Etude Ultrastructurale de Différents Types de Kystes d'Opalines

Deux types de structure kystique ont été observés au microscope éectronique. Dans le ler, qui correspond aux kystes d'infection ou gamontokystes, la cellule est relativement libre dans l'enveloppe kystique. Celle-ci est formée de 2 couches distinctes d'inégale épaisseur (ectokyste, endokyste) sécrétées par la cellule et doublées intérieurement par un mince feuillet cytoplasmique dûà une extension des plis cuticulaires. C'est la seule modification du cortex cellulaire. Par contre, dans le 2ème type les modifications sont beaucoup plus importantes. La cellule est étroitement accolée aux parois du kyste; crêtes et flagelles ont disparu de la surface. Cependant on retrouve leurs traces dans la région corticale, sous forme d'axonèmes intracytoplasmiques plus ou moins désorganisés et d'empilements de saccules associés à des rangées de microtubules. Ce seraient des kystes de résistance. Les structures observées dans ces derniers kystes nous permettent de discuter quelques idées sur la participation des microtubules et des systèmes membranaires à la morphogénèse du cortex des Opalines.     

ARCHAEORADIOLITES, A NEW GENUS FROM THE UPPER APTIAN OF THE MEDITERRANEAN REGION AND THE ORIGIN OF THE RUDIST FAMILY RADIOLITIDAE

Abstract:  Archaeoradiolites gen. nov. (Radiolitidae), mainly characterized by radially arranged branching walls structuring the outer shell layer, includes two species, Archaeoradiolites primitivus gen. et sp. nov. and Archaeoradiolites hispanicus gen. et sp. nov. (type species), the distinction of which is based on size, shell habit and development of the radially branching microstructure. Their geographical distribution is restricted to south-east Spain and south-west France, i.e. the Western European Tethyan margin, whereas data from the Black Sea coast of Turkey suggest a possible extension to the Eastern European Tethyan margin. Each species has a distinct biostratigraphic distribution within the Upper Aptian (mainly the Gargasian). Agriopleura is suggested to be the direct ancestor of Archaeoradiolites, which in turn is considered as the progenitor of Eoradiolites. The onset of the Radiolitidae is associated with global oceanic changes that favoured calcite as opposed to aragonite biomineralization. The acquisition of a porous shell microstructure appears, in many respects, biologically advantageous and may account for gaining a rapid (< 1 myr) ecological ability for efficient colonization and occupation of space of the family in the earlier phase of its radiation.     

Extensive Predator Space Use Can Limit the Efficacy of a Control Program

ABSTRACT Reduced to small isolated groups by anthropogenic habitat losses or habitat modifications, populations of many endangered species are sensitive to additive sources of mortality, such as predation. Predator control is often one of the first measures considered when predators threaten survival of a population. Unfortunately, predator ecology is often overlooked because relevant data are difficult to obtain. For example, the endangered Gaspésie caribou (Rangifer tarandus caribou) has benefited from 2 periods of predator control that targeted black bears (Ursus americanus) and coyotes (Canis latrans) in an attempt to reduce predation on caribou calves. Despite a high trapping effort, the number of predators removed has remained stable over time. To assess impact of predator movements on efficacy of a control program, we studied space use of 24 black bears and 16 coyotes over 3 years in and around the Gaspésie Conservation Park, Quebec, Canada, using Global Positioning System radiocollars. Annual home ranges of black bears averaged 260 km² and 10 individuals frequented area used by caribou. Annual home ranges of resident coyotes averaged 121 km², whereas dispersing coyotes covered >2,600 km². Coyotes were generally located at lower altitudes than caribou. However, because coyotes undertook long-distance excursions, they overlapped areas used by caribou. Simulations based on observed patterns showed that 314 bears and 102 coyotes potentially shared part of their home range with areas used by female caribou during the calving period. Despite low densities of both predator species, extensive movement and use of nonexclusive territories seem to allow predators to rapidly occupy removal areas, demonstrating the need for recurrent predator removals. Our results underscore the necessity of considering complementary and alternative solutions to predator control to assure long-term protection of endangered species.     

Photoperiodism and seasonal breeding in aquatic and terrestrial Eumalacostraca

Summary

Seasonal reproduction in Crustacea is synchronized by environmental cues (e.g., temperature and photoperiod). Two types of responses occur: (1) in reptant decapods, short photoperiods and low temperatures are necessary to induce vitellogenesis; (2) in natant decapods and in most peracarids, both high temperatures and long photoperiods promote the onset of reproduction. In this context studies on the biological clocks involved in photoperiodic time measurement were performed on two crustaceans: the ditch shrimp Palaemonetes varians and the woodlouse Armadillidium vulgare, which is distributed worldwide outside polar and intertropical areas. The most important feature of the photoperiodic response curves was the same mean lag time in response to photophase length ≤ 12 h: short photophases delayed breeding but did not prevent it (i.e., “short-day effect”). On the contrary, long photophases promoted the onset of reproduction (i.e., “long-day effect”) differently in P. varians and A. vulgare. In A. vulgare strains the shape of the photoperiodic response curve depended on latitudinal origin. Results of “resonance” experiments provided evidence of involvement of an endogenous circadian component in the photoperiodic clocks of the two species according to the internal coincidence model developed for insects. Seeing that relations between reproduction and moulting were different in the two species, we proposed the hypothesis of an evolutionary change in the transition from the sea to the continental environment.     

DETERMINATION OF SENSORY OIL-WATER PARTITION COEFFICIENTS OF SINGLE AROMA COMPOUNDS COMBINING PANELIST FREE INTENSITY RATING AND THEORETICAL MODELING OF ODOR INTENSITY

Using an intensity rating with no external calibration, experiments were designed to measure the sensory oil-water partition coefficients of four aroma molecules (benzaldehyde, ethyl butyrate, linalool and acetophenone) as the ratios of concentration producing stimuli of equivalent intensities. Flavored water and oil phases were successively assessed for odor intensity by 24 panelists who were given total freedom regarding scaling strategy. Each session combined five concentration levels of three out of the four studied aromas in a solvent (water or oil). A predominant concentration effect was found for each aroma in both solvents and concentration dependencies of perceived intensity above water and oil were similar. Experimental data were modeled with Fechner, Stevens and Hill equations. Combining results above water and oil solutions to feed a common model led to the evaluation of an overall sensory oil-water partition coefficient for each aroma compound. All three models produced similar partition coefficient values for each aroma that were lower than the related instrumental partition coefficients. Biases previously detected when external calibration had been used were reduced in a large proportion while suggested enhancement of odor intensity by water vapor could not be excluded.     

Electric Fencing as a Measure to Reduce Moose-Vehicle Collisions

Abstract: We tested the effectiveness of electric fences to reduce moose (Alces alces)-vehicle collisions in 2 fenced sectors (5 km and 10 km) using weekly track surveys and Global Positioning System telemetry. Number of moose tracks along highways decreased by approximately 80% following fence installation. Only 30% (16/53) of moose tracks observed on the road side of the fence were left by moose that crossed an operational fence; moose mostly entered the fenced corridor through openings (e.g., secondary roads) or at fence extremities. Electric fences also prevented 78% (7/9) of collared moose from crossing the highway in fenced sectors. Fences were less effective during occasional power failures. We suggest that circuit breakers should be used to prevent power failures and that there should be no opening along the fence line unless anti-ungulate structures are used.     

Phytoplankton production and growth rate in Lake Tanganyika: evidence of a decline in primary productivity in recent decades

1. This study focused on phytoplankton production in Lake Tanganyika. We provide new estimates of daily and annual primary production, as well as growth rates of phytoplankton, and we compare them with values published in former studies.
2. Chlorophyll- a (chl- a ) in the mixed layer ranged from 5 to 120 mg chl- a  m⁻² and varied significantly between rainy and dry seasons. Particulate organic carbon concentrations were significantly higher in the south basin (with 196 and 166 mg C m⁻³ in the dry and the rainy season, respectively) than in the north basin (112 and 109 mg C m⁻³, respectively).
3. Carbon : phosphorus (C : P) ratios varied according to season. Phosphorus limitation seemed to occur more frequently than nitrogen limitation, especially during the rainy season. Severe P deficiencies were rare.
4. Measured particulate daily primary production ranged from 110 to 1410 mg C m⁻² day⁻¹; seasonal contrasts were well marked in the north basin, but less in the south basin, where primary production peaks occurred also in the rainy season. Estimates of annual primary production, based on daily primary production calculated from chl- a and water transparency, gave values lower than those reported in previous studies. Picophytoplankton accounted on average for 56% of total particulate production in the south basin during the wet season of 2003.
5. Phytoplankton growth rates, calculated from primary production, ranged from 0.055 to 0.282 day⁻¹; these are lower than previously published values for Lake Tanganyika.     

La reproduction saisonniére chez les isopodes terrestres: Contrôle photopériodique et neurohumoral

Summary

Seasonal reproduction in terrestrial Isopods is regulated by a neurohormone (VIH) synthesized in neurosecretory cells located in the protocerebrum median part. VIH restrains vitellogenin synthesis by the fat body. This inhibitory system is driven by the photoperiodic variations. Long days introduce a decrease in synthesis and—or—VIH release, allowing the oocytes to carry out the last vitellogenic phase. Other signals (mating, eggs in brood-pouch) tune the activity of the inhibitory system. Various aspects of photoperiodic and neurohormonal controls of reproduction are discussed: geographical variability and genetic determinism of the photoperiodic response; chemical nature, specificity and VIH mode of action; male physiology and VE synthesis, modalities of VIH synthesis and release.     

Plant Regeneration from Mesophyll Protoplasts of Several Nicotiana Species

In a search for model systems in plant cell genetics studies mesophyll protoplasts from eleven species of Nicotiana with low chromosome number (N. acuminata, N. alata, N. glauca, N. glutinosa, N. langsdorffii, N. longiflora, N. otophora, N. paniculata, N. plumbaginifolia, N. suaveolens, N. sylvestris) were shown to divide in a liquid culture medium. Plants were recovered from calli originating from protoplasts of all these species except N. glutinosa.