Female dominance in competition for gum trees in the Grey Mouse Lemur Microcebus murinus

Chez les mammifères, les femelles sont généralement plus limitées par les ressources alimentaires que les mâles, du fait de leur plus grand investissement dans la reproduction. Dans une forêt sèche décidue de l'ouest de Madagascar, le poids corporel, la distribution spatiale, les comportements alimentaires et sociaux de Microcèbes gris (Microcebus murinus) ont été suivis pendant la période d'engraissement automnal (mars-avril) à l'aide de captures-recaptures d'animaux marqués et d'observations comportementales. Seuls quelques animaux (23 %) ont pris du poids et les femelles étaient en général plus lourdes que les mâles. La distribution spatiale des captures des animaux des deux sexes s'est superposée à celle des arbres à gomme, lesquels sont apparus comme une ressource-clef à cette période (75 % du régime). De plus, les femelles étaient d'autant plus lourdes qu'elles étaient capturées près des arbres à gomme, alors que cette corrélation n'a pas été retrouvée chez les mâles. Une exclusion spatiale des captures de mâles et de femelles a également été observée. En fait, une compétition locale pour les ressources, confirmée par les observations comportementales, semble expliquer le poids corporel élevé d'animaux dominants, c'est-à-dire en particulier des femelles. La mise en réserve de graisse corporelle pourrait affecter à la fois la survie à la saison sèche et le succès reproducteur à la saison des pluies suivante. Ainsi, la compétition alimentaire à l'automne pourrait avoir des conséquences importantes sur l'organisation socio-spatiale du Microcèbe gris en produisant une grande variabilité intra- et inter-sexuelle.Due to their higher reproductive investment, female mammals are usually more dependent on food than males. In a dry deciduous forest of western Madagascar, body mass, spacing patterns, feeding and social behaviour of Grey Mouse Lemurs (Schmid and Kappeler, 1998) were investigated during the autumn fattening phase (March-April) using mark-recapture and behavioral observations. Only a few animals (23%) increased their body mass, and females were generally heavier than males. The spatial distribution of captures of both males and females followed the distribution of gum trees, which appeared as a keystone resource at this period (about 75% of the diet). Moreover, females trapped near gum trees were significantly heavier than others, whereas no such difference was observed in males. Spatial exclusion was noted between male and female capture locations. Local resource competition, confirmed by behavioural observations, may have led to higher body mass in dominant animals, and especially in females. Storage of fat may affect survival during the dry season and reproductive success at the ensuing rainy season. Therefore, feeding competition, by resulting in high inter- and intrasexual differences in fattening and use of space, may have implications for dynamics of populations and social organization

Economie et conservation de l'énergie au cours du cycle saisonnier chez un primate, Microcebus murinus (approches physiologique, comportementale et écologique)

PARIS13-BU Sciences (930792102) / SudocPARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceF

Prey taxonomy rather than size determines salp diets

International audienceSalps are gelatinous planktonic suspension feeders that filter large volumes of water in the food-dilute open ocean. Their life cycle allows periodic exponential growth and population blooms. Dense swarms of salps have a high grazing impact that can deplete the photic zone of phytoplankton and export huge quantities of organic matter to the deep sea. Previous studies described their feeding manner as mostly nonselective, with larger particles retained at higher efficiencies than small particles. To examine salp diets, we used direct in situ sampling (InEx method) of undisturbed solitary Salpa maxima. Aggregates ("chains") of Salpa fusiformis and Thalia democratica were studied using in situ incubations. Our findings suggest that in situ feeding rates are higher than previously reported and that cell removal is size independent with $ 1 μm picoeukaryotes preferentially removed over both larger eukaryotes and smaller bacteria. The prey : predator size ratios we measured (1 : 10 4-1 : 10 5) are an order of magnitude smaller than previously reported values and to the best of our knowledge, are the smallest values reported so far for any planktonic suspension feeders. Despite differences among the three species studied, they had similar prey preferences with no correlation between salp body length and prey size. Our findings shed new light on prey : predator relationships in planktonic systems-in particular, that factors other than size influence filtration efficiency-and suggest that in situ techniques should be devised and applied for the study of suspension feeding in the ocean

Characterization of the Interaction Between the Bacterial Wilt Pathogen Ralstonia solanacearum and the Model Legume Plant Medicago truncatula

The soilborne pathogen Ralstonia solanacearum is the causal agent of bacterial wilt and attacks more than 200 plant species, including some legumes and the model legume plant Medicago truncatula. We have demonstrated that M. truncatula accessions Jemalong A17 and F83005.5 are sus- ceptible to R. solanacearum and, by screening 28 R. solana- cearum strains on the two M. truncatula lines, differential interactions were identified. R. solanacearum GMI1000 infected Jemalong A17 line, and disease symptoms were dependent upon functional hrp genes. An in vitro root in- oculation method was employed to demonstrate that R. solanacearum colonized M. truncatula via the xylem and intercellular spaces. R. solanacearum multiplication was restricted by a factor greater than 1 × 105 in the resistant line F83005.5 compared with susceptible Jemalong A17. Genetic analysis of recombinant inbred lines from a cross between Jemalong A17 and F83005.5 revealed the presence of major quantitative trait loci for bacterial wilt resistance located on chromosome 5. The results indicate that the root pathosystem for M. truncatula will provide useful traits for molecular analyses of disease and resistance in this model plant species

HpaB-Dependent Secretion of Type III Effectors in the Plant Pathogens Ralstonia solanacearum and Xanthomonas campestris pv. vesicatoria

Plant pathogenic bacteria exerts their pathogenicity through the injection of large repertoires of type III effectors (T3Es) into plant cells, a mechanism controlled in part by type III chaperones (T3Cs). In Ralstonia solanacearum, the causal agent of bacterial wilt, little is known about the control of type III secretion at the post-translational level. Here, we provide evidence that the HpaB and HpaD proteins do act as bona fide R. solanacearum class IB chaperones that associate with several T3Es. Both proteins can dimerize but do not interact with each other. After screening 38 T3Es for direct interactions, we highlighted specific and common interacting partners, thus revealing the first picture of the R. solanacearum T3C-T3E network. We demonstrated that the function of HpaB is conserved in two phytopathogenic bacteria, R. solanacearum and Xanthomonas campestris pv. vesicatoria (Xcv). HpaB from Xcv is able to functionally complement a R. solanacearum hpaB mutant for hypersensitive response elicitation on tobacco plants. Likewise, Xcv is able to translocate a heterologous T3E from R. solanacearum in an HpaB-dependent manner. This study underlines the central role of the HpaB class IB chaperone family and its potential contribution to the bacterial plasticity to acquire and deliver new virulence factors

Biogeographic mechanisms involved in the colonisation of Madagascar by African vertebrates: rifting, rafting and runways

International audienc

Biogeographic mechanisms involved in the colonisation of Madagascar by African vertebrates: rifting, rafting and runways

International audienc

Laser power stabilization for Advanced VIRGO

International audienceSecond generation of laser interferometer gravitational wave detectors can now detect the fusion of compact stellar object pair weekly. To increase the sensitivity, an important change of design between first and second generation gravitational wave detectors is the use of homodyne detection instead of heterodyne. This modification has strongly increased the requirement on laser power stabilization for Advanced VIRGO [1] . The relative intensity noise (RIN) requirement depends on the effective defects of the interferometer mirrors and its operational state. It spans between 10 -8 Hz -1/2 and 1.2×10 -9 Hz -1/2 at 30 Hz for the most sensitive future configuration (2024)

Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum

The soil-borne pathogen Ralstonia solanacearum causes bacterial wilt in a broad range of plants. The main virulence determinants of R. solanacearum are the type III secretion system (T3SS) and its associated type III effectors (T3Es), translocated into the host cells. Of the conserved T3Es among R. solanacearum strains, the Fbox protein RipG7 is required for R. solanacearum pathogenesis on Medicago truncatula. In this work, we describe the natural ripG7 variability existing in the R. solanacearum species complex. We show that eight representative ripG7 orthologues have different contributions to pathogenicity on M. truncatula: only ripG7 from Asian or African strains can complement the absence of ripG7 in GMI1000 (Asian reference strain). Nonetheless, RipG7 proteins from American and Indonesian strains can still interact with M. truncatula SKP1-like/MSKa protein, essential for the function of RipG7 in virulence. This indicates that the absence of complementation is most likely a result of the variability in the leucine-rich repeat (LRR) domain of RipG7. We identified 11 sites under positive selection in the LRR domains of RipG7. By studying the functional impact of these 11 sites, we show the contribution of five positively selected sites for the function of RipG7CMR15 in M. truncatula colonization. This work reveals the genetic and functional variation of the essential core T3E RipG7 from R. solanacearum. This analysis is the first of its kind on an essential disease-controlling T3E, and sheds light on the co-evolutionary arms race between the bacterium and its hosts