CpDNA-based species identification and phylogeography: application to a complex of African tropical tree species

Despite their importance as a hotspot of biodiversity, the history of the African tropical lowland rainforests is poorly known. In particular the respective influence of past climatic factors, environmental heterogeneity and physical barriers on the demographic history of plant species still have to be studied. Molecular approaches that characterise the distribution of genetic diversity in plant species and try to interpret it in the light of past historical events are promising in this respect. We examine here the distribution of genetic diversity at maternally-inherited markers (chloroplast DNA) of two tropical timber tree species, Erythrophleum ivorense and Erythrophleum suaveolens (Leguminosae-Caesalpinioideae), in their Lower Guinea distribution (essentially Gabon and Cameroon). As for many tropical sister-taxa, species identification is almost impossible in the field when flowers or fruits are not available. Using a blind-sampling approach and confronting molecular and morphological markers it was possible to attribute sampled individuals to one or the other species. The two species appear to have different ecological requirements and are rarely found in sympatry. A phylogeographic signal was found for E. suaveolens and, for both species, higher levels of diversity were observed in the South than in the North of the Lower Guinea domain. A recent period of forest perturbation, potentially human-induced, has probably favoured the expansion of these two light-demanding species. An observed genetic signal of demographic decline and the poor recruitment of the species can be interpreted as consequences of the natural succession of the forest formations. (Texte intégral

Fine-scale spatial genetic structure in the frankincense tree Boswellia papyrifera (Del.) Hochst. and implications for conservation

The fine-scale genetic structure and how it varies between generations depends on the spatial scale of gene dispersal and other fundamental aspects of species’ biology, such as the mating system. Such knowledge is crucial for the design of genetic conservation strategies. This is particularly relevant for species that are increasingly fragmented such as Boswellia papyrifera. This species occurs in dry tropical forests from Ethiopia, Eritrea and Sudan and is an important source of frankincense, a highly valued aromatic resin obtained from the bark of the tree. This study assessed the genetic diversity and fine-scale spatial genetic structure (FSGS) of two cohorts (adults and seedlings) from two populations (Guba-Arenja and Kurmuk) in Western Ethiopia and inferred intra-population gene dispersal in the species, using microsatellite markers. The expected heterozygosity (HE) was 0.664–0.724. The spatial analyses based on kinship coefficient (Fij) revealed a significant positive genetic correlation up to a distance of 130 m. Spatial genetic structure was relatively weak (Sp = 0.002–0.014) indicating that gene dispersal is extensive within the populations. Based on the FSGS patterns found, we estimate indirectly gene dispersal distances of 103 and 124 m for the two populations studied. The high heterozygosity, the low fixation index and the low Sp values found in this study are consistent with outcrossing as the (predominant) mating system in B. papyrifera. We suggest that seed collection for ex situ conservation and reforestation programmes of B. papyrifera should use trees separated by distances of at least 100 m but preferably 150 m to limit genetic relatedness among seeds from different trees

Phylogenetic relationships in two African Cedreloideae genera (Meliaceae) reveal multiple rain/dry forest transitions

Establishing phylogenetic relationships allows investigating how species diversity has evolved in various ecosystems. The genera Entandrophragma and Khaya contain tree species distributed in different African biomes (lowland rain forest, lowland dry forest, mountain forest), allowing to examine how (single or multiple events) and when the processes of diversification led to biome transitions. Based on the sequencing of plastid genome (pDNA: c. 160,000 bp) and ribosomal DNA (rDNA: c. 7,000 bp) and habitat characteristic data for each species, we have: (1) reconstructed phylogenetic relationships between species and estimated the dates of divergence between the main lineages, and (2) reconstructed ancestral states regarding biome preferences. The globally consistent phylogenetic tree topologies obtained with both markers in Entandrophragma show five main clades that are quite consistent with previously-defined sections based on reproductive characters of flowers. By contrast, in Khaya, pDNA and rDNA show divergent topologies, possibly due to a more recent diversification involving incomplete lineage sorting and/or recurrent hybridization events. Two major periods of diversification were highlighted: one for Entandrophragma species during the Oligo- Miocene, and a second, during the Pleistocene, concerned both genera at the intraspecific level for Entandrophragma and at the interspecific level for Khaya. These different diversification periods coincide with three major biomes shifts in Entandrophragma. The first habitat transition from rain to dry forests occurred during the Oligo-Miocene and two other transitions were inferred during the Pleistocene, one from rain forest to dry forest and another from rain forest to high altitude mountain forest

Genetic diversity of Parkia biglobosa (African locust bean) and its implications for conservation strategies

Parkia biglobosa is an African Savannah tree with a wide range from Senegal to Uganda between the latitudes 5 and 15° in the North of equator. It is well-known as an agroforestry tree but also as a medicinal and food tree. Seeds, barks, roots, leaves and flowers are used to treat more than 80 diseases and complaints while fermented seeds and pulp of fruits have highly nutritional and commercial values. Understanding the level and distribution of genetic diversity of a widespread species such P. biglobosa is crucial for its conservation and sustainable utilisation. The genetic diversity and population structure were investigated using height nuclear microsatellites developed for the species. The sampling included 84 populations from twelve countries in West and Central Africa. The height microsatellite loci were highly polymorphic and did not show evidence of null alleles. A total of 217 alleles were revealed among the 1,610 genotypes of P. biglobosa. The number of alleles per locus was ranged from 17 to 50 with an average of 27 alleles per locus. The estimates of genetic diversity were moderate for the populations of extreme West Africa and Central Africa and were high to populations in the centre of West Africa. Individual-based assignment using admixture model with correlated allele frequencies revealed strong genetically structured populations across P. biglobosa range in West and Central Africa. The clustering analysis showed five most plausible subpopulations for the biogeographic study in West and Central Africa. Analysis of molecular variance partitioned the molecular variation 9.10% among groups, 2.71% among populations within groups and 88.19% within populations. Overall, the genetic differentiation among populations was moderate (FST=0.118; P<0.001). In regard to the distribution of intraspecific diversity, we also discussed the implications for conservation and sustainable use of the species

Integrability as a consequence of discrete holomorphicity: the Z_N model

It has recently been established that imposing the condition of discrete holomorphicity on a lattice parafermionic observable leads to the critical Boltzmann weights in a number of lattice models. Remarkably, the solutions of these linear equations also solve the Yang-Baxter equations. We extend this analysis for the Z_N model by explicitly considering the condition of discrete holomorphicity on two and three adjacent rhombi. For two rhombi this leads to a quadratic equation in the Boltzmann weights and for three rhombi a cubic equation. The two-rhombus equation implies the inversion relations. The star-triangle relation follows from the three-rhombus equation. We also show that these weights are self-dual as a consequence of discrete holomorphicity.Comment: 11 pages, 7 figures, some clarifications and a reference adde

Ensuring the future of the pygeum tree (Prunus africana)

This report is aimed at trainers and support organisations for farmers and tree owners, as well as commercial tree nursery operators, government extension agencies and NGOs, among others, who are interested in cultivating the pygeum tree

Management of Parkia biglobosa in the field of farmers in selected sites in Burkina Faso

Parkia biglobosa is ranked as one of the most important agroforestry multipurpose tree species in Sahelo-Sudanian zone. The National Tree Seed Center (CNSF) of Burkina Faso has been involved in a breeding programme of this species for many years and has already conducted several research activities (eg. germplasm collection, provenance trials establishment, selection of the best promising trees for propagation). To better conserve and guide the breeding program, it is important to understand how farmers perceive and manage the species in their fields. A survey was conducted in two villages in southern Burkina Faso to describe the farmers' practices with regard to encouraging regeneration of tree species in their fields, with a special emphasis on Parkia biglobosa. The survey targeted 150 people categorised by gender, ethnic group and status of residence. The results show that Parkia biglobosa is the most appreciated indigenous species across ethnic and gender groups. Its maintenance in the landscape is favoured by both the protection of spontaneous regeneration by farmers when they clear the land for agriculture, and by active planting. The species is valued both for its commercial use and human consumption in the household. The survey indicated a significant difference in the practices undertaken by women and men to safeguard regeneration. With regard to the preferred traits of Parkia biglobosa individuals, also some differences between genders emerge. The level of appreciation shown by farmers for Parkia biglobosa and the indications about what traits are most preferred are useful guidance in the identification of optimal sources of reproductive material to be made available to farmers through different channels. The results also indicated the need to couple the analyses of farmers' perception of trait variation among individuals with a systematic morphological characterisation of the various morphological types identified

Phylogéographie des arbres des forêts du Bas-Guinéen et histoire de la végétation

La phylogéographie tente d'identifier les liens phylétiques entre populations pour reconstruire leur histoire. C'est une source d'information pouvant aider à reconstruire l'histoire de la végétation durant le Quaternaire et notamment tester l'hypothèse des refuges forestiers. Nous avons entamé des études phylogéographiques sur une quinzaine d'espèces d'arbres du bassin Guinéo-Congolais. Les patrons phylogéographiques basés sur les gènes chloroplastiques ou des microsatellites nucléaires permettent le plus souvent d'identifier des pools géniques distincts (Distemonanthus benthamianus, Erythrophleum suaveolens, Greenwayodedron suaveolens, Milicia excelsa, Santiria trimera), traces possibles d'une fragmentation forestière passée. La comparaison entre espèces révèle qu'une disjonction nord-sud se répète sur plusieurs espèces, suggérant une possible séparation entre un bloc forestier nord et un bloc forestier sud. La répartition des allèles rares, traceurs potentiels de refuges forestiers, donne des résultats relativement hétérogènes. Une corrélation entre diversité allélique et position des refuges forestiers hypothétiques est observée chez certaines espèces (Santiria) mais pas d'une manière générale. (Texte intégral

Bridge Decomposition of Restriction Measures

Motivated by Kesten's bridge decomposition for two-dimensional self-avoiding walks in the upper half plane, we show that the conjectured scaling limit of the half-plane SAW, the SLE(8/3) process, also has an appropriately defined bridge decomposition. This continuum decomposition turns out to entirely be a consequence of the restriction property of SLE(8/3), and as a result can be generalized to the wider class of restriction measures. Specifically we show that the restriction hulls with index less than one can be decomposed into a Poisson Point Process of irreducible bridges in a way that is similar to Ito's excursion decomposition of a Brownian motion according to its zeros.Comment: 24 pages, 2 figures. Final version incorporates minor revisions suggested by the referee, to appear in Jour. Stat. Phy

Perspectives for sustainable Prunus africana production and trade

This brief documents current knowledge about pygeum (Prunus africana). It aims to inform decision makers in governments in producing and consumer countries, international and civil society organisations and researchers, about sustainable (international) trade and governance of the species