Showing papers in "The Biological Bulletin in 1995"
TL;DR: The data suggest that the patterns of bleaching seen in nature may be at least partially explained by different tolerances of the symbiotic algae in the corals, and that light plays a significant role in bleaching.
Abstract: Bleaching of reef corals, involving loss of symbiotic algae (= zooxanthellae), loss of algal pigments, or both, has been linked to temperature stress. In this study the effects of high temperature and light on zooxanthellae living in the Caribbean reef corals Montastrea annularis, M. cavernosa, Agaricia agaricites, and A. lamarcki were studied. Pieces of coral colonies were incubated at ambient seawater temperature (26{deg} +/- 1{deg}C), and at 30{deg}, 32{deg}, and 34{deg}C. Symbiotic algae from M. annularis, a species of coral from the forereef that commonly bleaches, showed the following sequence of events when exposed to natural light at 32{deg}C; loss of photosynthetic potential measured as fluorescence yield, corresponding reduction of both oxygen production per zooxanthella and P:R (photosynthesis:respiration) ratio, and subsequent reduction in density of algae in relation to surface area of the coral. These parameters were not significantly reduced and no deaths occurred for M. annularis or any ot...
298 citations
TL;DR: Variation in the adhesive protein gene sequences of Mytilus edulis, M. galloprovincialis, and M. trossulus collected in Delaware, Kamaishi (Japan), and Alaska, respectively, was analyzed by the polymerase chain reaction (PCR) using two sets of oligonucleotide primers.
Abstract: Variation in the adhesive protein gene se- quences of Mytilus edulis, M. galloprovincialis, and M. trossulus collected in Delaware, Kamaishi (Japan), and Alaska, respectively, was analyzed by the polymerase chain reaction (PCR) using two sets of oligonucleotide primers. The first set, Me 13 and Me 14, was designed to amplify the repetitive region. The length of the amplified fragments was highly variable, even among samples of the same species. Another set, Me 1.5 and Me 16, was designed to amplify a part of the nonrepetitive region. The length of the amplified fragments was uniform in each species and differed interspecifically; 180, 168, and 126 bp for M. edulis, M. trossulus, and M. galloprovincialis, respectively. The amplified sequence of M. trossulus resembled that of M. edulis. Mussels from other sites were also examined by PCR using Me 15 and Me 16. Wild mussels from Tromso (Norway) and cultured mussels from Brittany (France) were identified as M. edulis. Cultured mussels from the Mediterranean coast of France and wild mussels from Shimizu (Japan) were identified as M. galloprovin- cialis. Some wild mussels from Hiura (Japan) were iden- tified as a hybrid between M. galloprovincialis and M. trossulus. Thus, the length of this part (variable region) of the sequence is proposed as a diagnostic marker for
236 citations
TL;DR: The results demonstrate that both rheotaxis and chemotaxis are necessary for successful orientation in crabs, and suggest that crabs rely more heavily on spatial aspects of chemical stimulus distributions because their fluid dynamic environment creates a more stable plume structure, thus permitting chemot axis.
Abstract: Turbulence causes chemical stimuli to be highly variable in time and space; hence the study of animal orientation in odor plumes presents a formidable challenge. Through combined chemical and physical measurements, we characterized the transport of attractant released by clam prey in a turbulent aquatic environment. Concurrently, we quantified the locomotory responses of predatory crabs successfully searching for sources of clam attractant. Our results demonstrate that both rheotaxis and chemotaxis are necessary for successful orientation. Perception of chemical cues causes crabs to move in the upstream direction, but feedback from attractant distributions directly regulates movement across-stream in the plume. Orientation mechanisms used by crabs difler from those employed by flying insects, the only other system in which navigation relative to odor plumes has been coupled with fluid dynamics. Insects respond to odors by moving upstream, but they do not use chemical distributions to determine across-stream direction, whereas crabs do. Turbulent eddy diffusivities in crab habitats are 100 to 1000 times lower than those of terrestrial grasslands and forests occupied by insects. Insects must respond to plumes consisting of highly dispersed, tiny filaments or parcels of odor. Crabs rely more heavily on spatial aspects of chemical stimulus distributions because their fluid dynamic environment creates a more stable plume structure, thus permitting chemotaxis.
161 citations
TL;DR: Electrophoretic analysis of mussel and bacterial proteins on 12% polyacrylamide gels allowed the visual determination of incorporation of labeled amino acids into bivalve proteins and demonstrated that intact bacteria were not simply trapped in mussel tissues.
Abstract: Dreissena polymorpha consumed about 6 x 108 Escherichia coli from 20 ml of artificial pondwater (APW) in 30 min under laboratory conditions. The clearance rate per mussel was 143 +/- 25 ml g-1 dry tissue min-1. The E. coli used in these studies ranged from about 1.7 to 2.9 {mu}m in length. 35S-labeled E. coli were used to demonstrate that bacteria-derived nutrients were incorporated into mussel tissue. Electrophoretic analysis of mussel and bacterial proteins on 12% polyacrylamide gels allowed the visual determination of incorporation of labeled amino acids into bivalve proteins and demonstrated that intact bacteria were not simply trapped in mussel tissues. The conversion of bacterial-labeled amino acids into mussel protein was about 26%. Similarly, we demonstrated that D. polymorpha can use other bacterial species ranging in size from about 1.3 to 4.1 μm, including Citrobacter freundii, Enterobacter aerogenes, Serratia marcescens, Bacillus megaterium, and B. subtilus. The ability of D. polymorpha to tak...
109 citations
TL;DR: The compounds responsible for the pink and blue colors of two families of hermatypic corals from the southern Great Barrier Reef were isolated and biochemically characterized and the exploration of the function of the pink pigment was explored.
Abstract: The compounds responsible for the pink and blue colors of two families of hermatypic corals (Pocilloporidae, Acroporidae) from the southern Great Barrier Reef were isolated and biochemically characterized. Isolation of the pink pigment from Pocillopora damicornis (named pocilloporin, {lambda}max = 560 nm, 390 nm) revealed that it was a hydrophilic protein dimer with a native molecular weight of approximately 54 kD and subunits of 28 kD. The subunits are not linked by disulfide bonds. Attempts to dissociate the chromophore from the protein proved unsuccessful. Denaturing the protein with heat (60{deg}C) or 5% sodium dodecyl sulfate (SDS) removed the 560-nm absorbance peak without introducing a detectable bathochromic shift. In acetone, ethanol, ether, and chloroform, the pigment precipitates out of solution, leaving a colorless supernatant. These properties suggest that the protein and chromophore are covalently linked. Ion analysis revealed that the pigment does not have metal ions chelated to it. Coral pigments were also isolated from pink morphs of other pocilloporids, Seriatopora hystrix ({lambda}max = 560 nm) and Stylophora pistillata ({lambda}max = 560 nm); and from bluish regions of the acroporids, Acropora formosa (blue; {lambda}max = 590 nm) and Acropora digitifera (purple; {lambda}max = 580 nm). With the exception of A. formosa, all the corals examined had pigments with the same native (54 kD) and subunit (28 kD) molecular weights as those of P. damicornis. A. formosa pigment has a native molecular weight of about 82.6 kD and three subunits of 28 kD. The pigments isolated from each of these coral species have properties similar to those described for P. damicornis. Isolation and biochemical purification of the pigment enabled the exploration of the function of the pink pigment. Three possibilities were eliminated. The compound does not act as (i) a photoprotectant for shielding the photosynthetic pigments of symbiotic zooxanthellae against excessive irradiances, (ii) a fluorescent coupling agent for amplifying the levels of photosynthetically active radiation available for resident zooxanthellae, or (iii) a UV-screen against the high UV levels of shallow tropical marine environments.
102 citations
TL;DR: Investigation of mechanisms of temperature stress tolerance in scleractinian corals found hsps are involved in differences in thermotolerance and susceptibility to bleaching within and between the various species of Montastraea, and between species of reef cnidarians.
Abstract: Frequent widespread episodes of coral bleaching have made researchers aware of the sensitivity of reef corals to moderately elevated temperatures and led us to investigate mechanisms of temperature...
102 citations
TL;DR: A geographically distinct, Antarctic, open-ocean food chain which is of importance to air breathing predator species but where Antarctic krill, Euphausia superba, is absent is identified.
Abstract: Recent data from research cruises and explorator fishing in the Antarctic Polar Frontal Zone (APFZ) of the Scotia Sea, together with data from dietary studies of Antarctic vertebrate predators, have revealed a large, previously overlooked trophic system in the Southern Ocean (Fig. 1). The upper trophic levels of this open-ocean epipelagic community are exceptional in that they contain no fish species. Fishes are replaced by cephalopods, including the ommastrephid squid, Martialia hyadesi. This squid preys on mesopelagic m.yctophids (lanternfish), which feed largely on copepods. We identify here a geographically distinct, Antarctic, open-ocean food chain which is of importance to air breathing predator species but where Antarctic krill, Euphausia superba, is absent. This system is probably prevalent in areas of higher primary productivity, especially the Scotia Sea and near the peri-Antarctic islands. Squid stocks in the APFZ may have potential for commercial exploitation, but they, and the predators they support, are likely to be sensitive to overfishing. Squid have a short, semelparous lifecycle, so overfishing in a single year can cause a stock to collapse.
101 citations
TL;DR: It is shown that successful entrance into the light organ is necessary to induce morphogenesis, suggesting that induction results from bacterial interaction with internal crypt cells and not with the external ciliated epithelium.
Abstract: Recent studies of the symbiotic association between the Hawaiian sepiolid squid Euprymna scolopes and the luminous bacterium Vibrio Jischeri have shown that colonization of juvenile squid with symbiosis-com- petent bacteria induces morphogenetic changes of the light organ. These changes occur over a &day period and in- clude cell death and tissue regression of the external cil- iated epithelium. In the absence of bacterial colonization, morphogenesis does not occur. To determine whether the bacteria must be present throughout the morphogenetic process, we used the antibiotic chloramphenicol to clear the light organ of bacteria at various times during the initial colonization. We provide evidence in this study that a transient, 12-hour exposure to symbiosis-competent bacteria is necessary and sufficient to induce tissue regres- sion in the light organ over the next several days. Further, we show that successful entrance into the light organ is necessary to induce morphogenesis, suggesting that in- duction results from bacterial interaction with internal crypt cells and not with the external ciliated epithelium. Finally, no difference in development was observed when the light organ was colonized by a mutant strain of V. fischeri that did not produce autoinducer, a potential light organ morphogen.
100 citations
TL;DR: The linking of accumulation bodies within absorptive cells of oyster digestive diverticula with dinoflagellate autolysosomal bodies suggests a mechanism by which some dinof lagellates interfere with feeding in phytoplankton grazers.
Abstract: Effects of the dinoflagellate Prorocentrum minimum (strain EXUV) upon four life-history stages of the eastern oyster--embryos, feeding larvae, newly set spat, and juveniles--were investigated in laboratory exposure studies. Embryonic development was not affected significantly by living, heat-killed, or sonicated cells, or by growth-medium extracts from P. minimum cultures. Feeding larvae, however, showed poor growth and poor development of the digestive system when fed P. minimum, as compared with larvae fed Isochrysis sp. (strain T-ISO). Growth of larvae fed mixed P. minimum + Isochrysis diets was intermediate. Larvae and newly set spat that had been fed a diet of 1/3 P. minimum + 2/3 Isochrysis exhibited distinctive changes in digestive-system anatomy. Spat showed an abnormal accumulation of lipid in the stomach epithelium. Absorptive cells in the digestive glands of both larvae and spat contained accumulation bodies, often with a laminated, fibrous appearance in preparations for transmission electron microscopy. These accumulation bodies were PAS (periodic acid-Schiff) positive and may correspond to autolysosomal bodies within P. minimum cells. Juvenile oysters developed the ability to digest P. minimum, but only after a refractory period of about 2 weeks, during which most P. minimum was filtered but rejected as pseudofeces. The linking of accumulation bodies within absorptive cells of oyster digestive diverticula with dinoflagellate autolysosomal bodies suggests a mechanism by which some dinoflagellates interfere with feeding in phytoplankton grazers.
99 citations
TL;DR: To further evaluate somatic and germ cell parasitism in chimeric organisms, four key features are proposed that characterize cell lineage competition processes: the somatic embryogenesis mode of development, the capability for independent existence of stem cells, the disproportionate share of gametic output within chimeras, and the existence of hierarchial responses.
Abstract: Fusion between conspecifics (chimerism) is a well-documented phenomenon in a variety of taxa. Chimerism and the subsequent mixing of genetically different stem cell lines may lead to competition between cell lineages for positions in the germ line and to somatic and germ cell parasitism. It is suggested that somatic compatibility systems evolved to alleviate the costs and the threat of such cell lineage competition. Allogeneic colonies of the ascidian Botryllus schlosseri form vascular chimeras based on matching in one or both alleles on one highly polymorphic fusibility haplotype. Thereafter, one of the partners is completely or partially resorbed. Here we used a polymorphic molecular marker (PCR typing at a microsatellite locus) to follow somatic and gametic consequences of chimera formation. Twenty-two chimeras and subclone samples were established from 12 different genotype combinations, in which blood cells, zooids, and gonads were typed 45-130 days thereafter. Somatic coexistence of both partners wa...
98 citations
TL;DR: Exposure to high shear stresses substantially decreased fertilization success, probably by interfering with contact between egg and sperm in the purple sea urchin (Strongylocentrotus purpuratus).
Abstract: Life in the highly turbulent surf zone poses a severe challenge to reproduction in free-spawning animals. Not only can breaking waves quickly dilute the gametes shed by spawning organisms, but turbulence-induced shear stresses may limit fertilization and interfere with normal development. A Couette cell was used to re-create some of the effects of turbulent water motion to study effects of environmentally relevant shear stresses on fertilization in the purple sea urchin (Strongylocentrotus purpuratus). Although low shear stresses improved fertilization success (presumably by increasing mixing), exposure to high shear stresses (of the magnitude found in the surf zone) substantially decreased fertilization success, probably by interfering with contact between egg and sperm. Furthermore, eggs fertilized at high shear stresses often showed abnormal development and low survival of eggs through the blastula stage.
TL;DR: Visual examination of plastic replicas of the aquiferous system and electron microscopical analysis of sponge tissue revealed that the transcellular ostia are mostly located on the buried surface of the sponge, which maintains a large population of bacteriocytes, which contains bacteria of several different species.
Abstract: Infaunal soft-bottom invertebrates benefit from the presence of sediment, but sedimentation is po- tentially harmful for hard-bottom dwellers. Most sponges live on hard bottom, but on coral reefs in the Red Sea, the species Biemna ehrenbergi (Keller, 1889) is found ex- clusively in soft-bottom lagoons, usually in the shallowest part. This location is a sink environment, which increases the deposition of particulate organic matter. Most of the sponge body is covered by sediment, but the chimney- like siphons protrude from the sediment surface. The sponge is attached to the buried beach-rock, which reduces the risk of dislodgment during storms. Dye injected above and into the sediment revealed, for the first time, a sponge pumping interstitial water (rich with particles and nu- trients) into its aquiferous system. Visual examination of plastic replicas of the aquiferous system and electron mi- croscopical analysis of sponge tissue revealed that the transcellular ostia are mostly located on the buried surface of the sponge. The oscula, however, are located on top of the siphons; their elevated position and their ability to close combine to prevent the filtering system outflow from clogging. The transcellular ostia presumably remain open due to cellular mobility. The sponge maintains a large population of bacteriocytes, which contains bacteria of several different species. Some of these bacteria disinte- grate, and may be consumed by the sponge.
TL;DR: The present results favor the hypothesis that the dicyemids do not represent an early divergent metazoan group, but rather a group degenerated from a triploblastic ancestor.
Abstract: The dicyemid mesozoa, obligate symbionts in the cephalopod kidney, are simply organized multicellular animals. They have long been the subject of phylogenetic debates. Some authors have suggested that dicyemids represent an offshoot from an early metazoan ancestor. Other workers considered them to be degenerated progeny of higher metazoa, possibly parasitic trematodes. We determined the almost complete nucleotide sequences of 18S rDNA in two species of dicyemid, Dicyema orientale and Dicyema acuticephalum, isolated purely from cephalopod urine. We compared these sequences with sequences determined in the present study from three flatworm species, as well as with a variety of eukaryote sequences obtained from databases. The phylogenetic trees reconstructed with the use of the neighbor-joining, maximum-parsimony, and maximum-likelihood methods indicated that the dicyemids belong among the triploblastic animals (Bilateria). However, we cannot firmly establish the position of the dicyemids within the Bilateri...
TL;DR: It is shown that temperature is as important as photoperiod in cuing diapause timing in a population of D. sanguineus living in Bullhead Pond, Rhode Island.
Abstract: In many organisms, photoperiod and tem- perature are thought to be the most significant token cues for seasonally timed life history events, including diapause in arthropods. A common pattern in many species of ter- restrial insects and several copepod species is the existence of a critical daylength on one side of which the animals do not e&er diapause and on the other side of which they do. Temperature plays a secondary role as modifier of the critical daylength. In some species, however, including the freshwater copepod Diaptomus sanguineus, the frac- tion of females making subitaneous eggs (eggs that hatch immediately) undergoes a very gradual transition as day- length changes over the natural range of photoperiods experienced in nature. Here we show that temperature is as important as photoperiod in cuing diapause timing in a population of D. sanguineus living in Bullhead Pond, Rhode Island. When ecologically relevant photoperiod and temperature cues are provided in the laboratory, the copepods rapidly switch from producing subitaneous eggs to producing diapausing eggs in a way that is typical of the seasonal switch seen in the pond. We provide a graph- ical model that illustrates how copepod sensitivities to photoperiod and temperature interact to produce an abrupt transition, and we discuss how natural selection should act on D. sanguineus diapause response to produce the variation in diapause timing seen within and between natural populations.
TL;DR: The similarity of the early larva of P. exigua to planktonic brachiolariae suggests that the evolution of benthic lecithotrophy by this species involved modification of a planktonics larval form.
Abstract: Patiriella exigua (Lamarck) is a small asterinid sea star that deposits large eggs onto the substratum. Development is lecithotrophic and entirely benthic, proceeding without parental care. The embryos develop to the brachiolaria stage before hatching and there is no trace of a bipinnaria larva. In its early stage the larva of P. exigua resembles a planktonic brachiolaria in having one long central brachium and two short lateral brachia. By hatching, the brachia are equal in length, giving the larva a tripod-like appearance. Comparison of the larva of P. exigua with the brachiolaria of Patiriella species with planktonic development supports the hypothesis that the tripod larval form results from differential growth of the lateral brachia. At hatching, the P. exigua larva has a well-developed attachment complex composed of a large adhesive disk and three muscular brachia; the latter bear a striking resemblance to adult tube feet. This hypertrophic elaboration of the brachiolar complex is an adaptation for permanent benthic attachment. Internally, one large enterocoel forms at the anterior end of the archenteron. The archenteron then closes to form the rudiment for the adult gut. Metamorphosis involves gradual resorption of the brachiolar complex concomitant with formation of the first tube feet. The adhesive disk plays a major role in attachment during late metamorphosis but is gradually reduced to a plug of tissue as the tube feet become functional. Juvenile P. exigua are negatively geotactic and float on the water surface, behavior that may act as a mechanism for dispersal. The similarity of the early larva of P. exigua to planktonic brachiolariae suggests that the evolution of benthic lecithotrophy by this species involved modification of a planktonic larval form. These modifications include elimination and reduction of larval feeding structures, formation of one rather than three enterocoels, and hypertrophy of the brachiolar complex to form a tripod larva. Heterochronies in the ontogeny of P. exigua include the delay in hatching to the brachiolaria stage and the accelerated development of the juvenile form and adult skeleton.
TL;DR: One day in the fall of 1960, shortly after my arrival at Princeton from Japan, Dr. Frank Johnson showed me a small jar containing a spoonful of white powder that was a freeze dried “squeezate” made from the luminous jellyfish Aequorea, and asked me if I would be interested in studying the bioluminescence of this jellyfish.
Abstract: One day in the fall of 1960, shortly after my arrival at Princeton from Japan, Dr. Frank Johnson showed me a small jar containing a spoonful of white powder. He explained that the powder was a freeze dried “squeezate” made from the luminous jellyfish Aequorea, and that it would emit light when mixed with water. He asked me if I would be interested in studying the bioluminescence of this jellyfish. The powder did not emit any light when moistened. But I was quite impressed by Dr. Johnson’s description of the brilliant luminescence of live jellyfish and the great abundance of specimens around Friday Harbor, Washington. So my response was a definite “yes.” My experience in bioluminescence research at the time was meager and limited to only the luminescent system of the ostracod Cypridina. I imagined, vaguely, that the jellyfish would probably contain a kind of luciferin and a luciferase, possibly with one of the cofactors, such as ATP, FMN, or NADH, like the fireflies, luminous bacteria, and Cypridina that were known at that time. In the early summer of 196 1, we traveled from Princeton to Friday Harbor in Dr. Johnson’s station wagon, which he had newly purchased for the excursion. The car was fully loaded with necessary equipment and chemicals, including a MacNichol integrating photometer of gigantic size (a two-foot cube), and four travelers (my wife and Yo Saiga, an assistant, came along) with all of their baggage on the roof. It took us seven days to the West Coast, through Chicago and Glacier National Park. Dr. Johnson was the only driver throughout the trip, driving 12 hours a day with an admirable toughness. Upon arrival at the Friday Harbor Laboratories, we were welcomed by Dr. Robert Fernald, Director of the Lab. We set up our work space in Lab 1, a small building consisting of two rooms, and we started to work. There were three other scientists in the room, and one of them
TL;DR: The ability of squid to use dinoflagellate bioluminescence to locate and capture nonluminous prey is demonstrated and the burglar alarm theory of the adaptive significance of dinofLagellates biolumscence is supported.
Abstract: Predation by nocturnal cephalopods on nonluminous prey was examined in the presence of dinoflagellate bioluminescence. Sepia officinalis Linnaeus and Euprymna scolopes Berry were tested for predation efficiency in darkness illuminated by the luminescent dinoflagellate Pyrocystis fusiformis Murry. Prey were mysids, Holmesimysis sculpta (Tattersall); grass shrimp, Palaemonetes pugio Holthuis; and mosquito fish, Gambusia affinis Baird and Girard. Tests were conducted in aquaria containing 0-20 cells ml-1 of P. fusiformis. Predation increased as numbers of luminescent dinoflagellates increased. Controls were predation tests in the presence of P. fusiformis during nonluminescent photophase or in the absence of dinoflagellates. Movements of squid and prey readily stimulated luminescence. Behavior and correlated luminescence in infrared-illuminated aquaria were recorded by image-intensified and infrared video cameras. Sepia strikes on prey were common under luminescent conditions--85% occurred in less than 10 min; but strikes in darkness were rare. E. scolopes attacked more frequently than Sepia, and almost 90% obtained prey under luminescent conditions. This study demonstrates the ability of squid to use dinoflagellate bioluminescence to locate and capture nonluminous prey. The burglar alarm theory of the adaptive significance of dinoflagellate bioluminescence is supported.
TL;DR: Data show that although sudden increases in salinity produce an immediate decrease in the reproductive capacity of zebra mussels, acclimation to brackish water can occur, and zebra Mussels may be able to reproduce in brackian water below 7.0 ppt.
Abstract: Zebra mussels have dispersed from their original site of introduction in the Great Lakes into the Mississippi River, Hudson River, and other watersheds in which they will encroach upon brackish water estuaries. To investigate their likelihood of reproductive success in such estuaries, we investigated the conditions of temperature, salinity, and acclimation under which spawning and fertilization could occur. Reproductive function of mussels that were acclimated to salinities up to 7.0 parts per thousand (ppt) at 12°, 20°, and 27°C for 1 to 21 days was tested. Reproductive function of non-acclimated mussels that had been maintained in fresh-water aquaria was also tested in various salinities. Spawning was induced by serotonin, previously demonstrated to elicit spawning of fertile gametes in fresh water. Successful fertilization was indicated by oocyte cleavage after adding sperm. Nonacclimated mussels spawned in salinities of 1.75 and 3.5 ppt at 12°, 20°, and 27°C, but not at 7.0 ppt. Fertilization using ga...
TL;DR: Hemocyte cell suspensions obtained from male and female Penaeus japonicus were individually analyzed by flow cytometry through forward and side light-scatter parameters, and significant cyclic differences were detected among the molting stages in both sexes.
Abstract: Hemocyte cell suspensions obtained from male and female Penaeus japonicus were individually analyzed by flow cytometry through forward and side light-scatter parameters. The hemocyte cell suspensions were further characterized after cell sorting. This type of cell analysis has several advantages over microscopy techniques. After staining with phenoloxidase and per- oxidase, the hemocytes were classified into the three classic categories of hyaline, semigranular, and granular cells. Significant cyclic differences were detected among the molting stages in both sexes. The hyaline cell pop- ulation was predominant before and soon after the molt, decreasing over the intermolt. This decrease was, how- ever, more prolonged in females. Thus, the hyaline cell population was dominant in stages B, DO, and Dl in males and only in stages B and Dl in females. Semi- granular cells became predominant in females during the DO stage.
TL;DR: The brooding behavior in L. polaris serves mainly to keep the eggs clean, healthy, and protected against predation, suggesting that the embryos develop at the same rate even when not brooded.
Abstract: Our study focused on the precise reproductive behavior of the starfish Leptasterias polaris (Muller and Troschel) before and during spawning--a subject of much speculation and evident ecological importance. Between the third week of December 1992 and mid-January 1993, we observed spawning in the laboratory that roughly corresponded to field observations in the Lower St. Lawrence Estuary. In experimental tanks provided with natural environmental conditions, the spawning was preceded by 7 to 8 weeks of complex aggregative interactions among the starfish. The individuals, which usually avoid each other, began to make discreet arm contact, which intensified with time and eventually led to the superposition of two or more starfish, independently of sex. The interactions seem to be associated with decreasing temperature, because aggregative and spawning behaviors were not observed under stable temperature conditions. Male spawning is first initiated when the temperature falls to about 2{deg}C during minimum day...
TL;DR: The use of rhodamine-labeled phalloidin reveals that the terminal ganglion of adult crayfish is the fusion product of the anlagen of the sixth and seventh pleonic ganglia and an eighth hemiganglion that is devoid of engrailed expression.
Abstract: Segment formation in the embryonic pleon of the freshwater crayfish Cherax destructor was analyzed by using the monoclonal antibody mAb 4D9 against the product of the segment-polarity gene engrailed. As in other body regions, engrailed is expressed in transverse stripes in the posterior portion of segments in the pleon. Nine engrailed stripes are formed in the pleon. The anterior six stripes correspond to the six pleon segments of adult eumalacostracan crustaceans. The uropods are clearly the appendages of the sixth pleon segment. The seventh engrailed stripe marks the anlage of a seventh ganglion. Stripes eight and nine are transient and disappear before morphogenesis begins. The engrailed stripes seven to nine are interpreted as vestiges of ancestral segments. The seventh segment anlage is thus a recapitulation of the seventh pleonic segment, which is retained in recent adult leptostracans and is considered to be part of the malacostracan ground plan. The stripes eight and nine might point still further back into the phylogeny of crustaceans or even mandibulates. The use of rhodamine-labeled phalloidin reveals that the terminal ganglion of adult crayfish is the fusion product of the anlagen of the sixth and seventh pleonic ganglia and an eighth hemiganglion that is devoid of engrailed expression.
TL;DR: Correlations support the hypothesis that the energy demand depends upon the metabolic substrate concentration, and the role of the digestive gland in the respiratory metabolism of Penaeus setiferus adult males is determined.
Abstract: We determined the role of the digestive gland in the respiratory metabolism of Penaeus setiferus adult males as a step toward proposing a feeding schedule based on the cycle of activity in the digestive gland. We measured pre- and postprandial values for oxygen consumption rate and hemolymph glucose concentrations in live animals, and oxygen consumption rate and glycogen concentration in excised digestive gland. After the animals were fed, which enhanced general metabolic activity, these indices changed. There was a high correlation between the oxygen consumption rate of the animal and the glucose concentration in the hemolymph, and between the oxygen consumption rate by the digestive gland and the glycogen concentration in the digestive gland, all in relation to time after feeding. Correlations support the hypothesis that the energy demand depends upon the metabolic substrate concentration. In this theory, glucose sustains muscle activity (during ingestion of food) and glycogen is the product of the dige...
TL;DR: Results were consistent with the hypothesis that new juveniles reject (or are significantly slower to burrow into) disturbed sediment surfaces, if the disturbance is less than several hours old, and imply that the new juveniles are utilizing cues associated with a process, the disturbance of surface sediments, in addition to the species-specific cues described elsewhere.
Abstract: In marine sediments, many of the processes associated with high post-settlement mortality of infauna have similar effects on the sediment surface. In most cases the original sediment surface is either removed, buried, or mixed with subsurface sediment. The experiments re- ported here tested the ability of new juvenile infauna to discriminate between undisturbed and recently disturbed sediment surfaces (i.e., subsurface sediment exposed). Recently settled juveniles of two polychaete species (Nereis vexillosa and Arenicola cristata) and one bivalve species (Mercenaria mercenaria) were exposed to simu- lated erosional and mixing events as well as to fresh feces, burrow tailings, and feeding tracks. Where the disturbance buried or removed several millimeters of the sediment surface, the time to initiate burrowing or the percentage of individuals failing to burrow increased significantly over times and percentages for juveniles on undisturbed sur- faces. In all cases the results were consistent with the hy- pothesis that new juveniles reject (or are significantly slower to burrow into) disturbed sediment surfaces, if the disturbance is less than several hours old. For example, 5 1% of nereid juveniles did not burrow when placed on subsurface sediments, whereas 100% burrowed into sur- face sediments; their average burrowing time on surface sediments was 29.3 s compared with 109.7 s on fecal mounds of arenicolid polychaetes or 106.1 s on burrow tailings of thalassinid crustaceans. Individuals that did not indicate acceptance of a sediment surface by burrowing were all rapidly eroded from the surface in the presence of flow. Erosion of nonburrowing individuals occurred within 90 s of initiation of flow. Burrowing individuals were not eroded. The decision as to the acceptability of a sediment was made within 30 s. These data imply that
TL;DR: It appears that Mytilus hemocyte aggregation, in vitro, is a two-step process that requires metabolic energy and divalent cations (calcium and magnesium), and is temperature-sensitive.
Abstract: Within minutes of removal from the California mussel, Mytilus californianus hemocytes become sticky for one another and for foreign surfaces. We sought to understand the cell surface changes responsible for this altered state. Hemocyte aggregation and adhesion assays were used in experiments in which a variety of reagents potentially capable of interfering with aggregation were screened. Caffeine, nor-ethylmaleimide, cytochalasin B, and EDTA were completely or partially inhibitory towards aggregation and adhesion. However, RGD-containing peptides, glycosaminoglycans, protease inhibitors, heparin, or poly-L-lysine were without effect. Low temperature (4°C) slowed hemocyte adhesion and hemocyte cohesion. Based on the findings, it appears that (1) Mytilus hemocyte aggregation, in vitro, is a two-step process that requires metabolic energy and divalent cations (calcium and magnesium), and is temperature-sensitive; and (2) Mytilus hemocyte adhesion and hemocyte aggregation are two associated but different cell behaviors.
TL;DR: In resting animals, injection of serotonin, octopamine, and dopamine induced increases in heart rate after the regulatory nerves were cut, suggesting that these amines act on the cardiac ganglion as independent effectors.
Abstract: Control of decapod crustacean heart activity is believed to be dependent on the regulation of the cardiac ganglion by external input from the central nervous system as well as by circulating neurohormones. This study investigated the roles of these inputs on the heart rates of lobsters exercising on a treadmill. Heart rate increased rapidly at the onset of walking in control animals. This rapid phase was lost after the regulatory nerves were cut, but small increases still occurred. When stroke volume was reduced by cutting alary ligaments, the animals compensated by increasing heart rate; this compensation was lost when the regulatory nerves were cut. In resting animals, injection of serotonin, octopamine, and dopamine induced increases in heart rate. After the regulatory nerves were cut, only dopamine and serotonin injections caused increases in heart rate, suggesting that these amines act on the cardiac ganglion as independent effectors.
TL;DR: The colonial ascidian Botryllus schlosseri is a model organism for research on invertebrate histocompatibility, development, and evolutionary biology, but the basic life history of Pacific Ocean populations of the species remains unknown.
Abstract: The colonial ascidian Botryllus schlosseri is a model organism for research on invertebrate histocompatibility, development, and evolutionary biology. Nonetheless, the basic life history of Pacific Ocean populations of the species remains unknown. We determined field rates of growth, reproduction, and senescence in four cohorts of B. schlosseri colonies in Monterey Bay, California. Colonies grew exponentially as juveniles and reached sizes of up to 1400 zooids within 69 days. After a juvenile phase lasting at least 49 days, the colonies began to reproduce sexually. Each zooid produced up to 10 clutches, each with a maximum of 5 eggs, resulting in very high fecundity of up to 8000 eggs per colony. Following a short period (maximum 70 days) of continuous sexual reproduction, colonies abruptly senesced and died while still bearing a full clutch of eggs. Senescence progressed through four distinct stages over 1-2 weeks, and inevitably led to the simultaneous death of all zooids in the colony. Although senescence was the main cause of mortality, some colonies died as a result of predation or undermined causes. Certain life history traits varied significantly between cohorts that settled at different times of year. For example, lifespans in the field varied from about 3 months for spring to 8 months for fall-born colonies, but the lifetime fecundity of colonies did not vary between cohorts. The morphologies and life histories of colonies monitored in the field and reported here differed from those of colonies cultured previously in the laboratory.
TL;DR: Clams of the species Donax variabilis migrate shoreward during rising tides and seaward during falling tides; live clams emerge from the sand and move seaward even when dead ones do not.
Abstract: Clams of the species Donax variabilis migrate shoreward during rising tides and seaward during falling tides. These clams spend most of the time in the sand, emerging several times per tidal cycle to ride waves. Mi- gration is not merely a passive result of waves eroding clams out of the sand; rather clams actively jump out of the sand and ride specific waves. Such active migration is experimentally demonstrated during a falling tide by comparing the motion of dead and live clams; live clams emerge from the sand and move seaward even when dead ones do not. As low tide approaches, live clams become progressively less active. They cease migrating for 2 hours around low tide and resume jumping to migrate shoreward after the tide has turned. During the rising tide, far from being passive, the clams jump out to ride only the largest 20% of waves. Specifically, they choose swash that have the largest excursion, i.e., those swash that move furthest on the beach.
TL;DR: The morphology and mechanics of the tube feet, ampullae, and lateral and radial canals of the water vascular systems of Luidia clathrata and Astropecten articulatus were analyzed and no evidence was found for the previously suggested role of the radial canal in protracting thetube feet.
Abstract: The morphology and mechanics of the tube feet, ampullae, and lateral and radial canals of the water vascular systems of Luidia clathrata and Astropecten articulatus (Echinodermata, Asteroidea) were analyzed. Histological methods, based on embedding in both paraffin and glycol methacrylate, were used to document the arrangement of muscle and connective tissue. The tube foot wall includes longitudinal muscles and connective tissue fibers, the latter arranged in a crossed-fiber helical array, with a fiber angle of about 67{deg} in elongated tube feet. No evidence was found for the circular rings of connective tissue reported in earlier studies; the appearance of rings is probably an artifact of folding. The ampullae are bilobed and include circumferentially arranged muscle fibers and connective tissue fibers aligned 90{deg} to the muscle. The lateral canals are short and equipped with oneway flap valves similar to those described for other echinoderms. The radial canal is thin-walled, nonmuscular, and enclos...
TL;DR: The first evidence of a chemosensory response in a vent invertebrate to sulfides, which are prevalent in vent fluids and provide the energy, for chemosynthetic primary production at vents, is provided.
Abstract: Organisms dependent on deep-sea hydrothermal vents for their existence face extinction when their vents expire, unless they can establish populations on neighboring vents or on new vent sites. Propagules, including larvae and motile adults, are readily dispersed broadly by seafloor currents, but how they recognize active hydrothermal sites is problematical. Compelling evidence that vent organisms can find and colonize hydrothermal sites has been provided by a series of observations on the East Pacific Rise (1). New hydrothermal vents created there following a volcanic eruption on the seafloor in March 1991 were colonized by sessile invertebrates in less than one year. On the Mid-Atlantic Ridge, shrimp that normally cluster on sulfide surfaces have been observed to swim directly back to the surfaces when displaced from them. How do vent animals locate new or existing vents? Passive transport by currents (2) or active swimming without guidance by some physical cue is not likely to result in success (3). Chemicals present in hydrothermal fluids have been proposed as attractants. We provide the first evidence of a chemosensory response in a vent invertebrate to sulfides, which are prevalent in vent fluids and provide the energy,for chemosynthetic primary production at vents.
TL;DR: Improved methods to culture and observe healthy pre-metamorphic larvae in relatively deep containers demonstrated a prominent hovering behavior and may help account for the giant "amphioxides" and may be related to the curious asymmetry of the larval body.
Abstract: Larvae of lancelets (=amphioxus) are of special interest because they figure prominently in debates about vertebrate origins (1), can sometimes grow into a giant "amphioxides" form (2, 3), have a puzzling right-left asymmetry (4), and constitute a major zooplankton resource in parts of the Atlantic (5). By using improved methods (6, 7) to culture and observe healthy pre-metamorphic larvae in relatively deep containers, we demonstrated a prominent hovering behavior. The larvae spend most of their time suspended in midwater by metachronal beating of epidermal cilia. The body is usually tilted at an angle such that the anterior end and ventral side are oriented towards the water surface. This posture is maintained in the dark and in the light, although there is directional photosensitivity. Hovering may help account for the giant "amphioxides" and may be related to the curious asymmetry of the larval body.