History and biogeography of the mangrove ecosystem,based on a critical reassessment of the paleontological record

The geological record of mangrove plants is based on comparablemorphological characteristics of pollen, fruits and wood, of fossil andmodern species. But this record relies on the assumption that the ecologicaland habitat preferences of ancestral taxa have remained similar throughages. A reexamination of fossil evidence of Avicennia, Pelliciera,Sonneratia, Rhizophora, Bruguiera, Ceriops, etc.reveals that the modern mangrove flora was pantropic by the Eocene, andappears to have originated during Paleocene times. Earlier Paleozoic andMesozoic candidates for a mangrove ecology lack conclusive evidence oftheir exclusive association with tidal environments. It is therefore clear thatcontinental drift had a limited role in the dispersal and development ofmodern mangrove floras. The Eocene/Oligocene boundary crisis appears toherald a beginning of the biogeographic split between the current-dayeastern and western provinces of mangrove plants. But, while the climaticorigins of this major disjunction is not clearly understood, our reassessmentof Tertiary paleoclimates suggests that the major cooling events of themiddle Paleocene, the end of the Eocene and the middle Pliocene were themost likely influences on the evolution of mangrove floras. The associatedinvertebrates, especially molluscs, further support our assertion that amodern mangrove ecosystem was established only during the earliestEocene times. We summarize our interpretation in a set of 9 palinspasticmaps of fossil mangrove genera through their evolution ending with thecurrent, bipartite distribution of present day taxa.     

Un sol de mangrove fossilise dans les lignites du Soissonnais (Ypresien) a Verzenay (Marne)

At Verzenay, in the Reims area, the upper part of the “Lignites du Soissonnais” have been turned into a paleosol. A petrographical and geochimical study of this profile allow us to see there a fossilized mangrove soil.A palynological study carried out on the same samples shows typical taxons of the mangrove environment (Nypa, Bruguiera, Acrostichum aureum). Then, palynological results perfectly agree with the sedimentological interpretation.     

Molecular packing parameters of bipolar lipids.

The bipolar lipid fractions extracted from the thermophilic archaeobacterium Sulfolobus solfataricus have different chemical structures and geometrical shapes. The conditions which lead to the formation of vesicles were investigated in order to study the self-assembly of these molecules. Such conditions are fulfilled when an appropriate mixture of two different molecular species (both bipolar or bipolar and monopolar) is used. According to the theory introduced by Israelachvili and co-workers, lipid self-assembly results from the balance of interaction free energy, entropy and molecular geometry. We have shown that this theory can be extended to bipolar lipids, in spite of their more complex nature, and the experimental results obtained combining 1H-NMR, light scattering and entrapped volume techniques closely match theoretical expectations. To carry out calculations, it was necessary to introduce hypotheses about the disposition of bipolar molecules in the vesicle membrane. These hypotheses have been tested indirectly by measuring the transport properties mediated by carriers or channels, whose transport mechanism can be considered to be a probe of the membrane structure.