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Baxter AJ, Verschuren D, Peterse F, Miralles DG, Martin-Jones CM, Maitituerdi A, Van der Meeren T, Van Daele M, Lane CS, Haug GH, Olago DO, Sinninghe Damsté JS. Reversed Holocene temperature-moisture relationship in the Horn of Africa. Nature 2023; 620:336-343. [PMID: 37558848 PMCID: PMC10412447 DOI: 10.1038/s41586-023-06272-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Accepted: 05/25/2023] [Indexed: 08/11/2023]
Abstract
Anthropogenic climate change is predicted to severely impact the global hydrological cycle1, particularly in tropical regions where agriculture-based economies depend on monsoon rainfall2. In the Horn of Africa, more frequent drought conditions in recent decades3,4 contrast with climate models projecting precipitation to increase with rising temperature5. Here we use organic geochemical climate-proxy data from the sediment record of Lake Chala (Kenya and Tanzania) to probe the stability of the link between hydroclimate and temperature over approximately the past 75,000 years, hence encompassing a sufficiently wide range of temperatures to test the 'dry gets drier, wet gets wetter' paradigm6 of anthropogenic climate change in the time domain. We show that the positive relationship between effective moisture and temperature in easternmost Africa during the cooler last glacial period shifted to negative around the onset of the Holocene 11,700 years ago, when the atmospheric carbon dioxide concentration exceeded 250 parts per million and mean annual temperature approached modern-day values. Thus, at that time, the budget between monsoonal precipitation and continental evaporation7 crossed a tipping point such that the positive influence of temperature on evaporation became greater than its positive influence on precipitation. Our results imply that under continued anthropogenic warming, the Horn of Africa will probably experience further drying, and they highlight the need for improved simulation of both dynamic and thermodynamic processes in the tropical hydrological cycle.
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Affiliation(s)
- A J Baxter
- Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
| | - D Verschuren
- Department of Biology, Limnology Unit, Ghent University, Gent, Belgium
| | - F Peterse
- Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
| | - D G Miralles
- Department of Environment, Hydro-Climate Extremes Lab (H-CEL), Ghent University, Gent, Belgium
| | | | - A Maitituerdi
- Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of Marine Sciences, University of Haifa, Mount Carmel, Israel
| | - T Van der Meeren
- Department of Biology, Limnology Unit, Ghent University, Gent, Belgium
| | - M Van Daele
- Renard Centre of Marine Geology, Department of Geology, Ghent University, Gent, Belgium
| | - C S Lane
- Department of Geography, University of Cambridge, Cambridge, UK
| | - G H Haug
- Department of Climate Geochemistry, Max Planck Institute for Chemistry, Mainz, Germany
| | - D O Olago
- Institute for Climate Change and Adaptation, Department of Earth and Climate Science, University of Nairobi, Nairobi, Kenya
| | - J S Sinninghe Damsté
- Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
- Department of Marine Microbiology and Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, Den Burg, The Netherlands
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2
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Gosling WD, Miller CS, Shanahan TM, Holden PB, Overpeck JT, van Langevelde F. A stronger role for long-term moisture change than for CO 2 in determining tropical woody vegetation change. Science 2022; 376:653-656. [PMID: 35511966 DOI: 10.1126/science.abg4618] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Anthropogenically elevated CO2 (eCO2) concentrations have been suggested to increase woody cover within tropical ecosystems through fertilization. The effect of eCO2 is built into Earth system models, although testing the relationship over long periods remains challenging. Here, we explore the relative importance of six drivers of vegetation change in western Africa over the past ~500,000 years (moisture availability, fire activity, mammalian herbivore density, temperature, temperature seasonality, CO2) by coupling past environmental change data from Lake Bosumtwi (Ghana) with global data. We found that moisture availability and fire activity were the most important factors in determining woody cover, whereas the effect of CO2 was small. Our findings suggest that the role of eCO2 effects on tropical vegetation in predictive models must be reconsidered.
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Affiliation(s)
- William D Gosling
- Institute for Biodiversity & Ecosystem Dynamics, University of Amsterdam, Netherlands
| | | | - Timothy M Shanahan
- Department of Geological Sciences, University of Texas at Austin, Austin, TX, USA
| | - Philip B Holden
- School of Environment, Earth & Ecosystem Sciences, The Open University, Milton Keynes, UK
| | - Jonathan T Overpeck
- School for Environment & Sustainability, University of Michigan, Ann Arbor, MI, USA
| | - Frank van Langevelde
- Department of Environmental Sciences, Wageningen University & Research, Wageningen, Netherlands.,School of Life Sciences, University of KwaZulu-Natal, KwaZulu-Natal, South Africa
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3
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Gosling WD, Scerri EML, Kaboth-Bahr S. The climate and vegetation backdrop to hominin evolution in Africa. Philos Trans R Soc Lond B Biol Sci 2022; 377:20200483. [PMID: 35249389 PMCID: PMC8899624 DOI: 10.1098/rstb.2020.0483] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The most profound shift in the African hydroclimate of the last 1 million years occurred around 300 thousand years (ka) ago. This change in African hydroclimate is manifest as an east-west change in moisture balance that cannot be fully explained through linkages to high latitude climate systems. The east-west shift is, instead, probably driven by a shift in the tropical Walker Circulation related to sea surface temperature change driven by orbital forcing. Comparing records of past vegetation change, and hominin evolution and development, with this breakpoint in the climate system is challenging owing to the paucity of study sites available and uncertainties regarding the dating of records. Notwithstanding these uncertainties we find that, broadly speaking, both vegetation and hominins change around 300 ka. The vegetative backdrop suggests that relative abundance of vegetative resources shifted from western to eastern Africa, although resources would have persisted across the continent. The climatic and vegetation changes probably provided challenges for hominins and are broadly coincident with the appearance of Homo sapiens (ca 315 ka) and the emergence of Middle Stone Age technology. The concomitant changes in climate, vegetation and hominin evolution suggest that these factors are closely intertwined. This article is part of the theme issue 'Tropical forests in the deep human past'.
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Affiliation(s)
- William D Gosling
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
| | - Eleanor M L Scerri
- Max Planck Institute for the Science of Human History, Jena, Germany.,Department of Classics and Archaeology, University of Malta, Msida, Malta.,Department of Prehistoric Archaeology, University of Cologne, 50931 Cologne, Germany
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4
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Origin, Persistence, and Vulnerability to Climate Changes of Podocarpus Populations in Central African Mountains. FORESTS 2022. [DOI: 10.3390/f13020208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Background and objectives—Podocarpus latifolius (synonym of P. milanjianus) is a key tree representative of Afromontane forests where it is highly threatened by climate and land-use changes. While large populations occur in East Africa, only a few isolated and usually small populations remain in western Central Africa (Cameroon to Angola). Studying the evolutionary history of such relictual populations can thus be relevant to understand their resilience under changing environments. Materials and Methods—we developed nine polymorphic nuclear microsatellites (nSSRs) to estimate genetic variability, (historical) gene flow, and demographic changes among natural populations from Central to East Africa. Results—despite the extended distribution range of P. latifolius, a strong isolation-by-distance pattern emerges at the intra-population scale, indicating low seed and pollen dispersal capacities. Central African populations display a lower genetic diversity (He = 0.34 to 0.61) and are more differentiated from each other (FST = 0.28) than are East African populations (He = 0.65 to 0.71; FST = 0.10), suggesting high genetic drift in the Central African populations. Spatial genetic structure reveals past connections between East and West Africa but also a gene flow barrier across the equator in western Central Africa. Demographic modelling anchors the history of current lineages in the Pleistocene and supports a strong demographic decline in most western populations during the last glacial period. By contrast, no signature of demographic change was detected in East African populations. Conclusions—in Cameroon, our results exclude a recent (re)colonization from one source population of all mountain ranges, but rather indicate long-term persistence of populations in each mountain with fluctuating sizes. A higher impact of genetic drift and further loss of diversity can be expected by survival through climatically unfavorable periods in such small refugial populations. Tracking the Quaternary legacy of podocarp populations is thus essential for their conservation since there is a temporal gap between environment crises and an ecological/genetic answer at the population level.
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5
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Couvreur TL, Dauby G, Blach‐Overgaard A, Deblauwe V, Dessein S, Droissart V, Hardy OJ, Harris DJ, Janssens SB, Ley AC, Mackinder BA, Sonké B, Sosef MS, Stévart T, Svenning J, Wieringa JJ, Faye A, Missoup AD, Tolley KA, Nicolas V, Ntie S, Fluteau F, Robin C, Guillocheau F, Barboni D, Sepulchre P. Tectonics, climate and the diversification of the tropical African terrestrial flora and fauna. Biol Rev Camb Philos Soc 2021; 96:16-51. [PMID: 32924323 PMCID: PMC7821006 DOI: 10.1111/brv.12644] [Citation(s) in RCA: 54] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 08/07/2020] [Accepted: 08/13/2020] [Indexed: 12/30/2022]
Abstract
Tropical Africa is home to an astonishing biodiversity occurring in a variety of ecosystems. Past climatic change and geological events have impacted the evolution and diversification of this biodiversity. During the last two decades, around 90 dated molecular phylogenies of different clades across animals and plants have been published leading to an increased understanding of the diversification and speciation processes generating tropical African biodiversity. In parallel, extended geological and palaeoclimatic records together with detailed numerical simulations have refined our understanding of past geological and climatic changes in Africa. To date, these important advances have not been reviewed within a common framework. Here, we critically review and synthesize African climate, tectonics and terrestrial biodiversity evolution throughout the Cenozoic to the mid-Pleistocene, drawing on recent advances in Earth and life sciences. We first review six major geo-climatic periods defining tropical African biodiversity diversification by synthesizing 89 dated molecular phylogeny studies. Two major geo-climatic factors impacting the diversification of the sub-Saharan biota are highlighted. First, Africa underwent numerous climatic fluctuations at ancient and more recent timescales, with tectonic, greenhouse gas, and orbital forcing stimulating diversification. Second, increased aridification since the Late Eocene led to important extinction events, but also provided unique diversification opportunities shaping the current tropical African biodiversity landscape. We then review diversification studies of tropical terrestrial animal and plant clades and discuss three major models of speciation: (i) geographic speciation via vicariance (allopatry); (ii) ecological speciation impacted by climate and geological changes, and (iii) genomic speciation via genome duplication. Geographic speciation has been the most widely documented to date and is a common speciation model across tropical Africa. We conclude with four important challenges faced by tropical African biodiversity research: (i) to increase knowledge by gathering basic and fundamental biodiversity information; (ii) to improve modelling of African geophysical evolution throughout the Cenozoic via better constraints and downscaling approaches; (iii) to increase the precision of phylogenetic reconstruction and molecular dating of tropical African clades by using next generation sequencing approaches together with better fossil calibrations; (iv) finally, as done here, to integrate data better from Earth and life sciences by focusing on the interdisciplinary study of the evolution of tropical African biodiversity in a wider geodiversity context.
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Affiliation(s)
| | - Gilles Dauby
- AMAP Lab, IRD, CIRAD, CNRS, INRAUniversity of MontpellierMontpellierFrance
- Laboratoire d'évolution Biologique et Ecologie, Faculté des SciencesUniversité Libre de BruxellesCP160/12, Avenue F.D. Roosevelt 50Brussels1050Belgium
| | - Anne Blach‐Overgaard
- Section for Ecoinformatics & Biodiversity, Department of BiologyAarhus UniversityNy Munkegade 114Aarhus CDK‐8000Denmark
- Center for Biodiversity Dynamics in a Changing World (BIOCHANGE), Department of BiologyAarhus UniversityNy Munkegade 114Aarhus CDK‐8000Denmark
| | - Vincent Deblauwe
- Center for Tropical Research (CTR), Institute of the Environment and SustainabilityUniversity of California, Los Angeles (UCLA)Los AngelesCA90095U.S.A.
- International Institute of Tropical Agriculture (IITA)YaoundéCameroon
| | | | - Vincent Droissart
- AMAP Lab, IRD, CIRAD, CNRS, INRAUniversity of MontpellierMontpellierFrance
- Laboratoire de Botanique Systématique et d'Écologie, École Normale SupérieureUniversité de Yaoundé IPO Box 047YaoundéCameroon
- Herbarium et Bibliothèque de Botanique AfricaineUniversité Libre de BruxellesBoulevard du TriompheBrusselsB‐1050Belgium
- Africa & Madagascar DepartmentMissouri Botanical GardenSt. LouisMOU.S.A.
| | - Oliver J. Hardy
- Laboratoire d'évolution Biologique et Ecologie, Faculté des SciencesUniversité Libre de BruxellesCP160/12, Avenue F.D. Roosevelt 50Brussels1050Belgium
| | - David J. Harris
- Royal Botanic Garden Edinburgh20A Inverleith RowEdinburghU.K.
| | | | - Alexandra C. Ley
- Institut für Geobotanik und Botanischer GartenUniversity Halle‐WittenbergNeuwerk 21Halle06108Germany
| | | | - Bonaventure Sonké
- Laboratoire de Botanique Systématique et d'Écologie, École Normale SupérieureUniversité de Yaoundé IPO Box 047YaoundéCameroon
| | | | - Tariq Stévart
- Herbarium et Bibliothèque de Botanique AfricaineUniversité Libre de BruxellesBoulevard du TriompheBrusselsB‐1050Belgium
- Africa & Madagascar DepartmentMissouri Botanical GardenSt. LouisMOU.S.A.
| | - Jens‐Christian Svenning
- Section for Ecoinformatics & Biodiversity, Department of BiologyAarhus UniversityNy Munkegade 114Aarhus CDK‐8000Denmark
- Center for Biodiversity Dynamics in a Changing World (BIOCHANGE), Department of BiologyAarhus UniversityNy Munkegade 114Aarhus CDK‐8000Denmark
| | - Jan J. Wieringa
- Naturalis Biodiversity CenterDarwinweg 2Leiden2333 CRThe Netherlands
| | - Adama Faye
- Laboratoire National de Recherches sur les Productions Végétales (LNRPV)Institut Sénégalais de Recherches Agricoles (ISRA)Route des Hydrocarbures, Bel Air BP 1386‐ CP18524DakarSenegal
| | - Alain D. Missoup
- Zoology Unit, Laboratory of Biology and Physiology of Animal Organisms, Faculty of ScienceUniversity of DoualaPO Box 24157DoualaCameroon
| | - Krystal A. Tolley
- South African National Biodiversity InstituteKirstenbosch Research CentrePrivate Bag X7, ClaremontCape Town7735South Africa
- School of Animal, Plant and Environmental SciencesUniversity of the WitwatersrandPrivate Bag 3Wits2050South Africa
| | - Violaine Nicolas
- Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum national d'Histoire naturelle, CNRS, Sorbonne Université, EPHEUniversité des AntillesCP51, 57 rue CuvierParis75005France
| | - Stéphan Ntie
- Département de Biologie, Faculté des SciencesUniversité des Sciences et Techniques de MasukuFrancevilleBP 941Gabon
| | - Frédiéric Fluteau
- Institut de Physique du Globe de Paris, CNRSUniversité de ParisParisF‐75005France
| | - Cécile Robin
- CNRS, Géosciences Rennes, UMR6118University of RennesRennes35042France
| | | | - Doris Barboni
- CEREGE, Aix‐Marseille University, CNRS, IRD, Collège de France, INRA, Technopole Arbois MéditerranéeBP80Aix‐en‐Provence cedex413545France
| | - Pierre Sepulchre
- Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA‐CNRS‐UVSQUniversité Paris‐SaclayGif‐sur‐YvetteF‐91191France
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6
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Abstract
The African Middle Stone Age (MSA, typically considered to span ca. 300–30 thousand years ago [ka]), represents our species’ first and longest lasting cultural phase. Although the MSA to Later Stone Age (LSA) transition is known to have had a degree of spatial and temporal variability, recent studies have implied that in some regions, the MSA persisted well beyond 30 ka. Here we report two new sites in Senegal that date the end of the MSA to around 11 ka, the youngest yet documented MSA in Africa. This shows that this cultural phase persisted into the Holocene. These results highlight significant spatial and temporal cultural variability in the African Late Pleistocene, consistent with genomic and palaeoanthropological hypotheses that significant, long-standing inter-group cultural differences shaped the later stages of human evolution in Africa.
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7
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Individualistic evolutionary responses of Central African rain forest plants to Pleistocene climatic fluctuations. Proc Natl Acad Sci U S A 2020; 117:32509-32518. [PMID: 33277432 DOI: 10.1073/pnas.2001018117] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Understanding the evolutionary dynamics of genetic diversity is fundamental for species conservation in the face of climate change, particularly in hyper-diverse biomes. Species in a region may respond similarly to climate change, leading to comparable evolutionary dynamics, or individualistically, resulting in dissimilar patterns. The second-largest expanse of continuous tropical rain forest (TRF) in the world is found in Central Africa. Here, present-day patterns of genetic structure are thought to be dictated by repeated expansion and contraction of TRFs into and out of refugia during Pleistocene climatic fluctuations. This refugia model implies a common response to past climate change. However, given the unrivalled diversity of TRFs, species could respond differently because of distinct environmental requirements or ecological characteristics. To test this, we generated genome-wide sequence data for >700 individuals of seven codistributed plants from Lower Guinea in Central Africa. We inferred species' evolutionary and demographic histories within a comparative phylogeographic framework. Levels of genetic structure varied among species and emerged primarily during the Pleistocene, but divergence events were rarely concordant. Demographic trends ranged from repeated contraction and expansion to continuous growth. Furthermore, patterns in genetic variation were linked to disparate environmental factors, including climate, soil, and habitat stability. Using a strict refugia model to explain past TRF dynamics is too simplistic. Instead, individualistic evolutionary responses to Pleistocene climatic fluctuations have shaped patterns in genetic diversity. Predicting the future dynamics of TRFs under climate change will be challenging, and more emphasis is needed on species ecology to better conserve TRFs worldwide.
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8
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Sánchez Goñi MF. Regional impacts of climate change and its relevance to human evolution. EVOLUTIONARY HUMAN SCIENCES 2020; 2:e55. [PMID: 37588361 PMCID: PMC10427484 DOI: 10.1017/ehs.2020.56] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The traditional concept of long and gradual, glacial-interglacial climate changes during the Quaternary has been challenged since the 1980s. High temporal resolution analysis of marine, terrestrial and ice geological archives has identified rapid, millennial- to centennial-scale, and large-amplitude climatic cycles throughout the last few million years. These changes were global but have had contrasting regional impacts on the terrestrial and marine ecosystems, with in some cases strong changes in the high latitudes of both hemispheres but muted changes elsewhere. Such a regionalization has produced environmental barriers and corridors that have probably triggered niche contractions/expansions of hominin populations living in Eurasia and Africa. This article reviews the long- and short-timescale ecosystem changes that have punctuated the last few million years, paying particular attention to the environments of the last 650,000 years, which have witnessed key events in the evolution of our lineage in Africa and Eurasia. This review highlights, for the first time, a contemporaneity between the split between Denisovan and Neanderthals, at ~650-400 ka, and the strong Eurasian ice-sheet expansion down to the Black Sea. This ice expansion could form an ice barrier between Europe and Asia that may have triggered the genetic drift between these two populations.
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9
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Helmstetter AJ, Amoussou BEN, Bethune K, Kamdem NG, Glèlè Kakaï R, Sonké B, Couvreur TLP. Phylogenomic approaches reveal how climate shapes patterns of genetic diversity in an African rain forest tree species. Mol Ecol 2020; 29:3560-3573. [PMID: 32743910 DOI: 10.1111/mec.15572] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 07/08/2020] [Accepted: 07/13/2020] [Indexed: 12/23/2022]
Abstract
The world's second largest expanse of tropical rainforest is in Central Africa, and it harbours enormous species diversity. Population genetic studies have consistently revealed significant structure across Central African rainforest plants. In particular, previous studies have repeatedly demonstrated a north-south genetic discontinuity around the equatorial line, in a continuous expanse of rainforest where a climatic inversion is documented. Here, we took a phylogeographic approach by sequencing 351 nuclear markers in 112 individuals across the distribution of the African rainforest tree species Annickia affinis (Annonaceae). We showed for the first time that the north-south divide is the result of a single, major colonization event across the climatic inversion from an ancestral population located in Gabon. We suggested that differences in ecological niche of populations located on either side of this inversion may have contributed to this phylogenetic discontinuity. We found evidence for inland dispersal, predominantly in northern areas, and variable demographic histories among genetic clusters, indicating that populations responded differently to past climate change. We show how newly developed genomic tools can provide invaluable insights into our understanding of tropical rainforest evolutionary dynamics.
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Affiliation(s)
| | - Biowa E N Amoussou
- IRD, UMR DIADE, Université de Montpellier, Montpellier, France.,Faculté des Sciences Agronomiques, Université d'Abomey-Calavi, Cotonou, Benin
| | - Kevin Bethune
- IRD, UMR DIADE, Université de Montpellier, Montpellier, France
| | - Narcisse G Kamdem
- Laboratoire de Botanique Systématique et d'Ecologie, Département des Sciences Biologiques, Ecole Normale Supérieure, Université de Yaoundé I, Yaoundé, Cameroon
| | - Romain Glèlè Kakaï
- Laboratoire de Biomathématiques et d'Estimations Forestières, Université d'Abomey-Calavi, Cotonou, Bénin
| | - Bonaventure Sonké
- Laboratoire de Botanique Systématique et d'Ecologie, Département des Sciences Biologiques, Ecole Normale Supérieure, Université de Yaoundé I, Yaoundé, Cameroon
| | - Thomas L P Couvreur
- IRD, UMR DIADE, Université de Montpellier, Montpellier, France.,Laboratoire de Botanique Systématique et d'Ecologie, Département des Sciences Biologiques, Ecole Normale Supérieure, Université de Yaoundé I, Yaoundé, Cameroon
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10
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Migliore J, Lézine AM, Hardy OJ. The recent colonization history of the most widespread Podocarpus tree species in Afromontane forests. ANNALS OF BOTANY 2020; 126:73-83. [PMID: 32193530 PMCID: PMC7304463 DOI: 10.1093/aob/mcaa049] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 03/18/2020] [Indexed: 06/10/2023]
Abstract
BACKGROUND AND AIMS Afromontane forests host a unique biodiversity distributed in isolated high-elevation habitats within a matrix of rain forests or savannahs, yet they share a remarkable flora that raises questions about past connectivity between currently isolated forests. Here, we focused on the Podocarpus latifolius-P. milanjianus complex (Podocarpaceae), the most widely distributed conifers throughout sub-Saharan African highlands, to infer its demographic history from genetic data. METHODS We sequenced the whole plastid genome, mitochondrial DNA regions and nuclear ribosomal DNA of 88 samples from Cameroon to Angola in western Central Africa and from Kenya to the Cape region in eastern and southern Africa to reconstruct time-calibrated phylogenies and perform demographic inferences. KEY RESULTS We show that P. latifolius and P. milanjianus form a single species, whose lineages diverged during the Pleistocene, mostly between approx, 200 000 and 300 000 years BP, after which they underwent a wide range expansion leading to their current distributions. Confronting phylogenomic and palaeoecological data, we argue that the species originated in East Africa and reached the highlands of the Atlantic side of Africa through two probable latitudinal migration corridors: a northern one towards the Cameroon volcanic line, and a southern one towards Angola. Although the species is now rare in large parts of its range, no demographic decline was detected, probably because it occurred too recently to have left a genetic signature in our DNA sequences. CONCLUSIONS Despite the ancient and highly fluctuating history of podocarps in Africa revealed by palaeobotanical records, the extended distribution of current P. latifolius/milanjianus lineages is shown to result from a more recent history, mostly during the mid-late Pleistocene, when Afromontane forests were once far more widespread and continuous.
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Affiliation(s)
- Jérémy Migliore
- Sorbonne Université, Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN/IPSL), CNRS UMR, Paris, France
- Université Libre de Bruxelles, Faculté des Sciences, Service Evolution Biologique et Ecologie, Bruxelles, Belgium
- Muséum départemental du Var, Toulon, France
| | - Anne-Marie Lézine
- Sorbonne Université, Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN/IPSL), CNRS UMR, Paris, France
| | - Olivier J Hardy
- Université Libre de Bruxelles, Faculté des Sciences, Service Evolution Biologique et Ecologie, Bruxelles, Belgium
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11
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Afromontane Forest Diversity and the Role of Grassland-Forest Transition in Tree Species Distribution. DIVERSITY 2020. [DOI: 10.3390/d12010030] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Local factors can play an important role in defining tree species distributions in species rich tropical forests. To what extent the same applies to relatively small, species poor West African montane forests is unknown. Here, forests survive in a grassland matrix and fire has played a key role in their spatial and temporal dynamics since the Miocene. To what extent these dynamics influence local species distributions, as compared with other environmental variables such as altitude and moisture remain unknown. Here, we use data from the 20.28 ha montane forest plot in Ngel Nyaki Forest Reserve, South-East Nigeria to explore these questions. The plot features a gradient from grassland to core forest, with significant edges. Within the plot, we determined tree stand structure and species diversity and identified all trees ≥1 cm in diameter. We recorded species guild (pioneer vs. shade tolerant), seed size, and dispersal mode. We analyzed and identified to what extent species showed a preference for forest edges/grasslands or core forest. Similarly, we looked for associations with elevation, distance to streams and forest versus grassland. We recorded 41,031 individuals belonging to 105 morphospecies in 87 genera and 47 families. Around 40% of all tree species, and 50% of the abundant species, showed a clear preference for either the edge/grassland habitat or the forest core. However, we found no obvious association between species guild, seed size or dispersal mode, and distance to edge, so what leads to this sorting remains unclear. Few species distributions were influenced by distance to streams or altitude.
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12
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Abstract
Editorial summaries of selected papers relevant to Quaternary science published in high-impact multidisciplinary journals between December 2018 and February 2019 [...]
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