34 research outputs found
The successional status of tropical rainforest tree species is associated with differences in leaf carbon isotope discrimination and functional traits
International audienc
DiversitĂ© gĂ©nĂ©tique et dynamique des forĂȘts d Afrique centrale (Une Ă©tude multi-Ă©chelle de la structure de la diversitĂ© gĂ©nĂ©tique d un arbre pionnier, Aucoumea klaineana)
Cette thĂšse contribue Ă la comprĂ©hension des processus historiques, Ă©volutifs et Ă©cologiques liĂ©s au maintien de la forte diversitĂ© biologique dans les forĂȘts d'Afrique centrale. Notre approche est basĂ©e sur l'Ă©tude de la structuration de la diversitĂ© gĂ©nĂ©tique intraspĂ©cifique d'Aucoumea klaineana, arbre pionnier endĂ©mique du domaine forestier de Basse GuinĂ©e. Plusieurs Ă©chelles spatiales ont Ă©tĂ© considĂ©rĂ©es afin de dĂ©coupler les impacts des diffĂ©rents processus (historiques, Ă©volutifs et Ă©cologiques) qui agissent Ă des pas de temps diffĂ©rents sur la diversitĂ© gĂ©nĂ©tique. Nous avons montrĂ© qu'Ă l'Ă©chelle de l'aire de rĂ©partition, une grande part de l'hĂ©tĂ©rogĂ©nĂ©itĂ© de la diversitĂ© gĂ©nĂ©tique est expliquĂ©e par l'isolement historique de populations dans des refuges forestiers au cours du Dernier Maximum Glaciaire. Avec le retour des conditions favorables, les espĂšces forestiĂšres ont recolonisĂ© les savanes pour atteindre leurs aires de distribution actuelles. Pour A. klaineana, les effets de fondation responsable de la perte de diversitĂ© gĂ©nĂ©tique associĂ©s aux processus de colonisation ont Ă©tĂ© Ă©vitĂ©s grĂące Ă l'homogĂ©nĂ©itĂ© du succĂšs reproducteur des individus. A l'Ă©chelle des populations, la structure gĂ©nĂ©tique spatiale (SGS) rĂ©sulte du processus d'isolement par la distance, l'Ă©quilibre formĂ© entre flux de gĂšnes et dĂ©rive. Une telle structuration est observĂ©e chez A. klaineana, caractĂ©risĂ© par des distances de dispersion du pollen (128 m) et des graines (118 m) trĂšs limitĂ©es. Cet Ă©quilibre a Ă©tĂ© mis en Ă©vidence par des analyses de SGS qui laissent supposer que lorsque la densitĂ© d'arbre est plus faible et/ou que le milieu est ouvert, les distances de dispersion des gĂšnes sont plus fortes. Ce rĂ©sultat est liĂ© aux syndromes de dispersion de l'espĂšce qui contribuent ainsi localement au maintien de la diversitĂ© gĂ©nĂ©tique.This work contributes to our knowledge on historical, evolutionary and ecological processes linked with the high biological diversity in central Africa. We studied the structure of the genetic diversity of Aucoumea klaineana, a pioneer tree species, endemic to the Lower Guinea forest domain. Several spatial-scales were considered to infer impacts of the different processes (historical, evolutionary and ecological) acting with distinct time-scales on the genetic diversity. Considering the intraspecific genetic variation in the contemporary distribution of species, we showed that the heterogeneity in the distribution of the genetic diversity is due to the isolation of several source populations in forest refugia during the Last Glacial Maximum. After dry and cold periods, forest species recolonized savannahs and reached their current distribution areas. In A. klaineana, founder effects associated with colonization processes were avoided by the homogeneity in reproductive success in adult trees. At fine-scale, the spatial genetic structure (SGS) generally resulted from the isolation by distance process, the equilibrium between gene dispersal and drift. Such structure is observed for A. klaineana, characterized by both limited pollen and seed dispersal distances (128 and 118 m respectively). Here, SGS analyses may illustrate that reduced density of trees and/or forest opening is compensated by higher gene dispersal distances. This result is linked with dispersal syndromes of the species that locally contribute to the maintenance of the genetic diversity.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF
Ancient and recent evolutionary history of the bruchid beetle, Acanthoscelides obtectus Say, a cosmopolitan pest of beans
International audienceAcanthoscelides obtectus Say is a bruchid species of Neotropical origin, and is specialized on beans of the Phaseolus vulgaris L. group. Since the domestication and diffusion of beans, A. obtectus has become cosmopolitan through humanâmediated migrations and is now a major pest in bean granaries. Using phylogeographic methods applied to mitochondrial DNA (mtDNA) and nuclear microsatellite molecular markers, we show that the origin of this species is probably further south than Mesoamerica, as commonly thought. Our results also indicate that A. obtectus and its Mesoamerican sister species Acanthoscelides obvelatus , two morphologically close species differing principally in voltinism, speciated in allopatry: A. obtectus (multivoltine) arising in Andean America and A. obvelatus (univoltine) in Mesoamerica. In contrast to Mesoamerica where beans fruit once yearly, wild beans in Andean America fruit yearâround, especially in regions showing little or no seasonality. In such habitats where resources are continuously present, multivoltinism is adaptive. According to existing hypotheses, multivoltinism in A. obtectus is a new adaptation that evolved after bean domestication. Our data suggest the alternative hypothesis that multivoltinism is an older trait, adapted to exploit the yearâround fruiting of wild beans in relatively aseasonal habitats, and allowed A. obtectus to become a pest in bean granaries. This trait also permitted this species to disperse through humanâmediated migrations associated with diffusion of domesticated beans. We also show that diversity of Old World A. obtectus populations can be quite well explained by a single colonization event about 500 bp . Humanâmediated migrations appear not to be rare, as our results indicate a second more recent migration event from Andean America to Mexico
Leaf photosynthetic traits of 14 tropical rain forest species in relation to leaf nitrogen concentration and shade tolerance
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