Evolution de la composition en acides gras d'un phytoplancton lacustre (Lac Pavin,France)

Fatty Acid Composition of Lacustrian Phytoplankton (Pavin Lake, France) Fatty acid composition of lacustrian phytoplankton was established during a study carried out on Lake Pavin (France) from May to September 1981. Fatty acid spectra point out even numbers of carbon atoms (ranging from 14 to 22) and in particular unsaturated fatty acids preponderance. In addition, the occurrence of some unsaturated fatty acids is directly linked to phytoplankton taxonomic composition, but also to physiological state of the cells. Lastly, the main types of phytoplankton populations differ in the degree of unsaturation of their total fatty acids.     

Presence de Gazella deperdita (Gervais) 1847 du gisement du Miocene superieur (Turolien) des Mistrals (Vaucluse,Sud-Est de la France)

Among the two bovid genera represented in the turolian locality Mistrals I, Gazella and Miotragocerus, the most abundant is a gazelle which, after comparison with Gazella deperdita from the Mont-Luberon, turns out to belong to this species. Resemblances between the two faunas, already noticed in the study of the Hipparions, are thus comfirmed.     

Biostratigraphie des Terebratulidae et des Zeilleriidaedu lias et du Dogger de la region toulonnaise (Var,France)

A lot of brachiopods have been sampled in stratigraphically well-defined beds of Liassic and Dogger periods in the region of Toulon (South of France). Now, numerous terebratulid and zeilleriid species are studied (in progress), the main biostratigraphic results of which are developed here in (fig. 1).     

Facteurs de limitation des populations d'Aphis fabae dans l'ouest de la France

Résumé Dans l'ensemble d'études consacrées aux épizooties àEntomophthoraceae surAphis fabae (Scopoli) en Bretagne, ce travail présente les résultats obtenus de 1972 à 1974 à l'aide d'échantillons importants (100 à 300 plantes). Ces résultats concernent principalementNeozygites fresenii (Now.)Remaudière & Keller. En 1972, les conditions climatiques sont tamponnées et constamment favorables aux mycoses. Le nombre d'aphides sains et d'aphides mycosés suit une évolution exponentielle particulièrement régulière; l'effet (évolution du pourcentage de mycosés) n'en est pas moins très brusque. L'arrivée des mycoses dans la parcelle a lieu en même temps que celle des pucerons, ce qui plaide en faveur d'une contamination exogène à laquelle prendraient part les ailés de différentes espèces. Le début du développement de la maladie n'est pas homogène dans l'espace. Les tout premiers mycosés apparaissent dans n'importe quelle colonie, mais très vite on constate que ce sont les colonies les plus grosses qui comportent le plus de mycosés. Cependant, cette relation, qui reste valable pendant la suite de l'épizootie, est très lache. A un moment donné de son déroulement, quelle que soit la taille des colonies concernées, il y a une large gamme de variabilité dans leur taux de parasitisme. Les formes adultes sont systématiquement plus mycosées que les formes larvaires, mais la différence s'amenuise jusqu'à s'annuler à la fin de l'épizootie. En juillet, selon les années, les pucerons mycosés peuvent ou non former des spores durables; en 1972, seulement 2,6 % d'entre eux en forment, mais la répartition de ces individus dans le champ est très homogène.

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Summary This 4th study on epizootics that occur in the populations of the black bean aphid in Brittany, deals with data obtained between 1972 and 1974 using large samples (100 to 300 plants). The results concern mainlyNeozygites fresenii (Nowak) Remaudière & Keller. In 1972, the weather was not very changeable and always favourable for the fungi (table 1). The number of healthy aphids as well as the number of diseased ones, followed a remarkably regular exponential curve. As a result, the variation of the percentage of dead aphids was very sudden (fig. 1, fig. 2). The disease appeared in the fields at the same time as the aphids themselves; so it is possible to think that several species of winged aphids play a part in the introduction of the 1st inoculum into the field (table 2). At its beginning, the development of the disease was not homogeneous in space (table 4). The foremost diseased aphids could be found in any colony whatever its size, but before long it was found that the biggest colonies contained the greatest number of diseased aphids (table 3). Though this relation remained during the continuation of the epizooty, it was a loose one (table 5). At a given time, within colonies of a given size, the percentage of dead aphids was very variable (fig. 3). The adults (winged and apterae)_were systematically more diseased than the nymphs, but the difference became smaller as time went on, and it finally disappeared at the end of the epizooty (table 6). Some years in July, the diseased aphids could form resting spores; in 1972, 2.6% of them formed resting spores, and the spatial dispersion of these individuals was very regular (table 7).

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Les 3 premiers mémoires de cette étude ont été publiés dansEntomophaga respectivement parRobert, Rabasse & Scheltes (18, 1973, 61–75) parRabasse & Robert (20, 1975, 49–63) et parDedryver (23, 1978, 137–151).     

The physical structure and dynamics of a deep,meromictic crater lake (Lac Pavin,France)

The characteristic feature of the physical structure of Lac Pavin is a distinct and permanent chemically induced density increase between about 60 and 70 m depth. This chemocline separates the seasonally mixed mixolimnion from the monimolimnion, which is characterized by elevated temperature and salinity as well as complete anoxia. Previously published box-models of the lake postulated substantial groundwater input at the lake bottom, and consequently a short water residence time in the monimolimnion and high fluxes of dissolved constituents across the chemocline. We present a new view of the physical structure and dynamics of Lac Pavin, which is based on the results of high-resolution CTD profiles, transient and geochemical tracers (tritium, CFCs, helium), and numerical modeling. The CTD profiles indicate the existence of a sublacustrine spring above rather than below the chemocline. A stability analysis of the water column suggests that vertical turbulent mixing in the chemocline is very weak. A numerical one-dimensional lake model is used to reconstruct the evolution of transient tracer distributions over the past 50 years. Model parameters such as vertical diffusivity and size of sublacustrine springs are constrained by comparison with observed tracer data. Whereas the presence of a significant water input to the monimolimnion can clearly be excluded, the input to the mixolimnion – both at the surface and from the indicated sublacustrine spring – cannot be accurately determined. The vertical turbulent diffusivity in the chemocline is well constrained to K 5×10^-8 m² s^-1, about a factor of three below the molecular diffusivity for heat. Assuming thus purely molecular heat transport, the heat flow through the chemocline can be estimated to between 30 and 40 mW m^-2. With respect to dissolved constituents, the very weak turbulent diffusive exchange is equivalent to a stagnant monimolimnion with a residence time of nearly 100 years. Based on these results and vertical concentration profiles of dissolved species, diffusive fluxes between monimolimnion and mixolimnion can be calculated. A large excess of helium with a ³He/⁴He ratio of (9.09 ± 0.01)×10^-6 (6.57 R _a) is present in the monimolimnion, clearly indicating a flux of magmatic gases into the monimolimnion. We calculate a flux of 1.0×10^-12 mol m^-2 s^-1 for mantle helium and infer a flux of 1.2×10^-7 mol m^-2 s^-1 (72 t year^-1) for magmatic CO₂. The monimolimnion appears to be in steady state with respect to these fluxes.     

Repartition spatio-temporelle,biomasse et production des populations zooplanctoniques du lac d'aydat en periode estivale

Lake Aydat is a young eutrophic lake (mean depth 7.4 m, area 6o ha) situated in the french Central Massif. Secondary production was studied during the summer months June and July. In early summer, dissolved oxygen in the deep layers gradually gets depleted, and depletion reaches the 7m level in July. Zooplankton is therefore concentrated in the upper layers: Rotatoria are very abundant and the various species are segregated in space and / or succeed each other in time, thus maximally exploiting the water layers favorable to their development. Cladocera are represented by small species, which sharply increase in numbers at the time of maximum primary production, and cause a dramatic drop in primary production. They are in competition with the Rotatoria. Copepods are the least abundant group, but they were in a reproductive phase at the time of this study.88% of the Zooplankton biomass is accumulated in the Cladocera; the Rotifera represent 9%, and the Copepods 8%. Secondary production is intense, and due almost exclusively to filter-feeders in July. Since the carnivores are scarce in numbers, their maximum production is poor relative to that of the herbivores.The P/B coefficient was extremely high during the two summer months, and is indicative of a process of intense consumption of the resources of the lake during that particular short period of the year.     

Sur la presence de vegetaux a structure conservee du Viseen dans le poudingue mosaique du Stephanien du bassin de Saint-Etienne (France)

Upper Visean plant-bearing cherts have been discovered in association with others yielding a Stephanian A flora, in conglomerates (poudingue mosaïque) from the base of the Stephanian B at Grand'Croix. It confirms the distant source, from the Roanne region, of the Dinantian elements during the initial basin sedimentation and constitutes an excellent example of complex reworking of fossil plant material.     

Analyse de la structure fine des chromosomes du Gorille (Gorilla gorilla)

Summary Prometaphasic chromosomes of Gorilla, Homo and Pan are compared, using R, Q, T and H-bands techniques in complement of a previous work (Lejeune et al., 1973). Various mechanisms of chromosomal rearrangements are demonstrated with particular reference to heterochromatic segments. Some phylogenic conclusions are proposed.

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Zusammenfassung Prometaphase-Chromosomen von Gorilla, Mensch und Schimpanse werden mit hilfe der R-, Q-, T- und H-Bandentechnik verglichen; frühere Arbeiten (Lejeune et al., 1973) werden dadurch ergänzt. Verschiedene Mechanismen von Chromosomen-Rearrangements werden dargestellt; dabei finden die Heterochromatin-Segmente besondere Beachtung. Einige phylogenetische Folgerungen werden gezogen.

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Travail de l'E.R.A. n^o 47 du C.N.R.S.     

Utilisation des isotopes stables pour l’identification de l’origine du carbone dans la datation du charbon de bois du Paléolithique

Recent years have brought many results of radiocarbon dating the earliest periods of the Upper Palaeolithic that can bring light on the origins of figurative art by Sapiens or Neanderthals. These dates are often close to the limit of the field of radiocarbon dating; because they require measurements of the lowest amounts of radiocarbon, controls are particularly essential. Here we examine the case of the dating of charcoal, whose identification after decontamination is difficult. We suggest a method that does not require additional manipulation to determine whether carbon comes exclusively from charcoal: using the proportion of stable carbon isotopes 13C/12C which is often regarded as a signature (δ13C).     

Presence de pollens d'Hamamelis (Hamamelidaceae,Angiospermae) dans le pliocene du Sud de la France

Pollen-analysis shows the presence of the genus Hamamelis in the pliocene flora of southern France. It contributesto the knowledge of the past distribution of taxa which are now extinct in western Europe.     

Importance des racines seminales et adventives pour la croissance et la nutrition cationique du sorgho-grain (Sorghum dochna)

Resume Le système radiculaire normal du sorgho (T) est réduit à sa partie adventive (A) ou à sa partie séminale (S). Les racines séminales seules sont incapables d'assurer à long terme une croissance normale et une nutrition cationique satisfaisante; par contre, la présence des seules racines adventives suffit à assurer un développement normal de la plante. L'importance physiologique des deux types de racines est essentiellement liée, dans nos conditions expérimentales en culture hydroponique, à leur développement quantitatif. Bien qu'ayant une composition minérale très différente, les deux types de racines ne jouent pas de r?le différent dans l'alimentation cationique du sorgho. re]19750211

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Summary The whole root system (T) of sorghum is reduced to either its adventitious (A) or its seminal (S) parts. Seminal roots alone fail to allow the plant a normal growth and a satisfactory cationic nutrition. Adventitious roots alone are able to allow a normal plant development. The physiological significance of both kinds of roots essentially depends on their quantitive development, under the experimental conditions used (hydroponic culture). Although their mineral content is very different, there is no evidence that seminal and adventitious roots have a significantly different behaviour in the cationic nutrition of sorghum.

     

Chronostratigraphie de la fin de la derniere glaciation,a la lumiere des resultats de l'etude lithostratigraphique et palynologique du site de Maisieres-Canal (Belgique)

The upper part of the palaeoclimatic sequence of Maisières-Canal shows a succession of four mild episodes at thetransition between the Pleniglacial and the Late-Glacial. Those four mild fluctuations are respectively correlated with Langerie, Lascaux, Angles-sur-l'Anglin and Pré-Bölling oscillations.     

Evidence for a diurnal variation in the carotenoid content of acanthodiaptomus denticornis (Crustacea,copepoda) in Lac Pavin (Auvergne,France)

In Lac Pavin Acanthodiaptomus denticornis was found to be intensely reddish-orange coloured by keto-carotenoids of the astaxanthin type. Such pigments are not normally found in phytoplankton algae, and apparently these carotenoids result from the metabolism of pigments of dietary origin. The carotenoid content of the zooplankton showed a distinct 2.5-fold diurnal variation, with a minimum at night time and a maximum in the early morning. The possible impact of a diurnal difference in zooplankton feeding activity is discussed.     

Synthèse sur la flore des nodules du Lagerstätte de Montceau-les-Mines (Carbonifère supérieur,France)

The flora from the Montceau-les-Mines Lagerstätte (Late Pennsylvanian, Stephanian, France) is preserved in small sideritic nodules and was studied in three locations in the (1) Saint-Louis, (2) Saint-François, and (3) Sainte-Hélène opencast mines. Qualitative and quantitative analyses of plant diversity and floristic composition in about 7000 nodules indicate substantial variations in the floral composition of these opencast mines. More than 50 taxa are recognized and belong to groups typical of the Late Carboniferous flora (lycopsids, sphenopsids, tree ferns, and pteridosperms). Arborescent sphenopsids and tree ferns were the major components at Saint-Louis, whereas the flora from Saint-François consisted mainly of pteridosperms; the one from Sainte-Hélène has a more balanced composition. Taphonomic and sedimentological data show that the flora contained in the nodules was hypoautochthonous to parautochthonous. The Montceau Basin displayed a mosaic of paleoenvironments (e.g., deltaic lacustrine, paludal to fluvial) which favored colonization by plants and animals.