Le beach-rock de Temae (île de Moorea - Polynésie française) : signification géomorphologique et processus diagénétiques

Les beach-rocks de Temae (Moorea, Polynésie française) présentent un premier stade de cimentation lié à l'activité cyanobactérienne. Un réseau filamenteux microbien superficiel suffit à bloquer le sédiment et à lancer le processus d'induration. Ces observations viennent confirmer les résultats obtenus récemment dans les Cyclades, montrant par là que les paramètres climatiques et hydrodynamiques sont loin d'être les seuls pour expliquer la naissance d'un beach-roc

No signs of inbreeding despite long-term isolation and habitat fragmentation in the critically endangered Montseny brook newt (Calotriton arnoldi)

Endemic species with restricted geographic ranges potentially suffer the highest risk of extinction. If these species are further fragmented into genetically isolated subpopulations, the risk of extinction is elevated. Habitat fragmentation is generally considered to have negative effects on species survival, despite some evidence for neutral or even positive effects. Typically, non-negative effects are ignored by conservation biology. The Montseny brook newt (Calotriton arnoldi) has one of the smallest distribution ranges of any European amphibian (8 km2) and is considered critically endangered by the International Union for Conservation of Nature. Here we apply molecular markers to analyze its population structure and find that habitat fragmentation owing to a natural barrier has resulted in strong genetic division of populations into two sectors, with no detectable migration between sites. Although effective population size estimates suggest low values for all populations, we found low levels of inbreeding and relatedness between individuals within populations. Moreover, C. arnoldi displays similar levels of genetic diversity to its sister species Calotriton asper, from which it separated around 1.5 million years ago and which has a much larger distribution range. Our extensive study shows that natural habitat fragmentation does not result in negative genetic effects, such as the loss of genetic diversity and inbreeding on an evolutionary timescale. We hypothesize that species in such conditions may evolve strategies (for example, special mating preferences) to mitigate the effects of small population sizes. However, it should be stressed that the influence of natural habitat fragmentation on an evolutionary timescale should not be conflated with anthropogenic habitat loss or degradation when considering conservation strategies

Multi-model seascape genomics identifies distinct environmental drivers of selection among sympatric marine species

Background As global change and anthropogenic pressures continue to increase, conservation and management increasingly needs to consider species’ potential to adapt to novel environmental conditions. Therefore, it is imperative to characterise the main selective forces acting on ecosystems, and how these may influence the evolutionary potential of populations and species. Using a multi-model seascape genomics approach, we compare putative environmental drivers of selection in three sympatric southern African marine invertebrates with contrasting ecology and life histories: Cape urchin (Parechinus angulosus), Common shore crab (Cyclograpsus punctatus), and Granular limpet (Scutellastra granularis). Results Using pooled (Pool-seq), restriction-site associated DNA sequencing (RAD-seq), and seven outlier detection methods, we characterise genomic variation between populations along a strong biogeographical gradient. Of the three species, only S. granularis showed significant isolation-by-distance, and isolation-by-environment driven by sea surface temperatures (SST). In contrast, sea surface salinity (SSS) and range in air temperature correlated more strongly with genomic variation in C. punctatus and P. angulosus. Differences were also found in genomic structuring between the three species, with outlier loci contributing to two clusters in the East and West Coasts for S. granularis and P. angulosus, but not for C. punctatus. Conclusion The findings illustrate distinct evolutionary potential across species, suggesting that species-specific habitat requirements and responses to environmental stresses may be better predictors of evolutionary patterns than the strong environmental gradients within the region. We also found large discrepancies between outlier detection methodologies, and thus offer a novel multi-model approach to identifying the principal environmental selection forces acting on species. Overall, this work highlights how adding a comparative approach to seascape genomics (both with multiple models and species) can elucidate the intricate evolutionary responses of ecosystems to global change

Life history, climate and biogeography interactively affect worldwide genetic diversity of plant and animal populations.

Understanding how biological and environmental factors interactively shape the global distribution of plant and animal genetic diversity is fundamental to biodiversity conservation. Genetic diversity measured in local populations (GDP) is correspondingly assumed representative for population fitness and eco-evolutionary dynamics. For 8356 populations across the globe, we report that plants systematically display much lower GDP than animals, and that life history traits shape GDP patterns both directly (animal longevity and size), and indirectly by mediating core-periphery patterns (animal fecundity and plant dispersal). Particularly in some plant groups, peripheral populations can sustain similar GDP as core populations, emphasizing their potential conservation value. We further find surprisingly weak support for general latitudinal GDP trends. Finally, contemporary rather than past climate contributes to the spatial distribution of GDP, suggesting that contemporary environmental changes affect global patterns of GDP. Our findings generate new perspectives for the conservation of genetic resources at worldwide and taxonomic-wide scales

L'Archaïe : une région aux paysages fragiles et instables

Paysages d'Archaïe II, Dymè et son territoire, Actes du colloque « Dymè », p. 11-2

Bahreïn. l'exception naturelle du golfe

Exposition présentée à l'Institut du Monde Arabe du 18 mai au 29 août 199

Morphogenèse en Méditerranée orientale à l'époque historique

International audienc

Les variations récentes de la ligne de rivage à Chypre. Résumés

Colloque de Paris, 5-6 novembre 199

De la nécessaire prise en compte des sédiments dans la connaissance des variations récentes de la ligne de rivage : les exemples d'Aghios Andreas (Grèce) et de Guverdjine Kaya (Syrie)

International audienceLes études de morphodynamique littorale accordent de plus en plus un rôle prédominant à la tectonique et à ses manifestations brusques voire instantanées. Pourtant, une étude attentive des séquences sédimentaires montre que, dans de nombreux cas, il existe une origine autre que tectonique à l'évolution des littoraux ou bien que ce sont des mouvements tectoniques lents qui en sont la cause. Il semble en effet que les sédiments de plage, notamment au cours de leur cimentation,enregistrent mieux que d'autres supports rocheux les événements morphodynamiques que le littoral a vécus. C'est ce que montrent les deux exemples que nous avons choisi de comparer, la baie d'Aghios Andreas en Élide (Grèce) et la falaise calcaire de Guverdjine Kaya en Syrie. Dans ces deux cas, une interprétation fondée sur l'examen du substratum calcaire a d'abord conduit à expliquer l'histoire morphodynamique du secteur littoral considéré par un certain nombre de mouvements tectoniquesrapides. Mais une étude des épisodes sédimentaires concomitants démontre au contraire que les mouvements tectoniques ont été plus nombreux et que, de plus, certains d'entre eux ont été lent