摘要:

The external morphology of spermatozoa from 14 gastrotrich species belonging to the order Macrodasyida was examinedin vivoby SEM and light microscopy. In all species the spermatozoa are filiform and consist of two or three regions. The anterior region is a spiral, but its distal and proximal segments are often differently coiled. The central region is not coiled, is of varying length or may even be absent. Intemally it consists of either a crystalline mass or the nucleus surrounding a mitochondrial axis. The posterior region is the tail. The ultra-structural data confirm the similarity of the basic structural plan of the spermatozoa in the macrodasyids. However, the individual genera of the same family, as well as different species of the same genus, present particular features. Thus, sperm morphology is a useful taxonomic criterion at both generic and specific level.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652348

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The ultrastructural investigation of the spermatozoal morphology of the hydrothermal vent crabs,Bythograea thermydron, Austinograea alayseaeandSegonzacia mesatlantica(family Bythograeidae) reveals a consistent familial sperm type and a close similarity between the three genera and the deep water trapeziid,Calocarcinus africanus.Association of the bythograeids withCalocarcinusis supported (apart from general similarity) by three synapomorphies: modification of the xanthid ring, development of a well developed periopercular rim (weakly shared with some xanthid and potamid members) and, as a particularly striking link, the unique spiral configuration of the contents of the outer acrosome zone.Calocarcinusis distinguished by shortening of the posterior dense zone into a true xanthid ring and, less so, by a flatter operculum.BythograeaandSegonzaciaare apomorphic in the independent loss of the ragged outer acrosome profile. Their sister genusAustinograeahas no distinct apomorphies (with the possible exception of an apical perforation in the operculum). The similarity between the spermatozoa ofCalocarcinusand the investigated bythograeids and the dissimilarity betweenCalocarcinusand other trapeziids is evidence for possible inclusion ofCalocarcinusin the Bythograeidae. This hypothesized relationshipof Calocarcinuswithin the Bythograeidaesensu latoand its deep water distribution suggests origin of hydrothermal bythograeids fromCalocarcinus-likedeep water xanthoids which may have entered the hydrothermal system in or after the Eocene. Further investigation of somatic morphology is required to test this putative relationship.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652349

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A detailed morphological analysis of the carrefour, corresponding to the site of bifurcation of the hermaphroditic duct of the reproductive tract ofBiomphalaria tenagophila(Mollusca, Planorbidae), has been carried out by light and electron microscopy, including 3D anatomical reconstruction. The carrefour receives the tangential entrance of the ovispermiduct and secretory duct of the albumen gland in its posterior face whereas the exits to the oviduct and spermiduct are situated in its anterior face. Histologically, this bulbuous organ is very similar to the ovispermiduct and thus may be considered as a hermaphroditic structure. It is lined by highly ciliated columnar epithelium with a few mucous secretory cells. The he structural analysis of the epithelium reveals the presence of long and abundant cilia and numerous microvilli in the apical surface of the ciliated cells, along with signs of micropinocytic activity. The observation of basal membrane infoldings with associated mitochondria indicates the existence of an apex-base motion of fluid through the carrefour epithelium. In contrast, the mucous cells show an intense secretory activity. Germ cell trafficking and sorting inside the carrefour are very complex, involving the segregation of oocytes and spermatozoa produced in the ovotestis of the animal itself and the exogenous spermatozoa acquired by copulation. Based on morphological evidence presented in this work, we concluded that the flux produced by ciliary beating of the epithelial cells along with the insertion angle and relative positioning of the openings of the ducts in the carrefour are the most important factors in the traffic and differential destiny of the germ cells inside the organ. The presence of secretion of the albumen gland in the so-called fertilization pocket should prevent the sperm entrance into the oocyte and thus the zygote formation in this specialized region of the carrefour.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652350

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

During the life cycle of marine invertebrates, including corals with benthic and planktonic phases, embryogenesis leads to a free swimming larva which has to find a suitable habitat to settle and metamorphose. Initial settlement and induction of metamorphosis of benthic marine invertebrate larvae are generally determined by interaction of external biochemical and/or physical factors. In a preliminary study we showed that the phorbol ester 12-o-tetra-decanoyl-phorbol-13-acetate (TPA) induces metamorphosis in six Red Sea coral species. Phorbol esters are known to activate the enzyme protein kinase C (PKC) and therefore play an important role in studying the phosphatidy linositol signal (PI) transduction system. The potency of several phorbol esters to induce metamorphosis in planulae of the Red Sea soft coral speciesHeteroxenia fuscescensandXenia umbellatawas examined to find further indications for the involvement of PKC in anthozoan metamorphosis. All tested phorbol esters, 12-o-tetra-decanoyl-phorbol-13-acetate, phorbol-12, 13-didecanoate, 12-retinoyl-phorbol-13-acetate and phorbol-12, 13-dibutyrate triggered metamorphosis in planulae of both species in a concentration-dependent way. The maximum levels of metamorphosis achieved varied from 30% to 100%, depending on both the species tested and the phorbol ester applied, using concentrations ranging from 10−7to 10−9mol/l except for 12-retinoyl-phorbol-13-acetate. In addition, the response of planula fragments to artificial inducers was studied. Our results indicate that the different cnidarian taxa not only respond to a variety of metamorphic cues, but also possess divergent mechanisms for reception and transmission of metamorphic inducers. Phloretin, an inhibitor of mammalian PKC, completely blocked phorbol ester-induced metamorphosis inHeteroxenia fuscescensplanulae. Data which indicate the presence of PKC-related enzymes as the biochemical base for metamorphosis are now documented for species of the cnidarian classes Hydrozoa, Scyphozoa and Anthozoa. Based on our results, and the work of other authors, we therefore suggest that the phosphatidy linositol-signaling pathway might represent the general mechanism which regulates metamorphosis in cnidarians.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652351

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The male accessory glands of the Colorado potato beetle,Leptinotarsa decemlineata, produce an 8kDa peptide (Led-MAGP), whose primary structure and gene have been described. To investigate the possible function of this peptide in the female, we traced the passage of Led-MAGP through the male and female reproductive tracts during and after the mating process. We used immunohistochemical procedures to localize Led-MAGP employing a specific polyclonal antiserum which was raised against a recombinant Led-MAGP. Mating couples of Colorado potato beetles were interrupted after various time intervals after the initiation of mating and fixed by perfusion to immobilize the transferred male accessory gland secretions and sperm cells. Serial sections of reproductive tracts were prepared and immunolabelled. These time-lapse studies indicated that the contents of the male accessory glands are transferred during the first few minutes of mating and are deposited in the female spermathecal duct. Sperm cells are transferred later, 4–6 min after the beginning of mating. Led-MAGP is found in two forms, namely a granular, doughnut-shaped form and a homogeneously dispersed form. After deposition in the spermathecal duct, the irnmunoreactive product dissolved within 4–6 min. It is argued that the Led-MAGP crosses the duct wall and enters the hemolymph and that its function must therefore be sought outside the female reproductive tract.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652352

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The spermatozoa of the gymnolaematous bryozoanElectra pilosaare thread-like cells about 350 μm long. The head region is needle-shaped, consisting of a long thread-like nucleus tapering anteriorly. No acrosorne is present. The midpiece consists of an axoneme surrounded by two long mitochondrial derivatives and two thin, nonmembrane-bounded granular rods alternating with the mitochondria. The two mitochondrial derivatives are of unequal size. The larger one is provided with lamellae of alternating electron-dense and electron-transparent material. Both mitochondria have a crescent form when seen in transverse section. In the tail region the axoneme is surrounded by a tube-like sheath composed of a thick cell membrane. An annulus is located at the junction between midpiece and tail. The flagellum is of the 9+2 type and in the tail region the number of microtubules is reduced. The nine peripheral components of the axoneme continue as single microtubules. Spermatozoaof Electraare tightly arranged in unencapsulated aggregates of c. 30 (32) cells capable of active swimming. Sperm heads and midpiece regions have a regular parallel orientation in the spermatozeugmata and are probably connected with each other by mucus. The presence of spermatozeugmata is indicative of internal fertilization inElectra.Ent-aquasperm of the type found inElectra pilosaare probably the most common type of gymnolaemate sperm. Sperm structure supports the hypothesis that Stenolaemata and Gymnolaemata are more closely related with each other than either of them is with the Phylactolaemata.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652353

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The sperm ultrastructure ofMeganyctiphanes norvegicawas examined with the aim of investigating phylogenetic relationships between Euphausiacea and Decapoda. A noticeable feature of the spermatozoon ofM. norvegicais the presence of a thick, two-layered capsule that is in close contact with the plasma membrane. The sperm ultrastructure in this species appears to be similar to that ofEuphausiasp., the only other euphausiid investigated to date. The sperm of both euphausiids resemble those of some species of decapods in that they have a loose central chromatin surrounded by the cytoplasmic ring and lack an acrosome, nuclear envelope and radial arms. These features are suggested to represent eucarid plesiomorphic characters.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652354

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The gonad and maturity index cycles of the echinoidParacentrotus lividusand their relations with environmental abiotic parameters are assessed after 2 years of observation in southern Brittany, France. The gonadal cycle is briefly described and eight gonadal stages are characterized. The annual cycle, the time of spawning and the period of gonadal growth are well established, suggesting they are controlled externally. The reproductive cycle has three main phases: the growing phase (late autumn and winter) when gonads accumulate reserve material; the maturation phase (spring and early summer) in which gametogenesis then spawning take place; and the spent/regenerating phase when relict gametes are resorbed by the nutritive phagocytes, the gonads being virtually devoid of sexual cells. The maturity index based on the histological diagnosis of gonads and the use of circular data and polar graphical representation make it possible to reliably determine the spawning period, the rate of gametogenesis and the synchronization of males and females among the echinoid population. From this analysis, we can reasonably say that the gonadal cycle (represented by the gonad index), the rate of gametogenesis, and the end of the spawning period are influenced by temperature whereas the first spawning event appears to be triggered by day length.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652355

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Reproductive traits of the land snailHelix aspersaMüller were investigated under artificial conditions in a breeding population of a giant subspecies from North Africa, namelyHelix aspersa maxima.The results were compared with data obtained from experiments conducted under the same experimental with the common formHelix aspersa aspersafrom (1) a population from the same snail farm, which shares withHelix aspersa maximathe same environment since several generations and (2) a set of wild populations from habitats spanning environmental heterogeneity of the species range. The significantly higher egg production inHelix aspersa maximawas explained by the clutch number per snail rather than by clutch size. Moreover, an uncommon high egg weight (41.4–44.6 mg) was observed inmaximawhen compared with that ofHelix aspersa aspersafrom previous studies (28–33 mg). However, reproductive differences between the two subspecies can largely be explained by size-effects and, as a consequence, relative allocation trade-offs among components of current reproduction did not greatly differ among populations.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652356

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Between the two compartments of the telotrophic-meroistic trophocyte-oocyte syncytium isolated from early fifth instar larvae ofDysdercus intermedius(Heteroptera: Pyrrhocoridae), no differences in the resting membrane potentials (Em=- 18.3 m V for lateral trophocytes;Em=- 19.2 m V for presumptive oocytes) were recorded. Transition of the presumptive oocyte into a differentiating oocyte during the fifth instar coincides with comprehensive changes in the syncytium: (1) lateral trophocyte and differentiating oocyte hyperpolarize; (2) hyperpolarization in the trophocyte is stronger than in the oocyte resulting in a potential difference of ΔEm=-12.8 m V (ooplasm positive) across the syncytium; (3) activities in cytoplasmic calcium (aCa++) drop more strongly in the lateral trophocytes than in the differentiating oocyte so that a calcium gradient is established in the syncytium during oocyte transition. Linked up with results reported earlier, these observations imply the activation of a larval calcium current before the differentiation of a presumptive oocyte.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652357

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor