Showing papers in "The Biological Bulletin in 2010"

Zooxanthellar symbionts shape host sponge trophic status through translocation of carbon.

Abstract: Sponges belonging to the genus Cliona are common inhabitants of many coral reefs, and as bioeroders, they play an important role in the carbonate cycle of the reef. Several Cliona species maintain intracellular popula- tions of dinoflagellate zooxanthellae (i.e., Symbiodinium spp.), which also form symbioses with a variety of other invertebrates and protists (e.g., corals, molluscs, foraminif- era). Unlike the case of coral symbioses, however, almost nothing is known of the metabolic interaction between sponges and their zooxanthella symbionts. To assess this interaction, we performed a tracer experiment to follow C and N in the system, performed a reciprocal transplant experiment, and measured the stable carbon isotope ratio of Cliona spp. with and without zooxanthellae to study the influence of environment on the interaction. We found strong evidence of a transfer of C from zooxanthellae to their sponge hosts but no evidence of a transfer of N from sponge to zooxanthellae. We also saw significant influences of the environment on the metabolism of the sponges. Finally, we observed significant differences in carbon me- tabolism of sponge species with and without symbionts. These data strongly support hypotheses of metabolic inte- gration between zooxanthellae and their sponge host and extend our understanding of basic aspects of benthic-pelagic coupling in shallow-water marine environments.

The slipper snail, Crepidula: An emerging lophotrochozoan model system

Abstract: Recent developmental and genomic research focused on "slipper snails" in the genus Crepidula has positioned Crepidula fornicata as a de facto model system for lophotrochozoan development. Here we review recent developments, as well as earlier reports demonstrating the widespread use of this system in studies of development and life history. Recent studies have resulted in a well-resolved fate map of embryonic cell lineage, documented mechanisms for axis determination and D quadrant specification, preliminary gene expression patterns, and the successful application of loss- and gain-of-function assays. The recent development of expressed sequence tags and preliminary genomics work will promote the use of this system, particularly in the area of developmental biology. A wealth of comparative information on phylogenetic relationships, variation in mode of development within the family, and numerous studies on larval biology and metamorphosis, primarily in Crepidula fornicata, make these snails a powerful tool for studies of the evolution of the mechanisms of development in the Mollusca and Lophotrochozoa. By bringing a review of the current state of knowledge of Crepidula life histories and development together with some detailed experimental methods, we hope to encourage further use of this system in various fields of investigation.

Rubyspira, New Genus and Two New Species of Bone-Eating Deep-Sea Snails With Ancient Habits

Abstract: Rubyspira, a new genus of deep-sea snails (Gastropoda: Abyssochrysoidea) with two living species, derives its nutrition from decomposing whalebones. Molec- ular phylogenetic and morphological evidence places the new genus in an exclusively deep-sea assemblage that in- cludes several close relatives previously known as fossils associated with Cretaceous cold seeps, plesiosaur bones, and Eocene whalebones. The ability to exploit a variety of marine reducing environments may have contributed to the evolutionary longevity of this gastropod lineage.

Effects of Estradiol and Progesterone on the Reproduction of the Freshwater Crayfish Cherax albidus

Abstract: In this study we have investigated the role of 17-estradiol and progesterone in the reproduction of the crayfish Cherax albidus by using vitellogenin (VTG) as a biomarker. Early-vitellogenic (EV), full-vitellogenic (FV), and non-vitellogenic (NV) females of Cherax albidus were treated with 17-estradiol, progesterone, or both for 4 weeks. Levels of VTG mRNA in the hepatopancreas were detected by RT-PCR. The PCR product was sequenced and showed 97% homology with Cherax quadricarinatus VTG. 17-estradiol was more effective than progesterone and 17-estradiol plus progesterone in increasing the vitelloge- nin transcript in the hepatopancreas of EV and FV females. On the contrary, progesterone was more effective than 17- estradiol and 17-estradiol plus progesterone in increasing the vitellogenin concentration in the hemolymph of EV and FV females. Hepatopancreas histology and fatty acid com- position of females injected with hormones showed major modifications. No effects were registered in NV females. In conclusion, 17-estradiol and progesterone influence VTG synthesis, although our data indicate that they act through different pathways and are not effective until the proper hormonal environment is established, as demonstrated by their inefficacy in NV females.

A "Mimic Octopus" in the Atlantic: Flatfish mimicry and camouflage by Macrotritopus defilippi.

Abstract: The sand-dwelling octopus Macrotritopus de- filippi was filmed or photographed in five Caribbean loca- tions mimicking the swimming behavior (posture, style, speed, duration) and coloration of the common, sand-dwell- ing flounder Bothus lunatus. Each species was exceptionally well camouflaged when stationary, and details of camou- flaging techniques are described for M. defilippi. Octopuses implemented flounder mimicry only during swimming, when their movement would give away camouflage in this open sandy habitat. Thus, both camouflage and fish mimicry were used by the octopuses as a primary defense against visual predators. This is the first documentation of flounder mimicry by an Atlantic octopus, and only the fourth con- vincing case of mimicry for cephalopods, a taxon renowned for its polyphenism that is implemented mainly by neurally controlled skin patterning, but also—as shown here— by their soft flexible bodies.

Understanding the Effects of Low Salinity on Fertilization Success and Early Development in the Sand Dollar Echinarachnius parma

Abstract: Free-spawning marine invertebrates that live near shore or in estuaries may experience reduced fertiliza- tion success during low-salinity events. Although several studies have documented reproductive failure at reduced salinity in estuarine animals, few have looked at whether developmental failure is due to a failure of fertilization or to a failure of fertilized eggs to cleave. In this study, we examined the effects of salinities ranging from 18 to 32 psu on fertilization success and early development in the sand dollar Echinarachnius parma. In addition to decoupling the effects of low salinity on fertilization from its effects on early cleavage, we also assessed whether eggs or sperm were the weak link in accounting for reproductive failure. We found that both fertilization and cleavage failed at salinities below about 22 psu but that development could be partially rescued by returning zygotes to full-strength sea- water. We also found that sperm remained active and capa- ble of fertilizing eggs even after being exposed to low salinities for 30 min.. Taken together, these results suggest that reproductive failure at low salinities in E. parma is due more to an inability of the fertilized eggs to cleave than to an inability of sperm to fertilize eggs.

Microalgal cell surface carbohydrates as recognition sites for particle sorting in suspension-feeding bivalves.

Abstract: Cell surface carbohydrates play important roles in cell recognition mechanisms. Recently, we provided ev- idence that particle selection by suspension-feeding bi- valves can be mediated by interactions between carbohy- drates associated with the particle surface and lectins present in mucus covering bivalve feeding organs. In this study, we used lectins tagged with fluorescein isothiocya- nate (FITC) to characterize carbohydrate moieties on the surface of microalgal species and evaluate the effect of oyster mucus on lectin binding. These analyses revealed that concanavalin A (Con A), one of six lectins tested, bound to Isochrysis sp., while Nitzschia closterium reacted with Pi- sum sativum agglutinin (PNA) and peanut agglutinin (PEA). The cell surface of Rhodomonas salina bound with PNA and Con A, and Tetraselmis maculata cell surface was characterized by binding with PNA, PEA, and Con A. Pre-incubation of microalgae with oyster pallial mucus sig- nificantly decreased the binding of FITC-labeled lectins, revealing that lectins present in mucus competitively blocked binding sites. This decrease was reversed by wash- ing mucus-coated microalgae with specific carbohydrates. These results were used to design a feeding experiment to evaluate the effect of lectins on sorting of microalgae by oysters. Crassostrea virginica fed with an equal ratio of Con A-labeled Isochrysis sp. and unlabeled Isochrysis sp. pro- duced pseudofeces that were significantly enriched in Con A-labeled Isochrysis sp. and depleted in unlabeled microal- gae. Selection occurred even though two physical-chemical surface characteristics of the cells in each treatment did not differ significantly. This work confirms the involvement of carbohydrate-lectin interaction in the particle sorting mech- anism in oysters, and provides insights into the carbohy- drate specificity of lectins implicated in the selection of microalgal species.

Francisella philomiragia Biofilm Formation and Interaction With the Aquatic Protist Acanthamoeba castellanii

Abstract: The bacterium Francisella philomiragia has been isolated from environmental samples originating from around the globe. F. philomiragia-related strains cause fran- cisellosis of both farmed and wild fish. In addition, occa- sional human infections caused by F. philomiragia are found in victims of near-drowning and patients with chronic granulomatous disease. We have shown that F. philomira- gia forms in vitro biofilms with increased formation at 25 °C over 37 °C conditions. We found that F. philomiragia can form a biofilm in a co-culture with live Acanthamoeba castellanii, an aquatic amoeba. Interestingly, amoeba-con- ditioned supernatant has an inhibitory effect on production of biofilm by F. philomiragia, whereas Francisella-condi- tioned supernatant has no effect on growth of amoebae. We have shown that F. philomiragia can infect A. castellanii after only 5 days of co-incubation and that it infects A. castellanii more quickly than the related species F. novicida does. Our studies point to a potentially overlooked interac- tion between F. philomiragia and Acanthamoeba. This re- lationship in the marine lifecycle of F. philomiragia may support the persistence of the bacterium in waterways and its ability to infect fish. An understanding of the persistence of this organism in aquatic systems through biofilm forma- tion and its interaction with Acanthamoeba will be impor- tant in developing prevention strategies for this pathogen.

Rules of Engagement: Factors That Regulate Activity-Dependent Synaptic Plasticity During Neural Network Development

Abstract: Overproduction and pruning during develop- ment is a phenomenon that can be observed in the number of organisms in a population, the number of cells in many tissue types, and even the number of synapses on individual neurons. The sculpting of synaptic connections in the brain of a developing organism is guided by its personal experi- ence, which on a neural level translates to specific patterns of activity. Activity-dependent plasticity at glutamatergic synapses is an integral part of neuronal network formation and maturation in developing vertebrate and invertebrate brains. As development of the rodent forebrain transitions away from an over-proliferative state, synaptic plasticity undergoes modification. Late developmental changes in synaptic plasticity signal the establishment of a more stable network and relate to pronounced perceptual and cognitive abilities. In large part, activation of glutamate-sensitive N- methyl-D-aspartate (NMDA) receptors regulates synaptic stabilization during development and is a necessary step in memory formation processes that occur in the forebrain. A developmental change in the subunits that compose NMDA receptors coincides with developmental modifications in synaptic plasticity and cognition, and thus much research in this area focuses on NMDA receptor composition. We pro- pose that there are additional, equally important develop- mental processes that influence synaptic plasticity, includ- ing mechanisms that are upstream (factors that influence NMDA receptors) and downstream (intracellular processes regulated by NMDA receptors) from NMDA receptor acti- vation. The goal of this review is to summarize what is known and what is not well understood about developmen- tal changes in functional plasticity at glutamatergic syn- apses, and in the end, attempt to relate these changes to maturation of neural networks.

Difference in Thermotolerance Between Green and Red Color Variants of the Japanese Sea Cucumber, Apostichopus japonicus Selenka: Hsp70 and Heat-Hardening Effect

Abstract: We studied thermal tolerance limits, heat-hardening, and Hsp70 to elucidate the difference in thermotolerance between two color variants of the sea cucumber Apostichopus japonicus. Green and Red variants occupy different habitats and have different aestivation responses to high temperature in summer. In the absence of heat-hardening, the variants showed no difference in the temperature at which 50% of the individuals died: Green, 31.49 °C; Red, 31.39 °C. However, Green specimens acquired higher thermotolerance than Red after a prior sublethal heat exposure. After 72 h of recovery from a heat-hardening treatment (30 °C for 2 h), the survival of Green variants was more than 50% and that of Red was less than 5% when they were treated at 33 °C for 2 h. Levels of mRNA and protein for Hsp70 were significantly higher in Green than Red after the heat shock of 30 °C, and the stability of hsp70 mRNA of Green was significantly higher than that of Red. Our findings suggest that within the same species, different vari...

Sexual System, Sex Ratio, and Group Living in the Shrimp Thor amboinensis (De Man): Relevance to Resource-Monopolization and Sex-Allocation Theories

Abstract: The sexual system of the symbiotic shrimp Thor amboinensis is described, along with observations on sex ratio and host-use pattern of different populations. We used a comprehensive approach to elucidate the previously unknown sexual system of this shrimp. Dissections, scan- ning electron microscopy, size-frequency distribution anal- ysis, and laboratory observations demonstrated that T. am- boinensis is a protandric hermaphrodite: shrimp first mature as males and change into females later in life. Thor am- boinensis inhabited the large and structurally heterogeneous sea anemone Stichodactyla helianthus in large groups (up to 11 individuals) more frequently than expected by chance alone. Groups exhibited no particularly complex social structure and showed male-biased sex ratios more fre- quently than expected by chance alone. The adult sex ratio was male-biased in the four separate populations studied, one of them being thousands of kilometers apart from the others. This study supports predictions central to theories of resource monopolization and sex allocation. Dissections demonstrated that unusually large males were parasitized by an undescribed species of isopod (family Entoniscidae). Infestation rates were similarly low in both sexes (11%- 12%). The available information suggests that T. amboinen- sis uses pure search promiscuity as a mating system. This hypothesis needs to be formally tested with mating behavior observations and field measurements on the movement pat- tern of both sexes of the species. Further detailed studies on the lifestyle and sexual system of all the species within this genus and the development of a molecular phylogeny are necessary to elucidate the evolutionary history of gender expression in the genus Thor.

Coloration and defense in the nudibranch gastropod Hypselodoris fontandraui.

Abstract: The striking color patterns of chromodorid (and other) nudibranchs appear to be indicative of aposematism. In Mullerian mimicry, all the mimic species have a defense mechanism. It has been proposed that a group of blue, white, and yellow Mediterranean and northeastern Atlantic species of the genus Hypselodoris form a Mullerian mimetic circle. One of these, H. fontandraui, lacks the mantle dermal formations (repugnatorial glands) that are typically found in other members of this circle and are reservoirs of feeding deterrent compounds. It therefore seemed possible that this animal lacks chemical defense and acts like a Batesian mimic. Within this study, we found that this nudibranch contains the furanosesquiterpenoid tavacpallescensin, most probably derived from sponges of the genus Dysidea, upon which it probably feeds. The metabolite concentrations were measured from samples of the mantle rim, other external parts, and internal organs. Concentrations were about 4 times higher in the mantle rim than in th...

New family of allomorphic jellyfishes, Drymonematidae (Scyphozoa, Discomedusae), emphasizes evolution in the functional morphology and trophic ecology of gelatinous zooplankton.

Abstract: Molecular analyses have revealed many cryptic species in the oceans, often permitting small morphological differences to be recognized as diagnosing species, but less commonly leading to consideration of cryptic ecology. Here, based on analyses of three nuclear DNA sequence markers (ribosomal 18S, 28S, and internal transcribed spacer 1 [ITS1]), two mitochondrial DNA markers (cytochrome c oxidase subunit I [COI] and ribosomal 16S), and 55 morphological features, we revise the classification of the enigmatic jellyfish genus Drymonema. We describe a new scyphozoan family, Drymonematidae, elevating the previous subfamily Drymonemidae to accommodate three species: the type species D. dalmatinum from the Mediterranean region, for which we identify a neotype; the western South Atlantic species D. gorgo; and a new species, D. larsoni from the western Atlantic and Caribbean, which also is described here. This revision emphasizes the remarkable morphological disparity of Drymonematidae from all other scyphomedusae,...

Tooth Use and Wear in Three Iron-Biomineralizing Mollusc Species

Abstract: Chitons and limpets harden their teeth with biominerals in order to scrape algae from hard rock surfaces. To elucidate relationships between tooth structure and function, light and electron microscopy were used to examine naturally worn teeth in three species of mollusc with iron-mineralized teeth and to analyze the grazing marks left by members of these species feeding on wax. For the two chiton species, teeth wore down progressively from the medial to the lateral edge of the cusp, while for the limpet, wear was more evenly distributed across the edges of each cusp. In chitons, this pattern of wear matched the medially biased morphology of the cusps in their protracted position and relates to what is known about the mineral composition and substructure of the teeth. The patterns of progressive tooth wear for each of these species, together with the distinct grazing marks left by each species on the wax substrate, indicate that the teeth are designed to remain functionally effective for as long as possible, and have proved to be a valuable means of rationalizing the internal architecture of the teeth at a range of spatial scales. This information is critical for ongoing studies aimed at understanding the interactions between the organic matrix and mineral components of these teeth.

Role of Epicellular Molecules in the Selection of Particles by the Blue Mussel, Mytilus edulis

Abstract: This study provides evidence that the suspen- sion-feeding blue mussel, Mytilus edulis, uses biochemical cues to recognize its food. We identified lectins in mucus from the gills and labial palps, two pallial organs involved in the feeding process. These compounds were able to agglutinate rabbit and horse erythrocytes (RBC) and several species of marine microalgae representing different fami- lies. Additionally, the agglutination of RBC and microalgae was inhibited by several carbohydrates (fetuin, lipopolysac- charide (LPS), and mannose-related residues), suggesting that a suite of lectins may be present in mucus from the gills and labial palps. Results from feeding experiments, using microspheres with tailored surfaces, demonstrated that mus- sels preferentially ingested microspheres coated with the neoglycoproteins glucosamide-BSA and mannopyranosyl- phenyl-BSA but rejected in pseudofeces microspheres coated with BSA alone. The positive selection for neogly- coprotein-coated microspheres was inhibited when mussels were pre-incubated in seawater containing a solution of the same neoglycoprotein. Two surface properties of the micro- spheres, charge and wettability, had little effect on the observed selection process. Our results, along with our previous findings for oysters, suggest a new concept for the mechanism of particle selection in bivalves and perhaps other suspension-feeding organisms. Specifically, the selec- tion of particles involves interactions between epiparticulate carbohydrates and lectins in the mucus produced by feeding organs.

Ligand Field Theory and the Origin of Life as an Emergent Feature of the Periodic Table of Elements

Abstract: The assumption that all biological catalysts are either proteins or ribozymes leads to an outstanding enigma of biogenesis— how to determine the synthetic pathways to the monomers for the efficient formation of catalytic macromolecules in the absence of any such macro- molecules. The last 60 years have witnessed chemists devel- oping an understanding of organocatalysis and ligand field theory, both of which give demonstrable low-molecular- weight catalysts. We assume that transition-metal-ligand com- plexes are likely to have occurred in the deep ocean trenches by the combination of naturally occurring oceanic metals and ligands synthesized from the emergent CO2 ,H 2 ,N H 3 ,H 2S, and H3PO4. We are now in a position to investigate experi- mentally the metal-ligand complexes, their catalytic function, and the reaction networks that could have played a role in the development of metabolism and life itself.

Molecular phylogeny of the sacoglossa, with a discussion of gain and loss of kleptoplasty in the evolution of the group.

Abstract: Sacoglossan sea slugs retain the chloroplasts from food algae in their cells (kleptoplasty) and obtain the photosynthetic products, but the capability of kleptoplasty differs among species. One evolutionary hypothesis for kleptoplasty is that the family Volvatellidae is the ancestral sacoglossan lineage in which kleptoplasty arose, but this is based on ambiguous phylogenetic relationships. To test this hypothesis, we analyzed sacoglossan phylogeny for concat- enated sequences (approximately 4000 bp) of nuclear (18S rRNA) and mitochondrial (CO1, trnV, and 16S rRNA) genes of 18 sacoglossan species, using neighbor-joining, maximum parsimony, maximum likelihood, and Bayesian methods. The resultant phylogenetic trees clearly revealed monophyly of the order Sacoglossa (including the debatable genus Cylindrobulla), which contained two sister clades: the shelled sacoglossan group (Oxynoacea Cylindro- bulla) and the non-shelled group (Plakobranchacea). The family Volvatellidae was in a derived position within the Oxynoacea. The most parsimonious rearrangement of the character states of kleptoplasty on the phylogenetic tree suggested that (1) kleptoplasty was acquired at the basal position of the Sacoglossa (including Cylindrobulla) as non-functional kleptoplasty, (2) functional kleptoplasty was gained in the Plakobranchacea clade, and (3) non-functional kleptoplasty was lost in the Volvatellidae lineage in the Oxynoacea clade.

Dwarf Males of Octolasmis warwickii (Cirripedia: Thoracica): The First Example of Coexistence of Males and Hermaphrodites in the Suborder Lepadomorpha

Abstract: In the lepadomorph barnacle Octolasmis war- wickii, individuals are often found attached to the scutum of conspecifics living externally on the crab hosts. To test whether these conspecific-attached individuals are dwarf males, as are known to occur in other suborders of barna- cles, we compared the pattern of attachment, size-frequency distribution, and reproductive status of the conspecific-at- tached (Con-A) and crab-attached (Crab-A) individuals. Con-As were smaller than Crab-As. There was a positive relationship between the body size of Crab-As and the number of individuals on them. Con-As had longer penises than Crab-As of the same body size, and their testes were better developed. The four largest Con-As examined were brooding eggs. These results indicate that Con-As of O. warwickii are dwarf males, with a potential to become hermaphroditic. This represents the first known example of coexistence of males and hermaphrodites in the suborder Lepadomorpha. The mating group size of O. warwickii was smaller than in its hermaphroditic congeners but larger than in barnacles with dwarf males and females, which supports the current theories that group size is important for the evolution of sexuality patterns in barnacles.

Laboratory Spawning and Development of the Bahama Lancelet, Asymmetron lucayanum (Cephalochordata): Fertilization Through Feeding Larvae

Abstract: Here we report on spawning and development of the Bahama lancelet, Asymmetron lucayanum. Ripe adults collected in Bimini spawned the same evening when placed in the dark for 90 minutes. The developmental morphology is described from whole mounts and histological sections. A comparison between development in Asymmetron and the better known cephalochordate genus Branchiostoma reveals similarities during the early embryonic stages but deviations by the late embryonic and early larval stages. Thus, the initial positions of the mouth, first gill slit, and anus differ between the two genera. Even more strikingly, Hatschek's right and left diverticula, which arise by enterocoely at the anterior end of the pharynx in Branchiostoma, never form during Asymmetron development. In Branchiostoma, these diverticula become the rostral coelom and preoral pit. In Asymmetron, by contrast, homologs of the rostral coelom and preoral pit form by schizocoely within an anterior cell cluster of unproven (but likely endodermal) or...

Rearing and Growth of the Octopus Robsonella fontaniana (Cephalopoda: Octopodidae) From Planktonic Hatchlings to Benthic Juveniles

Abstract: Globally, octopus larviculture is one of the challenges faced in the attempt to diversify aquaculture and achieve cephalopod farming. Currently, only juveniles of Octopus vulgaris, Octopus joubini, and Enteroctopus dofleini have been obtained at an experimental level. This is the first study to look at the characteristics of planktonic and benthic Robsonella fontaniana juveniles in an effort to analyze the morphometric changes occurring during their planktonic and benthic phases and to explore the feasibility of obtaining settlement under controlled conditions. The morphometric measurements varied exponentially over time and did not show different tendencies before and after settlement. Mantle growth in relation to total length fit a logarithmic regression, whereas arm length and eye diameter increased linearly with respect to total length throughout the entire paralarval and juvenile periods. This suggests that the size of the mantle decreases with age in proportion to the total octopus length, whereas the organs more directly involved in catching prey tend to increase in direct proportion to the total length. The present study shows that R. fontaniana can be reared from hatching through the final paralarval stage on a diet of Lithodes santolla (king crab) zoeae; after settlement, the juveniles can be reared on a diet of crab such as Petrolisthes.

Spikey Bivalves: Intra-Periostracal Crystal Growth in Anomalodesmatans

Abstract: The external shell surfaces of most anomalodesmatan bivalves are studded with small spikes, particularly at the posterior end. We have studied the morphology, mode of growth, and distribution among taxa of these spikes. In this study we found that spikes vary widely in morphology, from acute spikes to flat plaques. Optical and electron microscopy has revealed that the periostraca of Laternula, Myadora, and Thraciopsis consist of an outer dense layer and an inner translucent layer. The dense layer grows at the expense of the inner layer as it progresses toward the shell edge. The spikes begin to grow in the free periostracum, within the translucent periostracal layer, immediately below the dense layer. With growth, they push the dense periostracal layer upward but without penetrating it. Those parts of the spike in contact with this layer cease to grow, which explains the typical conical shape of spikes. When fully grown, spikes reach the base of the translucent layer, becoming incorporated into the outer shell layer. Scanning electron microscopy and electron backscatter diffraction analysis reveal that the spikes of Lyonsia norwegica and Lyonsiella abyssicola are prisms of aragonite composed of twinned crystals, with the c-axis vertical. A survey of the occurrence of spikes within the anomalodesmatans shows that they are present in all but a few families. Elsewhere within the closely related palaeoheterodonts, intra-periostracal calcification is also known in Neotrigonia and unionids, which indicates that this character may be plesiomorphic for these bivalves. The present data do not support the homology of spikes in other bivalve groups (e.g., veneroids) or in the aplacophorans or polyplacophorans.

Capture of particles by direct interception by cilia during feeding of a gastropod veliger.

Abstract: Ciliary feeders vary in the arrangement of ciliary bands and mechanisms of capture of food. Some larvae use opposed parallel bands of preoral (prototroch) and postoral (metatroch) cilia. Hypotheses for the mechanism of particle capture include filtration by adhesion to a cilium that overtakes a particle (direct interception), but until now unequivocal evidence for this mechanism has been lacking. Here, high-speed video recordings of veliger larvae of the gastropod Lacuna vincta demonstrated direct interception of particles by prototrochal cilia. Adhesion between cilium and particle was seen when a prototrochal cilium tugged a diatom chain into the food groove while in contact with one part of the chain. In several recorded events, a prototochal cilium overtook a particle during its effective stroke and subsequently pulled the particle inward with its recovery stroke; thereupon, the particle was deposited onto the food groove and transported to the mouth. Captures varied, however. In some cases the particle was intercepted multiple times in one capture event; in others, several cilia passed a particle without interception. Particles occasionally remained in the area of recovery strokes, indicating retention without continuing adhesion to a cilium. In three events, a particle lost from prototrochal cilia was intercepted and moved into the food groove by metatrochal cilia. Particles as wide as or wider than the food groove were also captured and transported but were not ingested.

How Does a Change in Labial Tooth Row Number Affect Feeding Kinematics and Foraging Performance of a Ranid Tadpole (Lithobates sphenocephalus)

Abstract: Recent studies have explored feeding kinematics in tadpoles with intact labial teeth; however, it is unknown how missing teeth impacts foraging. We explored the impact of missing labial teeth on the feeding mechanics and foraging performance of Southern leopard frog (Lithobates sphenocephalus [= Rana sphenocephala]) tadpoles by controlling the pattern of labial tooth loss; that is, by surgically removing one row of labial teeth. We then used high-speed (500 frames/second) videography to test the hypothesis that tooth loss reduces the time that tadpoles attach to and graze upon an algal-covered substrate. We next conducted trials of foraging efficiency and foraging activity to test the hypothesis that tadpoles with fewer teeth forage less effectively than control tadpoles. The teeth of tadpoles from the surgery treatment slipped while closing and were in contact with an algal-covered substrate for a shorter duration compared to control tadpoles. Surprisingly, tadpoles with missing labial teeth obtained sim...

Influence of Sperm and Phytoplankton on Spawning in the Echinoid Lytechinus variegatus

Abstract: The cues triggering large-scale broadcast-spawning events in marine invertebrates are not fully understood. Using the sea urchin Lytechinus variegatus, we tested the effectiveness of a variety of potential spawning cues in eliciting a spawning response. In the laboratory, during two consecutive spawning seasons, about 400 isolated sea urchins were exposed to phytoplankton, sperm, or eggs, singly or in combination. The likelihood of spawning, time to spawning, and spawning behavior were recorded for both sexes. Sperm was most successful at inducing spawning. No response to eggs was noted. Phytoplankton alone did not trigger spawning, but when a phytoplankton cue was followed by the addition of sperm, spawning behavior was induced, the time between addition of sperm and spawning was reduced, and the variance among individuals in the time of spawning initiation was reduced. Males spawned sooner in response to cues than females and rarely spawned spontaneously in phytoplankton or control treatments. A semilun...

Effects of Sea Hare Ink Secretion and Its Escapin-Generated Components on a Variety of Predatory Fishes

Abstract: Sea hares, Aplysia californica, have a diversity of anti-predatory defenses. One is an actively released chemical defense: an ink secretion that is a mixture of two glandular products—ink from the ink gland and opaline from the opaline gland. The mechanisms of action of ink secretion and its components have recently been examined in detail against several predatory invertebrates. Our goal is to extend this mechanistic analysis to predatory vertebrates. Toward this end, the current study details the effects of ink, opaline, and one set of its components—the products of the reaction of escapin, an L-amino acid oxidase, with its natural substrates, L-lysine and L-arginine— on the palatability of food for five species of fishes: bluehead wrasses Thalas- soma bifasciatum, senorita wrasses Oxyjulis californica, pinfish Lagodon rhomboides, mummichogs Fundulus het- eroclitus, and bonnethead sharks Sphyrna tiburo. These fishes have different feeding styles, ranging from large fishes able to engulf sea hares to smaller fishes able to attack sea hares by pecking at them; and they live in a variety of habitats, including those that sea hares typically inhabit. We show that ink but not opaline significantly decreases the palatability of food for all five species, and that escapin products are mildly unpalatable to the two species of wrasses but not to the other species. These results, together with others, show that sea hare ink affects a diversity of predatory fishes, setting the stage for mechanistic studies using electrophysiological analysis of their chemosensory systems.

Nest-building behavior by the amphipod Peramphithoe femorata (Kroyer) on the kelp Macrocystis pyrifera (Linnaeus) C. Agardh from Northern-Central Chile.

Abstract: Many small arthropod herbivores from terres- trial and marine environments construct tubicolous nest-like domiciles on their host plants or algae by rolling up selected portions of the leaf or blade. Nests serve as both shelter and food, which results in conflicting needs for the grazers because feeding activity continuously destroys parts of the nests. While the nesting habit of ampithoid amphipods and other peracarid crustaceans is widely known, very little is known about the nest dynamics and how the conflict be- tween shelter and food requirements is resolved. Herein we examined the nest-building behavior and nest occupancy of the kelp-dwelling amphipod Peramphithoe femorata on the giant kelp Macrocystis pyrifera. Domiciles on the distal- most part of the blades were occupied by amphipods and were steadily advanced toward the blade base. Since the blades grow from a basal growth meristem, blades and nests develop in opposite directions. Thus, the amphipods exploit the kelp growth pattern to maintain their nests in the medi- um-distal part of the blades. During a 2-week-long experi- ment, we observed that blade elongation equaled nest ad- vancement during the first 8 days after nest construction. Thereafter, blade growth slowed down and was surpassed by nest advancement rates, possibly forcing amphipods to seek out new blades. Nest occupancy was generally short (1- 4 days), but some amphipods resided longer (4 days) in their nests. The sophisticated nest-building behavior of P. femorata and other ampithoids maximizes nest persistence, offers optimal protection against predators, and promotes feeding on nutritive or, alternatively, on less defended tis- sues.

Telomeres and telomerase activity in scleractinian corals and Symbiodinium spp.

Abstract: Telomeres are the repetitive sequences of DNA and associated proteins that cap the ends of eukaryotic chromosomes and play an essential role in maintaining chromosome stability. Compromised telomeres can lead to cell cycle arrest, senescence, apoptosis, or genetic instability, whereas maintenance of telomeres can endow cells with the capacity for indefinite self-renewal. Telomere integrity is maintained in most cells by the activity of telomerase, a ribonucleoprotein that can catalyze the addition of repeat sequences onto chromosome ends. Using the telomeric repeat amplification protocol (TRAP) assay, we detected telomerase activity in host nuclear extracts prepared from two scleractinian corals, Madracis auretenra and Madracis decactis, and also in cultured Symbiodinium, the symbiotic algae that live within corals. Sequencing the TRAP reaction products indicated that the telomeric DNA repeat sequence was TTAGGG for coral and TTTAGGG for Symbiodinium. Using this sequence information, we estimated telomere...

Photoresponses of the Compound Eye of the Sandhopper Talitrus saltator (Crustacea, Amphipoda) in the Ultraviolet-Blue Range

Abstract: The semi-terrestrial sandhopper Talitrus salta- tor uses celestial visual cues to orient along the sea-land axis of the beach. Previous spectral-filtering experiments suggested that it perceives directional information from wavelengths in the ultraviolet (UV)-blue range. Binary choice experiments between dark and UV (380-nm) light carried out on dark-adapted individuals of T. saltator showed photopositive movement to UV. Morphologically, each ommatidium in the eye consists of five retinula cells, four large and one small. In electroretinogram experiments, sensitivity of the dark-adapted eye is dominated by a recep- tor maximally sensitive at about 390-450 nm and second- arily sensitive at about 500-550 nm. Selective light-adap- tation experiments at 580 nm showed the apparent sensitivity decreasing at around the secondary sensitive range, thus disclosing the existence of UV-blue photorecep- tor cells. Here the existence of UV-blue detection is con- firmed, and evidence is provided that green and UV-blue visual pigments are located in the large and small retinula cells, respectively.

Circulation of Fluids in the Gastrovascular System of a Stoloniferan Octocoral

Abstract: Cilia-based transport systems characterize sponges and placozoans. Cilia are employed in cnidarian gastrovascular systems as well, but typically function in concert with muscular contractions. Previous reports sug- gest that anthozoans may be an exception to this pattern, utilizing only cilia in their gastrovascular systems. With an inverted microscope and digital image analysis, we used stoloniferan octocoral colonies growing on microscope cover glass to quantitatively describe the movement of fluids in this system for the first time. Flow in stolons (diameter 300 m) is simultaneously bidirectional, with average velocities of 100-200 m/s in each direction. Ve- locities are maximal immediately adjacent to the stolon wall and decrease to a minimum in the center of the stolon. Flow velocity is unaffected by stolonal contractions, suggesting that muscular peristalsis is not a factor in propelling the flow. Stolon intersections (diameter 500 m) occur below polyps and serve as traffic roundabouts with unidirectional, circular flow. Such cilia-driven transport may be the plesi- omorphic state for the gastrovascular system of cnidarians.

In vivo effects of brown tide on the feeding function of the gill of the northern quahog Mercenaria mercenaria (Bivalvia: Veneridae).

Abstract: The in vivo response of adult northern qua- hogs, Mercenaria mercenaria ,t oAureococcus anophagef- ferens (brown tide) at the level of the gill was determined using video-endoscopy. Feeding activity, particle-approach velocities, and ventral-groove-transport velocities were documented after the quahogs were exposed to Isochryis galbana (baseline observations) supplemented with either toxic or nontoxic A. anophagefferens at two bloom concen- trations (8 10 5 or 2 10 6 cells ml -1 ). Externally, there was no evidence of adverse effects of brown tide on feeding, as siphons remained extended and dilated. Toxic brown tide at both concentrations elicited gill muscular contractions, intermittent cessation of water flow, and decreased particle loading within the pallial cavity. The 8 10 5 cell ml -1 toxic treatment had no significant effect on approach velocities or ventral-groove-transport velocities after 2 h, although time- averaging showed significant reduction of the latter during the last 30 min of exposure. The higher concentration of toxic brown tide caused a significant decrease in these velocities after only 1 h. Nontoxic brown tide produced none of these effects. Thus, A. anophagefferens compro- mised quahog feeding by stimulating contractions of the branchial musculature and interfering with lateral and ven- tral groove ciliary beating. These effects were both time- and concentration-dependent and could be caused by either a dopaminergic or a serotonergic toxic factor.