Showing papers in "The Biological Bulletin in 2006"

Molecular Mechanisms of Memory Storage in Aplysia

Abstract: Cellular studies of implicit and explicit memory suggest that experience-dependent modulation of synaptic strength and structure is a fundamental mechanism by which these memories are encoded, processed, and stored within the brain. In this review, we focus on recent advances in our understanding of the molecular mechanisms that underlie short-term, intermediate-term, and long-term forms of implicit memory in the marine invertebrate Aplysia cali- fornica, and consider how the conservation of common elements in each form may contribute to the different tem- poral phases of memory storage.

The octopus: a model for a comparative analysis of the evolution of learning and memory mechanisms.

Abstract: Comparative analysis of brain function in invertebrates with sophisticated behaviors, such as the octopus, may advance our understanding of the evolution of the neural processes that mediate complex behaviors. Until the last few years, this approach was infeasible due to the lack of neurophysiological tools for testing the neural circuits mediating learning and memory in the brains of octopus and other cephalopods. Now, for the first time, the adaptation of modern neurophysiological methods to the study of the central nervous system of the octopus allows this avenue of research. The emerging results suggest that a convergent evolutionary process has led to the selection of vertebrate-like neural organization and activity-dependent long-term synaptic plasticity. As octopuses and vertebrates are very remote phylogenetically, this convergence suggests the importance of the shared properties for the mediation of learning and memory.

Mammalian and Avian Neuroanatomy and the Question of Consciousness in Birds

Abstract: Some birds display behavior reminiscent of the sophisticated cognition and higher levels of consciousness usually associated with mammals, including the ability to fashion tools and to learn vocal sequences. It is thus important to ask what neuroanatomical attributes these taxonomic classes have in common and whether there are nevertheless significant differences. While the underlying brain structures of birds and mammals are remarkably similar in many respects, including high brain-body ratios and many aspects of brain circuitry, the architectural arrangements of neurons, particularly in the pallium, show marked dissimilarity. The neural substrate for complex cognitive functions that are associated with higher-level consciousness in mammals and birds alike may thus be based on patterns of circuitry rather than on local architectural constraints. In contrast, the corresponding circuits in reptiles are substantially less elaborated, with some components actually lacking, and in amphibian brains, the major ...

Functional and phylogenetic analyses of phenoloxidases from brachyuran (Cancer magister) and branchiopod (Artemia franciscana, Triops longicaudatus) crustaceans.

Abstract: Arthropod phenoloxidases catalyze the melanization and sclerotization of the new postmolt exoskeleton, and they function in the immune response. Hemocyanin, phylogenetically related to phenoloxidase, can function as a phenoloxidase under certain conditions. We investigated the relative contributions of hemocyte phenoloxidase and hemocyanin in the brachyuran crab Cancer magister, using the physiological ratio at which they occur in the hemolymph, and found that hemocyte phenoloxidase has higher activity. They both convert diphenols to o-quinones, but only the hemocyte phenoloxidase is able to catalyze the conversion of monophenols to diphenols. The quaternary structure of hemocyanin affects its reactivity as phenoloxidase. We suggest that prophenoloxidase is released from hemocytes and moves across epidermis into new exoskeleton during premolt and is activated in early postmolt. In addition to functional studies, we have determined the complete cDNA sequence of C. magister hemocyte prophenoloxidase and par...

Migration, isolation, and speciation of hydrothermal vent limpets (Gastropoda; Lepetodrilidae) across the Blanco Transform Fault.

Abstract: The Sovanco Fracture Zone and Blanco Trans- form Fault separate the Explorer, Juan de Fuca, and Gorda ridge systems of the northeastern Pacific Ocean. To test whether such offsets in the ridge axis create barriers to along-axis dispersal of the endemic hydrothermal vent an- imals, we examined the genetic structure of limpet popula- tions previously identified as Lepetodrilus fucensis McLean, 1988 (Gastropoda, Lepetodrilidae). Mitochondrial DNA se- quences and patterns of allozyme variation revealed no evidence that the 150-km-long Sovanco Fracture Zone im- peded gene flow between the Explorer and Juan de Fuca populations. In contrast, the 450-km-long Blanco Transform Fault separates the limpets into highly divergent northern and southern lineages that we recognize as distinct species. We describe southern populations from the Gorda Ridge (Seacliff) and Escanaba Trough as Lepetodrilus gordensis new species and refer northern populations from the Ex- plorer and Juan de Fuca ridge systems to L. fucensis sensu stricto. The species are similar morphologically, but L. gordensis lacks a sensory neck papilla and has a more tightly coiled teleconch. To assess the degree of isolation between these closely related species, we used the Isolation with Migration method to estimate the time of population splitting, effective sizes of the ancestral and derived popu- lations, and rates of migration across the Blanco Transform Fault.

Interspecific comparison of the mechanical properties of mussel byssus

Abstract: Byssally tethered mussels are found in a variety of habitats, including rocky intertidal, salt marsh, subtidal, and hydrothermal vents. One key to the survival of mussels in these communities is a secure attachment, achieved by the production of byssal threads. Although many studies have detailed the unique biomechanical properties of byssal threads, only a few prevalent species have been examined. This study assesses the variation in the mechanical proper- ties of byssus in a broad range of mussel species from diverse environments, including intertidal and subtidal Mytilus edulis, Modiolus modiolus, Geukensia demissa, Ba- thymodiolus thermophilus, and Dreissena polymorpha. A tensometer was used to measure quasi-static and dynamic mechanical properties of individual threads, and several aspects of morphology were quantified. The results indicate that thread mechanical properties vary among mussel spe- cies, and several novel properties were observed. For ex- ample, of the species examined, D. polymorpha threads were the strongest, stiffest, least resilient, and fastest to recover after partial deformation. Threads of M. modiolus were characterized by the presence of two distinct yield regions prior to tensile failure. This comparative study not only provides insight into the ecological limitations and evolution of mussels, but also suggests new models for the design of novel biomimetic polymers.

Feeding in a Calcareous Sponge: Particle Uptake by Pseudopodia

Abstract: Sponges are considered to be filter feeders like their nearest protistan relatives, the choanoflagellates. Spe- cialized "sieve" cells (choanocytes) have an apical collar of tightly spaced, rodlike microvilli that surround a long fla- gellum. The beat of the flagellum is believed to draw water through this collar, but how particles caught on the collar are brought to the cell surface is unknown. We have studied the interactions that occur between choanocytes and intro- duced particles in the large feeding chambers of a syconoid calcareous sponge. Of all particles, only 0.1-m latex mi- crospheres adhered to the collar microvilli in large numbers, but these were even more numerous on the choanocyte surface. Few large particles (0.5- and 1.0-m beads and bacteria) contacted the collar microvilli; most were phago- cytosed by lamellipodia at the lateral or apical cell surface, and clumps of particles were engulfed by pseudopodial extensions several micrometers from the cell surface. Al- though extensions of the choanocyte apical surface up to 16 m long were found, most were 4 m long, twice the height of the collar microvilli. These observations offer a different view of particle uptake in sponges, and suggest that, at least in syconoid sponges, uptake of particles is less dependent on the strictly sieving function of the collar microvilli.

Mechanisms of gravitaxis in Chlamydomonas.

Abstract: The mechanisms by which many free-swimming microorganisms are able to swim preferentially upward despite the sedimenting effects of gravity (termed gravitaxis) have long been the subject of debate. Early suggestions were that upward swimming could be caused by cells either being back-heavy (1, 2, 3) or possessing fore-aft body asymmetry (4). However, there is a widespread perception that simple physical mechanisms cannot explain how physiologically active agents can influence gravitaxis, or how non-gravitactic mutants can exist; it is therefore argued that cells must contain a biological gravity sensor which somehow directs active swimming (5, 6). Published quantitative data on the unicellular biflagellated green alga Chlamydomonas reinhardtii are used here to show that shape orientation is primarily responsible for upward orientation in this organism. It is also shown that the resulting gravitational response is governed by the cells’ own swimming patterns. It is concluded that gravitaxis in Chlamydomonas is explicable in purely physical terms, and that no biosensor need be involved. Chlamydomonas cells whose flagella have been immobilized by chemical agents are found to settle in suspension with their flagella uppermost (7, 8). There are only two possible explanations. One is that the cell is back-heavy, resulting from a longitudinal density gradient that displaces the center of gravity behind the center of buoyancy, thereby producing a gravitational torque on the cell that causes orientation. The other is that the asymmetry of cell body and flagella, even when of uniform density, causes shape orientation during sedimentation because the larger cell body sediments downward faster than the flagella. Both mechanisms result in orientation towards the vertical at a rate described by the relation d dt sin (1)

Encapsulation of attached ectoparasitic glochidia larvae of freshwater mussels by epithelial tissue on fins of naive and resistant host fish.

Abstract: To metamorphose into juveniles and subsequently mature into adults, the glochidia larvae of freshwater mussels in the order Unionoida must temporarily parasitize the gills, fins, or other external structures of fish. Once attached to the fish, the glochidium is encapsulated by host fish epithelial tissue. The migration of epithelial cells of the bluegill sunfish Lepomis macrochirus over glochidia of Utterbackia imbecillis was examined by time-lapse video microscopy, and the morphology was examined by scanning electron microscopy. Initially, the leading edge epithelial cells migrating over the larvae became rounded and the cells moved as a sheet until the attached glochidium was completely covered. Cyst formation on host fish that had been repeatedly exposed to mussel larvae was significantly delayed and morphologically irregular compared to that on naive fish. Cyst formation on other species of fish that are less successful as hosts was examined. In general, it took longer for glochidia to become encapsulated on these less suitable potential hosts. The delay and irregularities in cyst formation on resistant fish and nonhost fish species may result in increased mortality and reduced success of metamorphosis of glochidia.

Molecular Characterization of NMDA-Like Receptors in Aplysia and Lymnaea: Relevance to Memory Mechanisms

Abstract: The N-methyl-d-aspartate (NMDA) receptor belongs to the group of ionotropic glutamate receptors and has been implicated in synaptic plasticity, memory acquisition, and learning in both vertebrates

Color Polymorphism and Genetic Structure in the Sea Star Pisaster ochraceus

Abstract: The sea star Pisaster ochraceus is one of the more striking species on the rocky shores of the Northeast Pacific, in part due to the dramatic color polymorphism of the adults. Along the open Pacific coast, Pisaster populations are 6%–28% orange, with a small percentage of brilliant purple stars and a large percentage of reddish-brown to dull purple ones. However, populations in the San Juan Island Archipelago (Washington, USA) and the southern Strait of Georgia (British Columbia, Canada) are almost entirely brilliant purple. The factors that maintain the color polymorphism, and those that contribute to among-site variation in color frequencies, remain unknown. We examined the relationships between color frequencies and several ecological and morphological variables, and conducted a large-scale phylogeographic survey of Pisaster populations. We found very low population genetic structure, suggesting that gene flow is high and geographic variation in color frequencies is not a vestige of Pleistocene glacial...

Programmed Cell Death in the Apical Ganglion During Larval Metamorphosis of the Marine Mollusc Ilyanassa obsoleta

Abstract: The apical ganglion (AG) of larval caenogas- tropods, such as Ilyanassa obsoleta, houses a sensory organ, contains five serotonergic neurons, innervates the muscular and ciliary components of the velum, and sends neurites into a neuropil that lies atop the cerebral commissure. During metamorphosis, the AG is lost. This loss had been postu- lated to occur through some form of programmed cell death (PCD), but it is possible for cells within the AG to be respecified or to migrate into adjacent ganglia. Evidence from histological sections is supported by results from a terminal deoxynucleotidyl transferase dUTP nick end label- ing (TUNEL) assay, which indicate that cells of the AG degenerate by PCD. PCD occurs after metamorphic induc- tion by serotonin or by inhibition of nitric oxide synthase (NOS) activity. Cellular degeneration and nuclear conden- sation and loss were observed within 12 h of metamorphic induction by NOS inhibition and occur before loss of the velar lobes, the ciliated tissue used for larval swimming and feeding. Velar disintegration happens more rapidly after metamorphic induction by serotonin than by 7-nitroinda- zole, a NOS inhibitor. Loss of the AG was complete by 72 h after induction. Spontaneous loss of the AG in older com- petent larvae may arise from a natural decrease in endoge- nous NOS activity, giving rise to the tendency of aging larvae to display spontaneous metamorphosis in culture.

Immune Defense Reduces Respiratory Fitness in Callinectes sapidus, the Atlantic Blue Crab

Abstract: Crustacean gills function in gas exchange, ion transport, and immune defense against microbial pathogens. Hemocyte aggregates that form in response to microbial pathogens become trapped in the fine vasculature of the gill, leading to the suggestion by others that respiration and ion regulation might by impaired during the course of an im- mune response. In the present study, injection of the patho- genic bacterium Vibrio campbellii into Callinectes sapidus, the Atlantic blue crab, caused a dramatic decline in oxygen uptake from 4.53 to 2.56 mol g 1 h 1 . This decline in oxygen uptake is associated with a large decrease in post- branchial Po2, from 16.2 (0.46 SEM, n7) to 13.1 kPa (0.77 SEM, n9), while prebranchial Po2 remains un- changed. In addition, injection of Vibrio results in the dis- appearance of a pH change across the gills, an indication of reduced CO2 excretion. The hemolymph hydrostatic pres- sure change across the gill circulation increases nearly 2-fold in Vibrio-injected crabs compared with a negligible change in pressure across the gill circulation in saline- injected, control crabs. This change, in combination with stability of heart rate and branchial chamber pressure, is indicative of a significant increase in vascular resistance across the gills that is induced by hemocyte nodule forma- tion. A healthy, active blue crab can eliminate most invad- ing bacteria, but the respiratory function of the gills is impaired. Thus, when blue crabs are engaged in the immune response, they are less equipped to engage in oxygen-fueled activities such as predator avoidance, prey capture, and migration. Furthermore, crabs are less fit to invade environ- ments that are hypoxic.

Signaling to the enemy? - Body pattern expression and its response to external cues during hunting in the cuttlefish Sepia officinalis (Cephalopoda)

Abstract: Cuttlefish can rapidly alter their appearance by using neurally controlled chromatophore organs. This abil- ity may provide a window into their cognitive capacity. We test whether the changes in body pattern that occur during hunting depend on context. If they do, then it may be possible to use these changes to study cephalopod cognition while the animal is engaged in ecologically relevant tasks. We found consistent individual differences in the tendency of cuttlefish to hunt with the first two arms raised. We also found that cuttlefish usually darken their skin after they seize a prey item. This darkening is observed regardless of the identity of the prey (fish, crab, or shrimp), prey context (buried in sand, in a bare tank, or on top of a rock pile), or the presence of a sudden stimulus. The sudden stimulus was created by presenting an overhead model bird to the cuttle- fish. The model induced components of the Deimatic Dis- play, which is a form of antipredator behavior, suggesting that the model was perceived as a potential threat. Passing Cloud displays and the Darkening of the arms were signif- icantly reduced after exposure to the model bird. The effect of a potential predator on body pattern expression during hunting suggests it may be possible to use these changes as a sensitive indicator of ecologically relevant learning.

Sponge Systematics by Starfish: Predators Distinguish Cryptic Sympatric Species of Caribbean Fire Sponges, Tedania ignis and Tedania klausi n. sp. (Demospongiae, Poecilosclerida)

Abstract: Tedania ignis (Duchassaing and Michelotti, 1864), the fire sponge, is common throughout the tropical western Atlantic, and is a popular species for studies of ecology, larval biology, and chemistry. T. ignis is readily consumed by seagrass-dwelling starfish, and so finding sponges similar to this species in a seagrass meadow pro- voked closer scrutiny. A variety of ecological, morpholog- ical, and molecular traits consistently and unambiguously distinguish T. ignis from a cryptic sympatric congener, here described as Tedania klausi, n. sp. Starfish that consume T. ignis reject T. klausi, and angelfish consume T. klausi less quickly. In Belize, T. ignis individuals transplanted to a seagrass meadow inhabited by T. klausi were consumed by starfish, and individuals of T. klausi transplanted to a man- grove-lined creek in which T. ignis flourishes, died. In Panama, many individuals of T. klausi were diseased in May 2004, while adjacent individuals of T. ignis were unaffected. Spicule types are the same in the two forms, and sizes overlap; but within individuals, the relative sizes of styles and tylotes differ in a pattern that distinguishes the two forms. Comparison of DNA sequences for mitochon- drial cytochrome c oxidase subunit I (COI) revealed that 8 single nucleotide mutations consistently differ between the two forms regardless of habitat (seagrass vs. mangrove) and geographically separated sites (Belize vs. Panama).

Peritrophic membrane of the penaeid shrimp Sicyonia ingentis: structure, formation, and permeability.

Abstract: Peritrophic membranes (PTMs) are secreted acellular layers that separate ingested materials from the gut epithelium in a variety of invertebrates. In insects and crustaceans, PTMs are produced in the midgut trunk (MGT, or intestine), but the MGT in decapod crustaceans, unlike that of insects, is not involved with digestion or absorption of food. We demonstrate that the PTM in the penaeid shrimp Sicyonia ingentis is similar to that in other crustaceans that have been studied and is primarily composed of chitin. The lectin WGA binds only to the PTM and glycocalyx along the microvilli of the midgut cells, which is consistent with the suggestion that the chitin is synthesized along the microvilli. The PTM is only permeable to inert particles smaller than 20 nm. We also describe the secretion of granules, which fill the apices of the epithelial cells, into the ectoperitrophic space. Although their function is not clear, they do not contribute to the PTM.

Expression Profiles of Na+,K+-ATPase during Acute and Chronic Hypo-osmotic Stress in the Blue Crab Callinectes sapidus

Abstract: During acclimation to dilute seawater, the specific activity of Na+,K+-ATPase increases substantially in the posterior gills of the blue crab Callinectes sapidus. To determine whether this increase occurs through regulation of pre-existing enzyme or synthesis of new enzyme, mRNA and protein levels were measured over short (<24 h) and long (18 days) time courses. Na+,K+-ATPase expression, both mRNA and protein, did not change during the initial 24-h exposure to dilute seawater (10 ppt salinity). Thus, osmoregulation in C. sapidus during acute exposure to low salinity likely involves either modulation of existing enzyme or mechanisms other than an increase in the amount of Na+,K+-ATPase enzyme. However, crabs exposed to dilute seawater over 18 days showed a 300% increase in Na+,K+-ATPase specific activity as well as a 200% increase in Na+,K+-ATPase protein levels. Thus, it appears that the increase in Na+,K+-ATPase activity during chronic exposure results from the synthesis of new enzyme. The relative amounts of mRNA for the alpha-subunit increased substantially (by 150%) during the acclimation process, but once the crabs had fully acclimated to low salinity, the mRNA levels had decreased and were not different from levels in crabs fully acclimated to high salinity. Thus, there is transient induction of the Na+,K+-ATPase mRNA levels during acclimation to dilute seawater.

Bryostatin Enhancement of Memory in Hermissenda

Abstract: Bryostatin, a potent agonist of protein kinase C (PKC), when administered to Hermissenda was found to affect acquisition of an associative learning paradigm. Low bryostatin concentrations (0.1 to 0.5 ng/ml) enhanced mem- ory acquisition, while concentrations higher than 1.0 ng/ml down-regulated the pathway and no recall of the associative training was exhibited. The extent of enhancement de- pended upon the conditioning regime used and the memory stage normally fostered by that regime. The effects of two training events (TEs) with paired conditioned and uncondi- tioned stimuli, which standardly evoked only short-term memory (STM) lasting 7 min, were—when bryostatin was added concurrently— enhanced to a long-term memory (LTM) that lasted about 20 h. The effects of both 4- and 6-paired TEs (which by themselves did not generate LTM), were also enhanced by bryostatin to induce a consolidated memory (CM) that lasted at least 5 days. The standard positive 9-TE regime typically produced a CM lasting at least 6 days. Low concentrations of bryostatin (0.5 ng/ml) elicited no demonstrable enhancement of CM from 9-TEs. However, animals exposed to bryostatin concentrations higher than 1.0 ng/ml exhibited no behavioral learning. Sharp-electrode intracellular recordings of type-B photo- receptors in the eyes from animals conditioned in vivo with bryostatin revealed changes in input resistance and an en- hanced long-lasting depolarization (LLD) in response to light. Likewise, quantitative immunocytochemical measure- ments using an antibody specific for the PKC-activated Ca 2 /GTP-binding protein calexcitin showed enhanced an- tibody labeling with bryostatin. Animals exposed to the PKC inhibitor bisindolylmaleim- ide-XI (Ro-32-0432) administered by immersion prior to 9-TE conditioning showed no training-induced changes with or without bryostatin exposure. However, if animals received bryostatin before Ro-32, the enhanced acquisition and demonstrated recall still occurred. Therefore, pathways responsible for the enhancement effects induced by bryo- statin were putatively mediated by PKC. Overall, the data indicated that PKC activation occurred and calexcitin levels were raised during the acquisition phases of associative conditioning and memory initiation, and subsequently returned to baseline levels within 24 and 48 h, respectively. Therefore, the protracted recall measured by the testing regime used was probably due to bryostatin- induced changes during the acquisition and facilitated stor- age of memory, and not necessarily to enhanced recall of the stored memory when tested many days after training.

Source and Specificity of Chemical Cues Mediating Shelter Preference of Caribbean Spiny Lobsters (Panulirus argus)

Abstract: Caribbean spiny lobsters display a diversity of social behaviors, one of the most prevalent of which is gregarious diurnal sheltering. Previous research has demon- strated that shelter selection is chemically mediated, but the source of release and the identity of the aggregation signal are unknown. In this study, we investigated the source and specificity of the aggregation signal in Caribbean spiny lobsters, Panulirus argus. We developed a relatively rapid test of shelter choice in a 5000-l laboratory flume that simulated flow conditions in the spiny lobster's natural environment, and used it to examine the shelter preference of the animals in response to a variety of odorants. We found that both males and females associated preferentially with shelters emanating conspecific urine of either sex, but not with shelters emanating seawater, food odors, or the scent of a predatory octopus. These results demonstrate specificity in the cues mediating sheltering behavior and show that urine is at least one source of the aggregation signal.

Stocking Density at Early Developmental Stages Affects Growth and Sex Ratio in the European Eel (Anguilla anguilla)

Abstract: To investigate the effect of stocking density on growth and sex ratio in European eel, four constant density conditions were tested during the transition from the glass to the elver stage for 90 days (Period 1). The test conditions combined the weight of fish per unit surface or volume (surface density or volume density) resulting in four exper- imental groups: low surface density (0.5 kg/m 2 ) and low volume density (5 kg/m 3 ) (group S 0.5 V 5 ); low surface den- sity (0.5 kg/m 2 ) and high volume density (10 kg/m 3 ) (group S0.5V10); high surface density (2 kg/m 2 ) and low volume density (5 kg/m 3 ) (group S2V5); and high surface density (2 kg/m 2 ) and high volume density (10 Kg/m 3 ) (group S2V10). Subsequently, fish from the S0.5V5 ,S 2V5, and S2V10 groups were transferred to low density conditions (0.1-0.4 kg/m 2 or 0.1-0.3 kg/m 3 ) for another 21 months (630 days; Period 2). After Period 1, fish maintained at high surface density, regardless of the volume density, showed higher standard growth rates (SGRs) and RNA/DNA ratio in muscle than those cultured at low surface density. The percentage of mortality was similar in three of the groups (34.2%- 41.8%), but not in the S 2 V 10 group (83.3%). At the end of Period 2, most fish (about 95%) exhibited fully differenti- ated gonads, but different sex ratios were observed in each group. Thus, the S2V5 group showed a higher proportion of females (36.1%) and a lower proportion of males (56.8%) than the S0.5V5 group (11.4% and 72.5%, respectively), while all survivor fish from the S2V10 group developed into females. The gonadosomatic index and SGR were higher in females than in males. These results suggest that glass eels maintained at high surface density during the first months of growth tend to develop into females. The data also indicate that growth and sex ratio are linked processes during eel development, with growth seeming to be sex dependant rather than being influenced by the density conditions in which glass eels are maintained.

Patterns of motor activity in the isolated nerve cord of the octopus arm.

Abstract: The extremely flexible octopus arm provides a unique opportunity for studying movement control in a highly redundant motor system. We describe a novel prep- aration that allows analysis of the peripheral nervous system of the octopus arm and its interaction with the muscular and mechanosensory elements of the arm's intrinsic muscular system. First we examined the synaptic responses in muscle fibers to identify the motor pathways from the axial nerve cord of the arm to the surrounding musculature. We show that the motor axons project to the muscles via nerve roots originating laterally from the arm nerve cord. The motor field of each nerve is limited to the region where the nerve enters the arm musculature. The same roots also carry afferent mechanosensory information from the intrinsic muscle to the axial nerve cord. Next, we characterized the pattern of activity generated in the dorsal roots by electri- cally stimulating the axial nerve cord. The evoked activity, although far reaching and long lasting, cannot alone account for the arm extension movements generated by similar electrical stimulation. The mismatch between patterns of activity in the isolated cord and in an intact arm may stem from the involvement of mechanosensory feedback in nat- ural arm extension.

Lessons From a Crab: Molecular Mechanisms in Different Memory Phases of Chasmagnathus

Abstract: Consolidation of long-term memory requires the activation of several transduction pathways that lead to post-translational modifications of synaptic proteins and to regulation of gene expression, both of which promote stabilization of specific changes in the activated circuits. In search of the molecular mechanisms involved in such processes, we used the context-signal associative learning paradigm of the crab Chasmagnathus. In this model, we studied the role of some molecular mechanisms, namely cAMP-dependent protein kinase (PKA), extracellular-signal-regulated kinase (ERK), the nuclear factor kappa B (NF-κB) transcription factor, and the role of synaptic proteins such as amyloid β precursor protein, with the object of describing key mechanisms involved in memory processing. In this article we review the most salient results obtained over a decade of research in this memory model.

Development of Embryonic and Larval Cells Containing Serotonin, Catecholamines, and FMRFamide-Related Peptides in the Gastropod Mollusc Phestilla sibogae

Abstract: The present immunocytochemical study pro- vides one of the first detailed descriptions of the develop- ment of cells containing a variety of neurotransmitters dur- ing much of the larval life of a nudibranch gastropod. Throughout much of early development, serotonergic cells were located only in the apical organ; as larvae approached metamorphosis, serotonergic cells were also detected in the cerebropleural and pedal ganglia. Cells exhibiting tyrosine hydroxylase immunoreactivity (indicative of catecholamine synthesis) were first located near the mouth but by late embryonic stages were also located in the apical organ and near the velum and eyes. By late larval stages, numerous catecholaminergic cells were found in the foot, with con- centrations in the propodium. Finally, the first cells exhib- iting FMRFamide immunoreactivity were detected posterior to the neuropil of the cerebropleural ganglia in the early embryo. Fibers that presumably originated from these cells subsequently invaded the cerebral and pedal ganglia and the apical organ. By early larval stages, a second pair of pep- tidergic neurons was located near the first pair, and addi- tional peptidergic neurons were located in the apical organ and peripheral positions in the foot and medial and dorsal to the eyes. In addition to providing a unique phyletic perspec- tive to our understanding of gastropod neural development, the present study also sets the stage for future studies into changes in the nervous system as this gastropod undergoes metamorphosis.

Morphological and genetic variation indicate cryptic species within Lamarck's little sea star, Parvulastra (=Patiriella) exigua.

Abstract: The asterinid sea star Parvulastra exigua (Lamarck) is a common member of temperate intertidal marine communities from geographically widespread sites around the southern hemisphere. Individuals from Austra- lian populations lay benthic egg masses (through orally directed gonopores) from which nonplanktonic offspring hatch and metamorphose without a dispersing planktonic larval phase. Scattered reports in the taxonomic literature refer to a similar form in southern Africa with aborally directed gonopores (and possibly broadcast spawning of planktonic eggs and larvae); such differences would be consistent with cryptic species variation. Surveys of mor- phology and mtDNA sequences have revealed cryptic spe- cies diversity in other asterinid genera. Here we summarize the taxonomic history of Lamarck's "Asterie exigue¨" and survey morphological variation (the location of the gono- pores) for evidence that some P. exigua populations include cryptic species with a different mode of reproduction. We found strong evidence for multiple species in the form of two phenotypes and modes of reproduction (oral and aboral gonopore locations) in populations from southern Africa and islands in the Atlantic and Indian oceans. Both modes of reproduction have broad geographic ranges. These results are consistent with previously published genetic data that indicate multiple species in African and island (but not Australian) populations.

Effect of Salinity on Osmoregulatory Patch Epithelia in Gills of the Blue Crab Callinectes sapidus

Abstract: In euryhaline crabs, ion-transporting cells are clustered into osmoregulatory patches on the lamellae of the posterior gills. To examine changes in the branchial osmoregulatory patch in the blue crab Callinectes sapidus in response to change in salinity and to correlate these changes with other osmoregulatory responses, crabs were acclimated to a range of salinities between 10 and 35 ppt. When crabs that had been acclimated to 35 ppt were subsequently transferred to 10 ppt, both the size of the osmoregulatory patch on individual gill lamellae and the specific activity of Na+,K+-ATPase in whole-gill homogenates increased only after the first 24 h of exposure to dilute seawater. Enzyme activity and size of patch area increased gradually and reached their maxima (increasing by 200% and 60%, respectively) 6 days following transfer to 10 ppt seawater and then remained at these levels. Patch size at acclimation varied inversely with the salinity for seawater dilutions below 26 ppt (the isosmotic point of the cr...

Role of protein kinase C, G-protein coupled receptors, and calcium flux during metamorphosis of the sea urchin Strongylocentrotus purpuratus

Abstract: Artificial inducers have been used to study signal-transduction pathways involved in metamorphosis of some marine invertebrates. However, the transduction mechanisms for echinoderms have been less ...

Light-enhanced calcification and dark decalcification in isolates of the soft coral Cladiella sp. during tissue recovery.

Abstract: Light-enhanced calcification is a general characteristic of zooxanthellate corals, suggesting a link between calcification by the coral and photosynthesis by the zooxanthellae, but the relationship...

Orientation and Navigation Relative to Water Flow, Prey, Conspecifics, and Predators by the Nudibranch Mollusc Tritonia diomedea

Abstract: Progress in understanding sensory and locomo- tory systems in Tritonia diomedea has created the potential for the neuroethological study of animal navigation in this species. Our goal is to describe the navigational behaviors to guide further work on how the nervous system integrates information from multiple senses to produce oriented loco- motion. Observation of T. diomedea in its habitat has sug- gested that it uses water flow to navigate relative to prey, predators, and conspecifics. We test these hypotheses in the field by comparing slug orientation in time-lapse videos to flow direction in circumstances with and without prey, predators, or conspecifics upstream. T. diomedea oriented upstream both while crawling and after turning. This trend was strongest before feeding or mating; after feeding or mating, the slugs did not orient significantly to flow. Slugs turned downstream away from an upstream predator but did not react in control situations without an upstream predator. These data support the hypothesis that T. diomedea uses a combination of odors (or some other cue transported down- stream) and water flow to navigate relative to prey, preda- tors, and conspecifics. Understanding the context-dependent choice between upstream and downstream crawling in T. diomedea provides an opportunity for further work on the sensory integration underlying navigation behavior.

Phylogeny and genetic diversity of palolo worms (Palola, Eunicidae) from the tropical North Pacific and the Caribbean.

Abstract: Palolo worms (Palola, Eunicidae) are best known for their annual mass spawnings, or "risings," in the South Pacific. Palola currently contains 14 morphologically similar species, mostly from shallow tropical waters. In this study, 60 specimens of Palola from nine locations in the tropical North Pacific and the Caribbean were sequenced for the two mitochondrial markers cytochrome c oxidase sub- unit I and 16S ribosomal RNA to infer phylogenetic rela- tionships, genetic diversity, and phylogeography within the taxon. Phylogenetic analysis was performed using Bayesian statistics and parsimony. Vouchers of the same specimens were examined morphologically. Two major clades (A and B) can be distinguished within the monophyletic Palola. A number of individuals in clade B bear rows of ventral eyespots in the posterior body region, typical for swarming P. viridis and probably a synapomorphy for clade B. No morphological synapomorphy was found for clade A. Hap- lotypes from divergent clades often co-occur in the same location. Some haplotypes are geographically widespread, in one case covering the entire east-west expansion of the tropical Pacific. These results imply that despite the appar- ent absence of teleplanic larvae in eunicid polychaetes, long-distance dispersal is possible in at least some lineages of Palola. With the first taste of palolo I understood the Samoans' love for it. Certainly it suggested a salty caviar, but with something added, a strong, rich whiff of the mystery and fecundity of the ocean depths. —R. Steinberg. Pacific and Southeast Asian cooking. Time-Life Books, New York, 1970

The cellular mechanisms of learning in Aplysia: of blind men and elephants.

Abstract: Until recently, investigations of the neurobiological substrates of simple forms of learning and memory in the marine snail Aplysia have focused mostly on plastic changes that occur within the presynaptic sensory neurons. Here, I summarize the results of recent studies that indicate that exclusively presynaptic processes cannot account for simple forms of learning in Aplysia. In particular, I present evidence that postsynaptic mechanisms play a far more important role in nonassociative learning in Aplysia than has been appreciated before now. Moreover, I describe recent data that suggests the intriguing hypothesis that the persistent, learning-induced changes in Aplysia sensory neurons might depend critically on postsynaptic signals for their induction. Finally, I discuss the potential applicability of this hypothesis to learning-related synaptic plasticity in the mammalian brain.