Showing papers in "The Biological Bulletin in 1998"

Zebra Mussel Spawning Is Induced in Low Concentrations of Putative Serotonin Reuptake Inhibitors

Abstract: Serotonin (5hydroxytryptamine, 5-HT) and its receptor ligands induce both oocyte maturation and spawning in zebra mussels (Dreissena polymorpha). The selective serotonin reuptake inhibitors (SSRIs) fluvoxa- mine ("Luvox"), fluoxetine ("Prozac"), and paroxetine ("Paxil") are commonly prescribed drugs for the treat- ment of depression in humans. They act to increase 5- HT neurotransmission by inhibiting reuptake transport proteins at synapses. I tested the efficacy of these drugs at inducing spawning in zebra mussels. All three compounds induced spawning in both sexes at concentrations lower than that for 5-HT itself. Fluvoxamine was particularly potent, inducing spawning in 100% of both sexes at lo-' and 10e6 M. The concentration that induced a significant percentage of animals to spawn was as low as lop9 M for males and and lo-' M for females. The lowest concentra- tion of fluvoxamine to induce spawning was lo-* M for females (40%) and lo-" M for males (20%). Gametes spawned in fluvoxamine ( 10m5 M and lower) were viable, and swimming trochophores were formed within 20 hours. Fluoxetine was also an effective spawning inducer, causing 100% of males to spawn at 5

Cell locomotion and focal adhesions are regulated by the mechanical properties of the substrate.

Abstract: portant interactions that modulate intracellular signaling pathways, as well as various cellular events from gene expression to cell locomotion (Juliano and Haskill, 1993). The full response to adhesion seems to involve not only the cross-linking of integrins but also mechanical input through these receptors (Craig and Johnson, 1996; Wang et al., 1993; Ingber, 1993; Chrzanowska-Wodnika and Burridge, 1996; Choquet et al., 1997). To explore this possibility, we have examined the motility and cytoskeletal organization of NRK epithelial cells and 3T3 fibroblasts cultured on substrates having varying mechanical properties (Pelham and Wang, 1997). Flexible, optically clear substrates were prepared by covalently linking type I collagen to polyacrylamide sheets. The flexibility of the substrate was manipulated by maintaining the acrylamide concentration at 10% while varying the bis-acrylamide contents between 0.03% and 0.26%. In this manner, we were able to maintain a constant chemical environment regardless of substrate flexibility. The Young's Modulus of the substrate, determined by measuring the extent of stretching in response to known applied forces, showed a 13-fold difference between sheets of 0.26% and 0.03% bis-acrylamide. When probed microscopically with a calibrated microneedle, the substrates showed 16-fold difference in compliance (-7.3 x 10-7 newtons/tm versus ~4.6 X 10-8 newtons/ym). On more rigid substrates, both NRK epithelial cells and 3T3 fibroblasts were well spread and appeared indistinguishable from those cultured on glass or plastic sur-

Temperature and embryonic development in relation to spawning and field occurrence of larvae of three Antarctic echinoderms

Abstract: The effects of temperature on development and viability were measured at 14 levels between -2?C and +3?C on embryos of two asteroids (Odontaster val- idus and Odontaster meridionalis) and an echinoid (Sterechinus neumayeri) from Signy Island, Antarctica. Development rates were 2 to 10 times slower than those for temperate or tropical echinoderms, with times to hatching up to 240 h. Development rates for the two asteroids differed by 1.15 x, and rates for both species approximately doubled over the experimental tempera- ture range. In 0. validus, embryo viability was indepen- dent of temperature, but in 0. meridionalis viability declined with increasing temperature. Development rates for S. neumayeri were little affected by tempera- ture above +0.2?C, but declined rapidly at lower tem- peratures. Conversely, the number of nonviable eggs was low and constant below + 1.7?C, but rose rapidly at higher temperatures. A window of optimal temperature, between +0.2?C and +1.7?C, has therefore been pro- posed for development time and embryo viability in this population of S. neumayeri. Spawning trials and field observations of larvae indicated that the time of gamete release and periods of larval development in S. neumay- eri coincided with austral summer sea temperatures in the same window. Embryos of 0. meridionalis and 0. validus are released in winter, when temperatures are constantly below -1.6?C. Comparison of the different strategies suggests that larval food supply and predation during planktonic phases are not the dominant ecologi- cal factors for these species.

Sampling the light-organ microenvironment of Euprymna scolopes: description of a population of host cells in association with the bacterial symbiont Vibrio fischeri.

Abstract: The symbiosis between the squid Euprymna scolopes and the luminous bacterium Vibrio fischeri has a pronounced diel rhythm, one component of which is the venting of the contents of the light organ into the surrounding seawater each day at dawn. In this study, we explored the use of this behavior to sample the microenvironment of the light-organ crypts. Intact crypt contents, which emerge from the lateral pores of the organ as a thick paste-like exudate, were collected from anesthetized host animals that had been exposed to a light cue. Microscopy revealed that the expelled material is composed of a conspicuous population of host cells in association with the bacterial symbionts, all of which are embedded in a dense acellular matrix that strongly resembles the bacteria-based biofilms described in other systems. Assays of the viability of expelled crypt cells revealed no dead bacterial symbionts and a mixture of live and dead host cells. Analyses of the ultrastructure, biochemistry, and phagocytic activity of a subset of the host cell population suggested that some of these cells are macrophage-like molluscan hemocytes.

Migratory Behavior of Ovigerous Blue Crabs Callinectes sapidus: Evidence for Selective Tidal-Stream Transport

Abstract: In the late summer and early fall, newly inseminated female blue crabs (Callinectes sapidus) leave low-salinity areas of estuaries and migrate seaward to spawn near the entrance. We tested the hypothesis that migration of female C. sapidus to spawning grounds is facilitated by selective tidal-stream transport (STST). We monitored the swimming direction of adult crabs from a stationary platform located about I km inside the entrance to the Newport River Estuary (Beaufort, North Carolina). Swimming activity near the sur$ace occurred primarily at night and most crabs avoided swimming against tidal currents. Eighty-one percent of the crabs observed moving downestuary toward the inlet during ebb tide were ovigerous females. Of the 36 gravid females captured traveling in ebb currents, 97% possessed dark egg masses containing late-stage embryos. Conversely, nearly all (98%) adult crabs observed traveling in flood currents lacked egg masses, and all the females captured while migrating upestuary exhibited signs of recent spawning. These observations indicate that ovigerous blue crabs use ebb-tide transport to migrate seaward to spawn and flood-tide transport to reenter the estuary shortly after larval release. Atlantic blue crabs (Cullinectes supidus Rathbun), like many brachyuran crabs, possess a complex life cycle that includes both estuarine and coastal migratory phases, making them ideal models for studying the intricacies of hydrodynamic transport, dispersal, and recruitment [see

Stimulation of Metamorphosis in the Polychaete Hydroides elegans Haswell (Serpulidae).

Abstract: The serpulid polychaete Hydroides elegans is a common, cosmopolitan warm-water biofouling organ- ism. Competent larvae of H. elegans metamorphose rap- idly after induction by marine biofilms. Only 15 min after coming in contact with the metamorphic cue, larvae have completed secretion of the primary tube; secretion of the secondary, calcareous tube begins 1.5 h after the primary tube has been deposited. Metamorphosis is characterized by disappearance of the prototroch and differentiation of the tentacular crown in the head region, the collar and thoracic membrane in the thoracic region, and the pygid- ium at the tip of the abdomen. These morphogenetic events were used to gauge the responses of larvae to biofilms, as well as to the artificial inducers Cs' and Kf. A maximal metamorphic response to the two ions requires exposure to different concentrations and durations, i.e., a 3-h pulse of 10 mA4 CsCl, or a 24-h continuous exposure to 50 r&Z excess KCl. The metamorphic response to Cs+ or K+ is much slower than the response to biofilms, dem- onstrating that the tissues respond differently to artificial inducers. The differences in the kinetics of the responses to the natural and cationic inducers suggest that the induc- tion mechanisms are not the same. When these artificial inducers were used, some, but not all, of the metamor- phosed juveniles never attached to the substratum or se- creted a primary tube, probably as a result of secondary effects of the ions on processes of tube formation. The exact mechanisms by which Cs' and excess K+ induce metamorphosis are still unclear, although we assume, as do others, that these agents act by depolarizing the mem- branes of excitable sensory cells and not by interacting with specific receptors.

Effect of Larval Swimming Duration on Growth and Reproduction of Bugula neritina (Bryozoa) Under Field Conditions.

Abstract: A growing body of evidence indicates that even subtle events occurring during one portion of an animal's life cycle can have detrimental, and in some cases, lasting effects on later stages. Using a laboratory-field transplant design, postmetamorphic costs associated with the duration of larval swimming were investigated in the bryozoan Bugula neritina. Larvae were induced to metamorphose in the laboratory after swimming for either less than 1 h or between 23 and 24 h; colonies that developed from these two groups of larvae are referred to hereafter as "1-h colonies" and "24-h colonies," respectively. After completing metamorphosis, individuals were transplanted to the field, where rates of growth and reproduction were monitored. In a study of the interaction between colony orientation (up or down) and larval swimming duration, both factors significantly affected the number of autozooids produced. For example, 14 days after metamorphosis, 1-h colonies facing up were approximately 40% smaller than 1-h colon...

Characterization of Aplysia Attractin, the First Water-borne Peptide Pheromone in Invertebrates

Abstract: Although animals in the genus Aplysia are solitary during most of the year, they form breeding ag- gregations during the reproductive season. The aggrega- tions contain both mating and egg-laying animals and are associated with masses of egg cordons. The egg cordons are a source of pheromones that establish and maintain the aggregation, but none of the pheromonal factors have been chemically characterized. In these studies, speci- mens of Aplysia were induced to lay eggs, the egg cordons collected and eluted, and the eluates fractionated by Cl8 reversed-phase HPLC. Four peak fractions were bioas- sayed in a T-maze. All four increased the number of animals attracted to a nonlaying conspecific and were thus subjected to compositional and microsequence analysis. Each contained the same NH,-terminal peptide sequence. The full-length peptide ("attractin") was isolated from the albumen gland, a large exocrine organ that packages the eggs into a cordon. The complete 58-residue sequence was obtained, and it matched that predicted by an albumen gland cDNA. Mass spectrometry showed that attractin is 2 1 wt. % carbohydrate as the result of N-linked glycosyla- tion. T-maze bioassays confirmed that the full-length pep- tide is attractive. Attractin is the first water-borne peptide

Celestial Mechanics, Sea-Level Changes, and Intertidal Ecology

Abstract: Celestial mechanics has long been known to affect life on Earth, but exploration of these influences has been hampered by long temporal scales and complex biological relations. Here we report on a periodic fluctuation in tidal exposure driven by the 18.6-y oscillation of the moon's orbital inclination, which can change by almost 50% the average time that intertidal organisms are exposed to air. The temperature of nearshore water and the upper limits to mussels are shown to vary with the lunar oscillation. Such variation challenges the value of ecological and physiological generalizations based on snapshot measures, and highlights the value of long-term studies.

Plectin Sidearms Mediate Interactions of Intermediate Filaments With Microtubules and Other Components of the Cytoskeleton

Abstract: The IF-associated protein plectin has been proposed to be a cytoplasmic cross-linker (Foisner and Wiche, 1991). We recently reported unique “millipede-like” structures in mammalian cell cytoskeletons revealed after removal of actin by treatment with gelsolin (Svitkina et al., 1995, 1996). Here we demonstrate, by immunogold labeling, that the millipede structures are composed of cores of vimentin IFS with sidearms containing plectin. The dimensions of the sidearms (up to 200 nm long and 2-3 nm wide) match the size of plectin molecules (Foisner and Wiche, 1987), suggesting that sidearms are made of individual plectin molecules, or a few of them in register. These plectin sidearms connect IFS to microtubules, the actin-based cytoskeleton, and possibly to membrane components. Plectin binding to microtubules is significantly increased in cells from transgenic mice lacking IFS (MFT16 cell line, courtesy of Dr. R. Evans). Numerous sidearms are associated with microtubules in these cells, giving them an unusual “hairy” appearance. After microinjection of exogenous vimentin in MFT-16 cells, IFS of variable length are formed within 3 h; the IFS have a very high density of associated plectin, whereas microtubules lose most of their plectin sidearms. These results suggest the existence of a pool of plectin that preferentially associates with IFS, but that may also be competed for by microtubules. The association of IFS with microtubules shows

Cellular Basis of Mechanotransduction

Abstract: Physical forces, such as those due to gravity are fundamental regulators of tissue development. To influence morphogenesis, mechanical forces must alter growth and function. Yet little is known about how cells convert mechanical signals into a chemical response. This presentation attempts to place the potential molecular mediators of mechanotransduction within the context of the structural complexity of living cells.

A protein identical to the yolk protein is stored in the testis in male red sea urchin, Pseudocentrotus depressus

Abstract: Female sea urchins store the major yolk protein (MYP) in ovarian nutritive phagocytes before vitellogenesis. Using immunological procedures, we detected MYP in the testicular nutritive phagocytes of Pseudocentrotus depressus, the red sea urchin, and then compared the distribution of MYP between sexes during gametogenesis. MYP was purified from unfertilized eggs by ion exchange chromatography (Q Sepharose) and gel filtration (Superdex 200), and an antiserum (anti-MYP) was raised against MYP. Immunoblot analysis demonstrated that immature testes, as well as ovaries, contained a large quantity of MYP. Immunohistochemistry showed that MYP was distributed in the nutritive phagocytes occupying the follicular lumen in both males and females. In both sexes, as gametogenesis proceeded, the nutritive phagocytes degenerated and the gonadal lumen filled with gametes. MYP accumulated in ripe ova as a yolk protein in the mature ovary. In contrast, MYP was not detected in mature testes, because stored spermatozoa did no...

Effect of Colony Size, Polyp Size, and Budding Mode on Egg Production in a Colonial Coral.

Abstract: The factors that influence egg production in the massive coral Goniastrea aspera were examined in colonies of various sizes collected before the first spawn- ing of the year. Particular attention was given to polyp size, measured in three dimensions as volume. Although a polyp in a colony containing as few as 13 polyps produced eggs, colonies with fewer than 60 polyps had fewer eggs per unit volume of polyp. The relationship between colony size and colony fecundity suggested that 60 polyps is the minimum size at which a colony can achieve active maturity. Polyp volume of small colonies before maturation was also smaller than that of the larger colonies, suggesting that colony size, as well as polyp size, is crucial for sexual maturity. The position of a polyp in the colony (and thus its mode of budding) also affects its maturity (and thus its egg production). Marginal polyps (those on the edge of the colony) usually exhibited extratentacular budding, and the resulting polyps were initially immature. Conse- quently, egg production by such polyps is a function of their age, calculated from the time of their formation by extratentacular budding. In contrast, non-marginal polyps always exhibited intratentacular budding. Moreover, in the non-marginal areas of large colonies (>84 polyps), the polyps produced by intratentacular budding were al- ways mature. In all colonies, marginal polyps were smaller in volume and had a lower number of eggs for each unit of volume than did non-marginal ones. This suggests that polyps play different roles according to their position in a colony: marginal polyps contribute to de- fense and expansion of the area of attachment, whereas

Body Polarity and Mineral Selectivity in the Demosponge Chondrosia reniformis

Abstract: The skeleton of the common Mediterranean demosponge Chondrosia reniformis lacks endogenous spicules; but exogenous siliceous material is selectively incorporated into its collagenous ectosome, strengthening this layer. Nevertheless, the settling of sponge buds during asexual reproduction necessitates an active incorporation of the calcareous substratum through the sponge lower ectosome. This fact suggests the presence of a polarity in the sponge, with the lower surface selecting primarily carbonates, and the upper surface selecting exclusively silicates and quartz. Our observations under experimental conditions showed that the strong selectivity of the upper ectosome is realized only when the sponge is fixed to the substratum; if detached, the sponge incorporates both quartz and carbonates. In laboratory experiments, the incapacity of both kinds of ectosome to regenerate into a new complete sponge suggests that this polarity arises early in ontogeny.

Vestimentiferan on a whale fall

Abstract: Discovery of chemosynthetic communities associated with whale bones led to the hypothesis that whale falls may serve as stepping-stones for faunal dispersal between disjunct hydrothermal vents and cold seeps on the ocean floor (1). The initial observation was followed by a faunal inventory that revealed a diverse assemblage of microbes and invertebrates, supported by chemoautotrophic production, living in close proximity to whale remains (2, 3). To date, the conspicuous absence from whale falls of vestimentiferan tubeworms (a predominant constituent of eastern Pacific vent and seep habitats) has been a major objection to the stepping-stone hypothesis (4-5). We report the first evidence of a vestimentiferan tubeworm associated with a whale fall (Fig. 1). The tubeworm, Escarpia spicata, was identified by morphological criteria and DNA sequence data from a portion of the mitochondrial cytochrome oxidase C subunit I (COI) gene. Additionally, the bacterial endosymbiont in the tubeworm possessed a 16S rRNA gene...

Choosing Objective Lenses: The Importance of Numerical Aperture and Magnification in Digital Optical Microscopy

Abstract: Microscopic images are characterized by a number of microscope-specific parameters--numerical aperture (NA), magnification (M), and resolution (R)--and by parameters that also depend on the specimen--for example, contrast, signal-to-noise ratio, dynamic range, and integration time. In this article, issues associated with the microscope-specific parameters NA, M, and R are discussed with respect to both widefield and laser scanning confocal microscopies. Although most of the discussion points apply to optical microscopy in general, the main application considered is fluorescence microscopy.

Effect of Methyl Farnesoate on Late Larval Development and Metamorphosis in the Prawn Macrobrachium rosenbergii (Decapoda, Palaemonidae): A Juvenoid-like Effect?

Abstract: Methyl famesoate (MF), the unepoxidated form of insect juvenile hormone III, was detected in larvae of the freshwater prawn Macrobrachium rosenbergii, which metamorphose to post-larvae following 11 larval stages. The possible role of MF as a morphogen was studied by administering the compound to M. rosenbergii larvae via an Artemia vector. Higher MF levels caused earlier retardation of late larval growth, and the highest dose retarded larval development. Furthermore, MF sig- nificantly affected the patterns of metamorphosis and the appearance of intermediate individuals exhibiting both larval and post-larval morphology and behavior. Three intermediate types were defined, two of which were found only at the MF-treated groups and one that was exclusive to the higher dose treatments. The relative abundance of intermediate specimens increased from 2% in the control to 32% in the high MF concentration, which suggests that MF has a juvenoid-like effect in this decapod crustacean.

Carbohydrates of the Organic Shell Matrix and the Shell-Forming Tissue of the Snail Biomphalaria glabrata (Say).

Abstract: Sulfated carbohydrates may play a role in the biomineralization of the molluscan shell. The carbohydrates of the extracted water-insoluble organic shell matrix (IM) of the freshwater snail Biomphalaria glabrata were identified as glucose, mannose, galactose, and N-acetyl-glucosamine, whereas the water-soluble organic matrix (SM) additionally contained N-acetyl-galactosamine. A specific lectin binding pattern of the matrix was obtained. One prominent protein of the SM, with a size of 19.6 kDa and a pI of 7.4, was shown to be a glycoprotein with terminal glucosyl or mannosyl moieties. The acidic constitutents of the matrix showed a variety of possible terminal sugars, indicating a heterogenous mixture of proteoglycans or glycosaminoglycans (GAGs) and glycoproteins. At the shell-forming mantle edge, an alcian-blue-positive material was observed in the periostracum groove (PG), the belt, and apically in the cells of the outer mantle epithelium (OME). With the help of lectins, all sugars in question were detected in the PG and the belt, whereas the OME was bound by glucose/mannose- and GlcNac-specific lectins only. Although the complete set of GAGs will be produced in the PG and the belt, a very acidic fraction of GAGs and the 19.6-kDa protein can also be delivered by the OME.

Transparency and Visibility of Gelatinous Zooplankton from the Northwestern Atlantic and Gulf of Mexico

Abstract: Transparency measurements (at 400 to 700 nm) were made on living specimens of 29 common spe- cies of gelatinous zooplankton from the Northwestern At- lantic Ocean and Gulf of Mexico. Percent transparency ranged from 91% for the hydromedusa Sibogota typa to 0.5 1% for the pteropod Clione limacina. Percent transpar- ency was linearly and positively correlated with wave- length, with slopes of the regression lines (normalized to the percent transparency at 480 nm) ranging from O.O27%/nm for Sibogota typa to 0.5 1 %/nm for the cteno- phore Mnemiopsis mactydi (average 0.17 2 O.O19%/nm). There was no significant correlation between the percent transparency of an animal and its daytime depth distribu- tion. The relationship between percent transparency and sighting distance when viewed from below was modeled and showed that, due to the increase of the minimum contrast threshold for object detection at lower light lev- els, the usefulness of transparency as camouflage in- creases dramatically with depth. A preliminary account of these results was presented by the authors at the four- teenth meeting of the Ocean Optics Society in November

Metamorphic-Signal Transduction in Hydroides elegans (Polychaeta: Serpulidae) Is Not Mediated by a G Protein.

Abstract: Evidence from larvae of hydrozoans, gastropods, and barnacles suggests that G protein-coupled receptors mediate induction of settlement and metamorphosis in response to environmental cues. We examined responses of larvae of the serpulid polychaete Hydroides elegans to neuropharmacological agents to determine if G protein-coupled receptors or their associated signal-transduction pathways regulated induction of metamorphosis by bacterial cues. Larvae of Hydroides elegans metamorphose rapidly and in high proportions when exposed to bacterial biofilms. Neither the G-protein activator Gpp[NH]p nor the inhibitor GDP-{beta}-S affected metamorphosis. Although the nonspecific phosphodiesterase inhibitors IBMX, theophylline, and papaverine induced larvae to metamorphose, RO-20-1724 (an inhibitor selective for cAMP-specific phosphodiesterase IV) and the cyclic nucleotide analogs db-cAMP and db-cGMP had no effect on metamorphosis. The adenylate cyclase activator forskolin inhibited responses of larvae to inductive ba...

Bacterial Symbionts Colonize the Accessory Nidamental Gland of the Squid Loligo opalescens via Horizontal Transmission

Abstract: The accessory nidamental gland (AN gland), a reproductive organ of the mature female squid Loligo opalescens, harbors a dense culture of bacteria of unknown function. A multilayered sheath surrounding the L. opalescens egg case is similarly colonized by bacteria that presumably originate in the AN gland, as evidenced by their presence in the egg case at oviposition. This study investigates how these bacteria are transmitted to juvenile squid and examines some morphological consequences of bacterial colonization of AN gland tissues. By observing the structure of the AN gland in adults and the development and bacterial colonization of the gland in juveniles raised in captivity, we determined that the AN gland was absent in newly hatched squid and did not appear until 87 days post-hatching. At 129 days posthatching, the organ displayed tubules composed of a single layer of epithelial cells and expressing numerous cilia and microvilli. These tubules were not yet fully formed and thus were open to the mantle cavity and external seawater, possibly to aid in the acquisition of microorganisms. Since the AN gland developed a considerable time after hatching, it most likely acquires its symbionts horizontally from environmental seawater and not vertically from the egg case sheath. The switch from expression of cilia to production of microvilli on the epithelial cell surface may dictate the competence of the tissue for bacterial colonization. Electron microscopic examination of juvenile and adult AN glands revealed that an analogous process occurs during the development of the related light organ of other cephalopod species that harbor symbiotic bacteria.

Effects of Salinity on Sperm Motility, Fertilization, and Development in the Pacific Herring, Clupea pallasi

Abstract: We investigated the effects of salinity on fertilization and early development in a population of Pacific herring, Clupea pallasi, that migrate from oceanic waters into the San Francisco Bay estuary to spawn. The salinity range for fertilization fell between 8 and 28 ppt, with an optimal range of about 12 to 24 ppt. In comparison, the range for a population of C. harengus membras (Airisto Sound, Finland) that reside year-round in the Baltic Sea was 4 to 24 ppt. Roles for both Na+ and K+ were indicated in C. pallasi fertilization since increasing Na+ in the presence of 10 mM K+ (concentration of seawater) mimicked the effects of increased overall salinity, whereas reduced effects were obtained if [K+] was held at 5 mM (that of half-strength seawater). The initiation of C. pallasi sperm motility by components of the egg chorion, a prerequisite for fertilization, was inhibited at both elevated (28 and 32 ppt) and reduced (4 and 8 ppt) salinities. Embryonic development through larval hatching in C. pallasi exhibited a salinity tolerance similar to that of fertilization; optimum development was obtained at salinities between 8 and 24 ppt. A comparison of developmental progression in 3.5, 14, and 28 ppt seawater revealed that salinity effects became evident during the post-gastrulation stages of development and that progression to hatching was delayed in both the lower and higher salinities for those embryos that completed development.

Cloning by Ophiuroid Echinoderm Larvae.

Abstract: Larvae of the brittle star Ophiopholis aculeata, common to the North Pacific coast of the United States, and an unidentified species of ophiuroid, collected from waters off the eastern coast of Florida, undergo asexual reproduction of the primary larva to produce a secondary larval clone. Generation of a secondary larva begins with the release of the larval posterolateral arms, which are initially retained by the settled juvenile. In O. aculeata, the released arms regenerate all the structures typical of the primary ophiopluteus. Tissue and energy reserves required for formation of the secondary feeding larva appear to be supplied by the absorption and reorganization of part of the posterolateral arms. Various developmental stages of the unidentified ophiopluteus were collected from plankton samples taken off the coast of Florida. These included just-released posterolateral arms, plutei, and metamorphosed juveniles with the posterolateral arms still attached. The identification of regenerating arms from the plankton demonstrates that asexual reproduction by ophiuroid larvae is not restricted to a single, laboratory-cultured species. In both O. aculeata and the unidentified Atlantic ophiopluteus, cloning involves the dedifferentiation of primary larval tissue and a developmental progression similar to that followed by the zygote, although it is not known whether the formation of the secondary larva follows the same pathway utilized by the primary larva or a novel developmental program. Asexually produced secondary larvae of O. aculeata undergo metamorphosis, settle to the benthos, and initiate a tertiary larval generation, indicating that cloned larvae could be added to the population as long as environmental conditions could support a planktonic existence. This phenomenon represents an unusual potential to increase the geographic range and the number of juveniles of a given parentage in future generations without additional reproductive input from the adult.

Peptides Controlling Stiffness of Connective Tissue in Sea Cucumbers

Abstract: We present the first evidence of a system of four bioactive peptides that affect the stiffness of sea cucumber dermis. The body wall dermis of sea cucumbers consists of catch connective tissue that is characterized by quick and drastic stiffness changes under nervous con- trol. The peptides were isolated from the body wall, their amino acid sequences determined, and identical peptides synthesized. Two peptides, which we named holokinins, are homologous with bradykinin. We tested the effect of the peptides on the mechanical properties of sea cucumber dermis. Both of the holokinins softened the dermis, and a pentapeptide that we designated as NGIWYamide stiff- ened it. Both effects were reversibly suppressed by anes- thesia with menthol. We called the fourth peptide sticho- pin; it had no direct effect on the stiffness of the dermis but suppressed action of the neurotransmitter acetylcho- line reversibly. The results suggest that the peptides are neuropeptides and are part of a sophisticated system of neurotransmitters and neuromodulators that controls the connective tissue stiffness of sea cucumber dermis.

Recovery of Claw Size and Function Following Autotomy in Cancer productus (Decapoda: Brachyura).

Abstract: We examined recovery of claw size and func- tion following autotomy in red rock crabs Cancer pro- ductus. We also tested for costs of regeneration to growth and documented the frequency of claw injury in C. pro- ductus populations in Barkley Sound, Canada. Field and laboratory results indicated that crabs required at least three molts to recover a full-length cheliped. For injured crabs, regenerating claws were significantly less powerful than contralateral, normal (i.e., uninjured) claws even two instars after autotomy. Greater mechanical advantage in normal claws of injured (versus uninjured) crabs, how- ever, suggests some morphological response by the re- maining normal claw to increased exercise. Despite this compensatory response, our experiments indicate that in- jured crabs remain at a significant disadvantage while foraging. After adjusting for differences in propodus length, both regenerating and normal claws of injured crabs delivered significantly lower crushing forces than did claws of intact crabs. Energetic costs, in the form of reduced body size increase at the molt, were detected only for crabs regenerating both claws. High incidences of single claw loss in C. productus in Barkley Sound, together with our experimental data, suggest that much of the population experiences a prolonged foraging handicap following injury.

Modified Laboratory Culture Techniques for the European Cuttlefish Sepia officinalis

Abstract: The cuttlefish Sepia officinalis Linnaeus, 1758, is an important model for a variety of biological and biomedical investigations (1). To introduce this organism to the North American research communities, and make it readily available, various methods have been used to maintain or culture the species. The most intensive efforts and successes have been achieved by Forsythe and colleagues at the University of Texas Medical Branch in Galveston (2,3). Their most noteworthy achievement was to culture seven consecutive generations in large-scale recirculating seawater systems. Recently, cuttlefish were brought to the Marine Resources Center (MRC) of the Marine Biological Laboratory, where they have also been cultured successfully through their life cycle. Presently the third laboratory generation is under culture. Unlike previous work on Sepia culture in the United States, our focus has been to use a mostly open (flow-through) seawater system modified to function well through a northern winter, and to develop feeding methods that are suitable for our locale.

Structural strengthening of urchin skeletons by collagenous sutural ligaments

Abstract: Sea urchin skeletons are strengthened by flexible collagenous ligaments that bind together rigid calcite plates at sutures. Whole skeletons without ligaments (removed by bleaching) broke at lower apically applied forces than did intact, fresh skeletons. In addition, in three-point bending tests on excised plate combinations, sutural ligaments strengthened sutures but not plates. The degree of sutural strengthening by ligaments depended on sutural position; in tensile tests, ambital and adapical sutures were strengthened more than adoral sutures. Adapical sutures, which grow fastest, were also the loosest, suggesting that strengthening by ligaments is associated with growth. In fed, growing urchins, sutures overall were looser than in unfed urchins. Looseness was demonstrated visually and by vibration analysis: bleached skeletons of unfed urchins rang at characteristic frequencies, indicating that sound traveled across tightly fitting sutures; skeletons of fed urchins damped vibrations, indicating loss of vibrational energy across looser sutures. Furthermore, bleached skeletons of fed urchins broke at lower apically applied forces than bleached skeletons of unfed urchins, indicating that the sutures of fed urchins had been held together relatively loosely by sutural ligaments. Thus, the apparently rigid dome-like skeleton of urchins sometimes transforms into a flexible, jointed membrane as sutures loosen and become flexible during growth.

Gastrovascular Circulation in an Octocoral: Evidence of Significant Transport of Coral and Symbiont Cells.

Abstract: The gastrovascular system in the Red Sea soft coral Purerythropodium fulvum fulvum comprises two interconnected networks of canals filled with fluid and circulating cells. The first network is composed of narrow canals (50-80 pm in width) located below the upper ectodermal layer; the second network includes larger canals (300-500 pm in width) that are located deeper in the coral tissue. Particle movement in the second network is faster than in the superficial network, but in both, coral cells with and without healthy zooxanthellae circulate freely. To investigate the movement of metabo- lites and cellular components within the colony, coral fragments were exposed to 14C-labeled seawater for 24 h in the laboratory and in situ under saturating photosyn- thetic photon flux and then grafted back to their original colonies. Grafts fused after 24 h. In the laboratory experi- ment, up to 45% of the fixed 14C was translocated to the unlabeled colony within 48 h after fusion. In the in situ experiment, significant translocation of labeled materials occurred at the furthest parts of the colonies, 390 mm away from the fusion line, in 24 h. Even though the amount of labeling varied between colonies, labeled mate- rial spread throughout all the unlabeled parts. It thus ap- pears that the gastrovascular system in Purerythropodium jiilvum jiilvum functions as an effective circulatory appa- ratus for fast translocation of organic compounds and cellular components within the colony.

Population Size and Site Fidelity of Fundulus heteroclitus in a Macrotidal Saltmarsh Creek

Abstract: Fundulus heteroclitus (mummichog) is the numerically dominant fish species found in salt marshes from Florida to Nova Scotia. These areas exhibit a wide range of fluctuation in environmental conditions such as temperature, salinity, and tidal range. Mummichogs are known to be eurythermal and euryhaline, but there is little information about the influence of tidal range on population dynamics. Our purpose was to determine whether extreme tides (>3 m) in a tidal creek system would affect the population density and site fidelity of F. heteroclitus. Both population density and site fidelity were measured by mark-recapture experiments in a primary saltmarsh creek (named here Sweeney Creek) off the Rowley River in Plum Island Estuary, a macrotidal (>3 m) estuary (Fig. 1). Both branches were approximately 300 m long from the confluence to the upland end. From 18 June to 3 I July 1998, temperature (data logger), salinity (refractometer), and fish abundance were monitored. Six, 6.35mm-mesh minnow traps were set in the center and randomly apart on both branches at around 180 m (East) and 120 m (West) from the confluence (Fig. 1). Specimens of F. heteroclitus 2 40 mm caught in the traps were counted and marked yellow (West) and blue (East) by injection of acrylic dye under the skin on the left dorsal side, then released. Population size was estimated using the Bailey model (1). Site fidelity was measured as the number of marked fish recaptured in different locations. Opposite-colored fish found in a marking zone were recorded and remarked on the opposite dorsal side with the color of the branch in which captured. To determine how far and by what path fish moved, we set traps in three locations. In the secondary creek, two traps were set at five stations 22 to 106 m from the confluence. Nine traps were set in the mosquito ditches, and traps were set upstream of the marking locations. The pannes and secondary creek were also seined. Time intervals between mark and recapture were variable, averaging a 14.75 hour catch per unit effort. Temperature and salinity were within the normal range for F. heteroclitus. Water temperature averaged 20°C at night and 26°C during the day for both branches. Salinity ranged from 8 to 25 ppt for the East branch, and 10 to 26 ppt for the West.

Molecular Phylogeny of Zooxanthellate Bivalves

Abstract: The aim of this research was to analyze the phylogenetic relationships of zooxanthellate bivalves belonging to the genera Tridacna, Hippopus, Fragum, and Corculum as well as to the closely related azooxanthellate bivalves belonging to Vasticardium and Fulvia. The small-subunit ribosomal RNA genes (18S rDNAs) from these bivalves were amplified by polymerase chain reaction with universal eukaryotic primers and were then sequenced. The sequence data from each species were analyzed by the neighbor-joining, maximum parsimony, and maximum likelihood methods, and phylogenetic trees were constructed. The results were essentially consistent with the morphological taxonomy of these bivalves. Thus, the zooxanthellate clams branch into two lineages, one composed of the genera Fragum and Corculum in the family Cardiidae, and the other composed of the genera Tridacna and Hippopus in the family Tridacnidae. However, present results indicate that the azooxanthellate clams analyzed (Vasticardium flavum and Fulvia mutica) ...