Éditeur(s) : HAL CCSD
Résumé :  Diffusion du document : INRA Antilles-Guyane, UMR ECOFOG, F97387 Kourou, Guyane (France)Diplôme : Master Recherche
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Origin and maintenance of species diversity is one of the main questions in evolutive biology. Species complexes, ie sister species still exchanging genes, are common in tropical forests and contribute to this diversity. This poster describes the organization of the genetic diversity in two closely related tree species, Carapa guianensis and C. procera, which are in sympatry in French Guiana. By using a clustering method based on nuclear markers (Pritchard et al. 2000), 506 trees sampled in French Guiana have been assigned to a species. Interestingly, many individuals harbored intermediate genome and we assigned to an hybrid group. The geographic distribution of these individuals revealed the presence of a contact zone between the two carapa species in the Eastern part of French Guiana. We then analysed genetic diversity at cholroplast genome and revealed a symmetrical gene flow between the two sister species. In addition, hybridization between hybrids and parental species ar likely possible but still need validations thanks to control crosses. Within species, we finally revealed the presence of a departure from the neutral equilibrium in thedirection of a population expansion likely related to Holocene perturbations. This expansion may have contributed to the hybrid zone formation in French Guiana.
L'origine et le maintien de la diversité spécifique des forêts tropicales humides est une question clé en biologie évolutive. Ce travail contribue à améliorer la compréhension de ces mécanismes à travers l'étude de la distribution de la diversité génétique de deux espèces sœurs interfertiles, le Carapa procera et C. guianensis en Guyane. L'assignation botanique des arbres échantillonnés (506) a été effectuée en adoptant une approche moléculaire qui repose sur l'analyse de la répartition des fréquences alléliques de six microsatellites nucléaires (Pritchard et al. 2000). Chaque locus présente des allèles dont les différences de fréquences entre espèces sont importantes, permettant ainsi d'envisager des outils simples de reconnaissances pour ces espèces difficilement identifiables sur la seule base de leurs caractères phénotypiques. Une zone de contact des deux espèces où les phénomènes d'hybridations sont fréquents a par ailleurs été localisée. En associant une analyse de la diversité au niveau du génome chloroplastique sur un sous ensemble d'individus (244), j'ai pu montrer que l'introgression est bidirectionnelle et que les backcross sont possibles. Les flux de gènes entre les deux espèces sont fréquents, et à l'intérieur des espèces, les populations sont peu structurées bien que la différenciation soit significative entre les sites les plus éloignés. Enfin, ce travail met en évidence que les populations de chacune des deux espèces présentent un signal d'expansion de population, avec un signal plus fort pour le C. procera, qui laisse présager une expansion récente, vraisemblablement à l'origine de la zone de contact. L'impact des évènements climatiques et/ou des activités amérindiennes des 10 000 dernières années pourrait expliquer la restriction puis l'expansion de ce genre post pionnier.
https://hal.archives-ouvertes.fr/hal-01189488

hal-01189488
https://hal.archives-ouvertes.fr/hal-01189488
PRODINRA : 42333

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : Isozyme markers were used to characterize levels of diversity, genotypic structure and spatial genetic structure for the low-density tree species, Carapa procera (five adults per ha), within 300 ha of a continuous tropical rain forest stand. Both seed and adult stages were investigated, a high level of genetic diversity being found in both. Fixation indices showed excess homozygosity in seeds, and excess heterozygosity in adults, which might be caused by selection in favour of heterozygotes. Autocorrelation analysis of the spatial distribution of genotypes revealed no significant pattern in adults or in seeds before dispersal, and there was a high variability in correlogram shapes among alleles. This suggests that gene flow is extensive in C. procera, probably mainly through long-distance pollen dispersal, as seed dispersal is expected to be rather limited in this species (maximum distances of about 50 m). No clear-cut spatial pattern was observed in pollen allele frequencies, which supports the hypothesis of extensive pollen flow. This overall lack of structure is consistent with the data already available on the mating system of this predominantly outcroissing species.
ISSN: 0018-067X

hal-01032057
https://hal.archives-ouvertes.fr/hal-01032057
DOI : 10.1038/hdy.1997.124

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé :  
On 10 trees from 10 species of French Guyana tropical rainforest in a clear active process of restoring verticality growth strains were measured in situ in order to determine the occurrence of tension wood within samples. Wood specimens were cut in the vicinity of the growth strains measurements in order to measure some mechanical and physical properties. As suspected, tensile growth strains was very much higher in tension wood zone, because longitudinal modulus of elasticity was slightly higher. Longitudinal shrinkage was also much higher in tension wood than in opposite wood.
ISSN: 1286-4560

hal-01032110
https://hal.archives-ouvertes.fr/hal-01032110
DOI : 10.1051/forest:2007027

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Background : This study examines the radial trend in wood stiffness of tropical rainforest trees. The objective was to determine if the type of growing environment (exposed plantation or dense primary forest) would have an effect on this radial trend. Methods : The axial elastic modulus of wood samples, representing a pith to bark cross-section, of six trees from several French Guianese species (two of Eperua falcata, one of Eperua grandiflora, two of Carapa procera and one of Symphonia gloubulifera) was measured using a dynamic "forced vibration" method. Results : Primary forest trees were observed to have a decrease in wood stiffness from pith to bark, whereas plantation trees, from the same genus or species, displayed a corresponding increase in wood stiffness. Juvenile wood stiffness appears to vary depending on the environment in which the tree had grown. Conclusion : We suggest that the growth strategy of primary forest trees is to produce wood resistant to selfbuckling so that the height of the canopy may be obtained with the maximum of efficiency. In contrast, the growth strategy of the trees growing in an exposed plantation is to produce low-stiffness wood, important to provide flexibility in wind. Further experiments to study the behaviour of more species, with more individuals per species, growing across a range of physical environments, are required.
ISSN: 1286-4560

hal-00644335
https://hal.archives-ouvertes.fr/hal-00644335
https://hal.archives-ouvertes.fr/hal-00644335/document
https://hal.archives-ouvertes.fr/hal-00644335/file/McLean_al.pdf
DOI : 10.1007/s13595-011-0085-z

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Radial trends of vibrational properties, including the specific dynamic modulus (E'/r) and damping coefficient (tand), were investigated for 3 tropical rainforest hardwood species, Simarouba amara, Carapa procera and Symphonia globulifera by free-free flexural vibration test. The microfibril angle (MFA) was estimated through X-Ray diffraction. Consistent patterns of radial variations were observed for all studied properties. E'/r was found to decrease from pith to bark, which is strongly related to the increasing pith-bark trend of MFA. The variation of tand along the radius can be partly explained by MFA, and partly by the gradient of extractives due to heartwood formation. The coupling effect of MFA and extractives could be separated through the analysis of log(tand) - log(E'/r) diagram. For the studied species, the extractive content putatively associated to heartwood formation generally tends to decrease the wood damping coefficient. However, this weakening effect of extractives was not observed for inner part of the heartwood, suggesting the mechanical action of extractives was reduced during their chemical ageing.
ISSN: 1435-0211

hal-00797055
https://hal.archives-ouvertes.fr/hal-00797055
https://hal.archives-ouvertes.fr/hal-00797055/document
https://hal.archives-ouvertes.fr/hal-00797055/file/Radial_variations_vibrational_Zhang_al.pdf

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option B
Résumé : Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree species growing in the tropical rain forest of French Guiana. Leaf photosynthetic capacity (maximum rate of carboxylation and maximum rate of electron transport) was estimated by fitting a biochemical model of photosynthesis to response curves of net CO2 assimilation rate versus intercellular CO2 mole fraction. Leaf morphology described by leaf mass per unit leaf area (LMA), density and thickness, as well as area- and mass-based nitrogen (N) and carbon (C) concentrations, were recorded on the same leaves. Large interspecific variability was detected in photosynthetic capacity as well as in leaf structure and leaf N and C concentrations. No correlation was found between leaf thickness and density. The correlations between area- and massbased leaf N concentration and photosynthetic capacity were poor. Conversely, the species differed greatly in relativeNallocation to carboxylation and bioenergetics. Principal component analysis (PCA) revealed that, of the recorded traits, only the computed fraction of total leafNinvested in photosynthesis was tightly correlated to photosynthetic capacity.We also used PCAto test to what extent species with similar shade tolerances displayed converging leaf traits related to photosynthesis. No clear-cut ranking could be detected among the shade-tolerant groups, as confirmed by a one-way ANOVA.We conclude that the large interspecific diversity in photosynthetic capacity was mostly explained by differences in the relative allocation of N to photosynthesis and not by leafNconcentration, and that leaf traits related to photosynthetic capacity did not discriminate shade-tolerance ranking of these tropical tree species.
ISSN: 0829-318X

hal-01031522
https://hal.archives-ouvertes.fr/hal-01031522