180 research outputs found

    A surge in obsidian exploitation more than 1.2 million years ago at Simbiro III (Melka Kunture, Upper Awash, Ethiopia)

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    Pleistocene archaeology records the changing behaviour and capacities of early hominins. These behavioural changes, for example, to stone tools, are commonly linked to environmental constraints. It has been argued that, in earlier times, multiple activities of everyday life were all uniformly conducted at the same spot. The separation of focused activities across different localities, which indicates a degree of planning, according to this mindset characterizes later hominins since only 500,000 years ago. Simbiro III level C, in the upper Awash valley of Ethiopia, allows us to test this assumption in its assemblage of stone tools made only with obsidian, dated to more than 1.2 million years (Myr) old. Here we first reconstruct the palaeoenvironment, showing that the landscape was seasonally flooded. Following the deposition of an accumulation of obsidian cobbles by a meandering river, hominins began to exploit these in new ways, producing large tools with sharp cutting edges. We show through statistical analysis that this was a focused activity, that very standardized handaxes were produced and that this was a stone-tool workshop. We argue that at Simbiro III, hominins were doing much more than simply reacting to environmental changes; they were taking advantage of new opportunities, and developing new techniques and new skills according to them

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

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    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

    Mitochondrial phylogeography of baboons (Papio spp.) – Indication for introgressive hybridization?

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    <p>Abstract</p> <p>Background</p> <p>Baboons of the genus <it>Papio </it>are distributed over wide ranges of Africa and even colonized parts of the Arabian Peninsula. Traditionally, five phenotypically distinct species are recognized, but recent molecular studies were not able to resolve their phylogenetic relationships. Moreover, these studies revealed para- and polyphyletic (hereafter paraphyletic) mitochondrial clades for baboons from eastern Africa, and it was hypothesized that introgressive hybridization might have contributed substantially to their evolutionary history. To further elucidate the phylogenetic relationships among baboons, we extended earlier studies by analysing the complete mitochondrial cytochrome <it>b </it>gene and the 'Brown region' from 67 specimens collected at 53 sites, which represent all species and which cover most of the baboons' range.</p> <p>Results</p> <p>Based on phylogenetic tree reconstructions seven well supported major haplogroups were detected, which reflect geographic populations and discordance between mitochondrial phylogeny and baboon morphology. Our divergence age estimates indicate an initial separation into southern and northern baboon clades 2.09 (1.54–2.71) million years ago (mya). We found deep divergences between haplogroups within several species (~2 mya, northern and southern yellow baboons, western and eastern olive baboons and northern and southern chacma baboons), but also recent divergence ages among species (< 0.7 mya, yellow, olive and hamadryas baboons in eastern Africa).</p> <p>Conclusion</p> <p>Our study confirms earlier findings for eastern Africa, but shows that baboon species from other parts of the continent are also mitochondrially paraphyletic. The phylogenetic patterns suggest a complex evolutionary history with multiple phases of isolation and reconnection of populations. Most likely all these biogeographic events were triggered by multiple cycles of expansion and retreat of savannah biomes during Pleistocene glacial and inter-glacial periods. During contact phases of populations reticulate events (i.e. introgressive hybridization) were highly likely, similar to ongoing hybridization, which is observed between East African baboon populations. Defining the extent of the introgressive hybridization will require further molecular studies that incorporate additional sampling sites and nuclear loci.</p

    The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

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    Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard–Oeschger (D–O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D–O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73–15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U∕230Th, optically stimulated luminescence (OSL), 40Ar∕39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867

    The ‘mosaic habitat’ concept in human evolution: past and present

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    The habitats preferred by hominins and other species are an important theme in palaeoanthropology, and the ‘mosaic habitat’ (also referred to as habitat heterogeneity) has been a central concept in this regard for the last four decades. Here we explore the development of this concept – loosely defined as a range of different habitat types, such as woodlands, riverine forest and savannah within a limited spatial area– in studies of human evolution in the last sixty years or so. We outline the key developments that took place before and around the time when the term ‘mosaic’ came to wider palaeoanthropological attention. To achieve this we used an analysis of the published literature, a study of illustrations of hominin evolution from 1925 onwards and an email survey of senior researchers in palaeoanthropology and related fields. We found that the term mosaic starts to be applied in palaeoanthropological thinking during the 1970’s due to the work of a number of researchers, including Karl Butzer and Glynn Isaac , with the earliest usage we have found of ‘mosaic’ in specific reference to hominin habitats being by Adriaan Kortlandt (1972). While we observe a steady increase in the numbers of publications reporting mosaic palaeohabitats, in keeping with the growing interest and specialisation in various methods of palaeoenvironmental reconstruction, we also note that there is a lack of critical studies that define this habitat, or examine the temporal and spatial scales associated with it. The general consensus within the field is that the concept now requires more detailed definition and study to evaluate its role in human evolution

    Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia

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    Primary Research PaperSpecific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio

    Utilisation de la rétention chromatographique comme donnée prédictive pour l'analyse suspectée de micropolluants organiques par UHPLC-HRMS

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    International audienceIdentifier le plus grand nombre de contaminants organiques Ă©mergents dans les matrices environnementales est devenu un enjeu crucial pour amĂ©liorer les connaissances sur la contamination des milieux aquatiques. Parmi les stratĂ©gies d'analyses dĂ©ployĂ©es pour mettre en oeuvre cette identification, le criblage suspect connait un dĂ©veloppement considĂ©rable et devient largement utilisĂ© en laboratoire d'analyses. Il consiste Ă  rechercher dans un Ă©chantillon donnĂ© un ensemble de composĂ©s dont la prĂ©sence est pressentie. Ce criblage analytique est gĂ©nĂ©ralement menĂ© par chromatographie liquide couplĂ©e Ă  la spectromĂ©trie de masse haute rĂ©solution (UHPLC-HRMS). La comparaison des spectres de masse obtenus pour chaque pic chromatographique avec les informations disponibles dans les bases de donnĂ©es chimiques permet en gĂ©nĂ©ral d'Ă©tablir les structures potentielles des contaminants prĂ©sents dans l'Ă©chantillon. Cependant, la nĂ©cessitĂ© de croiser plusieurs informations pertinentes s'impose pour amĂ©liorer la confiance dans l'identification des composĂ©s. Nous prĂ©sentons ici le dĂ©veloppement de modĂšles de prĂ©diction des propriĂ©tĂ©s de rĂ©tention de contaminants organiques, permettant ainsi Ă  la rĂ©tention chromatographique d'ĂȘtre utilisĂ©e comme une donnĂ©e analytique supplĂ©mentaire dans l'identification de molĂ©cules suspectĂ©es dans des Ă©chantillons environnementaux. Ces modĂšles font le lien entre des descripteurs molĂ©culaires sĂ©lectionnĂ©s par Ă©tude bibliographique et les propriĂ©tĂ©s de rĂ©tention acquises expĂ©rimentalement. L'influence des paramĂštres analytiques sur ces modĂšles a Ă©tĂ© Ă©tudiĂ©e et aboutit Ă  la sĂ©lection de conditions expĂ©rimentales pour l'analyse suspectĂ©e de routine sur une colonne de type C18 avec une phase mobile eau/acĂ©tonitrile acidifiĂ©e Ă  pH 2,7. Ainsi, nous avons Ă©tabli un modĂšle validĂ© et applicable Ă  des Ă©chantillons environnementaux, permettant la prĂ©diction de la rĂ©tention chromatographique de contaminants organiques Ă  ±1,9min en temps de rĂ©tention dans les conditions analytiques choisies, pour une durĂ©e d'analyse de 20 min. Il est montrĂ©, dans cette Ă©tude, que ce modĂšle augmente de façon significative la confiance liĂ©e Ă  l'analyse suspectĂ©e par UHPLC-HRMS. Les donnĂ©es chromatographiques deviennent ainsi complĂ©mentaires aux informations obtenues par la spectromĂ©trie de masse pour mener Ă  bien l'identification de micropolluants organiques prĂ©sents dans les matrices environnementales

    Exposition de moules marines au diclofĂ©nac: bioconcentration, mĂ©tabolisation et mĂ©canisme d’action

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    International audienceLes produits pharmaceutiques humains, tels que les anti-inflammatoires non stĂ©roĂŻdiens, constituent une menace Ă©mergente pour les organismes du milieu marin. Leur bioaccumulation dans les organismes ainsi que leurs effets possibles sont prĂ©occupants comme le montre l’inclusion du diclofĂ©nac dans la premiĂšre liste de vigilance de l’Union EuropĂ©enne (DCE, 2015). Chez l’homme, le diclofĂ©nac est conçu pour inhiber deux isoformes de l'enzyme cyclo-oxygĂ©nase (COX-1 et COX-2), qui catalysent la synthĂšse des diffĂ©rentes prostaglandines Ă  partir de l'acide arachidonique. Les objectifs de cette Ă©tude Ă©taient ainsi de dĂ©terminer: i) si le diclofĂ©nac s’accumule dans les organismes aquatiques (et ici plus particuliĂšrement la moule mĂ©diterranĂ©enne), ii) s’il est mĂ©tabolisĂ© par cet organisme et iii) si son mĂ©canisme d’action chez cette espĂšce non-cible s’apparente Ă  celui connu chez l’homme. Pour rĂ©pondre Ă  ces objectifs, l’organisme modĂšle (Mytilus galloprovincialis) a Ă©tĂ© exposĂ© en laboratoire pendant 72 h Ă  deux concentrations de diclofĂ©nac (1 et 100 ”g/L). Une mĂ©thode sensible et spĂ©cifique basĂ©e sur le couplage chromatographie liquide, spectromĂ©trie de masse haute rĂ©solution a Ă©tĂ© dĂ©veloppĂ©e en vue de i) quantifier l’accumulation du diclofĂ©nac chez notre organisme modĂšle ainsi qu’identifier et quantifier les mĂ©tabolites formĂ©s chez cet organisme et ii) mesurer les prostaglandines PGF2a, PGE2 et PGD2 circulant chez la moule mĂ©diterranĂ©enne en vue d’étudier leur modulation suite Ă  l’exposition au diclofĂ©nac . Les concentrations en diclofĂ©nac mesurĂ©es dans l’eau et dans les tissus ont permis de dĂ©terminer un facteur de bioconcentration faible, de 27 L/kg, compatible avec la mĂ©tabolisation du diclofĂ©nac dans les organismes, hypothĂšse soutenue par la dĂ©tection de mĂ©tabolites hydroxylĂ©s et de mĂ©tabolites de phase II dans les tissus des organismes exposĂ©s. Concernant les prostaglandines, la PGD2 n’a jamais Ă©tĂ© dĂ©tectĂ©e. Si les concentrations en PGF2a sont apparues non impactĂ©es par une exposition au diclofĂ©nac , une tendance Ă  la sous-expression de la PGE2 chez les organismes exposĂ©s Ă  ce composĂ© (1 ”g/L) comparĂ©s aux individus non exposĂ©s a quant Ă  elle Ă©tĂ© mise en Ă©vidence, tendance confirmĂ©e et statistiquement significative chez les individus exposĂ©s Ă  la plus forte concentration (100 ”g/L)
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