Historique de la colonisation du milieu de la presqu' île d'Ampasindava : transformations du paysage et système de conservation

In the northwest of Madagascar, the Ampasindava peninsula is home to the essential part of what  remains of the forests of the Sambirano phytogeographic domain. The area has great importance in terms of biogeography, ecology, and socio-cultural aspects. The first documented human presence dates back  to the tenth century, during the development of the maritime trade in Madagascar, before becoming the first headquarters of the Sakalava kingdom in the  northwest of Madagascar. Several facts contributed to the degradation of the landscape, like the practice of the tavy and the war between Bemihisatra and  Merina. In the peninsula, the western part was the most affected, on contrary to the eastern part where are located the forest massifs which served as refuges during the tribal wars. After the annexion by France, of an important territory including the peninsula (August 6th, 1896), the Merina left the region,  and these forest massifs acquired a sacred status and as such were protected against destruction, preserving the characteristics of the primary forests of Sambirano. Elsewhere, a process of natural  reconstruction of the vegetation started. These historic facts lead us to conclude that the forests of Dypsis spp. (Arecaceae) and Sarcolaenaceae are not primary resulting from a difference in substrate or  climate, but are to be interpreted as old secondary forests, deriving from the long-term process of  reconstruction of the vegetation. For several years, the analysis of satellite imagery demonstrates that the rhythm of the tavy has dramatically increased in the region. This increase stems not only from a population growth, but also from a growing pressure for land to generate income for the purchase of manufactured products. The practice of the tavy represents a major threat to forests and different types of residual natural habitats. Secondary forests are the most sensitive and most suitable for rice production. Primary sacred forests have remained so far untouched. Their traditional protection is however recently shaken by the influx of immigrants, who show little respect to traditional ban.  Dans le Nord-ouest de Madagascar, la presqu’île d’Ampasindava abrite une partie essentielle des restes  des forêts du domaine du Sambirano. La région possède une grande importance tant biogéographique et écologique, que socio-culturelle. Elle a connu au Xe siècle sa première implantation humaine et il est  vraisemblable que l’Homme l’ait parcourue et utilisée régulièrement à l’époque du développement du réseau maritime à Madagascar, avant que le Sambirano ne devienne le premier siège du royaume  Sakalava dans le Nord-ouest de l’île. Plusieurs faits ont contribué à la déstructuration du paysage écologique initial, comme la pratique de l’abattis sur brûlis ou tavy et les guerres entre les Bemihisatra de la région et l’armée du royaume Merina. Si la zone Ouest de la région a été la plus touchée, celle de l’Est où se trouvent les grands massifs forestiers a servi de refuges durant ces guerres. Après l’annexion par la France, le 6 août 1896, d’un important territoire comprenant la presqu’île, les Merina ont quitté la région, et ces massifs forestiers acquirent un caractère sacré et furent ainsi protégés contre la destruction et le défrichement en conservant les caractéristiques des forêts climaciques intactes du Sambirano. Ailleurs, un processus de reconstitution naturelle de la végétation se mit en route. Ces divers aspects historiques permettent d’avancer que les forêts à Sarcolaenaceae et à Dypsis spp (Arecaceae), avec leurs caractéristiques physionomiques, structurales et floristiques, ne découlent pas tant de  caractéristiques du substrat ou du climat, mais seraient plutôt des forêts secondaires âgées, issues du long processus d’évolution progressive du dynamisme de la succession végétale. Depuis  quelques  années, l’analyse des images satellite montre que le rythme auquel le tavy est pratiqué s’intensifie dans la région. Cet accroissement découle non seulement de la croissance démographique, mais aussi d’un  besoin accru en terres pour générer les revenus nécessaires à l’achat de produits manufacturés. La pratique du tavy représente une des principales menaces pour les forêts et les différents types d’habitats naturels résiduels. Les forêts secondaires âgées qui sont situées hors des zones traditionnellement protégées sont les plus sensibles car elles sont les plus propices à la production de riz. Les forêts des   massifs sacrés, en revanche, ne semblent pas encore réellement menacées mais leur protection  traditionnelle est quelque peu ébranlée depuis par l’arrivée récente et massive d’immigrants qui  respectent peu les interdits traditionnels

Two Earth-sized planets orbiting Kepler-20

Since the discovery of the first extrasolar giant planets around Sun-like stars, evolving observational capabilities have brought us closer to the detection of true Earth analogues. The size of an exoplanet can be determined when it periodically passes in front of (transits) its parent star, causing a decrease in starlight proportional to its radius. The smallest exoplanet hitherto discovered has a radius 1.42 times that of the Earth's radius (R Earth), and hence has 2.9 times its volume. Here we report the discovery of two planets, one Earth-sized (1.03R Earth) and the other smaller than the Earth (0.87R Earth), orbiting the star Kepler-20, which is already known to host three other, larger, transiting planets. The gravitational pull of the new planets on the parent star is too small to measure with current instrumentation. We apply a statistical method to show that the likelihood of the planetary interpretation of the transit signals is more than three orders of magnitude larger than that of the alternative hypothesis that the signals result from an eclipsing binary star. Theoretical considerations imply that these planets are rocky, with a composition of iron and silicate. The outer planet could have developed a thick water vapour atmosphere.Comment: Letter to Nature; Received 8 November; accepted 13 December 2011; Published online 20 December 201

Dusty Planetary Systems

Extensive photometric stellar surveys show that many main sequence stars show emission at infrared and longer wavelengths that is in excess of the stellar photosphere; this emission is thought to arise from circumstellar dust. The presence of dust disks is confirmed by spatially resolved imaging at infrared to millimeter wavelengths (tracing the dust thermal emission), and at optical to near infrared wavelengths (tracing the dust scattered light). Because the expected lifetime of these dust particles is much shorter than the age of the stars (>10 Myr), it is inferred that this solid material not primordial, i.e. the remaining from the placental cloud of gas and dust where the star was born, but instead is replenished by dust-producing planetesimals. These planetesimals are analogous to the asteroids, comets and Kuiper Belt objects (KBOs) in our Solar system that produce the interplanetary dust that gives rise to the zodiacal light (tracing the inner component of the Solar system debris disk). The presence of these "debris disks" around stars with a wide range of masses, luminosities, and metallicities, with and without binary companions, is evidence that planetesimal formation is a robust process that can take place under a wide range of conditions. This chapter is divided in two parts. Part I discusses how the study of the Solar system debris disk and the study of debris disks around other stars can help us learn about the formation, evolution and diversity of planetary systems by shedding light on the frequency and timing of planetesimal formation, the location and physical properties of the planetesimals, the presence of long-period planets, and the dynamical and collisional evolution of the system. Part II reviews the physical processes that affect dust particles in the gas-free environment of a debris disk and their effect on the dust particle size and spatial distribution.Comment: 68 pages, 25 figures. To be published in "Solar and Planetary Systems" (P. Kalas and L. French, Eds.), Volume 3 of the series "Planets, Stars and Stellar Systems" (T.D. Oswalt, Editor-in-chief), Springer 201

Genome sequencing of the extinct Eurasian wild aurochs, Bos primigenius, illuminates the phylogeography and evolution of cattle

Background Domestication of the now-extinct wild aurochs, Bos primigenius, gave rise to the two major domestic extant cattle taxa, B. taurus and B. indicus. While previous genetic studies have shed some light on the evolutionary relationships between European aurochs and modern cattle, important questions remain unanswered, including the phylogenetic status of aurochs, whether gene flow from aurochs into early domestic populations occurred, and which genomic regions were subject to selection processes during and after domestication. Here, we address these questions using whole-genome sequencing data generated from an approximately 6,750-year-old British aurochs bone and genome sequence data from 81 additional cattle plus genome-wide single nucleotide polymorphism data from a diverse panel of 1,225 modern animals. Results Phylogenomic analyses place the aurochs as a distinct outgroup to the domestic B. taurus lineage, supporting the predominant Near Eastern origin of European cattle. Conversely, traditional British and Irish breeds share more genetic variants with this aurochs specimen than other European populations, supporting localized gene flow from aurochs into the ancestors of modern British and Irish cattle, perhaps through purposeful restocking by early herders in Britain. Finally, the functions of genes showing evidence for positive selection in B. taurus are enriched for neurobiology, growth, metabolism and immunobiology, suggesting that these biological processes have been important in the domestication of cattle. Conclusions This work provides important new information regarding the origins and functional evolution of modern cattle, revealing that the interface between early European domestic populations and wild aurochs was significantly more complex than previously thought

Influence of phenological barriers and habitat differentiation on the population genetic structure of the balearic endemic Rhamnus ludovici-salvatoris Chodat and R. alaternus L

[EN] Rhamnus ludovici-salvatoris, endemic to the Gymnesian Islands, coexists with the related and widespread R. alaternus in Mallorca and Menorca. In both species, the population genetic structure using RAPD, and flowering during a 3-year period to check for possible phenological barriers, were analyzed. Rhamnus ludovici-salvatoris showed lower genetic diversity and stronger population structure than R. alaternus, the Cabrera population being less diverse and the most differentiated. Rhamnus ludovici-salvatoris flowered one month later, although flowering of both species coincided sporadically. These congeners seem to have diverged through isolation by time and differentiation in habitat. The population genetic structure of R. ludovici-salvatoris could mainly be due to the existence of small populations on the one hand, and a gene flow caused by rare hybridization events on the other, which may also explain the presence of morphologically intermediate individuals in Menorca. 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Close 3D proximity of evolutionary breakpoints argues for the notion of spatial synteny

<p>Abstract</p> <p>Background</p> <p>Folding and intermingling of chromosomes has the potential of bringing close to each other loci that are very distant genomically or even on different chromosomes. On the other hand, genomic rearrangements also play a major role in the reorganisation of loci proximities. Whether the same loci are involved in both mechanisms has been studied in the case of somatic rearrangements, but never from an evolutionary standpoint.</p> <p>Results</p> <p>In this paper, we analysed the correlation between two datasets: (i) whole-genome chromatin contact data obtained in human cells using the Hi-C protocol; and (ii) a set of breakpoint regions resulting from evolutionary rearrangements which occurred since the split of the human and mouse lineages. Surprisingly, we found that two loci distant in the human genome but adjacent in the mouse genome are significantly more often observed in close proximity in the human nucleus than expected. Importantly, we show that this result holds for loci located on the same chromosome regardless of the genomic distance separating them, and the signal is stronger in gene-rich and open-chromatin regions.</p> <p>Conclusions</p> <p>These findings strongly suggest that part of the 3D organisation of chromosomes may be conserved across very large evolutionary distances. To characterise this phenomenon, we propose to use the notion of spatial synteny which generalises the notion of genomic synteny to the 3D case.</p