1,720,998 research outputs found
Grass-evolution and diversification : a phylogenetic approach
No full textTHESIS 8437The growth in size of phylogenetic trees, over the last 20 years, has allowed evolutionary biologists to better test hypotheses about the evolutionary history of organisms, and especially those of species rich taxa such as the grasses. Grasses are one of the most diverse families in the angiosperms, consisting of approximately 10,000 species and 600-700 genera and it is essential to investigate evolution and diversification in this group to advance the understanding of the processes shaping the diversity of its life forms. Therefore, this thesis aimed to provide comprehensive phylogenetic trees of the grass family in order to establish macro-evolutionary hypotheses and investigate patterns and processes of grass diversification. One aspect of this thesis was to infer the most comprehensive phylogenetic tree of the grasses in order to establish robust phylogenetic relationships among grass lineages. In Chapter 2, a much larger representation of grass diversity (82% of tribes and 42% of genera) was included than any previous study. Phylogenetic inferences using DNA sequences of three plastid regions: rbcL, matK and trnL-F were performed using maximum parsimony and Bayesian inferences. The resulting trees resolved most of the subfamily relationships within the BEP(Bambusoideae, Ehrhartoideae and Pooideae) and PACCAD (Panicoideae. Aristidoideae. Centothecoideae, Chloridoideae, Arundinoideae and Danthonioideae) clades, which had previously been unclear, such as, among others: (i) the composition of the BEP clade and the sister-relationship of Ehrhartoideae and Bambusoideae + Pooideae, (ii)the paraphyly of tribe Bambuseae, (iii) the position of Gynerium as sister to Panicoideae, and (iv) the monophyly of Eriachne + Micraira. The thesis also highlights how phylogenetic accuracy has been largely neglected in phylogenetic
studies of grasses and other organisms with respect to missing data. It is shown that accuracy can be maintained even with the presence of a relatively large amount of missing data in combined analyses (i.e. 33 % of the taxa lacking one or more genes in the combined analysis). However, bootstrap support values, and to a lesser extent Bayesian inference posterior probabilities, are generally louver in combined gene analyses involving missing data than those not including them. We propose a fully resolved tree for the grass family at subfamily level and indicate the most likely interrelationships of all included tribes in our analysis (i.e. 82% of total grass tribes)
Composition, structure et héritabilité des communautés de microorganismes racinaires et rhizosphériques associées à Pisum spp. au cours de son développement - GeHoPi
No full textNational audiencePlants interact with a multitude of microorganisms, including bacteria, some of which play a role inecological functions that impact their host. Symbiotic associations between plants andmicroorganisms are the most well-known and documented, the most famous being the Rhizobiagenus associated with legumes, enabling them to fix atmospheric nitrogen and illustrating a long coevolutionary history. Beyond these associations, numerous bacteria in non-symbiotic interaction withplants also impact their host. Significant gaps persist in understanding these complex microbialcommunities, requiring holistic approaches at different temporal and spatial scales.We conducted a greenhouse experiment to investigate the dynamics of bacterial communitiesassociated with Pisum throughout its developmental cycle, in various microhabitats provided by thehost. These microbiomes were analyzed using full-length 16S rRNA gene PACBIO sequencing withecological and phylogenetical approaches.Results revealed that plant microhabitats act as ecological filters, shaping the composition andstructure of bacterial communities. Shifts in bacterial communities were observed across plantgrowth stages, with these effects increasing with spatial proximity to the plant. Finally, spatial andtemporal patterns in associated bacterial community dynamics were linked to bacterial phylogeneticrelatedness. These findings enhance our understanding of the dynamics of plant-associated bacterialcommunity recruitment
Habitat coding of African Restionaceae
No full text0: coastal wetlands; 1: montane wetlands; 2: coastal drylands; 3: montane dryland
1000 posterior trees from the molecular dating analysis of African Restionaceae
No full textThe set of 1,000 trees from the posterior distribution of the BEAST analysis used for habitat reconstructions and models of evolutio
Chronogram (Maximum Clade Credibility Tree) of Restionaceae
No full textMolecular Dating using BEAST of African Restionacea
Bayesian consensus tree from MrBayes
No full textConsensus tree from the MrBayes analyses of African Restionacea
C4 grass functional traits are correlated with biotic and abiotic gradients in an African savanna.
No full text14 pagesInternational audienceSavanna is a species-rich biome, that includes many modern mammal lineages and C4 grass (Poaceae) species. The greater productivity and grazing pressure associated with savannas is likely attributable to the foliar traits of the grasses they support. Thus, it is important to understand the complex relationships between the abiotic environment, foliar attributes and the floristic composition of savanna grasses, and the supported grazer densities. We sampled 37 grass communities in the Kruger National Park (South Africa) across three soil types and along a rainfall gradient and found that these communities lack strong phylogenetic structure. We then measured specific leaf area and leaf tensile strength for 384 individuals representing 66 species and found that both traits were strongly phylogenetically structured and associated with both rainfall and soil type. Finally, we found that grazer densities in the Park are correlated with the foliar traits of the associated grass communities, but the resolution of our data do not allow for a thorough analysis of this association. Our results demonstrate the complex interactions between climate, soils and grazer densities relative to C4 grass functional traits
A revised evolutionary history of Poales: origins and diversification
No full textPoales represents more than one-third of all monocotyledons (c. 20 000 species in 16 families) and constitutes a microcosm of the angiosperms. The extreme variation in species richness among the families of Poales is still not understood: Poaceae includes ∼10 000 species, whereas six families have fewer than ten species. Here, using the largest phylogenetic analysis of Poales to date, molecular dating, ancestral reconstructions and diversification analyses, we develop a macro-evolutionary and macro-ecological approach to seek correlates for changing diversification patterns. We show that the poalean families diverged in the Late Cretaceous, a time of high levels of CO2 and high rainfall. Our habitat reconstructions indicate that Poales inhabited open and dry habitats in this environment. We also demonstrate that lineages with CO2-concentrating mechanisms inhabiting dry and open environments exhibited higher diversification rates than C3, shade and wet lineages. CO2-concentrating mechanisms counteract the effects of low atmospheric CO2 and reduce phototranspiration. It is believed that the parallel evolution of C4 and CAM (Crassulacean acid metabolism) photosynthesis in Poaceae, Cyperaceae and Bromeliaceae is an adaptation to changes in atmospheric CO2 concentrations. Combinations of extrinsic and intrinsic factors might have played a role in shifts in diversification rates and may explain the variation in species richness in Poales
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