Origin and history of the Dahomey Gap separating West and Central African rain forests: insights from the phylogeography of the legume tree Distemonanthus benthamianus

AimThe aim of this study was to understand the origin of the forest flora currently found in the Dahomey Gap (DG), a 200-km-wide forest-savanna mosaic separating the West African and Central African rain forest blocks. More specifically, using a widespread rain forest tree species, Distemonanthus benthamianus (Fabaceae), we will test the hypothesis that the DG populations are remnants of a population dating back from the African Humid Period of the Holocene, when West African and Central African rain forests were supposedly connected.LocationTropical forests of Upper Guinea (West Africa) and Lower Guinea (Atlantic Central Africa) and the forest-savanna mosaic of the DG extending from eastern Ghana to Benin.MethodsFour hundred and twenty-nine D. benthamianus samples from West to Central Africa were genotyped with 11 nuclear microsatellite markers. After detecting geographically coherent gene pools, their genetic diversity and differentiation were estimated and their demographic histories were inferred using coalescent simulations and approximate Bayesian computation (ABC) tests.ResultsFive parapatric gene pools were identified: three in Lower Guinea, one in Upper Guinea and one in the DG. ABC tests indicate that the DG gene pool probably originates from the admixture of adjacent Upper and Lower Guinean gene pools, with a higher contribution from Upper Guinea, at a timeframe consistent with the early Holocene (around 13–7 ka). The lower genetic diversity documented in the DG could result from a founder effect and/or from a demographic decline consistent with the Holocene climatic pejoration documented around 3 ka.Main conclusionsThis phylogeographical study inferring the history of the DG populations of D. benthamianus is consistent with palaeovegetation data that suggest that the forest flora of the DG might be essentially relicts of the early Holocene period when the Guineo-Congolian forest reached its maximum geographical distribution.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Isolation, characterisation and cross-species amplification of nuclear microsatellites in the african tree genus Greenwayodendron (Annonaceae)

Greenwayodendron is a genus of rainforest trees endemic to tropical Africa. Eight nuclear microsatellite loci, amplifiable in two multiplexed reactions, were developed in G. suaveolens and cross-amplified in the second species of the genus, G. oliveri, as well as in all subspecies and varieties recognised by current taxonomic treatments. Characterisation of the microsatellite markers in one population of G. suaveolens from Cameroon revealed polymorphism levels suitable for characterisation of the spatial genetic variation (7 to 16 alleles per locus and expected heterozygosity ranging from 0.57 to 0.89). The eight microsatellite loci optimised could help estimate genetic diversity levels in populations of G. suaveolens, G. oliveri and new local endemic species of Greenwayodendron in rainforests from western and central Africa.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Pleistocene population expansions of shade-tolerant trees indicate fragmentation of the African rainforest during the Ice Ages

The fossil record in tropical Africa suggests that dry conditions during the Ice Ages caused expansion of savannahs and contraction of the rainforest. Forest refugia have been proposed to be located in areas of Central Africa that currently harbour high rates of endemic species. However, to what extent the forest was fragmented remains unknown. Nuclear microsatellites and plastid sequences of 732 trees of two species occurring in the same habitat - mature lowland evergreen rainforests - but with remarkably different dispersal capacities - animal versus gravity - were analysed. Geographical information system tools revealed intraspecific lineages partially congruent across the two species, suggesting common past barriers to gene flow in Central Africa. According to approximate Bayesian computation, the intraspecific genetic clusters diverged during the Pleistocene (less than 2 Ma), so that intraspecific differentiation is the appropriate scale to test the aridification effect of the Ice Ages on tree populations. Demographic tests revealed clear genetic signals of population expansion in both taxa, possibly following bottleneck events after forest fragmentation, with stronger evidence of expansion after the Penultimate rather than after the Last Glacial Maximum. The differential dispersal capacity may have modulated the particular response of each species to climate change, as revealed by the stronger evidence of expansion found in the animal-dispersed species than in the gravity-dispersed one.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Evidence of past forest fragmentation in the Congo Basin from the phylogeography of a shade-tolerant tree with limited seed dispersal: Scorodophloeus zenkeri (Fabaceae, Detarioideae)

Background: Comparative phylogeographic studies on rainforest species that are widespread in Central Africa often reveal genetic discontinuities within and between biogeographic regions, indicating (historical) barriers to gene flow, possibly due to repeated and/or long-lasting population fragmentation during glacial periods according to the forest refuge hypothesis. The impact of forest fragmentation seems to be modulated by the ecological amplitude and dispersal capacities of each species, resulting in different demographic histories. Moreover, while multiple studies investigated the western part of Central Africa (Lower Guinea), few have sufficiently sampled the heart of the Congo Basin (Congolia). In this study, we look for genetic discontinuities between populations of the widespread tropical tree Scorodophloeus zenkeri Harms (Fabaceae, Detarioideae) in Central Africa. Additionally, we characterize genetic diversity, selfing rate and fine-scale spatial genetic structure within populations to estimate the gene dispersal capacity of the species. Results: Clear intraspecific genetic discontinuities occur throughout the species’ distribution range, with two genetic clusters in Congolia and four in Lower Guinea, and highest differentiation occurring between these bioregions. Genetic diversity is higher in Lower Guinea than Congolia. A spatial genetic structure characteristic of isolation by distance occurs within the genetic clusters. This allowed us to estimate gene dispersal distances (σg) for this outcrossing species with ballistic seed dispersal, which range between 100 and 250 m in areas where S. zenkeri occurs in high densities, and are in the low range of σg values compared to other tropical trees. Gene dispersal distances are larger in low density populations, probably due to extensive pollen dispersal capacity. Conclusions: Fragmentation of S. zenkeri populations seems to have occurred not only in Lower Guinea but also in the Congo Basin, though not necessarily according to previously postulated forest refuge areas. The lower genetic diversity in Congolia compared to Lower Guinea parallels the known gradient of species diversity, possibly reflecting a stronger impact of past climate changes on the forest cover in Congolia. Despite its bisexual flowers, S. zenkeri appears to be mostly outcrossing. The limited dispersal observed in this species implies that genetic discontinuities resulting from past forest fragmentation can persist for a long time before being erased by gene flow.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Pre-Pleistocene origin of phylogeographical breaks in African rain forest trees: New insights from Greenwayodendron (Annonaceae) phylogenomics

Aim: Palaeoecological records indicate that Pleistocene glaciations affected the African rain forest, probably causing its fragmentation, which could explain phylogeographical breaks documented in many tree species. This refuge hypothesis was further tested through species distribution models, hindcasting persistence during the Last Glacial Maximum. However, previous studies failed to estimate with sufficient precision the divergence time between phylogeographical entities to confirm their Pleistocene origin. Developing genomic tools on a representative tree of mature rain forests, we test if parapatric genetic clusters documented in widespread tree species can be interpreted as the legacy of past population fragmentation during the last glacial period(s). Location: Tropical Africa, Guineo-Congolian forests. Taxon: Greenwayodendron (Annonaceae). Methods: To further test the Pleistocene refuge hypothesis by molecular dating, we sequenced the plastome of 145 individuals of the shade-tolerant rain forest tree Greenwayodendron suaveolens and congeneric species, and genotyped the same samples using nuclear microsatellites to identify genetic clusters. Results: Five plastid phylogroups of G. suaveolens occur in parapatry throughout Central Africa, following a spatial pattern generally congruent with genetic clusters. Four of them diverged 3.5â4.5 Ma, whereas the fifth one, located in the Cameroon volcanic line (CVL), diverged 8.3 Ma, in the range of divergence times between Greenwayodendron species, highlighting the key role of the CVL in hosting ancient lineages. Within phylogroups, most nodes were dated from 0.9 to 3.2 Myr and a correlation between haplotype divergence and spatial distance was still perceptible, indicating a slow population dynamic. Main conclusions: The phylogeographical structures of Central African trees probably established during the Pliocene or early Pleistocene, and while they might have been reinforced during subsequent glacialâinterglacial cycles, interglacial phases did not lead to genetic homogenization. Therefore, interpreting phylogeographical patterns of African trees must account for a much deeper past than previously assumed, and cannot be limited to the last glacial period. © 2018 John Wiley & Sons LtdSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Contrasting genetic signal of recolonization after rainforest fragmentation in African trees with different dispersal abilities

Although today the forest cover is continuous in Central Africa, this may have not always been the case, as the scarce fossil record in this region suggests that arid conditions might have significantly reduced tree density during the ice ages. Our aim was to investigate whether the dry ice age periods left a genetic signature on tree species that can be used to infer the date of the past fragmentation of the rainforest. We sequenced reduced representation libraries of 182 samples representing five widespread legume trees and seven outgroups. Phylogenetic analyses identified an early divergent lineage for all species in West Africa (Upper Guinea) and two clades in Central Africa: Lower Guinea-North and Lower Guinea-South. As the structure separating the Northern and Southern clades—congruent across species—cannot be explained by geographic barriers, we tested other hypotheses with demographic model testing using δαδι. The best estimates indicate that the two clades split between the Upper Pliocene and the Pleistocene, a date compatible with forest fragmentation driven by ice age climatic oscillations. Furthermore, we found remarkably older split dates for the shade-tolerant tree species with nonassisted seed dispersal than for light-demanding species with long-distance wind-dispersed seeds. Different recolonization abilities after recurrent cycles of forest fragmentation seem to explain why species with long-distance dispersal show more recent genetic admixture between the two clades than species with limited seed dispersal. Despite their old history, our results depict the African rainforests as a dynamic biome where tree species have expanded relatively recently after the last glaciation.info:eu-repo/semantics/publishe

Are we underestimating the number of plant species in the tropics? New insights from population genetics approaches applied on African forest trees

info:eu-repo/semantics/nonPublishe

Are we underestimating the number of plant species in the tropics? New insights from population genetics approaches applied on African forest trees

info:eu-repo/semantics/nonPublishe

The prevalence of cryptic plant species in African rain forest trees - Insights from population genetics approaches

info:eu-repo/semantics/nonPublishe

Are there many cryptic plant species in the tropics? New insights from population genetics approaches applied on African rain forest trees

info:eu-repo/semantics/nonPublishe