Les etapes de la vitellogenese chez Thermobia Domestica (Packard) (Thysanura: Lepismatidae)

Study of the ultrastructural modifications of the follicular epithelium and of the oocytes during the high growth period of the terminal follicles has allowed us to characterize 4 successive phases and to pin-point their synchronisation with the moulting cycles in adults. During phase 1, which takes place near the end of a moulting cycle, the terminal oocytes still undergo previtellogenic growth, followed by the beginning of micropinocytosis and vitellogenesis (lipid droplets at first, then little protein granules), whereas the follicular cells remain joined together. The 2nd phase starts a little before ecdysis; this phase and the third one correspond to 2 steps of intense vitellogenesis, with simultaneous deposition of lipid and glycoprotein. Endogenous protein synthesis seems to be very limited, unlike most other Apterygota. The follicular cells gradually differentiate proteosynthetic organelles, but continue dividing; the intercellular spaces become greatly distended during the 2nd and 3rd phases. Vitellogenesis can be completed only if insemination takes place at the beginning of each moulting cycle. The 4th phase is marked by the formation of the vitelline envelope and of the chorion, while the follicular cells, once more joined together, become very flat and poor in organelles. Oviposition takes place in the middle of the intermoult period.     

Ecdysteroids in the haemolymph and the ovaries of the firebrat Thermobia domestica (Packard) (Insecta,Thysanura): Correlations with integumental and ovarian cycles

Ecdysteroids were analysed with radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC) in females of the apterygotous insect Thermobia domestica, which ahs overlapping moulting and reproductive cycles. During each moulting cycle, a peak in the haemolymph concentration of ecdysteroids occurs at day 9 (in the 11-day standard cycle), which can be correlated with apolysis and the beginning of new cuticle deposition. The ovaries show a peak of ecdysteroids at day 5 (i.e. one day before egg-laying), which suggests that these hormones are also involved in the reproductive cycle. In both cases, HPLC analysis combined with RIA suggests that the main ecdysteroid is 20-hydroxyecdysone. This duality in the function of ecdysteroids is discussed.     

Anther wall and pollen development in Ophrys mammosa L. (Orchidaceae)

The objective of this study was to investigate anther wall and pollen development in Ophrys mammosa. Primary sporogen tissue resembles longitudinal cells with divided archeosporal cells. Thereafter these primary sporogen tissue cells re-divide anticlinally and periclinally forming secondary sporogen tissue. Microsporogenesis was successive type. Microgametogenesis occurred at the distal poles of the microspores. In addition, dense starch accumulation was detected in the pollen. Pollinia and massulae are separated from each other by dead cells filled with callose, according to histochemical preparations. The anther wall was a four-layered “monocotyledon” type. There was ring-like wall thickening in the endothecium. The tapetum is of the glandular type. When these two developmental processes are compared, it is seen that the anther wall has become mature by the sporogen tissue phase and is composed of only epidermis and endothecium at the beginning of microgametogenesis.     

Vitellogenins in the firebrat,Thermobia domestica (Packard): Immunological quantification during reproductive cycles and in relation to insemination (Thysanura: Lepismatidae)

An antiserum raised against the major fractions (240 + 300 Kd) of the vitellins extracted from maturing oöcytes of Thermobia domestica, allowed the immunological relationship between these proteins and their haemolymph precursors (vitellogenins) to be established, as well as the female specificity of these protein fractions. Using rocket immunoelectrophoresis, the vitellogenin concentration in the female haemolymph was measured on each day of a reproductive cycle. The changes in vitellogenin titre appear to be correlated with ovarian maturation: very low levels during the previtellogenic phase and increasing levels during the vitellogenic growth phase of the basal oöcytes. Also, these changes are synchronized with the moulting cycles which persist in the adults of these primitive insects. An insemination at the beginning of the interecdysial period causes a large increase in the vitellogenin titre synchronized with accelerated oöcyte growth.     

The effect of cyproterone acetate on the antler cycle in red deer (Cervus elaphus L.)

The aim of the study was to test the effect of antiandrogen, cyproterone acetate (CA) on the antler cycle in the red deer (Cervus elaphus). CA was administered to three adult red deer stags (Edward, Fuks and Gacek) in weekly intervals. Edward and Fuks were given 600 mg + 600 mg of CA, whereas Gacek was given 600 mg + 300 mg. CA was injected during the hard antler phase: in mid-October (Edward), at the end of November (Fuks) and at the end of January (Gacek). CA caused the antler casting 17 to 22 days after the first injection. In all stags, the casting of antlers was followed by a period of intensive growth of new antlers. Edward was given CA at the end of October. This treatment was responsible for occurrence of the two antler cycles in the year of the experiment. When CA was administered during the middle of the hard antler phase an additional short antler cycle occurs followed by new antler growth. CA treatment in the later part of hard antler phase may cause a prolonged antler cycle.     

The formation of the pronuclei and their associated perinuclear cytoplasm; the determination of the phases of the first cleavage cycles in Crepidula fornicata (Mollusca,Gastropoda)

Summary

The behaviour of the male and the female pronuclei in Crepidula fornicata is studied, beginning at the formation of the second polar body. Shortly after the extrusion of the second polar body the female pronucleus is formed, and then the male pronucleus enters the yolk-free cytoplasm near the animal pole. Both pronuclei are enveloped by a typical nuclear membrane, and increase in size until the prophase; a zygote nucleus is not formed (“Ascaris type” of fertilization). In the meantime, the chromatin of both pronuclei is arranged in a meshwork in the centre of the pronuclei.

Shortly after the formation of the second polar body a special cytoplasm, the “perinuclear cytoplasm”, is formed in the vicinity of each of the pronuclei. During the early stages of the first cleavage cycle this cytoplasm is composed of numerous Golgi complexes, small dense Golgi vesicles, smooth endoplasmic reticulum vesicles, mitochondria and rosettes of glycogen-like granules. At later stages, when the pronuclei have met and their plasms coalesced, the number of Golgi elements decreases; at the same time, the small dense Golgi vesicles increase in number and aggregate in clusters.

The phases of the first three cleavage cycles are determined by cytophotometry. The nuclear DNA of the male pronucleus and that in the nuclei of the blastomeres of the 2- and the 4-cell stage is reduplicated between 7 and 33% of the normalized cleavage cycles; the G₂-phase is between 33 and 57%, while the mitotic phase occupies the last part of each cleavage cycle and the first 7% of the next cleavage cycle. There is no G j-phase. Since the female pronucleus lies just beneath the polar bodies, its DNA content could not be measured separately.     

The interstitial cells of the trout testis (Oncorhynchus mykiss): ultrastructural characterization and changes throughout the reproductive cycle

The major non-vascular cell types present in the interstitial compartment in trout testes have been ultrastructurally characterized and cell changes in the course of the two first reproductive cycles have been studied. Three major cell types are always present fibroblasts, myoid cells and Leydig cells. Their structure varies with the maturational stage of the gonad. Fibroblasts are centrally located in the interstitial areas. Numerous typical myoid cells are always present near the basal lamina. However, at the end of a cycle some of them display degenerative changes, then disappear. At the beginning of the next cycle, fibroblasts appear to differentiate to new myoid cells. Leydig cells present before the start of the first spermatogenesis are replaced by new ones which probably also arise from fibroblasts. These cells progressively differentiate during spermatogenesis, so that most of the Leydig cells present during the spermiation phase are fully-differentiated steroidogenic cells. At the end of a cycle, a certain number of the Leydig cells disappear and are replaced at the beginning of the next cycle by new ones most likely derived from fibroblasts. The remaining Leydig cells dedifferentiate to cells which may redifferentiate during gonadal activity. Macrophages are present mostly at the end of a cycle and participate at this time in the removal of dead interstitial cells. In conclusion, at least some fibroblast-like cells are precursor cells, able to replace myoid cells and Leydig cells which disappear between two consecutive reproductive cycles.     

Évolution du taux de présence de spermatophore chez les femelles de Nephrops norvegicus (L.) (Decapoda:Reptantia) et développement ovarien

Ovary development and the presence of spermatophore in females of Nephrops norvegiens (L.) (Nephropidae) from South Brittany were studied from July 1976 to October 1978 through size classes. Percentage of females bearing spermatophores increased slowly up to 1978 during which year a sudden and important decrease was observed. The percentage decreased to the lowest value obtained in 1976. A study of ovarian development showed that the proportion of small females taking part in reproduction was greater in 1978 than in 1977.The beginning of the decrease in the percentage of spermatophores present coincided with the beginning of spawning in each size class. It may be explained by the behaviour of ovigerous females which stay in burrows during the incubation season. The decrease is, however, very important as the proportion of mature females is high and because the time separating the autumn moulting from spawning is great.Spawning occurred in several months (4 months in 1978). The “mean size at first maturity” varied from year to year and also from month to month, even if the presence of spermatophores was taken as a criterion.     

Lipid metabolism of the female crab Pachygrapsus marmoratus during the moulting cycle

The moult induces important variations in the concentration and fatty acids composition of lipid classes during the moulting cycle of the female crab Pachygrapsus marmoratus regardless of the maturational degree of ovaries. Sexual maturity is characterized by a rise in lipids. Juveniles contain high levels of polyunsaturated fatty acids except in the ovary, whereas adults are composed mainly of monoethylenic acids. The moulting decrease of saturated fatty acids shows their importance during this crucial period, owing to their utilization as energy sources at the time of ecdysis. The late premoult fall of hepatopancreatic lipids results at once from inanition during the period before the exuviation and transfer of lipids through the hemolymph to the periphery in order to realize numerous changes occurring during the moulting process. The relative stability of lipid composition of ovaries in sexual pause during the moulting cycle agrees with a reduced metabolism of ovarian cells.     

Release of brain neurosecretory products from the neurohaemal part of the aorta during egg-laying and egg-care in Labidura riparia (Insecta,dermaptera)

The exocytosis level in the neurosecretory terminals of the aorta wall, was studied by electron-microscopy in female Labidura riparia during different stages of the reproductive period: end of vitellogenesis, beginning, middle and end of egg-laying, and during egg-care.The exocytosis level (L. ex) in the terminals which are filled with big dense elementary granules is low at the end of vitellogenesis (L. ex = 0.28), the level increases 8 times when the first egg is passing under the genital plate, reaching a maximum level (2.46) when approximately ten eggs have been laid. The level then decreases at the end of egg-laying (1.8) and abruptly falls when the female begins her egg-care cycle. Throughout this period, the exocytosis level stays between 0.54 and 0.76.These results show a significant release of brain neurosecretory product at the neurohaemal part of the aorta during egg-laying. This suggests that egg-laying could be regulated by a brain hormone.     

Ultrastructural modifications of the glandular epithelium of the receptaculum seminis in Thermobia domestica (Insecta: Thysanura) during the moulting period

Summary The wall of the receptaculum seminis of Thermobia domestica is composed of numerous glandular units, each with four enveloping cells (denoted 1 to 4) separated by ordinary epithelial cells and associated with a cuticular apparatus. During the moulting periods, which continue to occur in the adult stage, these cells undergo a series of transformations. Just before apolysis there is a dedifferentiation of numerous cytoplasmic organelles, but no mitosis has been observed. When the intima lifts off, the apical system of each glandular unit, i.e. the distal parts of the C2 and C3 cells surrounding the end apparatus, is also eliminated. Then at the apex of each glandular unit, a new ductule is formed in the cavity of which a long ciliary process grows up from cell C1. Finally comes the phase of cuticle formation, i.e., epicuticle for the ductules, epi-and endocuticle for the intima lining the central cavity of the receptaculum. Various cell types participate in secretion of cuticle, the ciliary cells (C1) being responsible for the formation of the porous end apparatus. At ecdysis almost all of the new intima has been secreted and the apical systems are once more differentiated. These transformations are compared with those recently described in other exocrine glands of arthropods, e.g., tegumentary glands and accessory glands of the genital ducts.     

Ultrastructure of the phallic glands of the firebrat,Thermobia domestica (packard) (Thysanura : Lepismatidae)

The exocrine glands located in the penis of Thermobia domestica (Thysanura : Lepismatidae) are composed of about 100 distinct units, each containing several cell types: one large secretory cell with an apical reservoir; 2 groups of envelope cells, an inner group of 2 superimposed cells, and an outer group of 4 cells arranged in a ring, and also 2 basal cells, called ciliary cells owing to their elongated processes, which look like the dendrite of a sensory cell. Each functional unit includes cuticular differentiations: a tubular bristle, fixed on a small tubercle; and a long “internal” ductule communicating basally with the reservoir of the glandular cell and opening distally at the tip of the bristle. A study of the modifications affecting the phallic glands during moulting, shows that the inner envelope cells deposit the cuticle that forms the ductule, the outer envelope cells elaborate the cuticule of the tubercle, while a temporary distal projection of only one of these cells ensures the formation of the bristle. In addition, a lengthening of the outer dendritic segment of the 2 ciliary cells takes place before ductule formation, but this segment partially degenerates after ecdysis. These findings are compared with data already obtained on the morphogenesis of other insect integumental glands. In T. domestica, the secretion of the phallic glands is presumed to be used, during the mating sequences, for spinning fine threads before spermatophore deposition.     

Enzymes of the tricarboxylic acid cycle in Obeliscoides cuniculi (Nematoda; Trichostrongylidae) during parasitic development

The specific activities of the enzymes of the tricarboxylic acid cycle; citrate synthase, aconitase, isocitrate dehydrogenase, succinate dehydrogenase, fumarase, and malate dehydrogenase, were determined in early fifth-stage, young and mature adult Obeliscoides cuniculi, the rabbit stomach worm. ∝-Ketoglutarate dehydrogenase activity could not be determined in any fraction. Fumarate reductase activity was found only in the mitochondrial fraction while all other enzymes, including an NADP-dependent malic enzyme were localized in the cytoplasm. Glutamate dehydrogenase, acid and alkaline phosphatase activities were also recorded. High levels of those enzymes acting in the “reversed” direction, i.e. MDH and fumarase relative to the enzymes of the “forward” direction, i.e. citrate synthase, aconitase and isocitrate dehydrogenase suggests that under anaerobic conditions a modified tricarboxylic acid cycle can operate. Some variations in specific activities were apparent as the worms matured but no qualitative differences were observed.     

Stimulation of metamorphosis in an estuarine crab, Chasmagnathus granulata (Dana, 1851): temporal window of cue receptivity

The larvae of most benthic marine invertebrate species must develop for a minimum of time in the plankton before they become competent for settlement and metamorphosis in response to stimulating external cues. In an experimental laboratory study, we identified the temporal window of cue receptivity within the moulting cycle of the megalopa stage of an estuarine crab, Chasmagnathus granulata Dana. This species shows an export strategy including an early larval transport to coastal marine waters where zoeal development takes place, followed by the return of the megalopa stage to brackish habitats where the adults live. In two series of experiments (A, B), megalopae were exposed for differential periods to a combination of metamorphosis-stimulating cues which had previously been found effective (seawater conditioned with adult odor and presence of mud). In experimental series A, these cues were added on successively later days of the moulting cycle, while series B comprised treatments in which the cues were provided from the first day (postmoult) and removed on successively later days of the moulting cycle. Each series of experiments was repeated with larvae originating from two different females (F1, F2). The average development time of megalopae kept continuously in the presence of cues (control experiments, C1) ranged in the two hatches from 9.3 to 9.6 days. In the inverse controls where no cue was added at any time (C2), megalopal development to metamorphosis took on average 11.2-12.0 days. In series A, development duration in treatments with exposure to the cues commencing within 3-4 days after moulting was not significantly different from that in the permanently exposed C1 controls. Later beginning of the exposure, by contrast, had no stimulating effect (significant delay compared to C1, no significant difference from unexposed control, C2). In series B, no significant differences in development time were observed between the C1 controls and treatments with an initial exposure for a minimum of 4 or 6 days of the moulting cycle (F1, F2, respectively). Shorter initial periods of exposure had no metamorphosis-stimulating effects (no significant difference from C2). In conclusion, our results from both experiments suggest that the megalopa stage of C. granulata is most receptive of stimulating cues during a period lasting from ca. one third to one half of the moulting cycle, which coincides with the transition between stages C (intermoult) and D₀ (early premoult) of Drach's classification system. This suggests an interaction of extrinsic stimulating cues with intrinsic (hormonal) factors involved in the control of the moulting cycle.     

Ecdysone-induced changes in morphology and protein synthesis in Drosophila cell cultures.

Permanent cell lines derived from embryonic Drosophila melanogaster show pronounced morphological and biochemical changes in response to the addition of β-ecdysone, the moulting hormone, or two of its analogs. Schneider's line 3 cells, and the French line Kc, morphologically differentiate into what appear to be neural-like cells. During this period levels of acetylcholinesterase activity increase 10- to 30-fold, and DNA synthesis ceases. The level of choline acetyltransferase activity remains unchanged in line 3, and is very low. Schneider's line 2 cells show no morphological transformation in response to β-ecdysone, but undergo a marked change in the pattern of protein synthesis. The six major ecdysone proteins are not “heat shock” proteins.     

Moulting fast and time constraint for reproduction in the king penguin

King penguins (Aptenodytes patagonicus) replace their complete plumage during a 3- to 4-week moulting fast on shore. After moulting, birds forage at sea for 2-3 weeks to store energy reserves for reproduction. Using an automatic identification and weighing system coupled with visual observations, we investigated the trade-off between the moulting fast and the following breeding attempt, in terms of body condition and in relation to time constraints, in free-living king penguins. King penguins reached their lowest body mass of the yearly cycle at the end of the moulting fast; this was lower than that at the end of the incubation fasts and not different from the body mass at egg desertion. Later in the season, the duration of the moulting fast became shorter and old feather loss occurred earlier after arrival ashore. Postmoulting foraging trips were shorter, but at the expense of body condition at the beginning of courtship. These results are discussed in relation to the synchronisation of the breeding cycle with food availability and mate choice.     

Oxygen consumption by Nephrops norvegicus (L.), (Crustacea: Decapoda) in relationship with its moulting stage

The study of the rate of oxygen consumption by Nephrops norvegicius (L.) at each moulting stage has been carried out in closed respiration chambers, using an oxygen electrode to measure the oxygen concentration.Although the mean respiration rate seems to be low when compared with other decapod crustaceans of similar weight, the general trends of the variation of the oxygen consumption during the moulting cycle are similar to those described for other species of decapods. It should be noted that, during the process of the ecdysis, there is no oxygen consumption.     

Ecdysone during ovarian development in Locusta migratoria

Considerable amounts of ecdysteroids are produced during each ovarian cycle in adult females of Locusta when vitellogenesis is almost completed. The hormonal molecules are synthesized at the end of the maturation of the terminal oöcytes during each cycle, at the time when vitellogenesis is almost completed. No synthesis takes place in the absence of ovarian development (allatectomy, ovariectomy), whereas extirpation of the prothoracic glands at the beginning of adult life does not affect ecdysteroid production. More than 95% of the total ecdysteroid content of female adults can be recovered from the ovaries. In vitro studies show that the ovaries produce ecdysteroids and convert labelled cholesterol into ecdysone. Microsurgical experiments indicate that this synthesis takes place in the follicle cells surrounding the oöcyte. The newly synthesized ecdysteroids do not enter massively into the blood, but pass into the oöplasm where they are progressively converted to polar compounds; as a result, at the end of each ovarian cycle, egg-laying corresponds to the disappearance of ecdysteroids from the female insects, the hormonal molecules can easily be recovered from the eggs. A gas chromatographic analysis coupled to mass spectrometry shows that the principal ecdysteroid synthesized by the adult females of Locusta is by far ecdysone. Ecdysterone, the paramount ecdysteroid of the larvae of Locusta, is not present in noticeable amounts in the female adult of this species.