Showing papers in "The Biological Bulletin in 2007"

Chemical defenses: from compounds to communities.

Abstract: Marine natural products play critical roles in the chemical defense of many marine organisms and in some cases can influence the community structure of entire ecosystems. Although many marine natural products have been studied for biomedical activity, yielding important information about their biochemical effects and mechanisms of action, much less is known about ecological functions. The way in which marine consumers perceive chemical defenses can influence their health and survival and determine whether some natural products persist through a food chain. This article focuses on selected marine natural products, including okadaic acid, brevetoxins, lyngbyatoxin A, caulerpenyne, bryostatins, and isocyano terpenes, and examines their biosynthesis (sometimes by symbiotic microorganisms), mechanisms of action, and biological and ecological activity. We selected these compounds because their impacts on marine organisms and communities are some of the best-studied among marine natural products. We discuss the ...

Pathogen-induced defense and innate immunity in macroalgae.

Abstract: Animals and vascular plants are known to defend themselves facultatively against pathogens, with innate receptors mediating their resistance. Macroalgal defense against microorganisms, in contrast, has until recently been regarded mainly as constitutive. Indeed, many macroalgae appear to be chemically defended at constantly high levels, and this is possibly one of the reasons why the first evidence of pathogen-aroused resistance in a macroalga was detected only a decade ago. Here, I summarize the results of studies that indicate the existence of pathogen-activated or pathogen-induced macroalgal defense. Most indications so far come from molecular investigations, which revealed major functional similarities among the defense systems of distant macroalgal clades and the innate immune systems of vascular plants and metazoans. Homologies exist in the primary and secondary defense-activating signals, as well as in the enzymes that are involved and the cellular responses that are activated. This strongly suggests that innate immunity also exists in relatively distinct macroalgal clades. However, a macroalgal receptor still needs to be isolated and characterized, and the molecular concept of macroalgal receptor-mediated immunity needs to be complemented with an ecological perspective on pathogen-induced defense, to develop a joint neuroecological perspective on seaweed-microbe interactions.

Escape by Inking and Secreting: Marine Molluscs Avoid Predators Through a Rich Array of Chemicals and Mechanisms

Abstract: Inking by marine molluscs such as sea hares, cuttlefish, squid, and octopuses is a striking behavior that is ideal for neuroecological explorations. While inking is generally thought to be used in active defense against predators, experimental evidence for this view is either scant or lacks mechanistic explanations. Does ink act through the visual or chemical modality? If inking is a chemical defense, how does it function and how does it affect the chemosensory systems of predators? Does it facilitate escape not only by acting directly on predators but also by being an alarm signal for conspecifics? This review examines these issues, within a broader context of passive and active chemical defensive secretions. It focuses on recent work on mechanisms of defense by inking in sea hares (Aplysia) and extends what we have learned about sea hares to other molluscs including the cephalopods.

Endogenous green fluorescent protein (GFP) in amphioxus.

Abstract: remains to be learned about the taxonomic distribution and biological function of these proteins in nature. To date, GFPs have been found in only two major groups in the metazoan tree: specifically, in a number of cnidarians, rel atively near the base of the tree, and in a few copepod crustaceans, relatively derived within the protostome branch (2, 3). The cnidarian GFPs are often associated with biolu minescence, but those found so far in copepods are not. We now report that the limited taxonomic distribution of ani mals with endogenous GFPs may be partially due to inad equate sampling efforts, because we have found such mol ecules in the cephalochordate amphioxus. About 10 years

Effects of temperature and UV radiation increases on the photosynthetic efficiency in four scleractinian coral species.

Abstract: Experiments were performed on coral species containing clade A (Stylophora pistillata, Montipora aequi- tuberculata) or clade C (Acropora sp., Pavona cactus) zooxanthellae. The photosynthetic efficiency (Fv/Fm )o f the corals was first assessed during a short-term increase in temperature (from 27 °C to 29 °C, 32 °C, and 34 °C) and acute exposure to UV radiation (20.5 W m 2 UVA and 1.2 Wm 2 UVB) alone or in combination. Increasing temper- ature to 34 °C significantly decreased the Fv/Fm in S. pistillata and M. aequituberculata. Increased UV radiation alone significantly decreased the Fv/Fm of all coral species, even at 27 °C. There was a combined effect of temperature and UV radiation, which reduced Fv/Fm in all corals by 25% to 40%. During a long-term exposure to UV radiation (17 days) the Fv /Fm was significantly reduced after 3 days' exposure in all species, which did not recover their initial values, even after 17 days. By this time, all corals had synthesized mycosporine-like amino acids (MAAs). The concentration and diversity of MAAs differed among spe- cies, being higher for corals containing clade A zooxanthel- lae. Prolonged exposure to UV radiation at the nonstressful temperature of 27 °C conferred protection against indepen- dent, thermally induced photoinhibition in all four species.

How Do Predators Cope With Chemically Defended Foods

Abstract: Many prey species (including plants) deter predators with defensive chemicals. These defensive chemicals act by rendering the prey's tissues noxious, toxic, or both. Here, I explore how predators cope with the presence of these chemicals in their diet. First, I describe the chemosensory mechanisms by which predators (including herbivores) detect defensive chemicals. Second, I review the mechanisms by which predators either avoid or tolerate defensive chemicals in prey. Third, I examine how effectively free-ranging predators can overcome the chemical defenses of prey. The available evidence indicates that predators have mixed success overcoming these defenses. This conclusion is based on reports of free-ranging predators rejecting unpalatable but harmless prey, or voluntarily ingesting toxic prey.

Kinematics of Soft-bodied, Legged Locomotion in Manduca sexta Larvae

Abstract: Caterpillar crawling is distinct from that of worms and molluscs; it consists of a series of steps in different body segments that can be compared to walking and running in animals with stiff skeletons. Using a three- dimensional kinematic analysis of horizontal crawling in Manduca sexta, the tobacco hornworm, we found that the phase of vertical displacement in the posterior segments substantially led changes in horizontal velocity and the segments appeared to pivot around the attached claspers. Both of the motions occur during vertebrate walking. In contrast, vertical displacement and horizontal velocity in the anterior proleg-bearing segments were in phase, as expected for running gaits coupled by elastic storage. We propose that this kinematic similarity to running results from the muscular compression and release of elastic tissues. As evidence in support of this proposal, the compression and extension of each segment were similar to harmonic oscil- lations in a spring, although changes in velocity were 70° out of phase with displacement, suggesting that the spring was damped. Measurements of segment length within, and across, intersegmental boundaries show that some of these movements were caused by folding of the body wall be- tween segments. These findings demonstrate that caterpillar crawling is not simply the forward progression of a peri- staltic wave but has kinetic components that vary between segments. Although these movements can be compared to legged locomotion in animals with stiff skeletons, the un- derlying mechanisms of caterpillar propulsion, and in par- ticular the contribution of elastic tissues, remain to be dis- covered.

Direct benefits of social dominance in juvenile crayfish.

Abstract: Crayfish are known for their innate aggressiveness and willingness to quickly establish dominance relationships among group members. Consequently, the formation of dominance hierarchies and the analysis of behavioral patterns displayed during agonistic encounters have mostly been tested in environments that provide no immediate resources besides space. We tested the hypothesis that social hierarchy formation in crayfish serves to determine access to future resources. Individuals within groups of three juvenile crayfish were allowed to form a social hierarchy in a featureless environment before a single food resource was presented. Higher dominance indices were significantly correlated with increased access to the food. The highest ranked crayfish spent more time in contact with the food than did medium-ranked and lowest ranked crayfish, and crayfish of medium rank spent more time in contact with the resource than did lowest ranked animals. The highest ranked crayfish consolidated their dominant status in ...

Molecular Phylogenetic and Embryological Evidence That Feeding Larvae Have Been Reacquired in a Marine Gastropod

Abstract: Evolutionary transitions between different modes of development in marine invertebrates are thought to be biased toward the loss of feeding larvae. Because the morphology of feeding larvae is complex and nonfeeding larvae or encapsulated embryos with benthic development often have simplified morphologies, it is presumed to be easier to lose a larval stage than to reacquire it. Some authors have gone so far as to suggest that feeding larvae, morphologically similar to the ancestral feeding larvae, cannot be reacquired. However, the larval structures of some groups, most notably gastropods, are often retained in the encapsulated embryos of species that hatch as benthic juveniles. Therefore the re-evolution of feeding larvae using the same structures may be possible in these groups. Here we present the first well-substantiated case for the recent re-evolution of feeding larvae within a clade of direct-developers. DNA sequence data show that Crepipatella fecunda, a species of calyptraeid gastropod with plankt...

Neuroecology, Chemical Defense, and the Keystone Species Concept

Abstract: Neuroecology unifies principles from diverse disciplines, scaling from biophysical properties of nerve and muscle cells to community-wide impacts of trophic interactions. Here, these principles are used as a common fabric, woven from threads of chemosensory physiology, behavior, and population and community ecology. The "keystone species" concept, for example, is seminal in ecological theory. It defines a species whose impacts on communities are far greater than would be predicted from its relative abundance and biomass. Similarly, neurotoxins could function in keystone roles. They are rare within natural habitats but exert strong effects on species interactions at multiple trophic levels. Effects of two guanidine alkaloids, tetrodotoxin (TTX) and saxitoxin (STX), coalesce neurobiological and ecological perspectives. These molecules compose some of the most potent natural poisons ever described, and they are introduced into communities by one, or only a few, host species. Functioning as voltage-gated sodium channel blockers for nerve and muscle cells, TTX and STX serve in chemical defense. When borrowed by resistant consumer species, however, they are used either in chemical defense against higher order predators or for chemical communication as chemosensory excitants. Cascading effects of the compounds profoundly impact community-wide attributes, including species compositions and rates of material exchange. Thus, a diverse array of physiological traits, expressed differentially across many species, renders TTX and STX fully functional as keystone molecules, with vast ecological consequences at multiple trophic levels.

Responses of Host Hemocytes During the Initiation of the Squid-Vibrio Symbiosis

Abstract: Within hours after colonization of the light organ of the squid Euprymna scolopes by its bacterial symbiont Vibrio fischeri, the symbiont triggers morphogen- esis of the light organ. This process involves the induction of apoptosis in the cells of two superficial ciliated epithelial fields and the gradual regression of these surface structures over a 96-h period. In this study, microscopic examination of various squid tissues revealed that host hemocytes spe- cifically migrate into the epithelial fields on the surface of the light organ, a process that begins before any other indication of symbiont-induced morphogenesis. Experimen- tal manipulations of symbiont-signal delivery revealed that hemocyte infiltration alone is not sufficient to induce regres- sion, and high numbers of hemocytes are not necessary for the induction of apoptosis or the initiation of regression. However, studies with mutant strains of V. fischeri that show a defect in the induction of hemocyte infiltration provided evidence that high numbers of hemocytes facilitate the regression of the epithelial fields. In addition, a change in hemocyte gene expression, as indicated by the up-regu- lation of the C8 subunit of the proteasome, correlates with the induction of light organ morphogenesis, suggesting that bacteria-induced molecular changes in the hemocytes are required for the participation of these host cells in the regression process.

Getting Under the Skin: Autonomous Implantation of Squid Spermatophores

Abstract: Squid spermatophores are complex structures that store sperm and, when transferred to the female, evert into sper matangia. Some deep-sea squid implant spermatangia into unmodified tissue of the female. Several hypotheses have been proposed to explain this peculiar implantation pro cess. Here, through on board observation of freshly caught deep-sea squid (Moroteuthis ingens), we show for the first time that spermatophores have an autonomous mechanism that enables them to migrate into body tissue. Cephalopod spermatophores are complex secreted struc tures that hold sperm masses and that consist, in part, of an ejaculatory apparatus for releasing the sperm mass and a cement body presumably for attaching the sperm mass to the female (1). Spermatophores are either transferred to the female by the male's hectocotylus, a specialized arm, or by a long penis, which is present in species that lack hecto cotyli (2). After being discharged from the spermatophore in the spermatophoric reaction, the sperm mass is encased in a thin covering, with the cement body at one end. This dis charged structure, the spermatangium, may attach to the skin of the female or be deeply embedded in her skin or muscle.

Morphological and ecological determinants of body temperature of Geukensia demissa, the Atlantic ribbed mussel, and their effects on mussel mortality.

Abstract: Measurements of body temperatures in the field have shown that spatial and temporal patterns are often far more complex than previously anticipated, particularly in intertidal regions, where temperatures are driven by both marine and terrestrial climates. We examined the effects of body size, body position within the sediment, and micro- habitat (presence or absence of Spartina alterniflora) on the body temperature of the mussel Geukensia demissa .W e then used these data to develop a laboratory study exposing mussels to an artificial "stressful" day, mimicking field conditions as closely as possible. Results suggested that G. demissa mortality increases greatly at average daily peak temperatures of 45 °C and higher. When these temperatures were compared to field data collected in South Carolina in the summer of 2004, our data indicated that mussels likely experienced mortality due to high-temperature stress at this site during this period. Our results also showed that body position in the mud is the most important environmental modifier of body temperature. This experiment suggested that the presence of marsh grass leads to increases in body temperature by reducing convection, overwhelming the ef- fects of shading. These data add to a growing body of evidence showing that small-scale thermal variability can surpass large-scale gradients.

An Extraordinarily Long Larval Duration of 4.5 Years from Hatching to Metamorphosis for Teleplanic Veligers of Fusitriton oregonensis

Abstract: Veliger larvae of the NE Pacific snail Fusitriton oregonensis were reared in culture for 4.5 to 4.6 years from hatching to metamorphosis and through postlarval growth to reproduction. Larval shells grew in length from 0.20 to 3.9 mm. Late veligers grew slowly, but shell sizes increased even in the 4th and 5th years. Widths of larval shells at late stages equaled or exceeded those of the protoconchs of two juveniles from the field. Cultured larvae did not metamor- phose until presented with subtidal rocks and associated biota. There was no indication of larval senescence: the first 2 years of postmetamorphic shell growth were slightly faster, and time from metamorphosis to first reproduction (3.3 years) was slightly less than for an individual that had developed to metamorphic competence in the plankton. A 4.5-year larval phase exceeds previous estimates for tele- planic larval durations and greatly exceeds estimates of the time for transport across oceans. This extraordinarily long larval period may exceed the usual duration in nature but shows that larval periods can be much longer than previ- ously suspected without complete stasis in growth and with little if any loss of viability.

Shear-Stress Dependence of Dinoflagellate Bioluminescence

Abstract: Fluid flow stimulates bioluminescence in dinoflagellates. However, many aspects of the cellular mechanotransduction are incompletely known. The objective of our study was to formally test the hypothesis that flow-stimulated dinoflagellate bioluminescence is dependent on shear stress, signifying that organisms are responding to the applied fluid force. The dinoflagellate Lingulodinium polyedrum was exposed to steady shear using simple Couette flow in which fluid viscosity was manipulated to alter shear stress. At a constant shear rate, a higher shear stress due to increased viscosity increased both bioluminescence intensity and decay rate, supporting our hypothesis that bioluminescence is shear-stress dependent. Although the flow response of non-marine attached cells is known to be mediated through shear stress, our results indicate that suspended cells such as dinoflagellates also sense and respond to shear stress. Shear-stress dependence of flow-stimulated bioluminescence in dinoflagellates is consistent...

Nitric oxide inhibits metamorphosis in larvae of Crepidula fornicata, the slippershell snail.

Abstract: This paper concerns the role of nitric oxide (NO) in controlling metamorphosis in the marine gastropod Crepidula fornicata. Metamorphosis was stimulated by the nitric oxide synthase (NOS) inhibitors AGH (aminoguani- dine hemisulfate) and SMIS (S-methylisothiourea sulfate) at concentrations of about 100 -1000 mol l 1 and 50 -200 mol l 1 , respectively. Metamorphosis was not, however, induced by the NOS inhibitor L-NAME (L-N G -nitroarginine methyl ester) at even the highest concentration tested, 500 mol l 1 . Moreover, pre-incubation with L-NAME at 20 and 80 mol l 1 did not increase the sensitivity of compe- tent larvae to excess K, a potent inducer of metamorphosis in this species; we suggest that either L-NAME is ineffective in suppressing NO production in larvae of C. fornicata ,o r that it works only on the constitutive isoform of the enzyme. In contrast, metamorphosis was potentiated by the guany- late cyclase inhibitor ODQ (1H-(1,2,4)oxadiazolo(4,3, -a)quinoxalin-1-one) in response to a natural metamorphic inducer derived from conspecific adults. Because NO typi- cally stimulates cGMP production through the activation of soluble guanylate cyclase, this result supports the hypothe- sis that NO acts as an endogenous inhibitor of metamor- phosis in C. fornicata. The expression of NOS, shown by immunohistochemical techniques, was detected in the api- cal ganglion of young larvae but not in older larvae, further

Effects of egg size on the development time of non-feeding larvae.

Abstract: The evolution of egg size in marine invertebrates remains a topic of central importance for life-history biologists, and the pioneering work of Vance has strongly influenced our current views. Vance's model and most models developed since have assumed that increases in egg size result in an increase in the prefeeding period of marine invertebrate larvae. For lecithotrophic species, this means that the entire development period should be correlated with egg size. Despite the importance of this assumption, it has not been tested at the appropriate scale-within species. We investigated the effects of egg size on development time for three lecithotrophic species from two phyla: the ascidians Phallusia obesa and Ciona intestinalis, and the echinoid Heliocidaris erythrogramma. We found that within individual broods of eggs, larger eggs took longer than smaller eggs to develop or become metamorphically competent larvae. It has long been recognized that producing larger eggs decreases fecundity, but our results show that increasing egg size also carries the extra cost of an extended planktonic period during which mortality can occur. The substantial variation in egg sizes observed within broods may represent a bet-hedging strategy by which offspring with variable dispersal potentials are produced.

Protein Stability in Artemia Embryos During Prolonged Anoxia

Abstract: Encysted embryos (cysts) of the brine shrimp, Artemia franciscana, are arguably the most stress-resistant of all animal life-history stages. One of their many adapta- tions is the ability to tolerate anoxia for periods of years, while fully hydrated and at physiological temperatures. Pre- vious work indicated that the overall metabolism of anoxic embryos is brought to a reversible standstill, including the transduction of free energy and the turnover of macromol- ecules. But the issue of protein stability at the level of tertiary and quaternary structure was not examined. Here I provide evidence that the great majority of proteins do not irreversibly lose their native conformation during years of anoxia, despite the absence of detectable protein turnover. Although a modest degree of protein denaturation and ag- gregation occurs, that is quickly reversed by a brief post- anoxic aerobic incubation. I consider how such extraordi- nary stability is achieved and suggest that at least part of the answer involves massive amounts of a small heat shock protein (p26) that acts as a molecular chaperone, the func- tion of which does not appear to require ribonucleoside di- or tri-phosphates.

Mitochondrial Delivery Is Essential for Synaptic Potentiation

Abstract: Mitochondria, as portable generators that power synaptic function, regulate the ATP supply and calcium homeostasis in the neuron. As molecular interactions within the synapses before and after the potentiation are beginning to be elucidated, the deciding moment during the tetanic stimulation that gives rise to the strengthening of the synapse remains a mystery. Here, I recorded electrically from an intact Drosophila nervous system, while simultaneously using time-lapse confocal microscopy to visualize mitochondria labeled with green fluorescent protein. I show that tetanic stimulation triggers a fast delivery of mitochondria to the synapse, which facilitates synaptic potentiation. Rotenone, an inhibitor of mitochondrial electron transport chain complex I, suppresses mitochondrial transport and abolishes the potentiation of the synapse. Expression of neurofibromin, which improves mitochondrial ATP synthesis in the neuron, enhances the movements of mitochondria to the synapse and promotes post-tetanic potentiation. These findings provide unprecedented evidence that the mitochondrial delivery to the synapse is critical for cellular learning.

Description and Relationships of Chaetopterus pugaporcinus, an Unusual Pelagic Polychaete (Annelida, Chaetopteridae)

Abstract: An extraordinary new species, Chaetopterus pugaporcinus, is described from eight specimens collected from deep mesopelagic waters off Monterey Bay, California, by remotely operated vehicles. All specimens exhibit a consistent combination of both adult and larval characteristics, leaving in question the maturity of the specimens. All specimens lack ciliated larval bands and the stout, modified chaetae (cutting spines) typically found in segment A4 of chaetopterids. If the specimens described here are larvae, they are remarkable for their size, which ranged from 10 to 21 mm total length, nearly twice the length of the largest polychaete larvae previously reported and 5 to 10 times larger than known chaetopterid larvae. Then too, their lack of segment addition prior to settlement would be atypical. If adult, they are particularly unusual in their habitat choice and body form. Morphology of the uncini and comparison to larval morphology indicated a close relationship to either Chaetopterus or Mesochaetopterus...

Changes in Embryonic Development and Hatching in Chionoecetes opilio (Snow Crab) With Variation in Incubation Temperature

Abstract: Water temperature affects the distribution, movement, and reproductive potential of female snow crab, Chionoecetes opilio. Ovigerous females of C. opilio from the eastern Bering Sea were held at five temperatures (1, 0, 1, 3, and 6 °C) in the laboratory while their embryos developed from gastrula to hatching. The duration of incu- bation increased by 105 d (30%) with decreasing tempera- ture; however, a switch to a 2-year duration of embryo incubation was not observed. For females held at 6, 3, and 1 °C, their embryos underwent a short period of diapause late in development; no diapause was observed for embryos of females held at 0 or 1 °C. Successful extrusion of a subsequent clutch and hatch timing comparable with that observed in the eastern Bering Sea indicated that tempera- tures of 0 to 3 °C may be optimal for multiparous female reproduction. We demonstrated that a switch from 1-year to 2-year reproduction cannot be triggered by changing the thermal regime after several months of embryonic develop- ment. The timing of female movement from colder to warmer waters may be important for maintaining population reproductive potential during the recent phase of warming and contraction of cold-water biomes in the Bering Sea.

Knockdown of actin and caspase gene expression by RNA interference in the symbiotic anemone Aiptasia pallida.

Abstract: Since the discovery of the ancient eukaryotic process of RNA-mediated gene silencing, the reverse-genetics technique RNA interference (RNAi) has increasingly been used to examine gene function in vertebrate and invertebrate systems. In this study, we report on the use of RNAi, adapted from studies on animal model systems, to manipulate gene expression in a symbiotic marine cnidarian. We describe gene knockdown of actin and of acasp--a cysteine protease, or caspase--in the symbiotic sea anemone Aiptasia pallida. Knockdown was assessed qualitatively with in situ hybridizations for both genes. Quantitative PCR and caspase activity assays were used as a quantitative measure of knockdown for acasp.

Molecular Quantification of Symbiotic Dinoflagellate Algae of the Genus Symbiodinium

Abstract: The dinoflagellate microalga Symbiodinium is the dominant algal symbiont in corals and related marine animals. To explore the incidence of mixed infections, methods employing real-time quantitative polymerase chain reaction (QPCR) and fluorescence in situ hybridization (FISH) were developed. In experiments focusing on Symbiodinium clades A and B, QPCR and FISH results were well correlated and generally more precise and sensitive than those from the endpoint PCR–restriction fragment length polymorphism analysis (PCR-RFLP) traditionally used for this application, thus increasing the detected incidence of mixed infections. For example, the prevalence of mixed infections in the sea anemone Condylactis gigantea was 40% by PCR-RFLP and 80%–90% by QPCR and FISH. However, the use of QPCR and FISH was limited by inter-host variation in the rRNA gene copy number per Symbiodinium cell, precluding any single conversion factor between QPCR signal and Symbiodinium cell number; and one FISH probe that gave excellent hyb...

Neurolipofuscin is a measure of age in Panulirus argus, the Caribbean spiny lobster, in Florida.

Abstract: Accurate age estimates for Panulirus argus, the commercially important Caribbean spiny lobster, would greatly enhance life history and population analyses. Most age approximations of P. argus are based on size and growth data, but size is generally considered a poor proxy for age of crustaceans in the field because of numerous environmental, density-dependent, and fishery-related factors. An established technique for aging crustaceans, employing histologically determined lipofuscin content in the nervous system, was investigated using known-age lobsters reared in the laboratory at ambient temperatures. We verified the presence of lipofuscin in eyestalk neural tissue by using autofluorescence and Sudan black staining and described its distribution in cell cluster A of the hemiellipsoid body. Neurolipofuscin accumulated with age; the overall trend was linear with indications of seasonal oscillation, whereas growth began to approach an asymptote after 3 years. Differences in the neurolipofuscin concentration...

Subtype Variation Among Bacterial Endosymbionts of Tubeworms (Annelida: Siboglinidae) from the Gulf of California

Abstract: Symbiosis involving chemoautotrophic bacteria allows vestimentiferan tubeworms to thrive in sulfidic marine environments. This study examined genetic variation among endosymbionts associated with three vestimentiferan species from the Gulf of California. Small subunit (16S) rRNA sequences identified two evolutionary lineages of -Proteobacteria in these worms. Phylotype-II bacteria associated with the hydrothermal vent species Riftia pachyptila exhibited no subtype variation upon examination of form II (cbbM) RuBisCO, whereas the phylotype-I bacteria associated with two cold-seep species, Escarpia spicata and Lamellibrachia barhami, were polymorphic. Bacterial subtypes distinguished by three RuBisCO alleles occurred at similar frequencies in both host species when sampled together from tubeworm clusters, offering, therefore, no evidence for host-specificity. Instead, the frequencies of these subtypes varied significantly among patchily distributed tubeworm clusters. Subtype variation on small spatial scales is consistent with prior evidence that vestimentiferans acquire their symbionts locally from the environment in which they settle as larvae. Adult vestimentiferans are nourished by endosymbiotic bacteria that oxidize inorganic sulfides and fix carbon via the Calvin-Benson cycle (1). These essential bacteria infect vestimentiferans de novo in each generation by penetrating the epidermis of trochophore larvae that settle on benthic substrates (2). Previous studies (summarized in reference 3) revealed two related phylotypes (i.e., a clade defined by 16S rRNA sequences) of -Proteobacteria associated with vestimentiferans worldwide. The two phylotypes segregate geographically and according to the kind of chemosynthetic habitat in which the hosts settle. Phylotype-I is found in cold-seep vestimentiferans worldwide and in hydrothermal vent vestimentiferans from the western Pacific. Phylotype-II has been found only in vestimentiferans from eastern Pacific hydrothermal vents. When distinct vestimentiferan species co-occur in a hab

Time and extent of ciliary response to particles in a non-filtering feeding mechanism.

Abstract: Mechanisms of suspension feeding are usually described by the physics of inanimate filters. High-speed videorecordings in this study demonstrated that sea urchin larvae concentrate particles without filtration. They actively captured individual particles. At most times and places, the effective strokes of the swimming/feeding ciliary band were away from the circumoral field. Cilia of this band responded to particles by a reversal of beat that redirected the particle toward the circumoral field. A change of beat occurred along approximately 80 m of ciliary band during particle capture. Cilia responded 0.02 to 0.06 s after the particle was within reach of effective strokes and reversed beat, usually for about 0.1 to 0.2 s. The whole event (disruption of forward beat) generally lasted between 0.13 and 0.5 s. These observations imply reversed movement of a parcel of water much larger than the included captured particle, but parti- cles are nevertheless greatly concentrated because water is directed toward the circumoral field only when and where a particle is sensed. Thus most of the concentration of parti- cles occurs by a temporarily and locally redirected current, without filtration, and size and quality of particles captured depends on sensory capabilities, not the mechanics of fil- tration.

Cost of protein synthesis and energy allocation during development of antarctic sea urchin embryos and larvae.

Abstract: Cold environments represent a substantial vol- ume of the biosphere. To study developmental physiology in subzero seawater temperatures typically found in the Southern Ocean, rates and costs of protein synthesis were measured in embryos and larvae of Sterechinus neumayeri, the Antarctic sea urchin. Our analysis of the "cost of living" in extreme cold for this species shows (1) that cost of protein synthesis is strikingly low during development, at 0.41 0.05 J (mg protein synthesized) 1 (n 16); (2) that synthesis cost is fixed and independent of synthesis rate; and (3) that a low synthesis cost permits high rates of protein turnover at 1 °C, at rates comparable to those of temperate species of sea urchin embryos developing at 15 °C. With a low synthesis cost, even at the highest synthesis rates mea- sured (gastrulae), the proportion of total metabolism ac- counted for by protein synthesis in the Antarctic sea urchin was 54%—a value similar to that of temperate sea urchin embryos. In the Antarctic sea urchin, up to 87% of meta- bolic rate can be accounted for by the combined energy costs of protein synthesis and the sodium pump. We con- clude that, in Antarctic sea urchin embryos, high rates of protein synthesis can be supported in extreme-cold environ- ments while still maintaining low rates of respiration.

Heat-Shock Response of the Upper Intertidal Barnacle Balanus glandula: Thermal Stress and Acclimation

Abstract: In the intertidal zone in the Pacific Northwest, body temperatures of sessile marine organisms can reach 35 °C for an extended time during low tide, resulting in poten- tial physiological stress. We used immunochemical assays to examine the effects of thermal stress on endogenous Hsp70 levels in the intertidal barnacle Balanus glandula. After thermal stress, endogenous Hsp70 levels did not in- crease above control levels in B. glandula exposed to 20 and 28 °C. In a separate experiment, endogenous Hsp70 levels were higher than control levels when B. glandula was exposed to 34 °C for 8.5 h. Although an induced heat-shock response was observed, levels of conjugated ubiquitin failed to indicate irreversible protein damage at temperatures up to 34 °C. With metabolic labeling, we examined temperature acclimation and thermally induced heat-shock proteins in B. glandula. An induced heat-shock response of proteins in the 70-kDa region (Hsp70) occurred in B. glandula above 23 °C. This heat-shock response was similar in molting and non-molting barnacles. Acclimation of B. glandula to rela- tively higher temperatures resulted in higher levels of pro- tein synthesis in the 70-kDa region and lack of an upward shift in the induction temperature for heat-shock proteins. Our results suggest that B. glandula may be well adapted to life in the high intertidal zone but may lack the plasticity to acclimate to higher temperatures.

Granular Chitin in the Epidermis of Nudibranch Molluscs

Abstract: Chitin is usually found in stiff extracellular coatings typified by the arthropod exoskeleton, and is not associated with the soft, flexible mollusc skin. Here, we show, however, that chitin in nudibranch gastropods (Opisthobranchia, Mollusca) occurs as intracellular granules that fill the epidermal cells of the skin and the epithelial cells of the stomach. In response to nematocysts fired by tentacles of prey Cnidaria, the epidermal cells of eolid nudibranchs (Aeolidacea) release masses of chitin granules, which then form aggregates with the nematocyst tubules, having the effect of insulating the animal from the deleterious action of the Cnidaria tentacles. Granular chitin, while protecting the animal, does not interfere with the suppleness and flexibility of the skin, in contrast to the stiffness of chitin armor. The specialized epidermis enables nudibranchs to live with and feed on Cnidaria.

Combining dissimilar senses: central processing of hydrodynamic and chemosensory inputs in aquatic crustaceans.

Abstract: Aquatic environments are by their nature dy- namic and dominated by fluid movements driven by lunar tides, temperature and salinity density gradients, wind- driven currents, and currents generated by the earth's rota- tion. Accordingly, animals within the aquatic realm must be able to sense and respond to both large-scale (advection) and small-scale (eddy turbulence) fluid dynamics, for chem- ical signals critically important for their survival are em- bedded within such movements. Aquatic crustaceans possess many types of near-field fluid-flow detectors and two general classes of chemorecep- tors on their body appendages: high-threshold, near-field receptors that may be somewhat equated with the sense of taste, and low-threshold far-field receptors that can be con- sidered as olfactory. This review briefly summarizes the distribution of hydrodynamic and high-threshold chemore- ceptors in aquatic crustaceans and the physiological char- acteristics of olfactory receptors in lobsters; it also examines recent physiological evidence for the central nervous inte- gration of inputs from olfactory receptors and hydrody- namic detectors, two dissimilar senses that must be com- bined within the brain for survival. Marine crustaceans have provided valuable insights about mechanisms of primary olfactory sensory physiology; their additional sensitivity to hydrodynamic stimulation makes them a potentially useful model for examining how these two critical sensory inputs are combined within the brain to enhance foraging behavior. Multimodal sensory processing is critically important to all animals, and the principles and concepts derived from these crustacean studies may provide generalities about neuronal processing across taxa.