A study of the morphology,ultrastructure, and histochemistry of the food of the pediveliger of Ostrea edulis

During the settlement of Ostrea edulis L., the foot of the pediveliger implements temporary attachment and cementing. The morphology of the foot has been re-examined to try to clarify its role during this period. The foot has a highly developed nervous system and musculature, but mainly consists of sub-epidermal gland cells of 9 different types. Cells of the first gland contain acid mucopolysaccharide, and open over the ventral surface of the foot. The second type of gland contains a neutral glycoprotein, and opens at the tip of the foot. The third gland opens mid-ventrally half way down the foot, and largely contains an aromatic protein. The fourth type of gland contains mainly proteoglycan, and the cells open mid-ventrally behind the third gland. The fifth gland contains acid mucopolysaccharide, and the cells open onto the heel of the foot. The sixth, seventh, eighth and ninth glands contain a variety of acid mucopolysaccharides, proteoglycans and possibly a neutral glycoprotein; their cells open into the byssus duct, which discharges at the base of the heel. The grouping of the glands, position of the openings of the cells, and histochemical properties of the secretions suggest that they may be involved in localised and general adhesion of the foot during temporary attachment, as well as in cementing of the larva.     

Observations on the function of the glands of the foot of the pediveliger of Ostrea edulis during settlement

The use during settlement of secretions of the 9 different types of gland in the foot of the pediveliger of Ostrea edulis L. was examined experimentally. During settlement, there is a progressive decrease in the crawling speed of the larva and a strengthening of its bond with the substratum. Both changes are related to (a) a change from ciliary to muscular pedal locomotion; (b) the increasing acidity and viscosity of the mucoid secretions used; (c) the secretion of a byssus thread by the glands of the byssus duet; (d) changes in the form and composition of this byssus. At the termination of settlement, the entire contents of 2 types of gland are discharged. Their secretions give rise to the cement which permanently fixes the larva to the substratum. The 9 types of gland are utilised sequentially in a manner closely related to the 6 phases recognised in settlement behaviour.     

Functional morphology of the larval tentacles of Phragmatopoma californica (Polychaeta: Sabellariidae): composite larval and adult organs of multifunctional significance

Larvae of the sabellariid polychaete Phragmatopoma californica (Fewkes), which were collected in San Diego, California and were competent to metamorphose after 18 to 30 d of development were observed in vivo by videoequipped light microscopy, and the fine structure of the larval tentacles was examined by transmission and scanning electron microscopy. Each tentacle has tufts of at least two types of immotile cilia arranged in dorsolateral and ventrolateral rows, and a ventral groove covered by two types of motile cilia that beat independently of each other. The epidermis is regionalized into glandular, sensory, locomotory, and support cell types and contains four longitudinal bundles of basiepithelial nerve fibers. A layer of connective tissue separates the epidermis and the nerve tracts from obliquely striated muscles that occur within the peritoneum that lines the central coelomic cavities. The peritoneum forms an intact coelomic epithelium that overlies and interdigitates with the muscle cells, with no intervening basal lamina. The muscle cells are considered to be intraperitoneal because they are located above the basal lamina and they lack intercellular junctions with the peritoneal cells. Specialized peritoneal cells form a striated myoepithelial blood vessel that partitions the coelom into medial and lateral cavities. No neuromuscular junctions were found, but both muscular and ciliary movement seem to be under neuronal control. The basiepithelial nerve terminals appear to synapse into the connective tissue layer toward the intraperitoneal muscle. Several similarities in tissue organization are noted between the larval tentacles of P. californica and the tube feet of echinoderms. Observations on the ontogeny, morphology, and behavior of the tentacles suggest that they are multifunctional organs involved in feeding, construction of the juvenile sand tube, locomotion, attachment, and sensory perception during larval and adult lives.     

Feeding deterrence properties of apo-fucoxanthinoids from marine diatoms. II. Physiology of production of apo-fucoxanthinoids by the marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana,and their feeding deterrent effects on the copepod Tigriopus californicus

The marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana have been shown to produce apo-fucoxanthinoid compounds which act as feeding deterrents against the harpacticoid copepod Tigriopus californicus. The amounts and types of apo-fucoxanthinoids produced were species specific. Th. pseudonana produced small quantities of apo-12-fucoxanthinal and apo-13-fucoxanthinone only during senescence, while P. tricornutum produced much greater quantities of these two compounds during both log and senescence phases, in addition to producing a third compound, apo-10-fucoxanthinal, only during senescence. For both species, production of apo-fucoxanthinoids increased as the cells entered senescence phase due to phosphate limitation. The amounts of apo-fucoxanthinoids necessary to reduce feeding in T. californicus by 50% ranged from 2.22 to 20.2 ppm. This range was approximately 1000 times lower than the total apo-fucoxanthinoid concentration in P. tricornutum. The amounts of apo-fucoxanthinoids necessary to cause a 50% mortality in a population of T. californicus ranged from 36.8 to 76.7 ppm. Thus, these compounds are present in concentrations which may have ecological significance in the control of bloom formation and grazing. The production of apo-fucoxanthinoids may be a phenomenon common to many diatoms, particularly as they enter senescence due to nutrient limitation.     

Settlement of barnacle larvae: surface structure of the antennular attachment disc by scanning electron microscopy

The surface morphology of the antennular attachment disc of the cypris larva of Balanus balanoides has been investigated by scanning electron microscopy, and its function is considered in the context of settlent behaviour. It is concluded that the attachment organ acts as an adhesive pad for temporary attachment while the larva explores the substratum. The surface of the disc is covered with villi, which could retain an adhesive substance thought to be produced by the antennular glands. The open-ended hair of the axial sense organ on the disc is shown.     

Hydrodynamic stress and habitat partitioning between indigenous (Perna perna) and invasive (Mytilus galloprovincialis) mussels: constraints of an evolutionary strategy

The ability of a mussel to withstand wave-generated hydrodynamic stress depends mainly on its byssal attachment strength. This study investigated causes and consequences of different attachment strengths of the two dominant mussels species on the South African south coast, the invasive Mytilus galloprovincialis and the indigenous Perna perna, which dominate the upper and the lower areas of the lower balanoid zone, respectively and co-exist in the middle area. Attachment strength of P. perna was significantly higher than that of M. galloprovincialis. Likewise solitary mussels were more strongly attached than mussels living within mussel beds (bed mussels), and in both cases this can be explained by more and thicker byssal threads. Having a wider shell, M. galloprovincialis is also subjected to higher hydrodynamic loads than P. perna. Attachment strength of both species increased from higher to lower shore, in response to a gradient of stronger wave action. The morphological features of the invasive species and its higher mortality rates during winter storms help to explain the exclusion of M. galloprovincialis from the low shore. The results are discussed in the context of the evolutionary strategy of the alien mussel, which directs most of its energy to fast growth and high reproductive output, apparently at the cost of reduced attachment strength. This raises the prediction that its invasive impact will be more pronounced at sites subject to strong but not extreme wave action.     

Mating behaviour in the penaeid shrimp Penaeus vannamei

Mating behaviour of Penaeus vannamei was observed during January, 1986. Mating behaviour was divided into four phases: (1) approach, (2) crawling, (3) chasing, and (4) mating. Male mating and spermatophore transfer to the mature female take place at intermolt stage C₄. The glutinous spermatophore emitted from the male can be transferred onto the female open thelycum during the ventralto-ventral position in mating in P. vannamei. Though male P. vannamei often chase males or immature females with undeveloped ovaries, no males were ever mated and mating only occurred in females with ripe ovaries.     

Modes of water manipulation by the lobate ctenophore Leucothea sp.

Examination of the lobate ctenophore Leucothea sp. has revealed new patterns of swimming and water manipulation in addition to the typical ctenophore mode of slow swimming with ctene plate (comb) ciliary propulsion. We distinguish between slow ctene propulsion and rapid ctene propulsion; the latter is accomplished by an increased ciliary beat that produces a coupled vortex wake, resulting in jet propulsion. The large oral lobes both capture prey and provide undulatory muscular propulsive power. The auricles exhibit distinct phasic synchrony and aphasic or sculling motions that generate small vortices in the water which facilitate prey capture. Distinctive papillae covering the exterior of Leucothea sp. may be chemo- or mechano-sensory structures. The integration of all of these structures results in an organism that is more complex behaviorally than might be expected on the basis of its superficially simple and delicate body plan. Field work involved blue-water diving in the waters of the California Bight during June and July, 1985.     

Discovery of postcopulatory mate guarding in Copepoda Harpacticoida (Crustacea)

Mating behaviour of four species of Tisbe (Tisbidae) and of Paramphiascella fulvofasciata (Diosaccidae) was filmed with a videocamera during 1992 and 1993 at the University of Oldenburg. This behaviour is complex and can be divided into different phases: grasping of the female; courtship; copula and postcopulatory mate guarding. During courtship both partners lie parallel in opposite directions with their ventral sides facing each other. The male strokes the abdomen of the female with his second to fourth peracopods. As a result the female becomes motionless. The copula is a quick process of only a few seconds during which spermatophore transfer takes place. When this has happened, males do not leave the females but become inactive and are carried around by them for varying lengths of time. This pattern and the fact that only adult partners are involved in these associations prove that this behaviour is very different from the precopulatory mate guarding presumed to be ubiquitous among Harpacticoida. Cases of postcopulatory mate guarding have never been explicitly demonstrated for Harpacticoida. The minimum duration of guarding was found to match the time necessary for spermatophore discharge. Guarding is, therefore, interpreted as a strategy to secure paternity. New definitions are given for courtship, copula and postcopulatory mate guarding in Harpacticoida to help avoiding misinterpretations of associations between adult partners. Such misinterpretations abound in the literature.     

The wartbiter spermatophore and its effect on female reproductive output (Orthoptera: Tettigoniidae,Decticus verrucivorus)

Summary Male wartbiters Decticus verrucivorus transfer elaborate spermatophores to females during copulation. The spermatophore is attached externally to the female's genitalia and consists of two parts: a large, gelatinous, sperm-free portion, the spermatophylax, eaten by the female after mating; and a sperm-containing ampulla, eaten after the spermatophylax has been consumed. Since females take longer to eat larger spermatophylaxes, the duration of ampulla attachment is positively correlated with spermatophylax size. Two series of experiments were carried out, one in which the size of the spermatophylax consumed by females and the duration of ampulla attachment were manipulated in concert and another in which they were manipulated independently. Some females were also maintained on a protein-free diet and either supplied with or deprived of spermatophylax material. The amount of protein in the diet, but not the amount of spermatophylax material consumed, influenced female longevity, lifetime fecundity, and egg weight. When females were deprived of the spermatophylax, an experimental increase in the duration of ampulla attachment induced longer periods of unreceptivity in females after mating, a more rapid onset of oviposition, and an increased oviposition rate. Consequently, the number of eggs laid by females during their nonreceptive refractory periods increased significantly with increasing duration of ampulla attachment up to 180 min; however, there was no significant increase in the number of eggs laid beyond 180 min of ampulla attachment. This closely corresponds to an ampulla attachment duration of 188 min expected when a male transfers a natural spermatophylax of mean size to the female. These results suggest that the amount of ejaculate transferred to the female, and not the amount of spermatophylax material per se, is the factor controlling female receptivity and oviposition behavior. Since we did not detect any effect of spermatophylax consumption on female fecundity or egg weight, we conclude that the spermatophylax of D. verrucivorus functions primarily as a sperm protection device rather than as a form of male parental investment.     

Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris

In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November 1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle, was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis could contribute to somatic growth, which occurs in late winter. Received: 3 March 1997 / Accepted: 23 July 1997     

Sand and wave induced mortality in invasive (<Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis>) and indigenous (<Emphasis Type="Italic">Perna perna</Emphasis>) mussels

The ability of an invasive species to spread in a new locality depends on its interaction with the indigenous community and on variation in time and space in the environment. The Mediterranean mussel Mytilus galloprovincialis invaded the South African coast 30 years ago and it now competes and coexists with the indigenous mussel Perna perna. The two species show different tolerances to wave and sand stress, two of the main environmental factors affecting this intertidal community. P. perna is more resistant to hydrodynamic stress than M. galloprovincialis, while the invasive species is less vulnerable to sand action. Our results show that mortality rates of the two species over a period of 6 months had different timing. The indigenous species had higher mortality than M. galloprovincialis during periods of high sand accumulation in mussel beds, while the pattern reversed during winter, when wave action was high. A negative correlation between sand accumulation and attachment strength of the two mussels showed that sand not only affects mussel mortality through scouring and burial, but also weakens their attachment strength, subjecting them to a higher risk of dislodgement. Here we underline the importance of variations in time and space of environmental stress in regulating the interaction between invasive and indigenous species, and how these variations can create new competitive balances.     

Glycogen storage in relation to the moult cycle in the two crustaceansEmerita asiatica andLigia exotica

InEmerita asiatica, the quantitative fluctuations in the glycogen content of the hepatopancreas were markedly related to the moult cycle. The glycogen content of the hepatopancreas was maximum during premoult stages. It has been suggested that reserve glycogen, in addition to meeting general metabolic needs, may be especially involved in the genesis of the sugar precursors of chitin. The marked fall in the hepatopancreas glycogen values following moulting is probably due to its utilization in chitin synthesis during and immediately following moulting. InE. asiatica, the storage of glycogen was found to be meagre in muscles, and muscle glycogen had no bearing on chitin synthesis during moulting. InLigia exotica, glycogen is stored to a lesser extent than inE. asiatica, and was found in connective tissue and muscles. Significant fluctuations were noted in glycogen values correlated with the phases in the moult cycle when chitin synthesis took place. InL. exotica, the hepatopancreas does not serve as a storage depot for glycogen related to chitin synthesis.     

Whitefly wax as a cue for phoresy in the broad mite, <Emphasis Type="Italic">Polyphagotarsonemus latus</Emphasis>(Acari: Tarsonemidae)

Summary. Broad mite, Polyphagotarsonemus latus (Acari: Tarsonemidae) exhibits a specific phoretic relationship with whiteflies. Under field conditions most broad mites, caught in sticky traps, are attached to whiteflies. Under laboratory conditions, attachment occurs equally well in the dark and light. Mites do not differentiate between the sexes of their phoretic host Bemisia tabaci. However, mite attachment to B. tabaci is greatly diminished by washing the host with various organic solvents, chloroform in particular. The effect of whitefly waxy particles on broad mite behavior was studied using wax from the whitefly Aleyrodes singularis and from the mealybug Planococcus citri. Broad mites were not only attracted specifically to the A. singularis waxy particles-treated leaf areas but were also attached to leaf trichomes in this area. The results of this study suggests the importance of olfactory cues from the whitefly waxy particles in the recognition process of the phoretic host and/or the induction of the attachment behavior to whitefly legs or leaf trichomes.     

Variation in strength of attachment to the substrate explains differential mortality in hybrid mussel (Mytilus galloprovincialis and M. edulis) populations

Mussel samples were collected from a hybrid mussel (Mytilus galloprovincialis and M. edulis) Population at Croyde, southwest England, in January, March and May 1990. The strength of attachment of each mussel to the substrate was measured with a spring balance. A number of diagnostic characters were also recorded. These are shell lengh, width and height, mantle colour and genotype at two allozyme loci, esterase-D and octopine dehydrogenase. Multiple-regression analysis was used to assess the effect of the diagnostic characters on strength of attachment as dependent variable. Mussels possessing the relatively high shells and darker mantle colouration characteristic of M. galloprovincialis had higher values, on average, for strength of attachment than mussels resembling M. edulis. Phenotypically intermediate mussels had intermediate values for strength of attachment. The results suggest an adaptive difference which can account for reports of differential mortality acting in favour of M. galloprovincialiis.     

Biochemical adaptations of the mudskipper Boleophthalmus boddaerti to a lack of oxygen

Specimens of the mudskipper Boleophthalmus boddaerti, collected along the estuarine canal at Pasir Ris, Singapore between April 1987 and December 1989, were examined in the laboratory. After being exposed to environmental hypoxia for 6 h, no accumulation of lactate, alanine or succinate was observed in the muscle tissue of B. boddaerti. In addition, the blood lactate content and muscle creatine phosphate (CrP), adenosine triphosphate (ATP) and glycogen contents were not significantly different from those of the control. During normoxic recovery, oxygen debt repayment was only a small fraction of the oxygen deficit incurred during the 6 h of hypoxic exposure. Therefore, it would appear that B. boddaerti coped with environmental hypoxia by undergoing metabolic rate reduction. After anoxic exposure, the CrP, ATP and adenosine diphosphate (ADP) contents in the muscle tissue of B. boddaerti were significantly lower than the corresponding control values. Lactate accumulated in the blood and muscle tissue of the anoxic fish though the muscle energy charge and glycogen content remained constant. Hence, B. boddaerti was able to cope with such a period of anoxia without increasing its glycolytic rate. Succinate, which was not detected in the muscle tissue of the control and hypoxia-exposed fish, accumulated in significant quantities in the muscle tissue of B. boddaerti exposed to environmental anoxia and functional hypoxia. In the case of functional hypoxia, there was a significant decrease in the muscle glycogen content, and the muscle lactate content increased 17.3-fold, indicating that glycolysis was activated to provide the source of energy during muscular exercise.     

Dominance relationship in the establishment of reproductive division of labour in a primitively eusocial wasp (Ropalidia marginata)

In mature post-emergence colonies of the tropical primitively eusocial polistine wasp Ropalidia marginata, the queen is not a behaviourally dominant individual. Nevertheless, she completely suppresses reproduction by the workers and becomes the sole egg-layer in the colony. Mechanisms by which a female is able to establish her exclusive reproductive status in the colony can be investigated by examining dominance-submission relationships and hierarchy formation at particular stages of the colony cycle when reproductive competition is behaviourally manifest. Observations on the behaviour of R. marginata females (1) during early stages of colony-founding, (2) when potential queens challenge the existing queen, and (3) immediately after queen replacement show that these wasps use highly aggressive dominance interactions to establish their reproductive status. Both the frequency and the intensity of dominance behaviours are significantly higher at these stages than those observed at phases of the colony when there is no apparent reproductive strife. Once her position as the only egg-layer of the colony has been established, the levels of dominance interactions initiated by the queen decrease and the nature of these interactions also becomes comparatively milder. Thus, the mechanisms by which a queen establishes her social status in her colony and those by which she continues to suppress reproduction of her nestmates in the absence of overt physical dominance may be quite different. Received: 17 November 1995/Accepted after revision: 20 April 1996     

Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis

The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s^-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.     

Ventilation rate and copulation in Octopus vulgaris

Typically three events occur when Octopus vulgaris Cuvier mates. The male inserts its hectocotylus into the mantle cavity of the female; the hectocotylus and the bodies of the male and female become quiescent; and the female increases its ventilation rate about 2.5 times, on the average, above its precopulatory base rate. It is hypothesized that the increased ventilation rate of the female provides the stimulus to the male to transfer its spermatophore to the oviduct. Since the insertion of the hectocotylus and the female's increased ventilation rate may be dissociated, it is suggested that copulation be defined as the attachment of the hectocotylus to the oviduct. A conditioned ventilation-rate increase in the female was observed with repeated testing. Observation of arching and pumping movements of the male as well as measurements of its ventilation rate before and during copulation indicate that only a few spermatophores are transferred per copulation.     

Morphological and habitat divergence in the intertidal limpet Patelloida pygmaea

In the intertidal limpet Patelloida pygmaea, two distinctive morphs, the forms pygmaea and conulus, have been recorded. The former possesses a flat elongated shell, and the latter has an extremely high round shell. It has been observed in the field that pygmaea is found on oyster shells Crassostrea gigas. The form conulus uses an unusual substrate for attachment. It is found on the living shells of the intertidal gastropod Batillaria cumingi. Although conulus is normally found only on shells of Batillaria, it can also be found on oyster shells when pygmaea and Batillaria shells are not present in nature. An electrophoretic analysis of allozymes showed that these two forms are reproductively isolated from each other and coexist without gene exchange on the same mudflat. Laboratory experiments showed that pygmaea prefers oyster shells and conulus prefers Batillaria shells as substrates for attachment when both oyster and Batillaria shells are present. The form pygmaea did not attach to Batillaria shells, even when only Batillaria shells were available. However, conulus also attached to oyster shells when Batillaria shells were not available. The proportion of individuals of conulus that attached to oyster shells decreased significantly when pygmaea was attaching to the oyster shells. These results suggest that pygmaea is ecologically more specialized to living on oyster shells than conulus.