Variations spatiales et saisonnières de la structure de groupements macrobenthiques littoraux en climat froid

Spatio-temporal variations of macrobenthic community structure were studied in the littoral zone of the Saint-Lawrence River (Québec). Its thermal regime is characterized by steep seasonal gradients from April to November and by a long ice-cover period with formation of an icefoot. Six sites were sampled each season for one year. Temporal variations are less important than spatial variations. They are mainly seasonal and depend on emergence and recruitment periods and on migrations but there are also long-term variations. An increase of the mean diversity index of sites corresponds to an increase of seasonal variations of community profile and to a decrease of seasonal variations of organism abundance; it is explained by a better exploitation of benthic resources rather than by environment stability. Spatial variations of community structure depend mainly on vegetation abundance. There is no faunal zonation corresponding to the icefoot action. In sites where Gastropods are abundant, icefoot does not change community profile but it explains diminutions of density and of species diversity. Chironomids are little affected by this phenomenon.     

dÉcologie des diatomées d'eau douce de la région centrale du Portugal

Tychoplanktonic and epilithic diatom samples were taken monthly during one year at 18 sites in small lowland rivers in the northern central region of Portugal. Canonical correspondence analysis was used to explore the relationships between measured environmental variables and patterns in the diatom assemblages. Conductivity, HCO₃⁻, and chemical oxygen demand (COD) were the most significant environmental variables influencing the structure of the tychoplankton and of the epilithon. Other less important variables, such as K⁺, Fe, N(NO₃⁻), and Na⁺ also explained significant (P < 0.05) amounts of variance. The ordination diagrams showed very similar distribution of the tychoplanktonic and epilithic diatom samples. At sites with similar geomorphology as in this study, it is possible to use only one of these samples for water quality evaluation. The optima and tolerances of some diatom taxa were calculated for the most influential variables. Although the diatoms showed high tolerances to some environmental parameters, it was possible to establish groups of taxa with defined and distinctive ecological preferences. Two species groups stood out depending on the alkalinity and mineralization of the water. With a moderate conductivity (> 600 μS·cm⁻¹), alkaline pH, HCO₃⁻ concentrations equal or higher than 150 mg·l⁻¹, the first group includes Achnanthes hungarica Grunow, Amphora pediculus (Kützing) Grunow, Bacillaria paxillifera (O. F. Müller) Hendey, Cymatopleura solea (Brébisson) W. Smith, Navicula accomoda Hustedt, Navicula lanceolata (Agardh) Ehrenberg, Navicula trivialis Lange-Bertalot, Nitzschia hungarica Grunow. In waters of lower conductivity (varying between 72 and 262 μS·cm⁻¹) slightly acid pH (6 to 6.5) and HCO₃⁻¹ lower than 46 mg·l⁻¹ the following species were common: Achnanthes oblongella Östrup, Achnanthes subatomoides (Hustedt) Lange-Bertalot, et Archibald, Cymbella gracilis (Ehrenberg) Kützing, Cymbella naviculiformis Auerswald, Diatoma mesodon (Ehrenberg) Kützing, and Eunotia exigua (Brébisson) Rabenhorst. Considering COD, two further groups were distinguished. At high values (> 40 mg·l⁻¹) the following taxa were observed: Achnanthes delicatula (Kützing) Grunow, Navicula capitata Ehrenberg var. hungarica (Grunow) Ross, Nitzschia nana Grunow, Pinnularia interrupta W. Smith, Thalassiosira pseudonana Hasle & Heimdal, Thalassiosira weisflogii (Grunow) Fryxell et Hasle. For lower values than 19 mg·l⁻¹, we found Cymbella naviculiformis Auerswald, Diatoma mesodon (Ehrenberg) Kützing, Eunotia exigua (Brébisson) Rabenhorst, Fragilaria arcus (Ehrenberg) Cleve, and Nitzschia epithemioides Grumow var. disputata (Carter) Lange-Bertalot.     

Le role ecologique de la température dans la distribution de deux espèces proches parentes de planaires d'eau douce: Etude expérimentale

Resumé Cette étude concerne l'influence de la température sur l'écophysiologie des deux espèces proches parentes de Planaires limnophiles: Polycelis tenuis et P. nigra, dans la region lyonnaise. Si les deux espèces font preuve de capacités voisines dans la zone des températures moyennes, la première l'emporte nettement dans les zones marginales, tant par sa tolérance à l'éffet létal de la chaleur que par son taux de reproduction au froid. En outre, l'existence de races physiologiques distinctes doit lui permettre de coloniser des milieux plus divers. P. tenuis apparait comme un animal vraiment eurytherme. Ces différents traits contribuent à expliquer l'habitat des deux espèces dans notre région.

---

Temperature as an ecological factor in the distribution of two closely related freshwater Triclads: an experimental study.The influence of temperature on the ecophysiology of two closely related limnophilic Triclads, Polycelis tenuis and P. nigra, in the Lyons region was investigated. Both species have the same physiological rate in the middle zone of the temperature range, but P. tenuis prevails at both ends of the range. It torelates higher temperatures and its reproduction rate is greater in the cold. Also, because of the existence of physiological races, it seems adapted to a greater diversity of situations. It appears as a real eurytherm These different points contribute an explanation for the habitat of both species in our region.

     

Variations de quelques aclivités enzymatiques (peroxydase, catalase, AIA-oxydase) et de la teneur en polyphénols au cours de la germination de I'Orge. Influence de la kinétine

Peroxidase catalase, IAA-oxidase and polyphenol content of growing barley coleoptile. Effect of kinetin. - Kinetin strongly inhibits root and coleoptile growth of germinating barley in the dark. Treated coleoptiles become senescent before the untreated ones. Soluble proteins content, peroxidase, catalase and IAA-oxidase activity were greatly increased in treated coleoptiles while the level of polyphenols was reduced. These biochemical effects joined with the other property of kinetin to diminish α-amylase synthesis in the endosperm are discussed in relation to growth and in connection with the classic view of a cytokinin retarded senescence.     

Facteurs influençant la structure des groupements de macro-invertébrés benthiques et phytophiles dans la zone littorale du Saint-Laurent (Québec)

In the littoral zone of the St-Lawrence River (Quebec, Canada), benthic and phytophilous macroinvertebrates were studied in order to find and to explain relationships between structure of these animal communities and abiotic (substrate, water depth, current velocity) or biotic (marophytes species) factors. Benthos was sampled at 16 sites in spring, when there was no macrophytic vegetation, and in summer. Phytomacrofauna was sampled at 30 sites in summer. The data were analyzed using simple and partial correlations, stepwise regression, reciprocal averaging and canonical correlation analysis.

     

Caractérisation des peuplements de macroinvertébrés benthiques à l’aide de la carte auto-organisatrice (SOM)

Macrobenthic organisms are much used nowadays as bio-indicators for their ability to reflect different disturbances of aquatic ecosystems. However, they have never been used to assess the ecological status of the lagoons of Benin. The current study aims at revealing the ecological state of the lagoon of Porto-Novo through the study of changes in the settlement of benthic organisms collected in this lagoon. The sampling was carried out from July 2007 to June 2009 on a frequency of four seasons of collection per year. The self-organizing map (SOM) of Kohonen has been used for various patterns of distribution of collected organisms. A discriminant analysis (AFD) has allowed the identification of the parameters that govern the patterns observed in this environment. Four groups of macrobenthic communities emerged that were well predicted (75%). The distribution of benthic macro invertebrates of this lagoon is therefore zonal, seasonal and discriminated by variables of mineralization and sediment grain size. The difference in taxonomic richness corresponds to environmental conditions of stations appearing more or less stable and highlighting a gradient of the stress on organisms. Places with unstable conditions are affected by human activities due to their proximity to homes that are enriched in organic matter. These places are full of polluted-tolerant species such as the Gastropods Potamididae, Cirratulidae Polychaetes, Diptera Chironomidae and Oligochaeta. The macrobenthic fauna, which is well differentiated in the groups, is then subjected to human disturbance.     

Inventaire des algues et phanérogames marines benthiques de la Tunisie

Abstract

Check list of the benthic marine flora of Tunisia. — 393 species, varieties, formae and stadii of algae and seagrasses are listed: 6 Bangiophyceae, 239 Florideophyceae, 1 Xanthophyceae, 82 Phaeophyceae, 20 Chlorophyceae, 45 Bryopsidophyceae and 5 seagrasses.     

Le comportement de la cellule végétale en présence de toxiques additionnés de substances tensio-actives

Résumé Le présent travail expose quelles sont les réactions de la cellule végétale lorsque cette dernière est soumise à l'association d'un toxique et d'un « mouillant » (Netzmittel).Les variables sont: la nature de la cellule végétale, celle du toxique et celle du mouillant.Alors que les mouillants cationiques, eux-mêmes toxiques, exercent une simple action additive, les mouillants anioniques révèlent dans de nombreux cas une synergie de toxicité. Celle-ci se manifeste surtout avec les champignons et les bactéries Gram+, les végétaux supérieurs se montrant indifférents. Cette synergie varie également avec la structure moléculaire du mouillant.Les mouillants non ioniques peuvent au contraire exercer une action antagoniste, c'est-à-dire diminuer la toxicité.Ce dernier phénomène se produit dans certains cas à la suite d'une réaction chimique entre le mouillant et le toxique; la nature de la cellule est alors indifférente. Dans d'autres cas, il y a absence de réaction chimique et le phénomène ne se produit qu'avec certains types de cellules (champignons surtout).La nature chimique du toxique joue, dans la synergie, un rôle moins important que dans l'antagonisme.Des hypothèses sont formulées pour tenter d'élucider le mécanisme des cas de synergie et d'antagonisme.     

Les communautés lombriciennes 120 ans après la restauration forestière de sols érodés sur marnes

One hundred and twenty years after restoration of badlands by reforestation with Pinus nigra Arn. ssp. nigra, the analysis of the soils on marls of the Saignon experimental watershed (Alpes-de-Haute-Provence) demonstrates the potentialities and the driving forces behind the distribution of earthworms in the main site types. The communities are young, and density and biomass are low to normal (up to 49 individuals and 27 g·m⁻², respectively) for these low productivity pine woods. Two main site-directed trajectories would lead marls to a mixed species association: the first one is initiated by the epi-anecic behaviour of Lumbricus terrestris L. in xeric conditions (south-oriented slope, thin soil); the second is initiated by Octolasion cyaneum Sav. (north-oriented slope).     

Étude en microscopie électronique et par cytophotométrie à balayage de la structure et de la distribution de la chromatine dans les noyaux des cellules cartilagineuses deTriturus cristatus âgés au cours de la régénération

Résumé Les cellules cartilagineuses des membres postérieurs deTriturus cristatus en régénération après amputation, ont été étudiées en microscopie électronique et par cytophotométrie à balayage. Nous nous sommes intéressés à la structure et à la distribution de la chromatine mais aussi à différents organites cytoplasmiques. Dans l'étude de cytophotométrie à balayage, la chromatine a été considérée à travers son constituant majeur, l'ADN, coloré par la réaction de Feulgen. Au cours de la régénération du membre, l'hétérochromatine initialement condensée, essentiellement accolée à la membrane nucléaire se décondense. Les vacuoles du cytoplasme, caractéristiques des animaux âgés par rapport aux animaux jeunes, disparaissent, les mitochondries et le reticulum endoplasmique rugueux deviennent plus abondants. Les caractéristiques nucléaires de l'activation cellulaire apparaissent précocement, précédent les modifications cytoplasmiques et conduisent à des cellules en tous points identiques aux cellules d'animaux jeunes en dehors de tout processus régénératif. Cette phase d'euchromatisation et de restructuration cytoplasmique est peut-être nécessaire à l'accroissement d'activité métabolique et à la division cellulaire qui suivent. Son déroulement peut expliquer tout au moins le ralentissement de la régénération observé chez les animaux âgés par rapport aux animaux jeunes.

---

Electron microscopic and scanning cytophotometric study of chromatin structure and distribution in nuclei of cartilaginous cells of agedTriturus cristatus during regeneration

Summary Cartilaginous cells of aged newts (Triturus cristatus) were studied during hind limb regeneration. The electron microscope was used to study the structure and distribution of chromatin in the cell nuclei, while the DNA content of the chromatin was measured by means of a scanning cytophotometer.Changes in the ultrastructure of the cytoplasm during regeneration were also studied.It was observed that the structure and distribution of chromatin in the activated cell is greatly modified. In the non-activated cell of the aged newt, the chromatin is found highly condensed and distributed peripherally close to the nuclear membrane. In contrast, in the activated cells, the chromatin is much less condensed and is distributed throughout the nucleus. Moreover, cytoplasmic vacuoles, found only in the non-activated aged cells, disappear and an increase in the mitochondria and rough endoplasmic reticulum is also observed.Changes in the nuclear structure are observed prior to the cytoplasmic modifications.It is interesting to note that the process of activation induces structural changes in the aged cells which make these cells appear to be structurally identical to the young cells. This process of rejuvenation takes 3–5 days in the newt.We suggest that these structural changes of the chromatin and cytoplasm in the aged cells are necessary to increase the metabolic activity which precedes cell division. It may also explain why regeneration takes a longer time in the aged animals than in the young ones.

     

Essai d'une théorie de la stabilité de la structure des sols

Sans résumé     

Étude de la variabilité de la clairance hépatique de la mébrofénine-99mTc en scintigraphie hépatobiliaire

AimThe purpose of this study was to investigate some of the parameters likely to influence mebrofenin-^99mTc hepatic clearance calculation and inter-and intra-observers reproducibility.Materials and methodsHepatic clearance (%/min m²) of 30 scintigraphies was calculated from the values of hepatic, cardiac, and total activities, according to the method recommended in the literature. We studied: 1) impact of injection–acquisition delay variations; 2) acquisition type: anterior face only (FA) or geometric mean (GM); 3) clearances calculated according to four different body surface area (BSA) formulas; 4) intra-and inter-observers reproducibility for three observers (two evaluations for each observer).Results1) Clearance differences between different studied intervals were statistically significant, more important if the studied interval was far from reference interval (150–350 secondes) and even more when the interval studied was too early (110–310 secondes). 2) There was a statistically significant difference between clearance calculated using either FA or GM datasets (0.85 %/min m²). 3) There were small but statistically significant differences for four of the clearance comparisons using different BSA formulas. 4) Despite differences in size of cardiac and hepatic regions of interest (ROI), intra-observer reproducibility of hepatic clearance was excellent for each observer. Inter-observers reproducibility was also excellent (r = 0.982).ConclusionHepatic clearance of mebrofenin-^99mTc appears to be a highly reproducible method provided that acquisition and clearance calculation are standardized. It provides additionnal functional information to morphological and biological data usually performed before major hepatectomy. Thereby, the definition of a standardized protocol would enable realization of multicentric studies.     

La structure logique de la contre-épreuve expérimentale

Résumé Claude Bernard a réservé à la contre-épreuve un rôle fondamental dans le raisonnement expérimental. Il a soutenu que la seule preuve qu'un phénomène joue le rôle de cause par rapport à un autre, c'est qu'en supprimant le premier on fait cesser le second. Cependant, la contre-épreuve expérimentale n'en reste pas moins une expérimentation; la structure logique des deux, preuve et contre-épreuve, est la même. Or, si la preuve exige la contre-épreuve, la dernière à son tour exige la première comme sa contre-épreuve. On arrive ainsi à une suite infinie d'expérimentations dont chaque membre se rapporte à l'autre comme soit à sa preuve, soit à sa contre-épreuve. Cependant, ce travail expérimental, qui s'arrête dans sa réalité à un moment choisi, il est vrai, plus ou moins arbitrairement, se poursuit dans la pensée de l'expérimentateur passant ainsi des résultats individuels à leur généralisation. Au sein du raisonnement expérimental il y a donc un raisonnement analogique et c'est le sentiment du déterminisme (Claude Bernard) et la pensée causale qu'il implique plutôt que le nombre des preuves et contre-épreuves qui surgissent comme les seuls critères de la vérité expérimentale.

---

Summary Claude Bernard ascribed to the counter-proof a fundamental role in his experimental method and the reasoning on which the method rests. He saw the only proof of the causal nature of a given phenomenon in the fact that the effect fails to appear after elimination of the alleged cause. However, the experimental counter-proof still remains an experiment; the logical structure of both proof and counter-proof, is the same; it is true that the proof calls for a counter-proof; but the latter in its turn calls for the proof as for its counter-proof. One thus arives at an infinite chain of experiments, each link referring to each other as to its proof or counter-proof. This experimental work, nevertheless, comes to its end, though at a moment still chosen more or less arbitrarily; the work continues however in the thought of the experimenter, thus passing from individual results to generalization. There is embodied in the experimental method and in experimental thought a reasoning by analogy. The sense of determinism (sentiment du déterminisme:Claude Bernard) and the causal thought on which this sense rests rather than the number of proofs and counter-proofs emerge as the ultimate criteria of experimental truth.

---

Zusammenfassung Claude Bernard hat dem experimentellen Gegenbeweis (oder Kontrollversuch) eine hervorragende Stellung in seiner experimentellen Methode und dem ihr zugrundeliegenden Denkvorgang eingeräumt. Seiner Überzeugung nach ist der einzige Beweis der ursächlichen Natur eines Faktors darin zu suchen, dass die Wirkung ausbleibt, wenn man den als Ursache angeschuldigten Faktor ausschaltet. Indessen ist auch der experimentelle Gegenbeweis nichts anderes und nicht mehr als ein Experiment. Beide, Experiment und Gegenexperiment, haben die gleiche logische Struktur. Wenn demnach jedes Experiment den Gegenbeweis verlangt, so bedarf auch der Gegenbeweis seinerseits des Beweises als seines Gegenbeweises. So gelangt man schliesslich zu einer unendlichen Kette von Experimenten, deren jedes Glied sich zu jedem anderen wie zu seinem Beweis oder Gegenbeweis verhält. Diese experimentelle Arbeit wird aber in einem mehr oder weniger willkürlich gewählten Augenblick abgebrochen; sie wird indessen in Gedanken vom Experimentalforscher fortgesetzt, der auf diese Weise schliesslich von den Einzelresultaten zu ihrer Verallgemeinerung schreitet. Innerhalb der experimentellen Methode trifft man also auf ein Denken nach Analogie. DerBernard-sche Kausal sinn (le sentiment du déterminisme) und das diesem zurgrundeliegende kausale Denken, nicht aber die Anzahl der experimentellen Beweise und Gegenbeweise sind es, welche die letzten Kriterien der experimentellen Wahrheit enthalten.

     

Observations sur la végétation de la zone littorale en Provence

Sans résuméReçu par la rédaction le 1.VII.1953.