摘要:

Sperm and spermatogenic ultrastructure in a member of the gastropod superfamily Lepetodriloidea (Lepetodrilus fucensis, Lepetodrilidae), is described for the first time and the results compared with available information on other major prosobranch taxa. The head of the sperm ofL. fucensisis comprised of an elongate nucleus (about 9 μm×0.4 μm mid-diameter) capped by a conical acrosome (2.3 μm) which sits on a centrally perforated basal plate. The acrosome is invaginated posteriorly, the invagination housing an axial rod. Posterior to the nucleus, the mid-piece consists of a complex centriolar apparatus and laterally positioned mitochondrion. The axoneme, which emerges from the centriolar complex, is surrounded anteriorly by a long (2.5 μm) cytoplasmic sheath which contains regularly spaced (periodicity 62 nm) electron-dense microtubules and filaments. Spermatozoa ofL. fucensisresembles most closely those of the lepetelloideanAddisoniasp. and to a lesser degree those of some skeneimorph vetigastropods. The electron-dense structures associated with the cytoplasmic sheath (seen inLepetodrilusandAddisonia) are strongly reminiscent of a similar, possibly homologous, feature observed in euspermatozoa of the Neritimorpha. Neritimorphs nevertheless show several sperm differences fromL. fucensisandAddisoniasp. Spermatogenesis inL. fucensisfollows a similar pattern to that described for many shallow water gastropods. Acrosome formation begins in spermatocytes with the production of small electron-dense vesicles, which, probably via fusion form the larger definitive acrosomal vesicle of spermatids. The pattern of chromatin condensation and nuclear elongation is typical of that of molluscs, but, as observed in other vetigastropods and the Neritimorpha, elongation of the nucleus occurs without the participation of a microtubular manchette.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672567

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Eusperm bundles and separated parasperm in the vesicula seminalis of the silkmoth,Bombyx mori, were separated by centrifugation in sucrose density gradients. Staining with aceto-orcein showed dissociation of eusperm bundles as well as stained nuclei. This dissociation was induced in the presence of all acids tested. Dilute solutions of endopeptidases dissociated the head part of the eusperm bundle, whereas dilute solutions of acids mainly dissociated the trunk and tail parts. On HPLC on a strongly acidic cation-exchanger column, seven acids were detected in the spermatophore. Of these, succinate was the main component, and only its concentration increased with time. We concluded that with initiatorin, a serine-endopeptidase secreted from the glandula prostatica, succinate serves as eupyrene sperm bundle-dissociating factor in the spermatophore. The possible mechanism of formation of succinate in the spermaophore, which may be associated with glycolysis and the arginine degradation cascade under hypoxic conditions, is discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672568

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Settlement and metamorphosis are induced by environmental cues in many marine invertebrates. These signals emanate from biotic or abiotic material indicating the presence of a suitable habitat. In Cnidarians, pelagic larvae undergo metamorphosis to a sessile polyp. Environmental signals reactivate the morphogenetically inactive larvae and internal mechanisms are turned onto coordinate the development of the polyp. In recent years developmental biologists, ecophysiologists and ecologists have shown a considerable interest in the metamorphosis of Cnidarians. The purpose of this review is to give a survey on what is known about the natural induction of metamorphosis and to provide information on the biochemical and cellular mechanisms underlying the metamorphic events in Cnidarians. The emphasis is on the external and internal signals and their transduction mechanisms used to control metamorphosis.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672569

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The sea cucumberCucumaria frondosaspawns in the spring, in the Guff of Maine, USA. The larvae remain pelagic for several weeks prior to recruitment to the benthos. In the western Gulf of Maine, a previous study showed that juvenileC. frondosaoccur exclusively inside mussel beds; adults are absent from the region. In the present investigation, recruitment and juvenile abundances in the field were examined from 1993–1995. A study conducted in the spring of 1993 in the Maine-New Hampshire coastal waters indicated that recruitment ofC. frondosato mussel beds was high. In the fell of 1994, no recruits were present on the benthos; juveniles were more abundant in coralline algae than in mussel beds or kelp holdfasts. In 1995, recruitment and juvenile abundance monitored over the recruitment season revealed that recruitment was highest in June. Toward the end of June and during early July, recruitment was significantly higher in mussel beds than in coralline algae and kelp holdfasts. In June, a 2-day intensive field study indicated that recruits were significantly more abundant in mussel beds than in kelp holdfasts or coralline algae, while juveniles were significantly more abundant in the mussel beds than coralline algae. Mussel beds may enhance early survival by providing a refuge from predation. A potential predator on new recruits are large nereid worms.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672570

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Monthly collections ofAstropecten brasiliensiswere made at depths of 30 and 45 m. The highest number of prey in the stomach occured in summer in both 1987 and 1988. Specimens larger than4 cm in radius had mature gonads. The reproductive cycle was determined by gonad indices and histological analysis of gonads. In 1988, the species exhibited an annual reproductive cycle with spawning in December. The pyloric caecum indices showed the highest values between April and July. The relationship between gonad index and pyloric caecum index was inverse. The pyloric caecum peak occurred during the down welling period (fall and winter) when warm tropical waters (Brazil Current) were inshore. The reproductive peak coincided with the upwelling period (during spring and summer) enabling the larvae to benefit from the richer water condition when phytoplankton are more abundant.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672571

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The size, structure, and density of a population ofLytechinus variegatuswere recorded from a shallow seagrass bed (Halodule wrightii) at 40-day intervals from April 1994 to April 1995. A local mass mortality was observed in May 1994. The density declined from 0.57±0.10 to 0.06±0.05 ind.m−2, mean size declined from 37.6±0.49 to 16.2±2.14 mm and maximum size from 75 to 40 mm. Ten months after mortality, the maximum and mean sizes had returned to initialvalues, but density had not (0.10±0.03 ind.m−2). A second, smaller mass mortality occurred in April 1995. High values of gonad index were recorded before mortality (9.40±5.97) and after population recovery (11.96±5.74). Recruitment was continuous throughout the year, but reached a peak from August to October. This can he related to the patterns of upwelling in the region. Mass mortality is probably an annual event in this population that can be correlated with the occurrence of low tides during daytime in the fell. The population can recover during the summer when low tides occur during the night. The massive input of recruits prevents extinction of the population during the season of high mortality. Population recovery depends on the magnitude of recruitment.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672572

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Serial confocal images of serotonergic (5HT) cells were collected from fluorescently labelled immunostained larvae of the sea starPatiriella regularis.Compared with results obtained by conventional epifluorescence microscopy of the same specimens, laser scanning confocal microscopy (LSCM) produced superior resolution of the 5HT positive cells at the larval surface and at depth. Three-dimensional (3-D) reconstructions of optical sections were used to view the larvae from different angles to follow the development of the 5HT positive cells, thus avoiding the need to physically move the specimens. Immunoreactive cells were first seen in the apical region of the gastrula. This was followed by the appearance of cells in the mid-region of the gastrula. By the bipinnaria stage 5HT immunoreactive cells were present around the oral hood where they formed lateral ganglia near the mouth. Confocal laser scanning microscopy and 3D computer reconstruction of the larvae represents a methodological improvement for the study of echinoderm neurogenesis because the position of the labelled cells can be determined nondestructively without the need for microtomy and geometric reconstruction.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672573

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We introduce a classification system for the sexual modes of modular (clonal and colonial) animals which incorporates both spatial and temporal components of modular sexuality. After explaining and illustrating each potential sexual mode, we compare the prevalence patterns of sexual modes among modular animals, unitary animals, and flowering plants. Our conclusions are: (1) There are far more potential colonial modes of sex, and more clonal modes of sex, than there are unitary modes of sex. This is a function of the tri-level and bi-level organization, respectively, of colonial and clonal animals, in contrast to the single level of unitary ones. (2)Only five of ten potential colonial modes of sex have known examples, while only four of six potential clonal modes of sex have known examples. (3) The sexual mode of many modular metazoans is not known, in part because of a previous lack of terms by which to refer to modular sex at all its levels of expression. (4) Comparison of clonal and colonial animals reveals that genet gonochorism is nearly twice as common in clonal as in colonial animals. Genet hermaphroditism achieved by gonochoric modules of both sexes (monoecy) is about three times as common in colonial as in clonal animals. (5) Comparison of unitary and modular animals reveals that genet sequential hermaphroditism, while moderately common among unitary animals, has virtually no examples among modular ones. Genet gonochorism is also more prevalent among unitary animals than among modular ones (and conversely, genet simultaneous hermaphroditism is far more prevalent among modular than unitary animals). (6) Despite striking differences in the prevalence of different sexual modes at the genet level, clonal, colonial, and unitary animals display very similar patterns of sexual mode when examined at the modular level. (7) Comparison of seed plants and modular animals reveals that both genet gonochorism and monoecy are considerably rarer in plants than in modular animals. Sequentially hermaphroditic genets may be more common among plants than among modular animals. Some sexual modes in our classification may be represented among plants, but not among animals.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672574

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The state of knowledge concerning the reproductive biology of zoanthids is reviewed. Colonies in the suborder Macrocnemina, with few exceptions, are gonochoric; those in Brachycnemina are probably basically hermaphroditic but accurate sampling in colonies that fragment is difficult and exceptions by species or populations occur. Two deepsea species ofEpizoanthusbreed continuously but temperate shallow water zoanthids, and those in the tropics outside ∼15° latitude are iteroparous with spawning in summer or when temperatures are rising. Oogenesis occurs over a few months but the spawning event may be very brief.Parazoanthus parasiticusin Bermuda spawns mainly on 1–2 nights in late August or September, apparently at full moon;Protopalythoasp. 1, and probablyPalythoa caesiain the Great Barrier Reef spawn 3–5 nights after full moon in November (early summer). These species with short, precisely defined spawning seasons may undergo a second, smaller-scale spawning event one month after the first. Some intertidal populations seem rarely to reproduce sexually, and there have been no studies on the annual cycles of zoanthids in near equatorial waters. With few exceptions gametogenesis occurs only in non-directive macrosepta; in hermaphroditic colonies oocytes and sperm cysts may be intermingled on the same septa or be separate. Germ cells inIsozoanthus giganteusoriginate only from the endocoelic face of the septa, but this has not been confirmed in other species. Nutritive structures (trophonemata) are present both in oocytes and sperm cysts, in the latter functioning also for the egress of sperm. Trophonemata may be conspicuous, as inPar-parasiticus, or poorly developed, as inProtopalythoasp. 1. Live eggs vary from −300 µm (most zoanthids) to ∼500 µm diameter inPalythoaspp.; in the two mass spawning species from the Great Barrier Reef they are shed as compact ovoid egg (or egg/sperm) bundles. Fecundity in zoanthids, from few studies, is variable and dependent on polyp size; estimates of 100–300×103ova 100 cm−2of colony have been made for Caribbean reef species. Internal brooding is known definitely only inIsozoanthus giganteus.Amongst zooxanthellate zoanthids, onlyProtopalythoasp. 1 is known to transmit zooxanthellae via its oocytes. Several zoanthids are known to produce palytoxin but it is unclear to what extent the toxin accumulates in the ova. Larval development is summarized. Zoanthella-larvae are known to be produced inPalythoa, ProtopalythoaandSphenopus, and zoanthina-larvae inIsaurusandZoanthus, all Brachycnemina. Larval type inEpizoanthusandParazoanthus, both Macrocnemina, is unknown. Early metamorphosis of zoanthella and zoanthina larvae has been reported but not studied; older larvae, taken from the plankton, may have lost competency to settle. All zoanthids, exceptSphenopus, form colonies, clones, or mixtures of the two, and propagate by budding. Attention is drawn to unusual methods of budding or cloning inAcrozoanthus, Isaurus, Palythoa, Sphenopus, andParazoanthus axinellae.In reefalIsaurus, Protopalythoa, andZoanthusactual colony size remains small due to fragmentation, but genet size may be substantial. Population structure depends on the interplay of recruitment, fragmentation, and local dispersal.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672575

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Previous studies on the fertilization rates in externally fertilizing marine invertebrates have been concerned principally with free spawning epifaunal organisms (e.g., Babcock et al., 1992). A technique has been developed to investigate fertilization success in the intertidal infaunal polychaeteArenicola marina.The spawning period at the East Sands, St Andrews, is predictable from previous data, and this facilitates the study of spawning behaviour. Female worms spawn within their burrows, where the eggs may remain for several days. Male worms release sperm puddles on to the surface of the sediment at low water. The sperm is carried on the incoming tide over the surface of the sediment where it is actively drawn into female burrows by pumping. The decrease in sperm concentration as the tide comes in has been measured, and it is estimated that there are typically about 106sperm.ml−1in the water column and available to the female at 1 min after covering by the incoming tide. By placing the worms into artificial plastic burrows with removable stoppers, they can be transplanted into the field prior to spawning, and removed afterwards whilst retaining all the contents of the tube (worms, gametes, sediment and water).Preliminary data on the fertilization success suggests that it is highly variable (between 0% and 90%), with typical values of 40–60% forArenicola marina.Laboratory assays investigating fertilization rate with varying sperm concentration have shown that there is a marked increase in success at 104and 105sperm per ml, with values of 30–70%. The field data therefore appear to be consistent with laboratory studies.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672576

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor