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  • 1
    Electronic Resource
    Electronic Resource
    Subitaneous and diapause eggs in Mediterranean populations ofPontella mediterranea (Copepoda: Calanoida): A morphological study (1990)
    Springer
    Marine biology 105 (1990), S. 83-90 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transmission electron microscope studies on the morphology of subitaneous and diapause eggs in the neustonic copepodPontella mediterranea, collected in coastal waters of the Gulf of Naples from May to December 1986, revealed striking structural differences between the two egg types and the existence of a third egg type that was morphologically similar to a diapause egg but which hatched within 2 to 3 d. In smooth, subitaneous eggs the plasma membrane was surrounded by a thin outer chorion as compared to the thick and highly complex four-layer structure enveloping subitaneous eggs with short spines, and diapause eggs. This coat may be assembled just prior to or after deposition since the morphology of developing oocytes was similar in females laying either subitaneous or diapause eggs. The only other major structural difference between the two egg types was the presence of numerous, disc-like bodies in the ooplasm of diapause eggs. Development was arrested for at least 3 mo, prior to the initiation of the first cleavage, suggesting that these eggs were kept dormant by some endogenous and, possibly, structural mechanism preceeding the termination of diapause.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01344273
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  • 2
    Electronic Resource
    Electronic Resource
    Diapause embryos in the neustonic copepodAnomalocera patersoni (1991)
    Springer
    Marine biology 108 (1991), S. 387-394 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The neustonic copepodAnomalocera patersoni Templeton, collected from the Gulf of Naples from January to May 1988, laid subitaneous and diapause eggs that were of equal size and dark and smooth in appearance. In January and February, most eggs were subitaneous and hatched within 2 to 3 d at room temperature. Conspicuous numbers of diapause eggs were first obtained in February when several clutches contained a second egg type which did not hatch in a subitaneous manner. By March and April, most clutches contained only diapause eggs. Transmission electron microscope studies of subitaneous and diapause eggs revealed striking morphological differences. Subitaneous eggs had a thin vitelline coat covering the plasma membrane, whereas diapause “eggs” were enveloped by a complex four-layer structure which is assembled after spawning and which probably serves as a protective shell during dormancy. No major morphological differences were discernible in the oogenic cycle of females spawning either of the two egg types. Diapause eggs were shown to be embryos in early stages of development, and segmentation of these embryos was arrested for the entire 6-mo period of investigation. Diapause eggs hatched after 7 mo of dormancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313647
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  • 3
    Electronic Resource
    Electronic Resource
    A comparative study of the inhibitory effect of diatoms on the reproductive biology of the copepod Temora stylifera (1995)
    Springer
    Marine biology 121 (1995), S. 533-539 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Egg production and viability in the copepod Temora stylifera (collected in the Bay of Naples, Italy in 1992) were strongly dependent on food type. A flagellate (Isochrysis galbana) diet induced the production of good quality eggs that developed to hatching. By contrast, two diatoms (Chaetoceros curvisetum, Phaeodactylum tricornutum) resulted in poor egg quality, with hatching success as low as 20% of total egg production. With the third diatom tested, Skeletonema costatum, females produced eggs for only 3 to 4 d, after which time they either became sterile or died. These results are discussed in relation to previous findings regarding the impact of the dinoflagellate Prorocentrum minimum and the diatom Thalassiosira rotula on the hatching success of T. stylifera eggs. Low egg viability was possibly not due to an absence of remating or a deficiency of some specific essential nutrient required for egg development but to the presence of inhibitory compounds blocking cell division during early copepod embryogenesis. This questions the traditional view that diatoms are an important food item regulating copepod secondary production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349463
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  • 4
    Electronic Resource
    Electronic Resource
    The diatom Thalassiosira rotula affects reproductive success in the copepod Acartia clausi (1996)
    Springer
    Marine biology 125 (1996), S. 279-286 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fecundity, egg viability and fecal pellet production are reported for Acartia clausi females collected in the Bay of Naples, Italy, from April to October 1992 and fed either with a diatom (Thalassiosira rotula) or dinoflagellate (Prorocentrum minimum) diet, at food saturated conditions. The diatom diet significantly reduced both egg and fecal pellet production as well as hatching success. Blockage of egg development occurred with both axenic and non-axenic cultures of T. rotula, suggesting that inhibitors were provided by the diatoms and not by the bacteria associated with diatom cultures. Low hatching success was also artificially induced by exposing newly spawned A. clausi eggs to high concentrations of diatom extracts, indicating the presence of deleterious, inhibitory compounds blocking copepod embryogenesis. Fecundity and hatching success diminished significantly with female age. In contrast, female longevity was not significantly modified by food type. The presence of males did not significantly alter fecundity or egg viability. Females continued to produce viable eggs throughout the period of incubation, with and without males, in both food conditions, indicating that remating is infrequent and not necessary to sustain viable egg production in this species. The succession in low and high population densities may therefore be the outcome of variations in survival rates of eggs, rather than reproductive protential perse; such variations may strongly depend on the adult copepod diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346308
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  • 5
    Electronic Resource
    Electronic Resource
    Reproductive biology of the planktonic copepod Temora stylifera (1989)
    Springer
    Marine biology 101 (1989), S. 187-194 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Laboratory studies on the reproductive cycle of the planktonic copepod Temora stylifera, collected from the Gulf of Naples between October 1987 and March 1988, showed that females oscillated between a light and dark gonadal condition. Histological preparations indicated that the dark condition corresponded to a ripe stage of oogenesis as compared to the light or unripe maturation state of primary oocytes. The number of eggs released within 24 h was strongly dependent on the reproductive status of the female at the time of incubation. Light unfed females rarely reverted to a dark or ripe condition and egg deposition in such cases was almost always zero. Dark females produced eggs within 24 h under all experimental food conditions, reverting from dark to light soon after egg deposition. Successively, the length of the interclutch period was strongly dependent on the type of food present. A high percentage of infertile eggs was almost always present. We suggest that short-term studies, not taking into consideration the condition of gonads at the time of incubation, will underestimate potential egg production rates. Females maintained for longer than three or four days produced mainly infertile eggs. After remating, females reinitiated the production of fertile eggs but egg viabilities never reached 100% hatching success, indicating poor efficiency in the fertilization of mature oocytes. We hypothesize a possible cause and effect relationship between egg viabilities and seasonal fluctuations in population densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391457
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  • 6
    Electronic Resource
    Electronic Resource
    The surface attachment structure: a unique type of integumental formation in neustonic copepods (1992)
    Springer
    Marine biology 113 (1992), S. 401-407 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A unique type of integumental formation is described for several members of the copepod family Pontellidae. This surface attachment structure (SAS) consists of a mass of fine setules arranged in two semicircles on a flattened area of the anterodorsal surface of the cephalosome. Using transmission electron microscopy, the SAS was shown to be continous with the cuticle and not linked to chemo- or mechanosensory cells; its function is purely mechanical. This structure is probably an energy-saving means for these large and heavy neustonts to stay attached to the surface film. The SAS is species-specific and may thus be of potential importance to the systematics and phylogeny of the Pontellidae, in the same manner as integumental pores and sensilla, which form patterns characteristic of several copepod families and genera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349165
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of diet on levels of amino acids during embryonic and naupliar development of the copepod Calanus helgolandicus (1999)
    Springer
    Marine biology 134 (1999), S. 89-98 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The contents of free amino acid (FAA) and total amino acid (TAA) pools were determined in the eggs, embryos and N1 and N2 nauplii generated by Calanus helgolandicus females fed either the diatom Phaeodactylum tricornutum or the dinoflagellate Prorocentrum minimum for 3 and 10 d. With both diets, egg production rates increased by a factor of 5 to 10, and free amino acid (FAA) and total amino acid (TAA) contents were double those measured in eggs spawned by wild females. Higher levels were measured for almost all amino acids, except methionine, taurine, glutamine, glutamic acid, aspartic acid and ornithine. When embryos developed to live nauplii, 50 to 72% of the initial concentration of the FAA content was used. There was no preferential utilisation of essential over non-essential amino acids. The TAA pool also varied with development. The mean FAA:TAA ratio remained between 11 and 19. With the Prorocentrum minimum diet, hatching success remained constantly 〉85%, whereas it declined to 0% at the end of the 10 d incubation period with Phaeodactylum tricornutum. After 10 d of feeding on this alga, the FAA content of developing embryos increased significantly, indicating liberation of amino acids due to proteolysis. None of these embryos developed to hatching. Inhibition of hatching success related to the ingestion of P. tricornutum was not due to a lack of any amino acid. The results indicate that the chemical composition of freshly spawned copepod eggs is sensitive to the maternal diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050527
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  • 8
    Electronic Resource
    Electronic Resource
    Water-soluble extracts of the diatom Thalassiosira rotula induce aberrations in embryonic tubulin organisation of the sea urchin Paracentrotus lividus (1999)
    Springer
    Marine biology 134 (1999), S. 147-154 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Eggs and embryos of the sea urchin Paracentrotus lividus were used as a model to study the effect at the cellular level of potential anti-mitotic compounds extracted from the diatom Thalassiosira rotula. Eggs and embryos incubated in a water-soluble diatom extract, corresponding to 5 × 106 and 107 cells ml−1, were totally blocked (i.e. cell division was blocked) at the one-cell stage. At lower concentrations (2.5 and 1.25 × 106 cells ml−1), the first mitotic division was inhibited in 32 ± 26% and 25 ± 3.5% of the zygotes, respectively, demonstrating the dose-dependent effect of diatom extracts on sea urchin development. Immunofluorescence dyes, specific for DNA and α-tubulin subunits, were used to stain nuclei and microtubules in sea urchin embryos during various phases of development. Images with the confocal laser scanning microscope showed that tubulin was not organised in filaments at the sperm aster and cortex levels, and that the pronuclei were not fused in embryos incubated soon after fertilisation with water-soluble diatom extracts corresponding to 107 cells ml−1. At lower diatom-extract concentrations (4 × 106 cells ml −1), fusion of the pronuclei occurred but the mitotic spindle was not formed. Microtubules were clearly de-polymerised and the chromatin appeared globular and compacted at the centre of the cell. A similar structure was observed for sea urchin embryos incubated with 0.1 mM colchicine, a potent anti-mitotic compound. When sea urchin embryos were incubated in water-soluble diatom extracts at different times prior to the first mitotic division, microtubules appeared de-polymerised at each step, from pronuclear fusion to telophase, and cell division was blocked. At the histological level, embryos incubated with 4 × 106 cells ml−1 diatom extract showed nuclear fragmentation without cytokinesis. The possible use of sea urchin embryos as a bioassay to test for other unknown compounds with cytotoxic activity in phytoplankton species is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050533
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  • 9
    Electronic Resource
    Electronic Resource
    Respiratory physiology in summer diapause embryos of the neustonic copepodAnomalocera patersoni (1996)
    Springer
    Marine biology 127 (1996), S. 229-234 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The respiratory physiology of summer diapausing eggs of the neustonic copepodAnomalocera patersoni, maintained under constant temperature (13 °C) and light (12 h light:12 h dark) conditions, was characterized by a bell-shaped curve, with low O2 uptake levels at the beginning of dormancy. This was followed by a steady rise in O2 consumption with maximum levels of 0.002 μl O2 embryo−1 h−1 70 d after spawning. A slow diminution in O2 uptake then occurred until Day 150 when minimum values of 0.0003 μl O2 embryo−1 h−1 were recorded, coinciding with the hatching of the first embryos. Embryos continued to hatch asynchronously up to 360 d from the moment of egg laying. When eggs were subjected to 20 °C, the respiratory activity was almost three times higher than at 13 °C, even though both respiratory curves were similar. The elevated metabolism in eggs kept at 20 °C led to death of the embryos possibly due to a total depletion of metabolic reserves. ATP content also differed at the two temperatures. Diapause eggs kept at 20 °C showed no rapid rise in ATP content as opposed to those kept at 13 °C. The results of temperature shock experiments, in which eggs were first kept at winter temperatures for several weeks, after which the temperature was raised to 20 °C for another number of weeks prior to a second period of chilling at 13 °C, showed that as long as embryos were kept at 20 °C no hatching occurred. By contrast, hatching was observed after 10 d following the resumption of winter temperatures, suggesting that low environmental temperatures are an essential prerequisite for hatching of these eggs. The type of diapause inA. patersoni differs considerably from the one described in insects and in another neustonic copepod,Pontella mediterrana. In this case, there is a U-shaped respiratory curve with greatest O2 consumption prior to the onset or upon breaking of diapause. Differences in the two types of diapause seem to involve not only differences in O2 consumption levels but also in the sequence of metabolic changes with time and the metabolic requirements during sommer and winter dormancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00942107
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  • 10
    Electronic Resource
    Electronic Resource
    Aldehyde suppression of copepod recruitment in blooms of a ubiquitous planktonic diatom (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 429 (2004), S. 403-407 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The growth cycle in nutrient-rich, aquatic environments starts with a diatom bloom that ends in mass sinking of ungrazed cells and phytodetritus. The low grazing pressure on these blooms has been attributed to the inability of overwintering copepod populations to track them temporally. We ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02526
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