Showing papers in "The Biological Bulletin in 2000"
TL;DR: The behavioral strategies employed by a variety of animals result in orientation responses that are appropriate for the dispersed, intermittent plumes dictated by the fluid-mechanical conditions in the environments that these different macroscopic organisms inhabit.
Abstract: Chemical signals mediate many of life's processes. For organisms that use these signals to orient and navigate in their environment, where and when these cues are encountered is crucial in determining behavioral responses. In air and water, fluid mechanics impinge directly upon the distribution of odorous molecules in time and space. Animals frequently employ behavioral mechanisms that allow them to take advantage of both chemical and fluid dynamic information in order to move toward the source. In turbulent plumes, where odor is patchily distributed, animals are exposed to a highly intermittent signal. The most detailed studies that have attempted to measure fluid dynamic conditions, odor plume structure, and resultant orientation behavior have involved moths, crabs, and lobsters. The behavioral mechanisms employed by these organisms are different but generally integrate some form of chemically modulated orientation (chemotaxis) with a visual or mechanical assessment of flow conditions in order to steer up-current or upwind (rheo- or anemo-taxis, respectively). Across-stream turns are another conspicuous feature of odor-modulated tracks of a variety of organisms in different fluid conditions. In some cases, turning is initiated by detection of the lateral edges of a well-defined plume (crabs), whereas in other animals turning appears to be steered according to an internally generated program modulated by odor contacts (moth counterturning). Other organisms such as birds and fish may use similar mechanisms, but the experimental data for these organisms is not yet as convincing. The behavioral strategies employed by a variety of animals result in orientation responses that are appropriate for the dispersed, intermittent plumes dictated by the fluid-mechanical conditions in the environments that these different macroscopic organisms inhabit.
436 citations
TL;DR: The results indicate that S. muscatinei co-occurs with a second dinoflagellate, S. californium, in mixed populations in central and southern California, and it is suggested that the geographic distribution of these dinof lagellates is related to the temperature cline created by latitude.
Abstract: We have analyzed the genetic profiles of dinoflagellate populations obtained from the Pacific coast sea anemone Anthopleura elegantissima (Brandt) at collection sites from Washington to California. Genetic differences within the symbiont populations of California anemones have been uncovered by restriction length polymorphism (RFLP) analysis of the small subunit (SSU) and large subunit (LSU) ribosomal RNA genes, and by denaturing gradient gel electrophoresis (DGGE) of the internal transcribed spacer region 2 (ITS 2). The existence of two Symbiodinium species is substantiated by sequence analysis of the variable regions V1, V2, and V3 of the SSUrDNA, which also establishes their phylogenetic relatedness to other members of the genus Symbiodinium. Anemones from Washington and Oregon harbor a single dinoflagellate species, for which we propose the name S. muscatinei sp. nov. At these northern locations, S. muscatinei either exists alone or co-occurs with the Chlorella-like green algal symbiont. Our results i...
363 citations
TL;DR: An algal dimethylsulfoniopropionate cleavage reaction that appears to deter protozoan feeding is detail and explored as a possible model for a rapidly activated, short-range chemical defense system.
Abstract: The activities of unicellular microbes dominate the ecology of the marine environment, but the chemical signals that determine behavioral interactions are poorly known. In particular, chemical signals between microbial predators and prey contribute to food selection or avoidance and to defense, factors that probably affect trophic structure and such large-scale features as algal blooms. Using defense as an example, I consider physical constraints on the transmission of chemical information, and strategies and mechanisms that microbes might use to send chemical signals. Chemical signals in a low Re, viscosity-dominated physical environment are transferred by molecular diffusion and laminar advection, and may be perceived at nanomolar levels or lower. Events that occur on small temporal and physical scales in the "near-field" of prey are likely to play a role in cell-cell interactions. On the basis of cost-benefit optimization and the need for rapid activation, I suggest that microbial defense system strate...
267 citations
TL;DR: There are now vast new opportunities for determining how organisms respond to chemical signals and employ chemical defenses under environmentally realistic conditions, and integrating findings within a larger ecological and evolutionary framework should lead to improved understanding of natural physicochemical phenomena that constrain biological responses at the individual, population, and community levels of organization.
Abstract: Understanding the mechanisms by which environmental chemical signals, chemical defenses, and other chemical agents mediate various life-history processes can lead to important insights about the forces driving the ecology and evolution of marine systems. For chemical signals released into the environment, establishing the principles that mediate chemical production and transport is critical for interpreting biological responses to these stimuli within appropriate natural, historical contexts. Recent technological advancements provide outstanding opportunities for new discoveries, thus allowing quantification of interactions between hydrodynamic, chemical, and biological factors at numerous spatial and temporal scales. Past work on chemically mediated processes involving organisms and their environment have emphasized habitat colonization by larvae and trophic relationships. Future research priorities should include these topics as well as courtship and mating, fertilization, competition, symbiosis, and mi...
260 citations
TL;DR: This work reviews some fluid dynamical concepts that are particularly useful in describing aspects of flow relevant to chemosensory navigation, and it considers studies of orientation in animals in light of these principles.
Abstract: The fluid mechanical environment provides the context in which denizens of aquatic realms, as well as terrestrial creatures, use chemoperception to search for objects. Our ability to understand the nature of olfactory-guided navigation rests on our proficiency at characterizing the fluid dynamic setting and at relating properties of flow to behavioral and sensory mechanisms. This work reviews some fluid dynamical concepts that are particularly useful in describing aspects of flow relevant to chemosensory navigation, and it considers studies of orientation in animals in light of these principles. Comparisons across broadly different fluid environments suggest that particular sensory and behavioral mechanisms may be tailored to specific flow regimes and stimulus environments. This is clearly evident when examining animals that operate in high vs. low Reynolds number flows. In other cases, animals may converge on common solutions in given flow regimes in spite of differences in taxonomic class or size. Potential parallels may include behavior of aquatic vs. terrestrial arthropods, and animals without fixed reference points in flows dominated by molecular vs. turbulent diffusion. In an effort to add further fluid dynamical underpinnings to navigational strategies, I suggest how simple nondimensional categorization of behavior in relation to flow may aid in identifying the forces underlying common elements, even across animals of seemingly disparate size and scale.
227 citations
TL;DR: It is suggested that procellariiforms foraging over vast distances may be able to recognize features reflected in the olfactory landscape over the ocean that aid seabirds in navigation or in locating profitable foraging grounds.
Abstract: Antarctic procellariiform seabirds forage over vast stretches of open ocean in search of patchily distributed prey resources. These seabirds are unique in that most species have anatomically well-developed olfactory systems and are thought to have an excellent sense of smell. Results from controlled experiments performed at sea near South Georgia Island in the South Atlantic indicate that different species of procellariiforms are sensitive to a variety of scented compounds associated with their primary prey. These include krill-related odors (pyrazines and trimethyl- amine) as well as odors more closely associated with phy- toplankton (dimethyl sulfide, DMS). Data collected in the context of global climatic regulation suggest that at least one of these odors (DMS) tends to be associated with predictable bathymetry, including upwelling zones and sea- mounts. Such odor features are not ephemeral but can be present for days or weeks. I suggest that procellariiforms foraging over vast distances may be able to recognize these features reflected in the olfactory landscape over the ocean. On the large scale, such features may aid seabirds in navi- gation or in locating profitable foraging grounds. Once in a profitable foraging area, procellariiforms may use olfactory cues on a small scale to assist them in locating prey patches.
196 citations
TL;DR: Results demonstrate that (1) the ASO-ablated larvae have not lost the ability to metamorphose and (2) the ions do not act only on the metamorphic-signal receptor cells, but at other sites downstream in the meetamorphic signal transduction pathway.
Abstract: On the basis of anatomy and larval behavior, the apical sensory organ (ASO) of gastropod veliger larvae has been implicated as the site of perception of cues for settlement and metamorphosis. Until now, there have been no experimental data to support this hypothesis. In this study, cells in the ASO of veliger larvae of the tropical nudibranch Phestilla sibogae were stained with the styryl vital dye DASPEI and then irradiated with a narrow excitatory light beam on a fluorescence microscope. When its ASO cells were bleached by irradiation for 20 min or longer, an otherwise healthy larva was no longer able to respond to the usual metamorphic cue, a soluble metabolite from a coral prey of the adult nudibranch. The irradiated cells absorbed the dye acridine orange, suggesting that they were dying. When larvae not stained with DASPEI were similarly irradiated, or when stained larvae were irradiated with the light beam focused on other parts of the body, there was no loss of ability to metamorphose. Together these data provide strong support for the hypothesis. Potassium and cesium ions, known to induce metamorphosis in larvae of many marine-invertebrate phyla, continue to induce metamorphosis in larvae that have lost the ability to respond to the coral inducer due to staining and irradiation. These results demonstrate that (1) the ASO-ablated larvae have not lost the ability to metamorphose and (2) the ions do not act only on the metamorphic-signal receptor cells, but at other sites downstream in the metamorphic signal transduction pathway.
159 citations
TL;DR: The authors' observations suggest that direct coral-fungal interaction is widespread, not only geographically, but taxonomically as well, and that fungal endoliths, acting as opportunistic pathogens, may play a greater role in the ecology of coral reef systems than previously recognized.
Abstract: Reef-building corals appear to exist in dynamic equilibria with four principal partners: interconnected polyps of a colonial coelenterate, endosymbiotic dinoflagellate zooxanthellae residing in the host’s endoderm, endolithic algae that penetrate coral skeletons, and endolithic fungi that attack both endolithic algae and the polyps. Although reports of fungal and algal-like endoliths in corals date back almost 150 years (1) and evidence of a fossil history extends as far back as the Upper Devonian (;370 ma) (2), most attention has been paid to the structure (3), function (4, 5), and diversity (6) of the coral-zooxanthellae interactions, ignoring the endolithic members of the consortium. Recently, Le Campion-Alsumard et al. (1995) (7, 8) described an interrelationship between endolithic algae and fungi within the massive coral Porites lobata Dana 1846 (Poritidae), on Moorea island near Tahiti, French Polynesia. Fungi were also found to penetrate the most recently deposited skeletal material and to be associated with pearllike skeletal deposits formed by polyps of P. lobata in response to attack by their heterotrophic, endolithic symbionts. Here we extend these observations to the pocilloporid coral Pocillopora eydouxi and to the acroporid corals Acropora cytherea, Acropora humulis, and Montipora cf. studeri, collected at Johnston Atoll, central Pacific Ocean. Our observations suggest that direct coral-fungal interaction is widespread, not only geographically, but taxonomically as well. Thus, fungal endoliths, acting as opportunistic pathogens, may play a greater role in the ecology of coral reef systems than previously recognized. The oligophotic, siphonal green alga Ostreobium quekettii is ubiquitous in skeletons of live corals (9, 10). It is also common in other carbonate substrates, including dead shells and limestone, down to a depth of 300 m in clear waters of the Bahamas (11). Two other phototrophic organisms were reported from skeletons of live corals, the filamentous cyanobacterium Plectonema terebrans and conchocelis stages of bangiacean rhodophytes (12). Endolithic fungi in coral skeletons are equally common. They penetrate the corallum (euendolithic) and are often intermingled with endolithic algae, frequently parasitizing the latter (7). Fungi attack algal filaments by specialized hyphal branches, or haustoria, and often continue to grow inside algal filaments. Dense populations of algal and fungal endoliths have been associated with black-stained bands in specimens of P. lobata (13). Although skeletons of dead corals are bored by a variety of endolithic microorganisms, there has been no evidence that endoliths can penetrate the layer of tissue that covers living coral surfaces, leading to the conclusion that infestation by a limited number of specialized endoliths occurs early in the life of a coral, and that endolithic algae and fungi continue to grow in parallel with the accretion of the corallum (8). Most filaments of O. quekettii and endolithic fungi extend in the direction of the axes of skeletal growth. In P. lobata, borings were detected in newly deposited skeletal spines (pali), demonstrating that the endoliths are able to keep up with the rates of skeletal accretion (7, fig. 2). The pearl-like skeletal deposits are always associated with fungal attacks during the residence of polyps in actively growing calicies. The polyps encapsulate the advancing hypha into dense repair aragonite, forming a distinct skeletal structure referred to as a “cone” (7). The present study has two main objectives: to determine whether the relationship exhibited between P. lobata and endolithic fungi as described from the island of Moorea, in Received 7 July 1999; accepted 29 November 1999. *To whom correspondence should be addressed. E-mail: cbentis @bu.edu Reference: Biol. Bull. 198: 254–260. (April 2000)
155 citations
TL;DR: Membrane potential can be measured optically using a variety of molecular probes, useful in studying function at the level of an individual cell, for determining how groups of neurons generate a behavior, and for studying the correlated behavior of populations of neurons.
Abstract: Membrane potential can be measured optically using a variety of molecular probes. These measurements can be useful in studying function at the level of an individual cell, for determining how groups of neurons generate a behavior, and for studying the correlated behavior of populations of neurons. Examples of the three kinds of measurements are presented. The signals obtained from these measurements are generally small. Methodological considerations necessary to optimize the resulting signal-to-noise ratio are discussed.
154 citations
TL;DR: Data for rates of expulsion, rates of division at different temperatures, and uptake of 3H-thymidine suggest that dividing algal cells are preferentially expelled from their hosts, suggesting that preferential expulsion of dividing cells may be a mechanism for regulation of algal population density.
Abstract: A wide range of both intrinsic and environmental factors can influence the population dynamics of algae in symbiosis with marine cnidarians. The present study shows that loss of algae by expulsion from cnidarian hosts is one of the primary regulators of symbiont population density. Because there is a significant linear correlation between the rate of algal expulsion and the rate of algal division, factors that increase division rates (e.g., elevated temperature) also increase expulsion rates. Additionally, 3H-thymidine is taken up to a greater extent by algae destined to be expelled than by algae retained in the host cnidarians. Taken together, data for rates of expulsion, rates of division at different temperatures, and uptake of 3H-thymidine suggest that dividing algal cells are preferentially expelled from their hosts. The preferential expulsion of dividing cells may be a mechanism for regulation of algal population density, where the rate of expulsion of algae may be an inverse function of the ability...
131 citations
TL;DR: Understanding the micromechanics of small-scale biological-physical-chemical interactions gives insight into factors influencing large-scale dynamics of copepod distribution, patchiness, and encounter probabilities in the sea.
Abstract: Copepods (1-10 mm aquatic crustaceans moving at 1-1000 mm s(-1)) live at Reynolds numbers that vary over 5 orders of magnitude, from 10(-2) to 10(3). Hence, they live at the interface between laminar and turbulent regimes and are subject to the physical constraints imposed by both viscous and inertial realms. At large scales, the inertially driven system enforces the dominance of physically derived fluid motion; plankton, advected by currents, adjust their life histories to the changing oceanic environment. At Kolmogorov scales, a careful interplay of evenly matched forces of biology and physics occurs. Copepods conform or deform the local physical environment for their survival, using morphological and behavioral adaptations to shift the balance in their favor. Examples of these balances and transitions are observed when copepods engage in their various survival tasks of feeding, predator avoidance, mating, and signaling. Quantitative analyses of their behavior give measures of such physical properties o...
TL;DR: A comparison of the energy expended during larval swimming calculated on the basis of oxygen consumption and of elemental carbon decrease suggests that larvae of Bugula spp.
Abstract: The amount of energy available to larvae dur- ing swimming, location of a suitable recruitment site, and metamorphosis influences the length of time they can spend in the plankton. Energetic parameters such as swimming speed, oxygen consumption during swimming and meta- morphosis, and elemental carbon and nitrogen content were measured for larvae of four species of bryozoans, Bugula neritina, B. simplex, B. stolonifera, and B. turrita. The larvae of these species are aplanktotrophic with a short free-swimming phase ranging from less than one hour to a maximum of about 36 hours. There is about a fivefold difference in larval volume among the four species, which scales linearly with elemental carbon content and, presum- ably, with the amount of endogenous reserves available for swimming and metamorphosis. Mean larval swimming speeds (in centimeters per second) were similar among species. Specific metabolic rate and larval size were in- versely related. For larvae of a given species, respiration rates remained similar for swimming and metamorphosis; however, because metamorphosis lasts about twice as long as a maximal larval swimming phase, it was more energet- ically demanding. Larger larvae expended more energy to complete metamorphosis than did smaller larvae, but in terms of the percentage of larval energy reserves consumed, swimming and metamorphosis were more "expensive" for smaller larvae. A comparison of the energy expended during larval swimming calculated on the basis of oxygen con- sumption and on the basis of elemental carbon decrease suggests that larvae of Bugula spp. may not use significant amounts of dissolved organic material (DOM) to supple- ment their endogenous energy reserves.
TL;DR: The formal description of the genus Symbiodinium, which describes the in situ symbionts, contains information that is based on artifact and should be revised.
Abstract: The fine structure of the symbiotic dinoflagellate genus Symbiodinium has been well described. All of the published descriptions are based on tissue that was fixed in standard aldehyde and osmium fixatives and dehydrated in an ethanol series before embedding. When the technique of freeze-substitution was used to fix tissue from Cassiopeia xamachana, Aiptasia pallida, and Phyllactis flosculifera and prepare it for embedding, thecal vesicles were revealed within the in situ symbionts of all three species. Although these structures have been identified in cultured symbionts, they have never been described in the in situ symbionts. A review of the literature has revealed several instances where thecal vesicles were either overlooked or identified incorrectly. Thus the formal description of the genus Symbiodinium, which describes the in situ symbionts, contains information that is based on artifact and should be revised. A revision of the genus is suggested, and the true nature of these structures and their si...
TL;DR: The first cladistic analysis of nearly all known gastrotrich genera using 71 morphological characters suggests that the Gastrotricha is a monophyletic group with its most primitive taxa distributed among the families Dactylopodolidae and Neodasyidae.
Abstract: Currently, the phylum Gastrotricha is divided into the orders Macrodasyida and Chaetonotida, with the structure of the myoepithelial pharynx being an important distinguishing feature. Macrodasyida currently has six recognized families, and Chaetonotida comprises seven families. However, within- group relationships are poorly understood. To arrive at a better understanding of gastrotrich systematics and phylogeny, we performed the first cladistic analysis of nearly all known gas- trotrich genera using 71 morphological characters. Results suggest that the Gastrotricha is a monophyletic group (support- ed by 82% of bootstrap replications) with its most primitive taxa distributed among the families Dactylopodolidae and Neodasyidae. Monophyly of Macrodasyida and Chaetonotida was supported by 90% and 52% bootstrap replications, respec- tively. Within the Macrodasyida, the families Dactylopodoli- dae, Turbanellidae, Macrodasyidae, and Thaumastodermatidae all formed monophyletic clades. The families Planodasyidae and Lepidodasyidae were paraphyletic. Among the Chaetonotida, the marine family Xenotrichulidae was mono- phyletic, supported by 51% of bootstrap replications. A second clade containing all freshwater families was supported by 62% bootstrap values. However, Chaetonotidae were paraphyletic. Using this analysis as a framework, we now can explore possible patterns of evolution within it, and arrive at a consen- sus of the gastrotrich ground pattern. Moreover, in future molecular studies of metazoan phylogeny, we will be able to select gastrotrich species that are more appropriate representa- tives of the phylum.
TL;DR: This work suggests that endobiont diatoms utilize the products of the metabolism of their host as an energy source, the first evidence indicating that an endobiotic autotrophic organism may parasitize its animal host.
Abstract: Antarctic sponges may host large populations of planktonic and benthic diatoms. After settling on the sponge, these diatoms enter its body through pinacocytes (1) and form, there, large mono- or pauci-specific assemblages. Yet the total amount of carbohydrates in the invaded sponge tissue is inversely correlated with that of chlorophyll-a. We suggest, therefore, that endobiont diatoms utilize the products of the metabolism of their host as an energy source. This is the first evidence indicating that an endobiotic autotrophic organism may parasitize its animal host. Moreover, this unusual symbiotic behavior could be a successful strategy that allows the diatom to survive in darkness.
TL;DR: A plate theory analysis of cuttlebone strength predicted maximum capture depths accurately in most species, despite the fact that Sepia species that live at greater depths had thicker septa and less space between pillars than did shallow species.
Abstract: The cuttlebone is a rigid buoyancy tank that imposes a depth limit on Sepia, the only living speciose cephalopod genus with a chambered shell. Sections of 59 cuttlebones from a geographically diverse sample of 11 species were examined using confocal microscopy. Sepia species that live at greater depths had thicker septa and less space between pillars than did shallow species. A plate theory analysis of cuttlebone strength based on these two measures predicted maximum capture depths accurately in most species. Thus cuttlebone morphology confers differing degrees of strength against implosion from hydrostatic pressure, which increases with increasing habitat depth. Greater strength may come at the cost of increased cuttlebone density, which impinges on the cuttlebone's buoyancy function.
TL;DR: The reproductive development of the Demospongiae species Halisarca dujardini, Myxilla incrustans and Iophon piceus from Chupa Inlet was studied histologically during 1982-1994 and 1997.
Abstract: The reproductive development of the Demo- spongiae species Halisarca dujardini(Halisarcida), Myxilla incrustans and Iophon piceus (Poecilosclerida) from Chupa Inlet (Kandalaksha Bay, the White Sea) was studied histo- logically during 1982-1994 and 1997. These species are all viviparous. Halisarca dujardini inhabits shallow waters (1.5-5 m); M. incrustans and I. piceus are common in a more stable environment at depths between 15 and 25 m. Initiation of sexual reproduction stages is dependent upon water temperature. Reproductive effort is low in Myxilla incrustans and I. piceus (reproductive elements contribute 7.3% and 12% of maternal tissue volume respectively), but much higher in H. dujardini (up to 69% of the parental tissue volume). Reproduction leads to localized destruction of maternal tissue for M. incrustans and I. piceus and complete disorder of central and basal parts of the choano- soma of H. dujardini after each period of reproduction. Myxilla incrustans and I. piceus reproduce throughout the hydrological summer, but reproduction in H. dujardini is restricted to 3 weeks. The average life span of M. incrustans and I. piceus is more than 4 years, and that of H. dujardini is about 7-12 months. The data suggest that M. incrustans and I. piceus are K-strategists, whereas H. dujardini is an r-strategist.
TL;DR: Catecholamines are likely to modulate metamorphosis in P. sibogae, but rising levels of catecholamine around the time of competence are insufficient alone to account for sensitivity to inducer in competent larvae.
Abstract: Larvae of the nudibranch Phestilla sibogae are induced to metamorphose by a factor from their adult prey, the coral Porites compressa. Levels of endogenous catecholamines increase 6 to 9 days after fertilization, when larvae become competent for metamorphosis. Six- to nine-day larvae, treated with the catecholamine precursor L-DOPA (0.01 mM for 0.5 h), were assayed for metamorphosis in response to coral inducer and for catecholamine content by high-performance liquid chromatography. L-DOPA treatment caused 20- to 50-fold increases in dopamine, with proportionally greater increases in younger larvae, so that L-DOPA-treated larvae of all ages contained similar levels of dopamine. A much smaller (about twofold) increase in norepinephrine occurred in all larvae. The treatment significantly potentiated the frequency of metamorphosis of 7- to 9-d larvae at low concentrations of inducer. In addition, L-DOPA treatment at 9 d increased aldehyde-induced fluorescence in cells that were also labeled in the controls, ...
TL;DR: The demonstration of early developing neurons and their transmitter phenotypes in A. californica presents new opportunities for a better understanding of the ontogeny and phylogeny of both behavioral and neuronal function in this important model species.
Abstract: This study demonstrates the presence of a relatively extensive but previously unrecognized nervous system in embryonic stages of the opisthobranch mollusc Aplysia californica. During the trochophore stage, two pairs of cells were observed to be reactive to antibodies raised against the neuropeptides FMRFamide and EFLRIamide. These cells were located in the posterior region of the embryo, and their anterior projections terminated under the apical tuft. As the embryos developed into veliger stages, serotonin-like immunoreactive (LIR) cells appeared in the apical organ and were later observed to innervate the velum. Also, aldehyde-induced fluorescence indicative of catecholamines was present in cells in the foot, oral, and possibly apical regions during late embryonic veliger stages. Just before the embryo hatches as a free-swimming veliger, additional FMRFamide-LIR and catecholamine-containing cells appeared in regions that correspond to the ganglia of what will become the adult central nervous system (CNS). Neurons and connectives that will contribute to the adult CNS appear to develop along the pathways that are pioneered by the earliest posterior FMRFamide-LIR cells. These observations are consistent with the hypothesis that, besides their presumed roles in the control of embryonic behaviors, some elements may also guide the development of the CNS. Embryonic nervous systems that develop prior to and outside of the adult CNS have also been reported in pulmonate and prosobranch species of molluscs. Therefore, the demonstration of early developing neurons and their transmitter phenotypes in A. californica presents new opportunities for a better understanding of the ontogeny and phylogeny of both behavioral and neuronal function in this important model species.
TL;DR: A cue for metamorphosis was isolated and characterized from D. pulchra and found to be a water-soluble complex of the sugar floridoside and isethionic acid in a 1:1 molar ratio.
Abstract: Most benthic invertebrates have complex life cycles with planktonic larvae that return to the substratum to settle and metamorphose into a benthic stage. Although naturally produced chemical cues have long been thought to be important for the settlement or metamorphosis of invertebrate larvae, few ecologically relevant chemical cues have been clearly identified. The marine echinoid Holopneustes purpurascens has a complex life cycle, with a planktonic, nonfeeding dispersive larva that metamorphoses into a benthic stage that lives in the canopy of subtidal benthic algae such as the red alga Delisea pulchra and the kelp Ecklonia radiata. Recently recruited juveniles are found primarily on D. pulchra, and we hypothesized that this was in response to a chemical cue produced by this alga. Competent larvae metamorphosed in the presence of D. pulchra, or seawater surrounding this alga, but not in response to the presence of E. radiata or its extracts. A cue for metamorphosis was isolated and characterized from D....
TL;DR: It is suggested that the structure of homorhabdic ctenidia does not preclude particle sorting, and that some ecosystem modifications attributed to zebra mussels may ultimately be due to ctenidial sorting mechanisms.
Abstract: The capture, transport, and sorting of particles by the gills and labial palps of the freshwater mussel Dreissena polymorpha were examined by endoscopy and video image analysis. More specifically, the morphology of the feeding organs in living zebra mussels was described; the mode and speeds of particle transport on the feeding organs was measured; and the sites of particle selection in the pallial cavity were identified. Particle velocities (outer demibranch lamellae, 90 microm s(-1); inner demibranch lamellae, 129 microm s(-1); marginal food groove of inner demibranchs, 156 microm s(-1); dorsal ciliated tracts, 152 microm s(-1)), as well as the movement of particles on the ctenidia and labial palps of D. polymorpha, are consistent with mucociliary, rather than hydrodynamic, transport. Particles can be sorted on the ctenidia of zebra mussels, resulting in a two-layer transport at the marginal food groove of the inner demibranch. That is: preferred particles are transported inside the marginal groove proper, whereas particles destined for rejection are carried superficially in a string of mucus. Sorting also occurs at the ventral margin of the outer demibranch; desirable particles are retained on the outer demibranch, whereas unacceptable particles are transferred to the inner demibranch and ultimately excluded from ingestion. We suggest that the structure of homorhabdic ctenidia does not preclude particle sorting, and that some ecosystem modifications attributed to zebra mussels may ultimately be due to ctenidial sorting mechanisms.
TL;DR: It is suggested that, where high-speed locomotion is not required, more efficient means of locomotion, such as fin swimming or medusoid arm propulsion, are more prevalent.
Abstract: The present study attempts to correlate the me- tabolism and locomotory behavior of 25 species of midwa- ter Cephalopoda from California and Hawaii with the maximal activities of key metabolic enzymes in various locomotory muscle tissues. Citrate synthase (CS) and octo- pine dehydrogenase (ODH) activities were used as indica- tors of aerobic and anaerobic metabolic potential respec- tively. CS activity in mantle muscle is highly correlated with whole-animal rates of oxygen consumption, whereas ODH activity in mantle muscle is significantly correlated with a species' ability to buffer the acidic end-products of anaerobic metabolism. Both CS and ODH activities in man- tle muscle declined strongly with a species' habitat depth. For example, CS and ODH activities ranged respectively from 0.04 units g 21 and 0.03 units g 21 in the deep-living squid Joubiniteuthis portieri,to 8.13 units g 21 and 420 units g 21 in the epipelagic squid Sthenoteuthis oualaniensis.The relationships between enzymatic activities and depth are consistent with similar patterns observed for whole-animal oxygen consumption. This pattern is believed to result from a relaxation, among deep-living species, in the need for strong locomotory abilities for visual predator/prey interac- tions; the relaxation is due to light-limitation in the deep sea. Intraspecific scaling patterns for ODH activities may, for species that migrate ontogenetically to great depths, reflect the counteracting effects of body size and light on predator- prey detection distances. When scaled allometrically, enzy- matic activities for the giant squid, Architeuthis sp., suggest a fairly active aerobic metabolism but little burst swimming capacity. Interspecific differences in the relative distribu- tions of enzymatic activities in fin, mantle, and arm tissue suggest an increased reliance on fin and arm muscle for locomotion among deep-living species. We suggest that, where high-speed locomotion is not required, more efficient means of locomotion, such as fin swimming or medusoid arm propulsion, are more prevalent.
TL;DR: The results show that mitosis of symbiotic dinoflagellates requires three factors: external food; a minimum period of time following feeding; and a period of light following feeding, presumably to provide carbon skeletons necessary for completing cytokinesis.
Abstract: The hydroid Myrionema ambionense, a fast- growing cnidarian (doubling time 5 8 days) found in shal- low water on tropical back-reefs, lives in symbiosis with symbiotic dinoflagellates of the genus Symbiodinium (here- after also referred to as zooxanthellae). The symbionts live in vacuoles near the base of host digestive cells, whereas unhealthy looking zooxanthellae are generally located closer to the apical end of the host cell. Cytokinesis of zooxanthellae occurred at night, with a peak in number of symbionts with division furrows (mitotic index, MI 5 12%-20%) observed at dawn. The MI of zooxanthellae decreased to near zero by the middle of the afternoon and remained there until the middle of the next night. Densities of live zooxanthellae living inside of host digestive cells peaked following cytokinesis, whereas densities of un- healthy looking symbionts were highest just before the division peak. Mitosis of host digestive cells was highest in the evening, also preceding the peak in zooxanthellar MI. This is the first study relating phased host cell division to diel zooxanthellar division in marine cnidarians. Food vacuoles were prevalent inside of digestive cells of field-collected hydroids within a few hours after sunset and throughout the night, coinciding with digestion of captured demersal plankton. Laboratory experiments showed that food vacuoles appeared in digestive cell cytoplasm within 2 h of feeding with nauplii of Artemia. The number and size of food vacuoles per digestive cell and the percentage of digestive cells with food vacuoles all decreased 5-7 h following feeding in laboratory experiments, and by mid- day in field-collected hydroids. Light and external food supply were important in main- taining phased division of the symbionts, with a lag in response time to both parameters of 11-36 h. Altering light and feeding during the night did not influence the level of the peak MI the next morning, though in one experiment the absence of light slowed final separation of daughter cells at the end of cytokinesis. In another experiment, hydroids starved for 3-7 d and "pulse-fed" Artemia nauplii fo r1ha t the beginning of the dark period showed continued low symbiont division (,5%) after 11 h, whether maintained in constant light or darkness, implying that most algal division is set more than 24 h prior to actual cytokinesis. Transferred to a 14:10 h light:dark cycle for another 24 h (36 h after feeding), the same hydroids exhibited a "normal" peak MI (ca. 15%) at dawn, but zooxanthellae from hydroids kept in constant darkness still showed a low MI. These results show that mitosis of symbiotic dinoflagellates requires three fac- tors: external food; a minimum period of time following feeding (11-36 h), presumably for digestion; and a period of light following feeding, presumably to provide carbon skel- etons necessary for completing cytokinesis.
TL;DR: The results suggest that only blastomeres that had been determined to develop into gastrodermal cells receive zooxanthellae during cleavage, and appears to take place, at the latest, by the second cell division at the four-cell stage.
Abstract: Some hermatypic corals spawn eggs that contain zooxanthellae. We followed development of zooxanthella-containing eggs of two such species, Pocillopora verrucosa and P. eydouxi. We also documented changes in the distribution pattern of zooxanthellae during development. Oocytes of both species took up zooxanthellae 3 to 4 days before spawning. At first, zooxanthellae were evenly distributed in oocytes, but they later moved to the hemisphere that contained the germinal vesicle. After fertilization, early cleavage events were holoblastic, progressing by furrow formation. The first cleavage furrow started at the hemisphere that contained zooxanthellae, dividing the zooxanthellate complement of the zygote about equally into the two blastomeres. The second division divided each blastomere into one zooxanthellae-rich cell and one with few zooxanthellae. With continued cell division, blastomeres containing zooxanthellae moved into the blastocoel. The blastocoel disappeared at about 5 h after the first cleavage, an...
TL;DR: The hemoglobin extracted from the copepod B. spiculifer has a very high and temperature-sensitive oxygen affinity, with no cooperativity or Bohr effect, and are adaptive for an animal living in a low-oxygen environment in which the primary function of the hemoglobin is most likely oxygen acquisition to support aerobic respiration.
Abstract: Deep-sea hydrothermal-vent fauna live in a highly variable environment where oxygen levels can be very low, and carbon dioxide and sulfide can reach high concentrations (1). These conditions are harsh for most aerobic metazoans, yet copepods can be abundant at hydro- thermal vents. Here we report the structure and functional properties of hemoglobin extracted from the copepod Ben- thoxynus spiculifer, which was found in large numbers in a paralvinellid/gastropod community collection made during a cruise to the Juan de Fuca Ridge in 1998. Although hemoglobin has been reported in some littoral copepods (2), this is the first study of the structure and functional prop- erties of copepod hemoglobin. Hemoglobin represents about 60% of the total soluble proteins extracted from B. spiculifer, and although it imparts a red color to the cope- pod, it does not provide a significant storage pool of oxygen. It is a 208-kDa protein, composed of 14 globin chains—7 of 14.3 kDa and 7 of 15.2 kDa. The hemoglobin has a very high and temperature-sensitive oxygen affinity, with no cooperativity or Bohr effect. These properties are adaptive for an animal living in a low-oxygen environment in which the primary function of the hemoglobin is most likely ox- ygen acquisition to support aerobic respiration. Copepods occur in both freshwater and marine environ- ments that range from pelagic to benthic and littoral to deep-sea (3). Red copepods have been observed at hydro- thermal vents of the Mid-Atlantic Ridge, Juan de Fuca Ridge, and East Pacific Rise (SH, pers. obs.). However, the
TL;DR: A comparison of winter and summer lobsters, both held at 15 degrees C for more than 4 weeks, revealed that although their responses to temperature changes were similar, winter lobsters had a significantly lower baseline heart rate and a shorter duration cardiac response than summer lobster, suggesting that some temperature-independent seasonal modulation of cardiac activity may be occurring.
Abstract: It is generally accepted that crustaceans detect, and respond to, changes in water temperature, yet few studies have directly addressed their thermosensitivity. In this investigation a cardiac assa...
TL;DR: Ten species in five genera and three families from continental shelf and deep-sea collections of neomenioid Aplacophora (Mollusca) are described, emphasizing external anatomy and hard parts--body shape, radula, epidermal spicules, and copulatory spicule--as well as the reproductive system.
Abstract: Ten species in five genera and three families from continental shelf and deep-sea collections of neomenioid Aplacophora (Mollusca) are described, emphasizing external anatomy and hard parts--body shape, radula, epidermal spicules, and copulatory spicules--as well as the reproductive system. One genus and seven species are new: Plawenia n.g., Plawenia sphaera, P. argentinensis, Dorymenia tortilis, Eleutheromenia bassensis, E. mimus, Kruppomenia levis, and K. delta. Also included are redescriptions of three published species, emphasizing hard parts for comparisons with the new species and genus: Dorymenia sarsii (Koren & Danielssen), Simrothiella margaritacea (Koren & Danielssen), and Plawenia schizoradulata (Salvini-Plawen). A cladistic analysis of species described here demonstrates the usefulness of hard parts for phylogeny. Specimens came from collections made in the southwest Pacific and the southwest and northeast Atlantic.
TL;DR: Seasonal changes in the giant axon's size and resistivity are not consistent with compensatory thermal acclimation, but instead serve to maintain a constant relationship between conduction velocity and temperature.
Abstract: To determine whether the electrical properties of the squid giant axon are seasonally acclimated, action potentials, recorded at different temperatures, were compared between giant axons isolated from Loligo pealei caught in May, from relatively cold waters (approximately 10 degrees-12 degrees C), and in August, from relatively warm waters (approximately 20 degrees C). Parameters relating to the duration of the action potential (e.g., maximum rate of rise, maximum rate of fall, and duration at half-peak) did not change seasonally. The relationship between conduction velocity and temperature remained constant between seasons as well, in spite of the fact that May axons were significantly larger than August axons. When normalized to the fiber diameter, mean May conduction velocities were 83% of the August values at all temperatures tested, and analysis of the rise time of the action potential foot suggested that a change in the axoplasmic resistivity was responsible for this difference. Direct measurements of axoplasmic resistance further supported this hypothesis. Thus seasonal changes in the giant axon's size and resistivity are not consistent with compensatory thermal acclimation, but instead serve to maintain a constant relationship between conduction velocity and temperature.
TL;DR: Cuvierian tubules constitute a very efficient defensive mechanism: their large number, sparing use, and particular regeneration dynamics make them an almost inexhaustible line of defense maintained at limited energy cost.
Abstract: When irritated, individuals of the sea cucumber Holothuria forskali expel a few Cuvierian tubules which lengthen, instantly become sticky, and rapidly immobilize most organisms with which they come into contact. After expulsion, the lost tubules are readily regenerated. When only a few tubules have been expelled, there is often a latent period before the regeneration starts. In contrast, when many tubules have been expelled, the regenerative process starts immediately but proceeds in successive waves of 10 to 30 tubules that begin to regenerate at 10-day intervals. However, in all cases, the complete regeneration of a given tubule takes about 5 weeks and may be divided into three successive phases: an initial repair phase including the overall 48-h post-autotomy period, a true regenerative phase taking about 4 weeks to complete, and a growth phase of about one more week. Initial regeneration events occur by epimorphosis, cell proliferation being essential to the regenerative process, whereas late events occur mainly by morphallaxis, with migration of the newly differentiated cells. The mesothelium is the tissue layer in which cell proliferation is the most precocious and the most important, involving both peritoneocytes and undifferentiated cells (which seem to be dedifferentiated peritoneocytes). As regeneration proceeds, the percentage of undifferentiated cells regularly decreases in parallel with the differentiation of granular (adhesive-secreting) cells and myocytes. The myocytes then separate off from the mesothelium and migrate within the connective tissue layer. Three types of pseudopodial cells follow one another in the tubule connective tissue during regeneration. Type 1 cells have all the characteristics of echinoderm phagocytes and may have a fibroblastic function, cleaning the connective tissue compartment before new collagen synthesis starts. Type 2 cells are rather undifferentiated and divide actively. The presence of type 3 cells is closely associated with the appearance of collagen fibers, and it is suggested that they have a fibroblastic function. In the inner epithelium, cells also divide actively, but only those in which spherules have not yet differentiated in the basal intraconnective processes. It appears, therefore, that in the three tissue layers of the tubules, regeneration proceeds by cell dedifferentiation, then proliferation, and finally by differentiation. Cuvierian tubules thus constitute a very efficient defensive mechanism: their large number, sparing use, and particular regeneration dynamics make them an almost inexhaustible line of defense maintained at limited energy cost.
TL;DR: The authors' experiments indicate that cloning generally occurs after larvae have attained asymptotic body length and only when food is abundant and of high quality, and production of clones under optimal conditions of temperature and food may serve to increase larval populations when the environment is most conducive to larval growth.
Abstract: A decade ago, cloning was first observed in the planktotrophic larvae of sea stars obtained from plankton tows. However, no controlled experimental studies have investigated what factors may regulate this remarkable phenomenon. In the present study we offer the first documentation of cloning in the planktotrophic larvae of Pisaster ochraceus from the northern Pacific coast. This species was used as a model system to investigate three factors that may influence the incidence of asexual reproduction (cloning) in planktotrophic sea star larvae. In an initial experiment, larvae were reared under nine combinations of three temperatures and three food (phytoplankton) concentrations. Larvae reared at 12-15 degrees C and fed the highest food concentrations grew larger than the other larvae and produced significantly more clones. In a second experiment, qualitatively different algal diets were fed to larvae reared under the conditions found to be optimal in the initial experiment. Up to 24% of the larvae consuming...