Showing papers in "The Biological Bulletin in 1996"

Eddy Chemotaxis and Odor Landscapes: Exploration of Nature With Animal Sensors.

Abstract: As Von Uexkiill, Von Frisch, Tinbergen, and Lorenz before him, Dethier developed methods to study animals from the animal's point of view: He wanted to know both how animals perceive their natural environment, and why animals perceive their environment in such speciesspecific ways. Thus, mirroring Tinbergen's famous four questions (1973), Dethier pursued his research with two interacting efforts: dissecting the mechanisms by which animals accomplish their perception of the world and deriving evolutionary ideas of the behavioral and genomic consequences of that particular "world view." Such diverse views then serve as models for human biologyboth by contrast and by analogy, if not homology. Building on the theme of animal world views serving as models for human perception and engineering, I will summarize some recent work on odor dynamics in which my colleagues and I have attempted to answer questions not unfamiliar to Vince Dethier (e.g., 1975, 1980): How do lobsters and humans see their odor worlds? In humans, odor evokes powerful memories-often visual images-of past experience. When humans dream of odor landscapes they may visualize the hills of Provence covered in fragrant thyme and lavender. On a foggy night, winds may carry the scent of pine forests and warn the sailor to watch or listen for nearby shores. And whiffs of fresh-baked bread may alert the bypasser to look for the bakery. For us, odor is an important and highly

Stimulants of Feeding Behavior in Fish: Analyses of Tissues of Diverse Marine Organisms.

Abstract: Analyses of the free amino acids, quaternary amines, guanido compounds, nucleotides, nucleosides, and organic acids in extracts of tissues from 10 species of marine teleost fishes and 20 species of invertebrates are reported. With multidimensional scaling techniques, the relative concentrations of the above chemicals in fishes, molluscs, and crustaceans are shown to cluster into separate taxon-specific groups. The greatest differences are between the fishes and the two groups of invertebrates. Similarities are more evident between the molluscs and crustaceans where eight of the nine most abundant substances are identical: i.e., betaine, taurine, trimethylamine oxide, glycine, alanine, proline, homarine, and arginine. The major tissue components in the fishes and invertebrates are correlated with compounds previously shown to stimulate feeding behavior in 35 species of fish. Glycine and alanine are major tissue components and are also the two most frequently cited feeding stimulants in the 35 species. Molluscs and crustaceans each contain high concentrations of five of the most frequently cited stimulants (glycine, alanine, proline, arginine, and betaine); these substances all occur in much lower concentrations in fish. Some minor tissue components, such as tryptophan, phenylalanine, aspartic acid, valine, and uridine 5`-monophosphate, are, however, important feeding stimulants for some fish species. Stimulants for herbivores and carnivores are often different. Several major feeding stimulants are substances that serve as "compensatory solutes," stabilizing enzymes and structural proteins.

An Ancient Chemosensory Mechanism Brings New Life to Coral Reefs

Abstract: The first scleractinians, progenitors of modern corals, began to appear 240 million years ago; by the late Jurassic (150 Ma) most families of modern corals had evolved and begun forming reefs (1, 2). Mechanisms controlling the recruitment of new corals to sustain these structures are, however, poorly understood (3). Corals, like many marine invertebrates, begin life as soft-bodied larvae that are dispersed in the plankton (3, 4). As the first step in developing a calcified coral colony, the larva must settle out of the plankton onto a suitable substratum and metamorphose to the single calcified polyp stage cemented to the reef (3, 5). Our analyses of the metamorphic requirements of larvae in divergent coral families surprised us by revealing the existence of a common chemosensory mechanism that is required to bring larvae out of the plankton and onto the reef. This mechanism appears to be quite old, predating both the phylogenetic divergence of these coral families and the development of different modes of coral reproduction.

Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa)

Abstract: Organisms develop through a series of stages leading to sexually mature adults. In a few cases ontogeny reversal is possible, but it does not occur typically after the onset of sexual reproduction. All stages of the medusa Turritopsis nutricula, from newly liberated to fully mature individuals, can transform back into colonial hydroids, either directly or through a resting period, thus escaping death and achieving potential immortality. This is the first metazoan known to revert to a colonial, juvenile morph after having achieved sexual maturity in a solitary stage. Selective excision experiments show that the transformation of medusae into polyps occurs only if differentiated cells of the exumbrellar epidermis and part of the gastrovascular system are present, revealing a transformation potential unparalleled in the animal kingdom.

Chemical Induction of Larval Settlement Behavior in Flow.

Abstract: The ability of dissolved chemical cues to induce larval settlement from the water column has long been debated. Through computer-assisted video motion analysis, we quantified the movements of individual oyster (Crassostrea virginica) larvae in a small racetrack flume at free-stream flow speeds of 2.8, 6.2, and 10.4 cm/s. In response to waterborne chemical cues, but not to seawater (control), oyster larvae moved downward in the water column and swam in slow curved paths before attaching to the flume bottom. Effective stimuli were adult-oyster-conditioned seawater (OCW) and a synthetic peptide analog (glycyl-glycyl-L-arginine) for the natural cue. The chemically mediated behavioral responses of oyster larvae in flow were essentially identical to those responses previously reported in still water. Our experimental results therefore demonstrate the capacity of waterborne cues to evoke settlement behavior in oyster pediveligers under varying hydrodynamic conditions.

Embryos at the Edge of Tolerance: Effects of Environment and Structure of Egg Masses on Supply of Oxygen to Embryos.

Abstract: Oxygen concentrations in gelatinous egg masses of two species of opisthobranch gastropods were examined with microelectrodes. Embryos in central positions are near the limit of the oxygen supply required for development. This limit is approached despite a diffusion constant for oxygen in masses that is close to that in water. Closed-chamber respirometry shows that oxygen is consumed by masses in the dark but generated in the light. Internal oxygen concentrations were greater in bright than in dim light. Thus photosynthesis and respiration of microorganisms associated with the masses affects the supply of oxygen to embryos within the mass. This effect of light was confirmed for egg masses of a polychaete. These observations, together with other published observations on the effects of hypoxia on development, indicate that the developmental rates of embryos in egg masses may depend on algal photosynthesis and metabolism. Flow around the masses also affects delivery of oxygen to embryos, but masses in dim li...

Cement Proteins of the Acorn Barnacle, Megabalanus rosa

Abstract: Components of the proteinaceous cement se- creted by barnacles have yet to be studied because of their insolubility. We solubilized and characterized the proteins of secondary cement, which is produced when the barnacle is detached from the substratum, in Megabalanus rosa. The cement was fractionated, according to its solubility in aqueous formic acid, into a soluble fraction, SF1 (2 1%); a fraction soluble after reduction, SF2 (37%); and a frac- tion insoluble after reduction, IF (42%). Analysis of the SF 1 and SF2 by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that they con- tained three polypeptides (SFl-60 k, -57 k, -47 k) and one polypeptide (SF2-60 k), respectively. The amino acid compositions of these polypeptides were similar and their N-terminal amino acid sequences were identical. These polypeptides had an unusual amino acid composition, rich in Set-, Thr, Ala, and Gly, like the tube cement of a marine polychaete, Phragmatopoma cal@rnica. The IF, solubilized in aqueous formic acid after cleavage with cy- anogen bromide, was shown by SDS-PAGE to contain eight fragment peptides (CB-peptides). N-terminal amino acid sequences of the CB-peptides were also determined. We conclude that the barnacle cement is composed of at least two types of protein: highly hydroxylated protein in the SF1 and SF2 and insoluble protein in the IF.

Serotonin injections induce metamorphosis in larvae of the gastropod mollusc Ilyanassa obsoleta.

Abstract: Bath-applied serotonin (5-HT) induces competent larvae of the marine snail Ilyanassa obsoleta to metamorphose. Previously, the mode of action of 5-HT, whether as an external ligand or as an internal neurotransmitter, was unknown. Larvae were injected with 10-4 M 5-HT and other pharmacological agents to provide evidence that serotonergic neurons are necessary for metamorphosis in Ilyanassa larvae and that serotonin functions as a neurotransmitter or neuromodulator during this process. About 50% of 5-HT-injected animals metamorphose within 48 hours. Fluoxetine, a 5-HT reuptake inhibitor, and alpha-methyl-5-hydroxytryptamine (αm5HT), a 5-HT agonist, were also effective inducers of metamorphosis. Gramine (3-[dimethylaminomethyl]indole), a 5-HT antagonist, inhibited the inductive activity of 5-HT, while the amino acid gammaaminobutyric acid (GABA) resulted in rates of morphological restructuring similar to those of controls. Collectively, the results of our experiments support the idea that serotonergic neurons are active during larval metamorphosis of Ilyanassa and that 5-HT does not induce metamorphosis by binding to epidermal chemoreceptors.

In situ Rates of Fertilization Among Broadcast Spawning Gorgonian Corals

Abstract: Fertilization rates among marine benthic taxa have implicitly been assumed to be uniformly high in most analyses of life history evolution, but in situ fertilization rates during natural spawning events are rarely measured. Fertilization rates of the Caribbean gorgonians Plexaura kuna and Pseudoplexaura porosa were measured at a site in the San Blas Islands, Panama, by collecting eggs downstream of colonies during syn- chronous spawning events during the summer months in the years 1988-1994. Eggs collected by divers were incubated, and the proportion of eggs that developed was determined. Proportions of eggs developing suggest fertilization rates that vary from 0% to 100%. Monthly means ranged from 0% to 60.4%. Failure of gametes to develop can be attributed to sperm limitation, as eggs collected during spawning had higher fertilization rates if incubated with an excess of sperm. Plexaura kuna fertilization rates were highest during the July spawning events. Fertilization of Plexaura kuna eggs was usually lower during the first two nights of the 4-6 night spawn- ing event. The proportion of eggs being fertilized when collected from a given place and time was highly vari- able, with one peak in the frequency distribution at or below 20% fertilization, and a second group of samples with greater fertilization rates. High variance in fertil- ization rates is evident at all levels of analysis: between replicate samples, times within nights, and among nights and months. This variance can be attributed to a combination of the effects of heterogeneity in the water

Intersex Red Claw Crayfish, Cherax quadricarinatus (von Martens): Functional Males with Pre-vitellogenic Ovaries

Abstract: Intersex individuals, possessing both male and female genital openings, were assessed in two groups-7 and 19 months old-of Australian red claw crayfish (Cherax quadricarinatus). All intersex individuals investigated were functional males, as suggested by their malelike morphology and the presence of testes, sperm ducts, androgenic glands, and viable spermatozoa. When an ovary was present in an intersex individual from either group, the gonadosomatic index, the diameter of the oocytes, and the ovarian cytosolic polypeptide profile were similar to those of immature, pre-vitellogenic females. We conclude that intersexuality in C. quadricarinatus does not indicate a case of protandric sequential hermaphroditism, as previously suggested. The case of intersexuality described here presents a unique model for the study of the role of the androgenic gland in the regulation of sex differentiation in crustaceans.

Vertical Transmission of Chemoautotrophic Symbionts in the Bivalve Solemya velum (Bivalvia: Protobranchia)

Abstract: Adults of the bivalve species Solemya velum live in symbiosis with chemoautotrophic bacteria in spe- cialized gill bacteriocytes. The bacteria play an essential nutritional role in the mature association, fixing CO2 via the Calvin cycle with energy obtained through the oxi- dation of reduced sulfur compounds. To understand how the continuity of this partnership is maintained between host generations, we investigated the mode of symbiont transfer in S. velum. A diagnostic assay using the poly- merase chain reaction and primers specific for the S. velum symbiont ribulose- 1 ,5-bisphosphate carboxylase (RubisCO) gene consistently detected bacterial sequence in female gonad tissue, suggesting the presence of sym- biont cells in host ovaries and a vertical mode of symbiont transmission from mother to offspring. Furthermore, in- tracellular bacteria were present in the developing gills of juveniles that had not yet hatched from the gelatinous capsule in which larval development occurs ( 11 days after fertilization). By 64 days postfertilization, the typical adult gill ultrastructure of alternating bacteriocytes and sym- biont-free intercalary cells was apparent. Knowledge about the mode of symbiont transfer in S. velum allows further study into the dynamics of host-symbiont interactions in chemoautotrophic associations.

Ontogeny of Copepod Predation in Juvenile Squid (Loligo opalescens)

Abstract: Copepods are the major prey of juvenile squid, and small species of squid such as Loligo opalescens face a great challenge in catching these erratically moving crustaceans. We studied the ontogeny of copepod predation in laboratory-reared animals and found that mastery of copepod capture develops progressively, starting shortly after hatch with strong attacks of a simple type. Modifications of the initial basic attack lead to more specialized strategies that effectively extend the range of capture to both longer and shorter distances. This progression culminates, by approximately 40 days post-hatching, in adult-like prey capture behavior involving tentacle extension and retraction. Squid raised exclusively on easily captured Artemia nauplii and introduced to a copepod diet 40 days after hatching displayed only basic attack behavior, characteristic of very young squid. All of these attacks were unsuccessful, and very few of these animals survived the transition. Copepod capture thus appears to be a skill t...

Effect of Larval Swimming Duration on Success of Metamorphosis and Size of the Ancestrular Lophophore in Bugula neritina (Bryozoa)

Abstract: There is a growing realization that events during one portion of an organism's life cycle can have both subtle and dramatic effects on other stages in the life history. Lethal and sublethal effects associated with the duration of larval swimming in marine invertebrates were examined for the bryozoan Bugula neritina. Larvae were kept swimming up to a maximum of 28 h at 20°C by exposure to continuous bright fluorescent illumina- tion. At 4-h intervals, samples of 20-40 larvae were re- moved from bright illumination and were exposed to seawater containing 10 mM excess KCl, an inducer of metamorphosis in this species. Over the first 12 h of lar- val swimming, an average of about 90% of the larvae ini- tiated and completed metamorphosis; at 16 h, the per- centage of larvae initiating and completing metamor- phosis dropped significantly. By 28 h, about half of the larvae were initiating metamorphosis, whereas only one- fifth were completing metamorphosis. Larval swimming duration also significantly affected the duration of meta- morphosis. By 30 h of larval swimming, individuals were taking about 25% longer to complete metamorphosis. Compared to ancestrulae that developed from larvae that were induced to metamorphose shortly after the on- set of swimming, those that swam for greater than 8 h had significantly smaller lophophores. For example, by 28 h of larval swimming the ancestrular lophophore de- creased in height, surface area, and volume by about 25%, 40% and 55%, respectively. This marked decrease in lophophore size may ultimately affect the ability of juveniles to sequester food, compete for space, and attain reproductive maturity. Thus, increasing the duration of

A Chemical Cue Induces Settlement of Sydney Rock Oysters, Saccostrea commercialis, in the Laboratory and in the Field

Abstract: The physical and chemical nature of a substratum's surface, including the presence of dissolved compounds or a bacterial film, may induce the settlement of invertebrate larvae. Based on previous observations of (1) enhanced recruitment of Sydney rock oysters (Saccostrea commercialis) on concrete surfaces and (2) high alkalinity at the surface of concrete due to the leaching of calcium hydroxide (Ca(OH)2) from the cement, experiments were designed to test the hypothesis that a surface containing Ca(OH)2 enhances settlement of oysters. The effect of a biofilm on settlement of Sydney rock oysters was also tested. The results obtained from the field experiment differed slightly from those obtained in the laboratory. In both the laboratory and the field, Ca(OH)2 had a positive effect on settlement. No significant effect of a biofilm on settlement on concrete substrata was observed in either experiment; a positive effect of a biofilm on substrata made with sand only or on sandstone was seen in both the laborato...

Particle Capture by the Gills of Dreissena polymorpha: Structure and Function of Latero-frontal Cirri.

Abstract: Microscopic techniques were used to exam inc the role of gill cim in particle captureby Dreissena polymorpha. The latero-frontal cirri, formed from two fused ciliary plates, consist ofabout 40 pairs ofcilia. Each cilium in the plate containsa typical 9 + 2 axonemein the fused region of the cirrus, but the structure of the axonemein the long, freeciliary tips is reduced.Thecilia in a cirrus are gradedin length, with the shortestcilia positionedfrontally. The cirral cilia movein unison, al lowing the cirrus to movefrom a flexedposition with its tip archedover the front of the gill filament, to an cx tendedposition with the cirrus projectedin the planeof the latero-frontal cell and extendingacrossthe interfil amentspace.In the latter position, the freeciliary tips of opposingand neighboringcirri form a “?�trap” (net) with a spacingof about 0.5 tim. Observationswith lasercon focal microscopy indicated that these structures can physically trap particles 1 @tm in diameter. Particles capturedby the extendedcirri are moved to the frontal surfaceofthe gill, wherethe cirri aresweptby the lateral mostfrontal cilia. During cirral movementthe shift from extendedto flexed position is, in part, achievedby the baseofthe cirrus pivoting at a hingeregion.Morpholog ically, the hinge region showsaxonemalspecializations that consistofelectron-denseplatesand other structures ofundefined function that maybeimportant in the over all movement of the cirrus. In addition to trapping by cirri, wealsoobservedparticlesmoving in the watercur rents,particularly in the frontal current locatedoverthe apical surfaceof the filament, suggesting that somepar tides arecapturedin thesewater currentswithout being physically trapped. Probably,therefore,trapping by the

Structure of the female reproductive tract in the Dungeness crab (Cancer magister) and implications for the mating system

Abstract: Anatomical and behavioral aspects of repro- duction in female Dungeness crab, Cancer magister, were investigated. Female crabs were collected over a two-year period and external indicators of reproductive condition were recorded. A subset of crabs was retained for mac- roscopic and histological examination of the reproductive tract. In addition, males and females were held in the laboratory for mating observations, thus providing females of known mating history for dissection. The spermatheca is of the "ventral type," i.e., the vagina and the oviduct open into the spermatheca in close proximity to each other. A novel organ that often contains sperm, the bursa, is separate and distinct from the spermatheca in both position and origin and is reported for the first time for a brachyuran crab. The bursa is located just inside the vulva, distal to the spermatheca, and opens into the va- gina. The sperm plug of C. magister, described here for the first time, is unique in form among cancrids. The sperm plug is placed in the vagina by the first male to mate with a soft-shelled female and prevents subsequent access to the spermatheca. However, the sperm plug does not occlude the vulva nor prevent subsequent copulation; ejaculates from subsequent matings are deposited in the bursa. Hypotheses of the possible function of the bursa are discussed.

Evolution of Intragonadal Development in the Diminutive Asterinid Sea Stars Patiriella vivipara and P. parvivipara with an Overview of Development in the Asterinidae.

Abstract: The diminutive asterinid sea stars Patiriella vivipara and P. parvivipara incubate their embryos in the gonads to the advanced juvenile stage. Despite the small size of their eggs (135-150 μm diameter), development is lecithotrophic. Development proceeds through the wrinkled blastula, gastrula, and brachiolaria larval stages. The gastrulae and larvae are uniformly ciliated and swim, propelled by the cilia, in the gonadal fluid. The brachiolaria is pear-shaped and has a vestigial brachiolar attachment complex composed of three small brachia. At no stage in development are the embryos attached to the gonad. Metamorphosis occurs as the larvae swim in the gonadal lumen. Internal development involves formation of one large enterocoel at the anterior end of the archenteron and one small posterior enterocoel on the left side of the archenteron. The archenteron closes to form the rudiment for the adult gut. As a result of the small size of the egg and the nonfeeding mode of development, the larvae of P. vivipara and P. parvivipara are minute, about 270 μm and 210 {mu}m in length, respectively. Newly metamorphosed juveniles are about 240 μm and 310 μm in diameter, respectively. Postmetamorphic development involves substantial growth of the juveniles, which leave the parent at a diameter between 1.0 and 5.0 mm. The presence of a vestigial brachiolar complex and lecithotrophic development indicates that these species had a free-living lecithotrophic brachiolaria in their ancestry. We suggest that the evolution of viviparity in Patiriella sp. involved retention of a large egg by an ancestor that had a lecithotrophic brachiolaria followed by a secondary reduction in the size of the ovum and simplification of the larva. The range of life histories seen in Patiriella is atypical of asteroid genera and supports the contention that the evolution of viviparity and other modes of modified development in the Asteroidea follows phylogenetic lineages.

Sources of Energy for Increased Metabolic Demand During Metamorphosis of the Abalone Haliotis rufescens (Mollusca)

Abstract: Pelagic, lecithotrophic (nonfeeding) larvae of the red abalone (Haliotis rufescens) settle and subsequently metamorphose into benthic juveniles capable of feeding on particulate food. Thus, metamorphosis must be fueled by either endogenous reserves or a nonparticulate food source such as dissolved organic material (DOM) in seawater. The metabolic rates (measured as oxygen consumption) of abalone larvae were found to increase by an average of 3- to 5-fold from the larva to early juvenile stage. The total cost of development from embryo to juvenile measured for three cultures ranged from 41.6 mJ to 55.0 mJ. Meeting this cost would require 1.3 to 1.7 {mu}g of biomass (ash-free dry mass), which is similar to the initial biomass of the spawned oocyte at 1.36 +/- 0.04 {mu}g (mean of four cultures). However, there was no net loss of biomass during development from the oocyte to the juvenile. The uptake of alanine and glucose from seawater by larvae and juveniles could provide one-third of the organic material re...

Echinoid Bioerosion as a Major Structuring Force of Red Sea Coral Reefs

Abstract: Echinoid bioerosion is ecologically important as a limiting factor for reef growth. Diadema setosum and Echinometra mathaei are the most abundant sea urchins in the Gulf of Eilat, Red Sea. Bioerosion by these urchins was estimated from field experiments with ur- chins placed in underwater chambers. A novel meth- odology was developed for measuring the CaC03 content of fecal pellets and total gut contents. This method is based on measurement of the amount of gas formed by total acidification of a mixed sample. The population density of the urchins was determined for the reef flat (depth 0.6-l m) and the reef slope (depth 6-8 m). D. setosum, which erodes 3 10 mg individual-' d-', is much less abundant on the reef flat (0.1 individuals mP2) than on the reef slope (6.4 individuals me*). In contrast, E. mathaei, which erodes 120 mg individual-' dP', is more dominant on the reef flat (10.5 individuals m-*) than on the reef slope (3.7 individuals m-*). We estimate that echinoid bioerosion converts to carbonate sediments 7%- 1 1% of the total reef flat calcification and 13%-22% of the total reef slope calcification. These findings empha- size the importance of echinoid bioerosion as a struc- turing force in the coral reef, and its potential importance to the dynamics of reef development. However, they im- ply that some previous studies may have overestimated the role of echinoid bioerosion, thus possibly underes- timating internal bioerosion.

The Economy of Winter: Phenotypic Plasticity in Behavior and Brain Structure

Abstract: Mobile animals must learn the spatial distributions of resources. The cost of foraging increases dramatically for temperate-zone animals during the winter. Two strategies may be used to balance the energetic budget: reducing costs of foraging and reducing need to forage. Both strategies are correlated with changes in brain structure, specifically in the hippocampus, a forebrain structure used by birds and mammals to map spatial distributions of resources. Small mammals that reduce their need to forage, through hibernation or reduction in body size, show a specific reduction in the structure and size of the hippocampus. The costs of foraging can be also decreased by migration to better foraging conditions or by food-storing, both of which decrease the temporal heterogeneity of food resources. Both of these latter strategies are associated with increased hippocampal structure; for food-storing birds, this increase is a seasonal phenomenon. Thus not only behavior, but also learning ability and even brain str...

Gas Exchange Rates in the Parker River Estuary, Massachusetts.

Abstract: Gas exchange rates between natural waters and the atmosphere are an important component of our understanding of the dynamics of biologically active gases. For example, estimates of whole system metabolism must account for the transfer of gas (OJ between the atmosphere and water. Previous studies in estuaries have relied on dome measurements to estimate O2 exchange rates ( 1,2). In this study we measured gas exchange rates using sulfur hexafluoride (SF,) as a tracer. SF6 is well suited for this application because it is chemically and biologically nonreactive, occurs at low background levels, and extremely low concentrations are readily detectable (3). The gas exchange coefficient, k, calculated for SF, can be related to the exchange coefficient for other gases (4). We injected -0.004 moles of SF, into the Parker River estuary, Newbury Massachusetts, and monitored the evasion of the gas over time by the decrease in its total mass. The tracer was allowed to mix for one tidal cycle and we then sampled SF, concentration in the water at each of seven successive high tides. Surface water samples were drawn into loo-ml glass syringes, transported, submerged in river water, to a field laboratory, and analyzed within 6 h using gas chromatography with electron capture detection. Windspeed and precipitation data were recorded continuously. Several previous surveys were used to determine cross-sectional reas along a IO-km stretch of the estuary. The total mass of SF, in the estuary was calculated by integrating concentration and water volume by estuarine distance. The distribution of the tracer changed over time in relation to processes controlling mixing and loss to the atmosphere (Fig. la). After the initial tidal cycle the tracer plume measured 5.2 km in length, and the distribution was gaussian. The exchange coefficient, k, and mass are related by the function k = In (M/Mo)h/t where M is the measured mass of SF, in the estuary, M. is the previously measured mass of SFs, h is the depth, and t is the time between samplings. Calculated values for kSF6 range from 1.1-6.2 cm. h-‘. Fluctuations in k are well correlated with wind velocity [in agreement with previous studies (4, 5)] and with precipitation (Fig. 1 b). These values are lower than those predicted from wind relations established from dome studies (Fig. 1 c). For estuarine systems with complicated geometry (e.g., channel longitudinal direction, marsh grass, and high tidal range), direct measurement of SF, evasion may be a more accurate determination of gas exchange rates. The importance of gas exchange as a process influencing the determination of system metabolism was determined by applying our measured gas exchange coefficient for SF6 to the calculation of O2 gas exchange. System respiration was calculated by mass loss of dissolved oxygen between dusk and dawn (Fig. Id) and corrected for gas exchange with the atmosphere. The gas transfer velocities of O2 and SF6 are related by the function k,,

Acid-Base Status of the Oyster Crassostrea virginica in Response to Air Exposure and to Infections by Perkinsus marinus

Abstract: Hemolymph acid-base variables were investigated in the Eastern oyster, Crassostrea virginica, to determine its responses to air exposure and to infections by the parasite Perkinsus marinus. Infected and uninfected oysters were subjected to two treatments of temperature (21° and 30°C) and air exposure (5 and 24 h). Upon exposure to air, oysters underwent a respiratory acidosis that remained uncompensated in uninfected oysters but was partially compensated in highly infected oysters at both 21° and 30°C. The acidosis was significantly greater in oysters with high infections. Hemolymph in uninfected oysters had a greater buffering capacity (-6.80 +/- 0.76 SEM slykes) than hemolymph in highly infected oysters (-3.30 +/- 0.50 SEM slykes). Calcium ion concentrations in hemolymph increase when the hemolymph becomes acidic, suggesting that shell decalcification plays a role in buffering the acid. During air exposure, although oysters do not visibly gape, they access air and are apparently not completely anaerobic.

Chemical Mediation of Sperm Activity and Longevity in the Solitary Ascidians Ciona intestinalis and Ascidiella aspersa.

Abstract: Sperm chemotaxis to compounds originating from eggs is common in solitary ascidians. This chemotactic response is associated with an increase in the activity level of the sperm. Here we examine the hypothesis that the period of sperm viability is reduced by the stimulation of increased activity by compounds associated with the eggs of solitary ascidians. The activity level and longevity of sperm from two species of solitary ascidian, Ciona intestinalis and Ascidiella aspersa, were measured after incubation in water that had been stored with homospecific eggs. Our results showed that the proportion of active sperm increased in homospecific egg water. This increase corresponded to a sharp decline in sperm longevity, which suggests a causal link between sperm activity and longevity. We suggest that sperm energy reserves are conserved in the absence of compounds associated with homospecific eggs, and that this may have significant ecological consequences for these organisms. Cross-reactivity in the chemotactic response of sperm from one species to the chemoattractant of another is common in ascidians, and increased sperm activity is associated with this response. Therefore, we investigated cross-reactivity in the activation of C. intestinalis and A. aspersa sperm to heterospecific egg water. Our results showed that A. aspersa sperm were activated by the egg water of C. intestinalis, resulting in a decline in sperm viability, but that this response was not reciprocated between the sperm of A. aspersa and the egg water of C. intestinalis. This suggests either that sperm of A. aspersa respond to compounds associated with the eggs with a higher degree of specificity than C. intestinalis sperm, or that compounds associated with A. aspersa eggs have more generalized activity than those of C. intestinalis.

Conspecific Recognition and Host Choice in a Pea Crab, Pinnixa chaetopterana (Brachyura: Pinnotheridae)

Abstract: The pea crab Pinnixa chaetopterana (Brachy- ura: Pinnotheridae) lives in the tubes of the host poly- chaetes Chaetopterus variopedatus and Amphitrite ornata. While attraction to host odor cues is common in sym- biotes, P. chaetopterana resident in Chaetopterus tubes apparently show no attraction to water-borne cues from either host. Because crabs resident in Amphitrite tubes are significantly reduced in their maximum body size and thus clutch size, switching between hosts should occur. We therefore tested the hypothesis that the crabs use odor cues from conspecifics or from the competing crab Po- lyonyx gibbesi (Anomura: Porcellanidae) when locating a new host. Crabs collected from Amphitrite are signifi- cantly attracted to Chaetopterus hosts which contain a mixed sex pair of conspecifics. Females show a strong tendency to avoid hosts containing Polyonyx, but males do not. Neither sex is attracted to unoccupied Chaetop- terus or Amphitrite hosts, but both are significantly at- tracted to isolated conspecifics. This attraction could serve as a reliable means of locating suitable new hosts when switching hosts in the field. Attraction to conspecific odors would also increase the chances of finding a suitable mate already present in a new host.

Convergence in the Feeding Apparatuses of Lophophorates and Pterobranch Hemichordates Revealed by 18S rDNA: An Interpretation

Abstract: Homology of the feeding apparatus of pterobranch hemichordates and the lophophore of bryozoans, brachiopods, and phoronids has been postulated but never rigorously tested I employ Patterson's (1, 2) three criteria of conjunction, similarity, and congruence to test this putative homology Although the conjunction and similarity criteria are satisfied, congruence is not The congruence test is based on a phylogeny derived from 18s rDNA sequence data which show that pterobranchs and lophophorates are in diRerent metazoan subkingdoms and are not closely related This finding indicates that a lophophore-like apparatus has evolved at least twice in metazoans even though the gross morphology, feeding mechanics, ultrastructure, and ciliary patterns of these organisms are very similar The high degree of morphological convergence presumably results from similar selective regimes acting on these taxa These findings indicate that major clades of organisms can evolve in a correspondingfashion despite independent origins

Antibacterial Properties of Isolated Amoebocytes From the Sea Anemone Actinia equina

Abstract: The antimicrobial defenses of anthozoans were investigated in vitro by extracting amoebocytes from the mesenteric filaments of the beadlet anemone, Actinia equina, and testing for their ability to phagocy- tose and kill the gram-negative bacterium Psychrobacter immobilis. Only the hyaline amoebocytes exhibited phagocytosis in vitro, with about 40% seen to ingest one or more bacteria over 45 min. Mixed cultures of viable amoebocytes were further found to produce 02- ions and other reactive oxygen species (ROS) after stimula- tion with phorbol myristate acetate or lipopolysaccha- ride. Co-incubation of viable amoebocytes with P. im- mobilis for 3 h in vitro resulted in reduced growth of the bacterium compared to saline-incubated bacteria, but because the growth of P. immobilis was also impaired by lysed control amoebocytes, the contribution made to bacterial killing by ROS could not be evaluated. Instead, as confirmed by additional experiments using lysate su- pernatants of the amoebocytes, it appears that the cells contain soluble bactericidal factors. The nature of these agents is at present unknown, although preliminary tests indicate that killing is not mediated by lysozyme.

The Role of Attention in Learning About Odorants

Abstract: The goal throughout this period was to understand the neural mechanisms mediating chemosensory responses and related behavior. At the same time, it was the behavior that was providing insight to the mechanisms. The behavioral approach was an exciting game of wits [emphasis added]. It proved to be a powerful tactic, and many of its findings were subsequently shown by electrophysiology to be gratifyingly accurate. --Dethier (1990)

Completely Direct Development of Abatus cordatus, a Brooding Schizasterid (Echinodermata: Echinoidea) from Kerguelen, With Description of Perigastrulation, a Hypothetical New Mode of Gastrulation.

Abstract: Development of the brooding schizasterid Abatus cordatus, a subantarctic echinoid endemic to Kerguelen, is described. Females spawn nonbuoyant eggs 1300 μm in diameter, which are fertilized by elongated sperm (head 1 μm wide and 15 μm long). The main characteristics of this development are (1) incomplete cleavage beginning at the animal pole that becomes holoblastic, giving a filled wrinkled blastula 26 days after fertilization; (2) apparent (fate-mapping studies have not been done) external migration of mesenchyme cells, in the perivitelline space, from the animal to the vegetal pole during gastrulation while the archenteron invaginates; (3) hatching occurring at the end of the gastrulation (65 days after fertilization); (4) differentiation of the vestibule from a thickening of the oral epidermis as soon as the end of gastrulation is attained; and (5) production of a juvenile directly from the gastrula without any larval stage. The juvenile that leaves the brood chamber is 2 mm in diameter and about 250 days old. A. cordatus is a true completely direct developer (no larva and no metamorphosis). We propose to use (1) the term perigastrulation, as a tentative one until more definitive studies are available, to describe the hypothetical peculiar movement of cells during gastrulation and (2) the terms of direct development only for completely direct developing species and abbreviated development for species that have more or less transformed plutei.

Transdifferentiation of Larval Flagellated Cells to Choanocytes in the Metamorphosis of the Demosponge Haliclona permollis

Abstract: The free-swimming parenchymella larvae of Haliclona permollis have a surface of flagellated cells that function in locomotion. These flagellated cells disappear from the larval surface soon after larval settlement, but the debate about their fate during metamorphosis has not been resolved. An improved method for electron microscopy enabled us to visualize minute ellipsoid granules characteristic of the larval flagellated cells of this sponge and to use these granules as natural markers to follow the fate of flagellated cells in metamorphs. On metamorphosis, the axonemes of the flagellated cells are withdrawn into the cell body and persist for some time, thus serving as a second natural marker for flagellated cells in postlarval forms. Within 12 h after settlement, the metamorphs have both markers in amoeboid cells derived from flagellated cells. The minute ellipsoid granules are found in the amoeboid cells of the metamorphs 24 h after settlement, and in the choanocytes of the juveniles 36 h after settlement. Therefore, it is proposed that the choanocytes derive from the larval flagellated cells by way of an amoeboid cell stage. These results suggest that the flagellated cells of parenchymella larvae participate in the formation of juveniles.

Biochemical and Enzymatic Characterization of an Acetylcholinesterase From Nereis diversicolor (Annelida, Polychaeta): Comparison With the Cholinesterases of Eisenia fetida (Annelida, Oligochaeta)

Abstract: This study constitutes the first report of a bio- chemical characterization, involving both substrates and inhibitors and electrophoretic analysis, of a cholinesterase (ChE) from a polychaete annelid (Nereis diversicolor). The ChE of N. diversicolor appears to be an acetylcholines- terase (AChE); i.e., it hydrolyzes acetylthiocholine iodide at a higher rate than other substrates and is inhibited by eserine but not by iso-OMPA. The ChEs of Eisenia,fetida are different from that of N. diversicolor and include at least two types of PrChEs. The AChE activity is located principally in the anterior region of the worm (head) in N. diversicolor, whereas the ChE activity of E. fetida is located throughout the body. The electrophoretic char- acterization of N. diversicolor and E. ,fetida ChEs showed, respectively, six and two isoforms with disc-PAGE, and three (55,000, 47,000, and 17,000) and five molecular forms (628,000, 301,000, 235,000, 106,000, and 53,800) with PAGGE; substantial activity remained at the top of the PAGGE gel in both species.