Showing papers in "The Biological Bulletin in 1991"

Influence of body size and population density on fertilization success and reproductive output in a free-spawning invertebrate

Abstract: Gamete production and fertilization influence zygote production. While gamete production is correlated positively with body size, individual fertilization success may be a function of population density. Usually it is assumed that when high population density leads to reduced body size and gamete production, per capita zygote production is diminished. This field study of the sea urchin Diadema antillarum Philippi provides a test of this assumption. Three experiments were conducted to determine the effect of male spawning on fertilization success. In the first experiment, unfertilized eggs were placed in Nitex bags at three distances up and downstream from a spawning male. In the second experiment, unfertilized eggs were released and captured at three distances downstream from a sperm source. In both experiments, fertilization decreased with distance from the sperm source. The final experiment tested the influences of male size and population density on fertilization success; the effect of density was sign...

Social Control of Sex Change in the Bluehead Wrasse, Thalassoma bifasciatum (Pisces: Labridae).

Abstract: While the bluehead wrasse has long been used as a test species in sex allocation theory, there is no published evidence that sex change in this species is socially controlled. Here we show that removal of large terminal color phase (TP) males from local populations leads to sex and color change in the largest initial color phase (IP) females. In contrast, no sex changes occurred in control populations in which the TP males were handled but replaced, and in which only the IP males were removed. The response to removals was quite precise, resulting in a nearly one-to-one replacement of TP males. Large individuals that had been seen spawning as female males on the day prior to the manipulation, initiated male behaviors within minutes of the removal of the TP males and spawned in the male role the same day. Color changes were noted within a day and were distinct within four days. Sex change was verified by histological examination of the gonads of the changing individuals. All had functional testes, and all showed evidence of recent transition from the ovarian condition. Mature sperm can be produced in as little as eight days after the initiation of sex change.

Kinetics of Fertilization in the Sea Urchin Strongylocentrotus franciscanus: Interaction of Gamete Dilution, Age, and Contact Time.

Abstract: Determining fertilization success of free spawning organisms in the field requires knowledge of how eggs and sperm interact under varying encounter fre- quencies and durations. In the laboratory, we investigated the relative influence of sperm concentration, egg con- centration, sperm-egg contact time, and sperm age on fer- tilization in the sea urchin Strongylocentrotus francis- canus. Our results indicated that sperm concentration, sperm-egg contact time, sperm age, and individual vari- ability were sequentially the most important factors in- fluencing fertilization success. Egg concentration was not significant over the range tested. A theoretical model of fertilization (Vogel-Czihak-Chang-Wolf model) was used to estimate the two rate constants of fertilization kinetics: the rate constant of sperm-egg encounter and rate constant of fertilization. This model explained 9 1% of the variation in fertilization success, provided estimates of the rate con- stants involved in fertilization, and indicated the propor- tion (3%) of sperm-egg contacts that result in fertilization. Estimates of sperm swimming velocity and egg diameter were used to independently calculate the rate of sperm- egg encounter and confirm the predictions of the model. This model also predicts the non-significant effect of egg concentration on fertilization success found empirically.

Synaptic Background Activity Influences Spatiotemporal Integration in Single Pyramidal Cells.

Abstract: The standard one-dimensional Rall cable model assumes that the electrotonic structure of neurons does not change in response to synaptic input. This model is used in a great number of both theoretical and anatomicalphysiological structure-function studies. In particular, the membrane time constant, em, the somatic input resistance, Ri., and the electrotonic length are used to characterize single cells. However, these studies do not take into account that neurons are embedded in a network of spontaneously active cells. Synapses from these cells will contribute scantly to the membrane conductance, especially if recent evidence of very high specific membrane resistance, Rm = 100 kfi cm2, is taken into account. We numerically simulated the electrical behavior of an anatomically reconstructed layer V cortical pyramidal cell receiving input from 4000 excitatory and 1000 inhibitory cells firing spontaneously at 0-7 Hz. We found that, over this range of synaptic background activity, rm and R. change by a factor of 10 (80-7 msec, 110-14 Mfl) and the electrotonic length of the cell changes by a factor of 3. We show that this significantly changes the response of the cell to temporal desynchronized versus temporal synchronized synaptic input distributed throughout the neuron. Thus, the global activity of the network can control how individual cells perform spatial and temporal integration. activity on the spatial and temporal integrative properties of individual pyramidal cells and discuss the functional implications of our results, both for interpreting data from an in vitro (e.g., slice or culture) preparation as well as for cortical information processing strategies.

Spatial Information in the Three-Dimensional Fine Structure of an Aquatic Odor Plume

Abstract: Turbulent odor plumes play an important role in many chemically mediated behaviors, yet the fine scale spatial structure of plumes has not been measured in detail. With the use of a newly introduced microelectrochemical recording technique, we have measured, in some detail, the fine structure of an aquatic odor plume in the laboratory. We sampled a turbulent odor plume at 10 Hz with a spatial sampling area of 0.02 mm2, approximately that of a chemoreceptor sensillum of the lobster, Homarus americanus. A 3-min record was sampled at 63 different sites in 3 dimensions (x, y, z). As expected from time averaging models, the mean values of pulse parameters such as height and onset slope were greatest near the source. However, what cannot be described by time averaging models is the instantaneous distribution of pulses: periodically high peaks with steep concentration slopes (well above the local average and far above predictions from averaging models) can be found far away from the source. However, the probability of above-average pulse heights decreases with distance from the source in x, y, and z directions. The most intense odor fluctuations occurred along the x axis (the cross-sectional center of the plume). Odor profiles were analyzed with three different models of sensory filters; logarithmic, probability, and temporal filters. This analysis indicates that features contained within the plume structure could be used as directional cues for orienting animals. It remains to be demonstrated that animals use such sensory filters to extract biologically relevant spatial information from odor plumes.

Particle Captures and the Method of Suspension Feeding by Echinoderm Larvae

Abstract: Motivated by discrepancies between two recent descriptions of the suspension-feeding mechanism employed by echinoderm larvae, I describe particle captures by the larvae of seven species of temperate eastern Pacific echinoderms from four classes. When videotape recordings of free-swimming larvae clearing plastic spheres from suspension were analyzed, two modes of particle capture were observed to operate. The majority of captured spheres were caught at the peripheral ciliated band and then transported to the mouth, often by repeated capture on portions of the band progressively nearer to the mouth. This description is consistent with the ciliary reversal model of suspension feeding described by R. R. Strathmann. A small minority of captured spheres followed broad, curving paths directly into the larval mouth without interception at the ciliated band. These particle paths resemble those described by T. H. J. Gilmour. The videotape recordings also permitted a quantitative comparison of suspension feeding by ...

Embryonic Development of the American Lobster (Homarus americanus): Quantitative Staging and Characterization of an Embryonic Molt Cycle.

Abstract: The growth of a single brood of lobsters (Homarus americanus Milne-Edwards 1837) maintained at constant temperature is studied from the naupliar stage to hatching, and the sequence of appearance of morphological, anatomical, and behavioral characteristics observed. A percent-staging system based upon Perkins' eye index (1972) is presented, and ten equally spaced embryonic stages are illustrated and characterized at different levels of resolution: whole eggs, dissected embryos, antennulae and telsons. The tegumentary and setal changes in the telson show that a complete molt cycle takes place in the egg starting at about 12% embryonic development (E12%) with the molt of the nauplius into the metanauplius and ending just after hatching when the metanauplius molts into a first stage larva (L1, first zoea). At E30%, the cuticle begins to separate from the setae in the telson; this signals the start of Drach's (1939) stage D0 of the metanaupliar embryonic molt cycle. At that time, the first sign of organogenesi...

Enzymatic Characterization of the Morphogen Recognized by Agaricia humilis (Scleractinian Coral) Larvae.

Abstract: Larvae of the common Caribbean scleractinian coral, Agaricia humilis, are induced to settle and metamorphose by contact with specific crustose (nongeniculate) coralline red algae. This requirement for an exogenous trigger of settlement and metamorphosis has been shown to control the distribution of recruits of this coral in the natural environment. Results reported here demonstrate that the stringency and specificity of this larval requirement persist for at least 30 days following the planktonic release of the brooded larvae, thus enhancing both the capacity for dispersal of the larvae and the substratum specificity of their metamorphosis and recruitment. The inducer of metamorphosis is shown to be associated with an insoluble macromolecular carbohydrate. This molecule is found with the partially purified cell walls obtained from a morphogenetic crustose red alga, Hydrolithon boergesenii, or its associated microflora. Because two non-inductive crustose red algal species also lack the cell wall-associated inducer, the substratum specificity of metamorphosis is probably the result of larval recognition of this molecule. In procedures that should prove widely applicable to other systems, purified and highly specific enzymes were used to cleave the inductive cell wall-associated polysaccharides and to solubilize the active morphogen. Enzymes were also used as probes with which to identify essential structural features required for the morphogenetic activity. These enzymatic and related biochemical studies show that the morphogen is associated with, and may itself contain, a sulfated glycosaminoglycan that includes multiple N-acetylglucosamine and galactose residues. The larval receptors that recognize this complex carbohydrate cue may thus be related to lectins. The solubilized morphogen induces normal settlement, attachment, and the metamorphosis of A. humilis and A. tenuifolia larvae on clean polystyrene surfaces, and the larvae seem to have no other requirement. This effect is apparently specific for larvae of species induced to settle by the intact alga; larvae of the sympatric coral Tubastraea aurea are not induced by this chemical, or by the intact algal surface. A wide variety of other natural and synthetic sulfated polysaccharides and related polymers have little or no inductive effect on the A. humilis larvae, suggesting that the larval receptors involved in substratum recognition are highly specific. A similar high specificity of lectin- and sulfated polysaccharide-mediated recognition, and the resulting control of differentiation, has been observed in a wide variety of biological systems.

Predation Risk and Avoidance Behavior in Two Freshwater Snails

Abstract: We examined the predator avoidance behav- iors of two common freshwater snails, Physella virgata and Planorbella trivolvis, to the crayfish Procambarus simulans. In response to crayfish predation, the snails crawled above the waterline for several hours, then re- turned to the water. A significant size-dependent rela- tionship existed between crawlout (vertical migration above the waterline) and vulnerability to predation. All observed size classes of P. virgata, and small P. trivolvis, were vulnerable and crawled out in response to crayfish predation. Large, invulnerable P. trivolvis did not display any overt avoidance behavior, but relied instead on strong shell architecture for defense. We suggest that, in these species, crawling above the waterline reduces the proba- bility of an encounter between vulnerable thin-shelled snails and crayfish. This behavior is an adaptive response to predation.

The First Historical Extinction of a Marine Invertebrate in an Ocean Basin: The Demise of the Eelgrass Limpet Lottia alveus.

Abstract: Lottia alveus, a gastropod limpet once found only on the blades of the eelgrass Zostera marina from Labrador to New York in the western Atlantic Ocean, is the first marine invertebrate known to have become extinct in an ocean basin in historical time. The last known specimens were collected in 1929, immediately prior to the catastrophic decline of Zostera in the early 1930s in the North Atlantic Ocean. The brackish water refugium of Zostera throughout the decline was apparently outside of this gastropod's physiological range, and the limpet became extinct. Few marine invertebrates have habits as specialized and ranges and tolerances as narrow as did L. alveus. The fact that most marine invertebrates have large effective population sizes may account for their relative invulnerability to extinction.

Calcium-Proton Exchange During Algal Calcification

Abstract: Extracellular calcification by the giant celled alga Chara corallina may involve active Ca2+ extrusion from the cell in exchange for protons. The following evidence is presented: CaCO3 incrustations accrete largely along the inside, facing the cell, as revealed by X-ray microanalysis using Sr2+ and Mn2+ as tracers for new mineralization. Inward proton currents are inhibited by the Ca2+ transport antagonists Gd3+ and La3+. Low Ca2+ concentrations inhibit pH banding and photosynthesis, and solutions of low Ca2+ activity support more photosynthesis in the presence of additional buffered calcium. The ratio of calcification to photosynthesis in moderately alkaline solutions containing sufficient calcium remains stable at about 1.0 independent of solution Ca2+ concentration. Ion specific microelectrodes placed close to the calcified surface sometimes detect increases in Ca2+ activity coincident with decreases in proton activity. As the pCa of solution increases, the maximum pH observed at the alkaline surface increases, as does the maximum solution pH which supports electrochemical currents by the cell. Combinations of extracellular pH and pCa approach the calculated thermodynamic limits for ATP driven 2H+/Ca2+ exchange against the cytosol.

Sulfide-Driven Autotrophic Balance in the Bacterial Symbiont-Containing Hydrothermal Vent Tubeworm, Riftia pachyptila Jones.

Abstract: Hydrothermal vent tubeworms, Riftia pa- chyptila Jones, were maintained alive and studied on board ship using flow-through pressure aquaria. Simul- taneous measurements of 02, ZC02, ZH2S fluxes showed that the intact symbioses reach maximum rates of uptake of xC02 (>2 pmole g-' h-') at about 90 pA4 Z1H2S. Mea- surements were made of hemolymph and coelomic fluid I;C02, ZH2S, thiosulfate, pH, and hemoglobin concen- trations in worms kept under various conditions of O2 and ZH2S. Normal hemolymph pH appears to be about 7.5 and is not affected by ZH2S and ZC02 concentrations within the ranges observed. We conclude that Riftia is specialized to provide sulfide to its symbionts with min- imal interaction of sulfide with the animal metabolism. The uptake of sulfide is apparently by diffusion into the hemolymph, facilitated by the sulfide-binding properties of the hemoglobins. Both ZC02 and Pcoz are elevated in the hemolymph above their levels in the medium, al- though they are reduced under autotrophic conditions. Thus inorganic carbon is apparently concentrated from the medium into the hemolymph by an unknown mech- anism.

Computation in the Learning System of Cephalopods

Abstract: The memory mechanisms of cephalopods consist of a series of matrices of intersecting axes, which find associations between the signals of input events and their consequences. The tactile memory is distributed among eight such matrices, and there is also some suboesophageal learning capacity. The visual memory lies in the optic lobe and four matrices, with some re-exciting pathways. In both systems, damage to any part reduces proportionally the effectiveness of the whole memory. These matrices are somewhat like those in mammals, for instance those in the hippocampus. The first matrix in both visual and tactile systems receives signals of vision and taste, and its output serves to increase the tendency to attack or to take with the arms. The second matrix provides for the correlation of groups of signals on its neurons, which pass signals to the third matrix. Here large cells find clusters in the sets of signals. Their output re-excites those of the first lobe, unless pain occurs. In that case, this set of cells provides a record that ensures retreat. There is experimental evidence that these distributed memory systems allow for the identification of categories of visual and tactile inputs, for generalization, and for decision on appropriate behavior in the light of experience. The evidence suggests that learning in cephalopods is not localized to certain layers or "grandmother cells" but is distributed with high redundance in serial networks, with recurrent circuits.

Differential ingestion and digestion of bivalve larvae by the scyphozoan Chrysaora quinquecirrha and the ctenophore Mnemiopsis leidyi

Abstract: We investigated predation on bivalve veligers by the scyphozoan Chrysaora quinquecirrha and the ctenophore Mnemiopsis leidyi. We found that the medusa stage of C. quinquecirrha captures, but does not digest, veliger larvae: 99% of oyster veligers (Crassostrea virginica) caught by medusae were egested alive within 7 h of capture, and 98% survived for 24 h after egestion; 98% of oyster, mussel (Mytilus edulis), and clam (Mulinia lateralis) veligers placed on the oral arms of medusae were rejected; all bivalve veligers in field-collected medusae were closed and full of tissue. Our laboratory evidence suggests that the shell of larval bivalves probably offers protection from medusae: 23% of dead, open veligers were ingested by medusae compared with 0.7% of live, closed veligers; open veligers were retained longer than closed veligers; and tissue excised from recently settled oyster larvae was ingested and digested. Freeswimming C. quinquecirrha ephyrae ingested but did not digest veligers. By contrast, the benthic scyphistoma stage ingested 69% of veligers that contacted their tentacles and digested 48% of those ingested. Each scyphistoma consumed an average of 1 veliger/day at densities of 0.3 veligers ml-1. However, larval settlement was not reduced on oyster shells bearing scyphistomae. By contrast to the results on C. quinquecirrha, ctenophores egested only 4% of veligers alive, and 25% of the veligers in their gut contents were digested. Predation on veligers by ctenophores was estimated to be 0.2 to 1.7%/day in Chesapeake Bay. We conclude that C. quinquecirrha medusae are not important predators of bivalve veligers, but rather may reduce their mortality by consuming ctenophores, which do eat veligers.

A Breeding Population of the Western Pacific Crab Hemigrapsus sanguineus (Crustacea: Decapoda: Grapsidae) Established on the Atlantic Coast of North America

Abstract: The west Pacific grapsid crab Hemigrapsus sanguineus was found in the United States for the first time in 1988. Additional crabs were recovered in 1990 from Townsends Inlet and Cape May Harbor, New Jersey (22 males, 16 females), and four of the females collected from June through September were ovigerous. Thus, H. sanguineus has now established itself in southern New Jersey, the first well-documented case of an exotic brachyuran becoming established along the east coast of the United States.

The Physiological Effect of Aureococcus anophagefferens ("brown tide") on the Lateral Cilia of Bivalve Mollusks.

Abstract: The "brown tide" alga, Aureococcus anophagefferens, had no effect on the activity of the lateral cilia of isolated gills of the bivalve mollusks Argopecten irradians, Geukensia demissa, and Mya arenaria. A. anophagefferens caused a significant decrease in the activity of lateral cilia of five other bivalve mollusks, Crassostrea virginica, Ostrea edulis, Mercenaria mercenaria, Modiolus modiolus, and Mytilus edulis. Exposure of isolated gills of M. edulis to the water from which A. anophagefferens had been removed, or to polystyrene beads at the same concentration as A. anophagefferens, had no effect upon the activity of the lateral cilia. Thus, the inhibition of the lateral cilia is not caused by a compound excreted into the water, nor is it the result of the high density of cells. The response of lateral cilia to dopamine was identical to the response to A. anophagefferens; lateral cilia that were inhibited by dopamine were also inhibited by A. anophagefferens. Pretreatment of the gills of M. edulis with the dopamine antagonist ergometrine blocked the inhibition of the lateral cilia by both dopamine and A. anophagefferens. A water-soluble inhibitory compound was released from A. anophagefferens by exposing the cells to amylase, and then removing the cells by filtration. The effect of this inhibitory compound was also blocked by ergometrine. We propose that the isolated gills are digesting the extracellular coat of A. anophagefferens releasing a water soluble dopamine-mimetic compound that causes inhibition of lateral cilia.

How Do Temperature and Salinity Affect Relative Rates of Growth, Morphological Differentiation, and Time to Metamorphic Competence in Larvae of the Marine Gastropod Crepidula plana?

Abstract: The influence of environmental conditions on rates of larval growth has been documented many times for various marine mollusks. But the factors that influence rates of morphological and physiological differentiation, particularly the rate at which larvae within a population become competent to metamorphose, remain obscure. In four experiments, we reared larvae of the gastropod Crepidula plana at 29°C, 25°C, and 20°C at 30 ppt salinity, and in two other experiments, in salinities between 4-30 ppt at 25°C. Rates of shell growth and morphological differentiation, and rates of becoming competent within populations were recorded. Larvae were considered to be competent to metamorphose if they could be stimulated to metamorphose by exposure to a high concentration of KCl (20 mM above ambient). Larvae consistently became competent faster at higher temperatures, but in only one of four experiments did temperature also consistently increase the rates of growth and morphological differentiation. Larvae took longer to become competent when reared at lower salinities, but the effects were poorly predicted by the influence of salinity on rates of growth and morphological differentiation. Competent larvae could also not be recognized by shell length; many individuals were competent at shell lengths of 600-800 μm, while many other individuals were still not competent at sizes exceeding 1000 μm. At 29°C, many individuals became competent at smaller sizes than those reared at lower temperatures. Presence of gill filaments or shell brims also did not correlate with individual metamorphic competence. The data suggest that growth rate, rate of morphological differentiation, and time required for larvae of C. plana to become competent can be uncoupled markedly by shifts in rearing conditions.

Embryogenesis and Larval Development of the Asteroid Patiriella regularis Viewed by Light and Scanning Electron Microscopy

Abstract: The sea star Patiriella regularis (Verrill, 1867) has indirect development through bipinnaria and brachiolaria larvae. Development of this species is typical of asteroids with planktotrophic larvae and takes 9-10 weeks. The embryos develop through a wrinkled blastula and hatch as early gastrulae. In contrast to most asteroids, a third enterocoel forms on the left side of the stomach of the bipinnaria. This structure gives rise to the left posterior coelom; its significance is discussed. We suggest that this coelom is homologous to the trunk coelom in enteropneust embryology. The surface features of the larvae were examined by scanning electron microscopy. Newly hatched gastrulae are covered by cilia, and the bipinnaria have bands of cilia that follow the contours of the larval processes. A previously undescribed plug-like structure positioned on the post-oral surface appears to function as a seal for the mouth. Brachiolaria larvae have three brachiolar arms and a centrally located adhesive disc. Each arm ...

Autotomy in Blue Crab (Callinectes sapidus Rathbun) Populations: Geographic, Temporal, and Ontogenetic Variation.

Abstract: Blue crab (Callinectes sapidus Rathbun) populations were examined at four sites in Chesapeake Bay and three additional sites along the southeastern Atlantic coast and Gulf of Mexico; the aims were to assess the incidence of limb autotomy and to determine whether injury patterns varied temporally, geographically, and ontogenetically. These data, which include four years of information from one site (Rhode River, Maryland, a subestuary of central Chesapeake Bay), make this study the most extensive and intensive survey of limb autotomy yet conducted in arthropods. A substantial percentage (17-39%) of the blue crab populations were either missing or regenerating one or more limbs, suggesting that autotomy is an important mechanism for their survival. The frequency of limb autotomy varied, both within and between years, and over broad geographical scales. Injury levels were generally correlated positively with crab size. Limb autotomy was independent of sex and molt stage, and frequencies varied little among s...

Opioid Systems and Magnetic Field Effects in the Land Snail, Cepaea nemoralis.

Abstract: Accumulating evidence shows that magnetic fields can affect a variety of opioid-mediated behavioral and physiological functions. The idea that endogenous opioids are involved in the mediation of fundamental behavioral responses in invertebrates is also gaining support. Evidence exists for opioid involvement in the mediation of nociceptive and antinociceptive ("analgesic") responses of the land snail, Cepaea nemoralis, and other mollusks, in a manner comparable to that in vertebrates. Exposure to various magnetic stimuli, including weak 60 Hz magnetic fields, has significant inhibitory effects on exogenous opiate-induced analgesia and endogenous opioid-mediated nociceptive responses of Cepaea in a manner analogous to that described for vertebrates. These effects of the magnetic stimuli are evident under both laboratory and natural conditions and include disruptions of the day-night rhythms of opioid-mediated nociception. These similar effects in Cepaea and rodents raise the possibility of a phylogenetic co...

The Function of Surface Sclerites in Gorgonians (Coelenterata, Octocorallia).

Abstract: Branches of a variety of species of gorgonians representing the common sclerite types were fixed in flexed (bent) positions and examined by scanning electron microscopy. To determine changes in position of sclerites associated with extension and compression, appropriate measures of sclerite density and angle were taken. From these and other data, probable function was hypothesized. Surface sclerites (spicules), called clubs, modify colony flexion by limiting compressibility of the outer cortex when they contact each other. Scaphoids progressively limit extension as their ventral tubercle belts engage similar tubercles on underlying spindles. Radiates limit both extension and compression by catching and locking up after a fixed, free-slide distance. Double-heads severely limit both extension and compression through random orientation of closely packed, spiny protruberences that preclude almost any freedom of movement. Unilaterally spinose spindles act as drawbridge-like, protective covers for polyps. They play no apparent role affecting whole colony mechanics. Possible roles of sclerites as mechanical systems are discussed briefly.

Growth, Size Rank, and Maturation of the Freshwater Prawn, Macrobrachium rosenbergii: Analysis of Marked Prawns in an Experimental Population

Abstract: For four months we marked and followed through female maturation and adult male mophotypic differentiation, the growth of all 150 individuals in an experimental population of Malaysian giant freshwater prawns (Macrobrachium rosenbergii) Small immature female prawns had high growth rates Growth of female prawns nearly ceased after maturation This compensatory growth process produces adult females having a unimodal, symmetrical size distribution with a mean above the size threshold for maturation (about 18-26 g) The small male morphotype has a low growth rate, while the orange claw male morphotype has a high growth rate As the orange claw males transform to the blue claw morphotype, growth ceases Examination of changes in size rank during the maturation process supported the leapfrog phenomenon The fastest growing, largest orange claw male is the first to metamorphose to the blue claw morphotype (at a size of 35 g) As other orange claw males exceed this size, they transform in a sequential process so that the most recent blue claw male is generally the largest blue claw male in the population Thus, growth of males is depensatory throughout the process of morphotypic differentiation, leading to a wide size range of orange and blue claw males The leapfrog phenomenon is discussed in terms of the reproductive success of the blue claw males and compared with related growth processes in male poeciliid fishes Im- plications of this growth process for aquacultural pro-

Short-Term Metallothionein and Copper Changes in Blue Crabs at Ecdysis

Abstract: We have previously demonstrated that the small metal-binding protein, metallothionein (MT), plays an important role in the metabolism of Cu and Zn during the molt cycle of the blue crab, Callinectes sapidus. To further delineate the role of MT in the regulation of both metals, the distribution of copper and zinc was examined immediately after ecdysis in the blue crab. Hemolymph, digestive gland, and stomach were analyzed, by atomic absorption spectrophotometry (AAS), for total metal concentration in crabs at different molt stages, from premolt (D3) through paper shell (B2), and including intermolt (C4). Cytosolic extracts were prepared from digestive glands of individual crabs and analyzed, by gel filtration chromatography and AAS, for MT, copper, and zinc. The short-term changes in metal concentrations in the tissues, and those in MT and metals in the cytosol were dramatic. Transient changes in the metals bound to MT correlated well with the loss of copper from the hemolymph and the digestive gland. The ...

The Induction of Carbonic Anhydrase in the Symbiotic Sea Anemone Aiptasia pulchella

Abstract: The activity and nature of carbonic anhydrase (CA, EC 4.2.1.1.) was measured and described in the tropical sea anemone Aiptasia pulchella. The hypothesis that high CA activity in animal tissue is induced by the presence of symbiotic algae was tested. CA activity was positively correlated with the number of symbiotic di- noflagellates (zooxanthellae) present. CA activity in apo- symbiotic anemone tissue was 2.5 times lower than that in control symbiotic animals or in aposymbiotic animals repopulated with algae. Polyclonal antisera against human CA were used to probe for the presence of CA in both symbiotic and aposymbiotic anemone tissue, and in freshly isolated and cultured zooxanthellae. The resulting immunoblots showed one band with a molecular weight of 30 kDa in symbiotic animal tissue and control mam- malian CA lanes, no bands in the aposymbiotic animal lanes, and one band at a molecular weight of 22.5 kDa in freshly isolated and cultured zooxanthellae lanes. Be- cause no 22.5 kDa band was detected in the symbiotic animal tissue lanes, the high CA activity found in sym- biotic animal tissue is considered to be due to the induc- tion of animal enzyme by the presence of algae. The lack of any band in the aposymbiotic lanes further supports the hypothesis that CA activity in A. pulchella is induced by the presence of algae. water pool to satisfy the high carbon demand. CO2 is the Ci species preferred as a substrate for carbon assimilation by ribulose bisphosphate carboxylase/oxygenase (RU- BISCO) in the zooxanthellae. Yet at an ambient pH of 8.2-8.3, Ci in seawater is present mostly as HC03-. Ad- ditionally, the movement of HC03- across unstirred boundary layers and the several animal and algal mem- branes to the site of photosynthesis could be relatively slow (Kerby and Raven, 1985). Weis et al. (1989) hypothesize that the supply of COZ for photosynthesis in algal/cnidarian symbioses is aug- mented by the presence in the cnidarian tissue of carbonic anhydrase (CA, EC 4.2.1. l.), an enzyme that catalyzes the inter-conversion of HC03- and CO2 . In the 22 species of cnidarians examined, CA activity in the animal tissue of symbiotic species was, on average, 29 times higher than in non-symbiotic species. In the symbiotic species, CA activity in the animal fraction was 2-3 times higher than that in the algae. These results suggest that CA activity in animal tissue is related to the presence of zooxanthellae. Two other findings indicate that CA activity in sym- biotic animal tissue is related to the presence of algae. First, CA activity is correlated with habitat irradiance in

Reproductive Ecology of an Intertidal Brachyuran Crab, Sesarma sp. (nr. reticulatum), from the Gulf of Mexico

Abstract: The natural history and reproductive ecology of a presently undescribed marsh crab endemic to the Gulf of Mexico were studied in both the laboratory and the field. Weekly sampling of populations in coastal Louisiana allowed us to determine the periodicity of molting and ovarian development, as well as the seasonal variation in egg laying and size of individual egg masses. Timing of molt, egg laying, and egg hatching were monitored in individual females under simulated tidal cycles in laboratory mesocosms. Peak periods of reproductive activity in Louisiana coincide with favorable temperatures and elevated primary productivity in coastal waters. Size cohort and fecundity differ between these periods. Egg-laying, larval release, and molting observed in individual females in the laboratory and extrapolated dates of egg-laying and larval release for those in field samples exhibit a semilunar influence throughout the season. Female receptivity to mating is tied to egg-laying. Rate of embryonic development was associated with decreases and increases in egg size. Behavior related to larval release is described. Adaptive significance in relation to the intertidal marsh habitat is discussed.

Immunochemical Detection of Predation on Ciliate Protists by Larvae of the Northern Anchovy (Engraulis mordax).

Abstract: New approaches are needed for investigating planktonic prey-predator interactions in situ, free from enclosures and long term incubations. Lengthy incubations can lead to several artifacts, including selective mortality of planktonic organisms (1) lysis of some taxa upon fixation (2), alteration of prey-predator encounter rates through perturbations of the turbulent flow field (3) and modification of natural search and avoidance behaviors of predators and prey (4). Microscopic analysis of the gut contents of predators is a feasible alternative only if prey leave digestion-resistant hard parts. Here we describe a different approach involving immunochemical methods. We report the development and first application of an immunoassay that permits detection of predation on soft-bodied, nonloricate ciliates (Strombidium sp.). Polyclonal antibodies raised against Strombidium sp. recognize both intact ciliates and partially assimilated ciliate antigens occurring in a predator’s gut. We demonstrate, by both immunochemical and conventional methods, unequivocal predation by first-feeding larvae of the northern anchovy (Engraulis mordax) on nonloricate ciliates. The intensity of the immunochemical reaction, quantified by enzymelinked dot blots and reflection densitometry, is proportional to prey density and to the predator’s ingestion rate. Polyclonal antisera were produced in New Zealand white rabbits (5) against Strombidium sp. cultured on a diet of the bacterium Vibrio natriegens (6). Immunoglobulin G (anti-Strombidium IgG) was isolated from the antiserum by precipitation in 45% (w/v) ammonium sulfate, desalted by gel filtration, then fractionated by diethylaminoethyl ion exchange chromatography. Detailed

Genetic Variation in the Timing of Gonadal Maturation and Spawning of the Eastern Oyster, Crassostrea virginica (Gmelin)

Abstract: The gonadal cycles of four groups of eastern oysters, Crassostrea virginica (Gmelin), including native stocks collected that year and inbred strains (reared in Delaware Bay for 5-6 generations) from both Long Island Sound and Delaware Bay, were compared in Delaware Bay in 1987. Inbred strains resembled their respective native stocks; both Long Island groups initiated gonadal development and spawning about one month earlier and spawned over a shorter duration than both Delaware Bay groups. Analysis of covariance revealed that the effect of time on gonadal development was statistically different (P ≤ 0.05) for all between-location group comparisons, but not for the two within-location comparisons. Thus, after six generations of inbreeding in Delaware Bay, Long Island oysters maintained their characteristic pattern of gonadal development and spawning, indicating the existence of genetically different environmental requirements for gonadal maturation between the two locations.

Responses of a Rocky Shore Gastropod to the Effluents of Predatory and Non-predatory Crabs: Avoidance and Attraction

Abstract: Laboratory experiments revealed that the rocky shore gastropod, Nucella lamellosa (Gmelin), could discriminate between the effluents of predatory and non- predatory crabs. N. lamellosa turned away from seawater that had passed over the large predatory crab, Cancer pro- ductus Randall. This avoidance behavior was observed in snails from two localities that, based on differences in shell form, presumably experienced different levels of predation intensity. The scent of the non-predatory crabs Pugettia producta (Randall) and Lopholithodes mandtii Brandt had no effect on the turning behavior of snails from either site. Surprisingly, snails from both sites were attracted to the scent of a small shore crab, Hemigrapsus nudus (Dana), but moved at random in response to a common prey item Balanus glandula Darwin. These results suggest that N. lamellosa can assess from a distance the relative risks posed by different species of crabs, and respond appropriately. The unexpected attrac- tion to H. nudus suggests that N. lamellosa may use this effluent to home in from a distance on potential refugia, because H. nudus are often associated with crevices and the undersides of boulders where N. lamellosa would be less vulnerable to larger predators.

Oxidative Breakdown Products of Catecholamines and Hydrogen Peroxide Induce Partial Metamorphosis in the Nudibranch Phestilla sibogae Bergh (Gastropoda: Opisthobranchia)

Abstract: Veliger larvae of the aeolid nudibranch Phestilla sibogae metamorphose in response to a soluble factor from their prey coral, Porites compressa. Metamorphosis begins with destruction of the velum, a ciliated structure used for swimming and feeding. Previous investigation had shown that P. sibogae larvae exposed to certain catecholamines lost the velum, but then failed to complete any subsequent steps characteristic of natural coral-induced metamorphosis. Because catecholamines oxidize rapidly in seawater, we have re-examined morphogenic effects of catecholamines using superfusion chambers that allow periodic replacement of test solutions. We report that fresh, unoxidized catecholamines do not induce velar loss, but that this morphogenic activity develops in aged, oxidized solutions of a variety of catecholamines and other catechol compounds. Evidence is presented that this activity is attributable to hydrogen peroxide, a byproduct of catechol autoxidation. Hydrogen peroxide induces velar loss at 10-4 M. The possible relationship of peroxide-induced velar loss to natural coral-induced metamorphosis is discussed.

Settlement, refuges, and adult body form in colonial marine invertebrates: a field experiment

Abstract: We examine the relationship between adult body form (sheet vs. arborescent) and larval settlement in colonial animals. Because thin sheet forms are more susceptible to overgrowth than arborescent forms, we predict that larvae of sheet forms should preferentially settle in refuges from competitors. On both natural and artificial substrata, the larvae of the sheet form (Mem- branipora membranacea) settled more often on high spots, which could serve as refuges from competition. The ar- borescent forms (Bugula neritina and Distaplia occiden- talis) settled around the bases of bumps more frequently than would be expected by chance. For many arborescent forms, their most vulnerable periods are the days im- mediately following settlement, when individuals can be consumed easily by predators or dislodged by physical disturbances. Settlement in a crevice (base of a bump) would provide protection from the bulky mouthparts of predators. Moreover, dislodgment would be less likely than if settlement had occurred on flat locations, such as the tops of bumps or the areas between bumps.