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The aims of this study were to investigate the appearance of strigolactones in the green lineage and to determine the primitive function of these molecules. We measured the strigolactone content of several isolated liverworts, mosses, charophyte and chlorophyte green algae using a sensitive biological assay and LC-MS/MS analyses. In parallel, sequence comparison of strigolactone-related genes and phylogenetic analyses were performed using available genomic data and newly sequenced expressed sequence tags. The primitive function of strigolactones was determined by exogenous application of the synthetic strigolactone analog, GR24, and by mutant phenotyping. Liverworts, the most basal Embryophytes and Charales, one of the closest green algal relatives to Embryophytes, produce strigolactones, whereas several other species of green algae do not. We showed that GR24 stimulates rhizoid elongation of Charales, liverworts and mosses, and rescues the phenotype of the strigolactone-deficient Ppccd8 mutant of Physcomitrella patens. These findings demonstrate that the first function of strigolactones was not to promote arbuscular mycorrhizal symbiosis. Rather, they suggest that the strigolactones appeared earlier in the streptophyte lineage to control rhizoid elongation. They may have been conserved in basal Embryophytes for this role and then recruited for the stimulation of colonization by glomeromycotan fungi.

E-mail Addresses: brouat@mpl.ird.fr; International audience; Aim : To investigate the phylogeographical structure of the Guinea multimammate mouse, Mastomys erythroleucus (Temminck, 1853), a widespread murid rodent in sub-Saharan (Sahel and Sudan) savannas, for a better understanding of the impacts of geographical and historical factors on the evolutionary history of this species, in the context of the growing database of phylogeographical studies of African savanna mammal species. Location Sahel and Sudan savannas, Africa. Methods : We sequenced the whole cytochrome b gene in 211 individuals from 59 localities distributed from Senegal to Ethiopia. Sequence data were analysed using both phylogenetic (several rooted tree-construction methods, median-joining networks) and population genetic methods (spatial analyses of molecular variance, mismatch distributions). Results : Haplotypes were distributed into four major monophyletic groups corresponding to distinct geographical regions across a west-east axis. Diversification events were estimated to have occurred between 1.16 and 0.18 Ma. Main conclusions : Vicariance events related to the fragmentation of savanna habitats during the Pleistocene era may explain the phylogeographical patterns observed. Genetic structure was consistent with a role of major Sahelian rivers as significant barriers to west-east dispersal. Recent demographic expansions probably occurred during arid phases of the Holocene with the southward expansion of savannas

Contact: laurent.granjon@ird.fr; International audience; Multi-mammate rats (Muridae, Murinae, Mastomys spp.) are Sub-Saharan pest rodents, the systematics of which has long remained confused due to poor morphologic differentiation. Cytotaxonomy and DNA sequencing have provided excellent diagnostic markers for species identification, thus improving the assessment of taxonomic diversity within the genus. In West and Central Africa, three species have been unambiguously identified and are now well documented: Mastomys erythroleucus, Mastomys natalensis and Mastomys huberti. However, recent studies suggest the existence of two other taxa on the basis of morphology, DNA sequencing (Mastomys verheyeni, from Nigeria and Northern Cameroon) or karyotypes (Mastomys cf. kollmannspergeri, from Northern Niger and Chad). In order to clarify the systematic status of the latter taxa, we collected all the available cytotaxonomic as well as cytochrome b sequencing data to which were added results obtained from recently trapped specimens in Northern Cameroon. Our combined molecular and cytogenetic analyses unambiguously confirm the presence of another Mastomys species inhabiting various habitats in Niger, Nigeria, Cameroon, Chad and Sudan. This taxon is clearly differentiated from M. erythroleucus, M. huberti and M. natalensis. Furthermore, the inclusion in our analysis of two M. verheyeni paratypes as well as individuals trapped in close vicinity to the type locality of M. kollmannspergeri supports the assignation of all specimens to M. kollmanspergeri, thus making M. verheyeni its junior synonym. Our study once again highlights the reliability of DNA- and karyotype-based methods to accurately assess specific diversity in African rodents, particularly in the Mastomys genus, which shelters several species of agricultural and epidemiological importance

Dispersal, one of the major factors affecting the gene flow between populations, shapes the spatial distribution of genetic diversity within species. Alouatta macconnelli and Saguinus midas are two Neotropical monkey species that sympatrically inhabit the Guiana shield in northern Amazonia and are likely to differ in their dispersal behavior and vagility. We took advantage of their sympatry to investigate, over a fine geographical scale (∼50 km long), the relationship between spatial genetic structure, on the one hand, and geographical features and the species' dispersal behavior on the other. A total of 84 A. macconnelli individuals from 25 social units and 76 S. midas individuals from 19 social units were genotyped for nine microsatellite markers. Both species displayed high genetic diversity and allelic richness. However, patterns of genetic structure differed between the two species. In A. macconnelli, no genetic substructuring was observed, while in S. midas we detected significant structuring, but this structuring was not correlated with geographical features, such as the location of individuals relative to the river and/or the distance between them. Instead, the geographical distribution of genetic variation observed for each species is predominantly explained by each species' dispersal pattern. We identified bisexual dispersal for both species, but with significant differences, either in the distance or in the rate of dispersal, between species and sexes. Genetic relatedness within social units was higher in S. midas than in A. macconnelli: gene flow between social units seems limited in S. midas, especially for females, while high dispersal characterizes A. macconnelli, where females seem to disperse at lower rate but at a longer distance than males.