron Age sites (prior to 1400 BP) and recent pre-colonial sites (two to eight centuries BP) are abundant, the period between 1600 and 1000 BP is characterized by a sharp decrease in human settlements, with a population crash between 1300 and 1000 BP over a large part of Central Africa. It is only in the eleventh century that new populations of metallurgists settled into the forest block. In this paper, we analyse the spatial and temporal distribution of 328 archaeological sites that have been reliably radiocarbon dated. The results allow us to piece together changes in the relationships between human populations and the environments in which they lived. On this basis, we discuss interactions between humans, climate and vegetation during the past five millennia and the implications of the absence of people from the landscape over three centuries. We go on to discuss modern vegetation patterns and African forest conservation in the light of these events.Peer reviewe

Long-Term Vegetation Change in Central Africa: The Need for an Integrated Management Framework for Forests and Savannas

peer reviewedTropical forests and savannas are the main biomes in sub-Saharan Africa, covering most of the continent. Collectively they offer important habitat for biodiversity and provide multiple ecosystem services. Considering their global importance and the multiple sustainability challenges they face in the era of the Anthropocene, this chapter undertakes a comprehensive analysis of the past, present, and future vegetation patterns in central African forests and savannas. Past changes in climate, vegetation, land use, and human activity have affected the distribution of forests and savannas across central Africa. Currently, forests form a continuous block across the wet and moist areas of central Africa, and are characterized by high tree cover (>90% tree cover). Savannas and woodlands have lower tree cover (<40% tree cover), are found in drier sites in the north and south of the region, and are maintained by frequent fires. Recent tree cover loss (2000–2015) has been more important for forests than for savannas, which, however, reportedly experienced woody encroachment. Future cropland expansion is expected to have a strong impact on savannas, while the extent of climatic impacts depends on the actual scenario. We finally identify some of the policy implications for restoring ecosystems, expanding protected areas, and designing sustainable ecosystem management approaches in the region

Végétation et climat dans les forêts du sud-ouest Cameroun depuis 4770 ans BP : analyse pollinique des sédiments du lac Ossa

L'analyse palynologique détaillée d'une carotte prélevée dans le lac Ossa, situé au coeur de la forêt littorale atlantique du SW Cameroun, apporte de nouvelles informations sur l'histoire botanique et climatique de cette région depuis 4 770 ans BP. La microflore pollinique inventoriée, riche et très diversifiée, indique la permanence de l'environnement forestier durant toute cette période. De 4 770 à 2 730 BP, les forêts Biafréenne et afromontagnarde sont bien représentées dans les spectres polliniques. Puis vers 2 730 BP (âge estimé), une modification majeure du paysage apparaît. La forêt de type primaire est remplacée par une forêt perturbée riche en arbres pionniers (#Alchornea, #Macaranga). Ultérieurement on note l'extension du palmier à huile (#Elaeis guineensis$) qui culmine vers 1 600 BP. (Résumé d'auteur