Sand Dollar Dendraster Excentricus Research Articles

Uptake of free amino acids by bacteria-free larvae of the sand dollar Dendraster excentricus.

Larvae of Dendraster excentricus were produced by collecting gametes and carrying out fertilization under aseptic conditions. Since gametes are free of bacteria in the gonad, bacteria-free (axenic) suspensions of larvae result. Net rates of entry of 14 amino acids and the rate of production of ammonia were simultaneously determined by high-performance liquid chromatography. The net rates of uptake of neutral amino acids were an order of magnitude greater than rates for basic and acidic amino acids. Influx of 14C-labeled leucine, arginine, and glutamate accurately reflects the net entry rate of these substrates. Uptake of amino acids by axenic suspensions of larvae was compared with uptake by suspensions prepared without aseptic precautions. There was no significant difference in net uptake of the 14 amino acids or in the pattern of oxidation and assimilation of [14C]leucine during short-term experiments of 4-h duration or less.

Factors determining the distribution of the sea pansy, Renilla kollikeri, in a subtidal sand-bottom habitat.

The biological and physical factors that affect the distribution of the subtidal, epibenthic, sand-dwelling cnidarian Renilla kollikeri along a depth gradient from 2 to 13 m were determined by manipulative field and laboratory experiments. The sea pansy's nearshore distributional limit (2.5 m in depth) was set by the animal's inability to remain anchored on the bottom in the face of increasing wave surge associated with shallow water. Renilla was outcompeted for space by the sand dollar Dendraster excentricus in an area between 6 and 9 m in depth and was largely excluded from the substrate when sand dollar densities exceeded 350/m2. Predator-prey interactions also influence the Renilla distribution. The asteroid Astropecten brasiliensis feeds on and removes Renilla 40 mm and less in diameter from areas seaward of the sand dollar bed (9 m in depth). Astropecten did not forage in the shallow area where Renilla was most abundant because of its intolerance to wave surge and because of its difficulty in crossing the sand dollar bed. The nudibranch Armina californica fed on Renilla throughout the depth gradient but did not remove colonies greater than 20 mm in diameter because of the Armina- specific escape behavior of Renilla. The foraging behavior of Armina was also curtailed by strong surge conditions. The nearshore area (3-6 m in depth) of high Renilla density was a refuge in which animals that had settled from the plankton could escape predation. As the animals grow they lose their ability to anchor in the substrate in shallow water and thus move into deeper water. The results of multiway interactions among sets of three species, particularly the beneficial results of the competitive interaction with Dendraster in light of the activities of the predators are discussed with reference to the abundance and distribution of Renilla.

Rhythmic Topography in a Mesotidal, Low-Wave-Energy Environment

ABSTRACT The intertidal zone in Craig Bay extends 1200 m offshore making it the broadest non-estuarine tidal flat on the east coast of Vancouver Island, British Columbia, Canada. Superimposed on the low gradient foreshore (1:360) are up to fourteen low amplitude (<=0.6 m) ridges with an average wavelength of 86.3 m. These are permanent fixtures of the intertidal zone exhibiting considerable stability in both form and position. They are generally symmetrical in cross section and in no instance is a landward slip face evident. The ridges have developed in medium-to-fine sand atop a coarse deltaic platform. The thickness of this surficial sand unit is often equal only to the height of the ridges, and the gravel sustrate is frequently exposed in the depressions. The morphology, sediments, and hydraulic environment of this rhythmic foreshore were examined to provide insight into the factors controlling ridge development and maintenance. Although the maximum tidal range exceeds 5.0 m, tidal currents are of limited importance; only in the major runnels are velocities sufficient to initiate sediment transport. Waves within the Strait of Georgia are locally generated (H1/3 <= 3.0 m, T1/3 <= 7.0 s) and appear to the the prime agent responsible for the formation and maintenance of this variant of ridge and runnel morphology. The dominant bedform across the intertidal zone is the wave-formed ripple, although current ripples may locally predominate. Small-scale cross-stratification, which is associated with these bedforms, is the most common primary physical sedimentary structure in the surficial sand unit. However, a large proportion of the cores were structureless. This is attributed to bioturbation by sand dollars (Dendraster excentricus) and to a lesser extent to air entrapment and water escape.

Larval abundance and recruitment of the sand dollar Dendraster excentricus in Monterey Bay, California, USA

Seasonal abundance of planktonic larvae of the sand dollar Dendraster excentricus was determined in Monterey Bay, California, USA. Larvae were counted from two offshore stations and also over a coastal sand dollar bed, and these data were compared with settlement in the sand dollar bed, with adult population structure and with adult reproductive condition. These measurements were made during the period July 1978 to October 1980 and in October 1981. Sand dollar larvae were most abundant in the plankton during the summer, a period when phytoplankton productivity tended to be high and currents were relatively slow and variable. In some years, small-scale current variations appeared to prevent many larvae in the open bay from reaching the nearshore sand dollar beds; however, in other years, massive shoreward transport of the larvae evidently did occur, since the adult population in the sand dollar bed exhibited a mode in size, indicating a large settlement. A comparison of settled individuals in 1980 and the adult size-frequency distribution in 1981 gives an estimated mortality rate of 88% yr^(-1) for early juveniles of D. excentricus.

Effect of 3′-deoxyadenosine (cordycepin) on the early development of the sand dollar, Dendraster excentricus

The embryos of the sand dollar Dendraster excentricus have been examined with regard to their ability to undergo the early events of larval development in the presence of cordycepin, a reported inhibitor of RNA adenylylation. It has been shown that all the morphogenetic events from hatching to prism are inhibited by cordycepin at a concentration of 25 μg/ml, while the aspects of development prior to hatching (cleavage, blastulation, and the formation of cilia) are not affected by cordycepin. The period of sensitivity of each developmental event to cordycepin has been determined; for the early developmental processes this period substantially precedes the event, while for later processes there is a closer temporal association. In embryos treated with cordycepin, DNA synthesis and cleavage are unaffected prior to hatching, but subsequently are blocked, whereas respiration and total RNA synthesis per cell remain unaffected.

Reproductive cycles in two populations of the Pacific sand dollar Dendraster excentricus

Populations of the sand dollar Dendraster excentricus (Eschscholtz) occur in different habitats along the west coast of the USA. Two subtidal populations from the San Diego, California, area, one from an exposed coastal location and a second from a protected tidal channel, were compared for several aspects of their population and reproductive biology. Both populations demonstrated a similar schedule of reproductive activity with peak gonad volumes occurring in the early spring. However, population reproductive readiness and individual reproductive effort and size varied considerably between the populations; individuals in the protected tidal channel were larger and produced proportionately larger gonads with ripe gametes for a longer period, than those on the exposed coast. The differences between the populations are explained by the greater demands of the rigorous exposed habitat for maintenance at the cost of reproductive effort and growth.

Transcripts of Reiterated DNA Sequences in the Determination of Blastomeres and Early Differentiation in Echinoid Larvae

RNA transcribed from repetitive DNA sequences during the early cleavages and RNA present in unfertilized eggs of the sand dollar Dendraster excentricus have been studied by means of molecular hybridization. Egg RNA, capable of competing in the hybridization reactions, is localized on particles in the cytoplasm. RNA populations synthesized during the first four cleavages are found to be very similar to egg RNA, are nuclear in origin, heterogeneous in size, and probably contain histone mRNA. Egg-type RNAs are present, and are synthesized in embryos throughout early development; the relative amounts of these RNAs increase to the late blastula stage and then decrease to a low level at the prism stage. Blastomeres were separated at the 16-cell stage to yield pure preparations of micromeres and a meso-plus macromere fraction. Competition-hybridization experiments showed that egg-type RNA populations present in embryos at the fourth cleavage were distributed almost equally in the isolated micromere and meso-plus macromere fractions. However, experiments with H3-RNA extracted from micromeres, obtained after pulse-labeling the 16-cell stage embryos, showed qualitatively new transcriptions from repeated DNA sequences. Such new transcripts could not be detected in H3-RNA isolated from the meso-plus macromere fraction. These observations are discussed in relation to current information on the synthesis of RNA and its involvement in early echinoderm development.

A NEW DESCRIPTION OFSYNDESMIS DENDRASTRORUM(PLATYHELMINTHES, TURBELLARIA), AN INTESTINAL RHABDOCOEL INHABITING THE SAND DOLLARDENDRASTER EXCENTRICUS

1. Syndesmis dendrastrorum occurs in the intestine of the sand dollar Dendraster excentricus.2. A detailed redescription of S. dendrastrorum is presented, clarifying the internal relationships of the reproductive organs.3. The most distinguishing characteristics of this species include single ovaries and testes occurring in a cis relationship, and a large male antrum.4. Juvenile stages of S. dendrastrorum possess only a digestive system and lack reproductive organs.

The Enrichment of Egg-type RNA in Cleavage Stage Embryos of the Sand Dollar Dendraster excentricus

RNA populations synthesized during the first four cleavages of the sand dollar Dendraster excentricus were almost entirely egg-type as determined by RNA-DNA hybridization under conditions which measure repetitive DNA sequences. The relative concentrations of these egg-type RNA populations increased progressively up to the late blastula stage, then decreased, beginning at mesenchyme blastula, to a low level at the early prism stage. The egg-type RNA populations were transcripts of nuclear DNA, were heterogeneous in size and were species specific. RNA-DNA duplexes containing this RNA were heterogeneous with respect to thermal stability.

Sand Dollar: A Weight Belt for the Juvenile

Juvenile sand dollars (Dendraster excentricus) selectively ingest heavy sand grains from the substrate and store them in an intestinal diverticulum which may function as a weight belt, assisting the young animal to remain in the shifting sandy environment. The sand disappears from the diverticulum when the animal reaches the length of 30 millimeters.

The appearance of α-amylase activity during gut differentiation in sand dollar plutei

α-Amylase activity appears during gut differentiation of plutei of the sand dollar Dendraster excentricus. The activity increases coincidentally with that of a β-1, 3-glucanase. The α-amylase appears to have maltase activity. Glucose in the surrounding seawater depresses the increase in β-glucanase activity but does not affect the normal α-amylase increase. This suggests that the glucose repression of β-glucanase activity may be quite specific and not result from some general effect of glucose on metabolism. Sodium dodecyl sulfate-acrylamide gel electrophoresis resolves the larval α-amylase into components of 52,000 and 76,000 molecular weight. The α-amylase from the intestines of adult sand dollars resolves as a single component of 57,000 molecular weight. The pH curves for adult and larval α-amylases are also different and it is probable that adult and larval α-amylases are different proteins.

The appearance of β-1,3-glucanohydrolase activity during the differentiation of the gut of sand dollar plutei

The appearance and the increase of the activity of a β-1,3-glucanohydrolase (β-glucanase) was found to be coincident with the differentiation of the gut of the pluteus of the sand dollar Dendraster excentricus. The β-glucanase is extremely stable and is not inactivated by 2.5% sodium dodecyl sulfate (SDS) or trypsinization. The enzyme releases glucose from laminarin, a polysaccharide composed mainly of β-1,3-linked glucose. The β-glucanase activity can be eluted from acrylamide gels containing SDS. The enzyme is bound to membranes or particles that sediment readily, and SDS or sodium deoxycholate is needed to solubilize the activity. The increase in β-glucanase activity during development was completely blocked by cycloheximide; 10 hr after removal of the drug, enzyme activity rises again at more than twice the rate of the control and attains a specific activity 15% higher than the controls. Larvae recovered from cycloheximide also show an increase in total RNA synthesis compared to controls. It is postulated that control mechanisms that regulate the transcriptional and translational events necessary for β-glucanase synthesis have been altered by cycloheximide. β-Glucanase accumulation is depressed by treating plutei with actinomycin D. The pH optimum of the larval β-glucanase is 6.0 while that of the adult is 5.5. The larval β-glucanase resolves into a major and minor peak of 50, 500, and 75,300 apparent molecular weight. The adult β-glucanase migrates as a single peak of 75,300 MW. It is possible that both isozymes are aggregates of a 25,000 MW unit that is inactive in these assay conditions. Alternatively, it is proposed that different sets of β-glucanase genes are operative in larval and adult stages and that a transition from larval genomic to adult genomic activity must occur at metamorphosis.

Field Observations of Dendraster excentricus, a Sand Dollar of Western North America

Observations were made on behavior, distribution, and biotic relationships of the sand dollar Dendraster excentricus along the Pacific coast of California and Baja California, Mexico. Populations occur on sandy bottom in bays, tidal channels, and along the outer coast. Orientation and feeding behavior, which are related to water movement, vary between populations in the different habitats. In sheltered bays, where there is relatively little water movement, sand dollars remain in shallow water, frequently move, and lie flat on the bottom where they feed on deposited material. In tidal channelsand protected areas of the outer coast, habitats with moderate water movement, adults are more stationary, usually are in an inclined position, and feed primarily on suspended material. Density estimates and aggregation values are greatest in these populations. In outer-coast areas consistently exposed to heavy seas, where water movement is greatest, sand dollars are usually buried, and presumably feed on deposited material. Two types of distribution patterns occur in populations along the protected outer coast. In one type, the populations run parallel to shore as dense bands, and maintain a characteristic pattern that is reformed when disrupted by occasional heavy seas. Usually juveniles are most abundant shoreward, and move seaward with age. The outer margin of these populations is well-defined in 4-12 m of water, and here the largest individuals and greatest densities occur. Most of our observations are of these populations. The other type of distribution is similar, except that it extends into deeper water, and below about 10-15 m; individuals become progressively smaller with depth. Various other organisms coexist with the sand dollars, many of them using the inclined sand dollars as shelter or a hard substrate. Known predators include fishes, crabs and sea stars. Fouling by the barnacle Balanus pacificus also may contribute to sand-dollar mortality. At present, separate taxa for the ecologically different populations of D. excentricus are not justified.

The mitotic behavior of chromosomes in echinoderm eggs following incorporation of bromodeoxyuridine

1. 1. When eggs of the sand-dollar Dendraster excentricus are cultured in concentrations of bromodeoxyuridine (BUDR) above 1 × 10 − M, cleavage produces a disordered mass of cells, but a blastula is not formed. The effect is completely antagonized by an adequate concentration of thymidine. 2. 2. The developmental abnormality is attributed to a disturbance of the separation of sister chromosomes at anaphase. Chromosome bridges are formed, which persist as the cleavage furrow divides the cytoplasm. As the interphase nucleus is organized from the two bridged groups of chromosomes, it takes the apparent form of a single nucleus extending through the furrow as a nuclear bridge. At the next prophase, the chromosomes in the bridges recondense in extended form in which they came out of the previous division. The original bridges are broken at this next division, as new bridges form through the new furrows. The developmental abnormalities are attributed to the abnormalities of the distribution of chromosomes. 3. 3. In eggs of several species of sea urchins, the nuclear bridges are not formed as a rule, and early development to the blastula stage is normal. 4. 4. Hypotheses relating the chromosome separation to the properties of DNA which has incorporated BUDR are considered.

CLEAVAGE OF THE SEA URCHIN EGG RECOVERED FROM THE CLEAVAGE-BLOCKING EFFECT OF DEMECOLCINE***

EmbryologiaVolume 7, Issue 1 p. 68-80 Free Access CLEAVAGE OF THE SEA URCHIN EGG RECOVERED FROM THE CLEAVAGE-BLOCKING EFFECT OF DEMECOLCINE*** NAOMASA KOBAYASHI, NAOMASA KOBAYASHI Zoological Institute, College of Science, University of Kyoto, KyotoSearch for more papers by this author NAOMASA KOBAYASHI, NAOMASA KOBAYASHI Zoological Institute, College of Science, University of Kyoto, KyotoSearch for more papers by this author First published: January 1962 https://doi.org/10.1111/j.1440-169X.1962.tb00160.xCitations: 7 * Contributions from the Seto Marine Biological Laboratory, No. 368. ** This work was supported by a grant in Aid for Fundamental Scientific Research of the Ministry of Education. Nos., 4066-4068. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Literature Beams, H. W. and T. C. Evans, 1940. Some effects of colchicine upon the first cleavage in Arbacia punctulata. Biol. Bull., 79, 188– 198. Gray, J., 1931. A text-book of experimental cytology. Cambridge University Press, London . Harvey, E. B., 1927. The effect of lack of oxygen on sea urchin eggs. Biol. Bull., 52, 147– 160. Kobayashi, N., 1961. Effect of demecolcine upon cleavage of sea urchin eggs and their reversibility. Mem. Coll. Sci. Univ. Kyoto, Ser. B, 28, 1– 9. Mazia, D., 1958. SH compounds in mitosis. I. The action of mercaptoethanol on the egg of the sand dollar Dendraster excentricus. Exp. Cell Res., 14, 486– 494. Mazia, D., and A. M. Zimmerman, 1958. SH compounds in mitosis. II. The effect of mercaptoethanol on the structure of the mitotic apparatus in sea urchin eggs. Exp. Cell Res., 15, 138– 153. Mazia, D., and P. J. Harris and T. Bibring, 1960. The multiplicity of the mitotic centers and the time-course of their duplication and separation. J. Bio-phys. Biochem. Cytol., 7, 1– 20. Wilson, E. B., 1902. Experimental studies in cytology. II. Some phenomena of fertilization and cell-division in etherized eggs. III. The effect on cleavage of artificial obliteration of the first cleavage-furrow. Arch. Entw. Mech., 13, 353– 395. Citing Literature Volume7, Issue1January 1962Pages 68-80 ReferencesRelatedInformation

The Multiplicity of the Mitotic Centers and the Time-Course of Their Duplication and Separation

In this study, the reproduction of the mitotic centers in the eggs of a sea urchin, Strongylocentrotus purpuratus and a sand dollar Dendraster excentricus has been studied by means of experimental designs that do not depend on the actual visualization of centrioles. The centers are defined in operational terms as potential poles. Blockage of mitosis by mercaptoethanol, it was found, inhibits the duplication of the centers, but does not inhibit the splitting and separation of centers that have already duplicated and thus potential poles could be realized as actual poles in multipolar divisions. At all times, the center is at least a duplex structure; that is, it contains two potential poles. The actual duplication process is the earliest event in a given mitotic cycle, taking place at very early interphase or in late telophase of the previous division. The splitting of the centers following duplication is a distinct process, dissociable from the duplication as such. Duplication and splitting normally occur at about the same time in the mitotic cycle, with a precession of the former. That is, as the two members of a pair of "old" centers split, each one gives rise to a new one, which remains associated with it until the next phase of splitting and duplication occurs. The results are consistent with what is termed a "generative" model of the self-reproduction of an intracellular body. According to this, the body does not immediately produce a full-fledged copy of itself, with simultaneous fission, but the primary duplication event involves only a part of the parent structure. This gives rise to a "germ" or "seed" which then grows to be equivalent to the parent body, and finally splits from it.

SH compounds in mitosis: I. The action of mercaptoethanol on the eggs of the sand dollar Dendraster excentricus

1. 1. Mercaptoethanol in adequate concentration (about 0.1 M) will block division of Dendraster excentricus eggs if applied at any time before metaphase. Since the time schedules of various echinoid eggs seem to be comparable, it may be useful to restate this finding in time units. In this case where the normal time from fertilization to first cleavage is 50 minutes, the mercaptoethanol block can be applied at any time from fertilization to about the fortieth minute. 2. 2. If the mercaptoethanol is applied after metaphase, it has no detectable effect on the division that is about to take place, but will block the next division. The discontinuity between the sensitive period and the insensitive period is very sharp. 3. 3. Concentrations of mercaptoethanol that are too low to block the first division may arrest cleavage at a subsequent division. In general, the lower the concentration, the more divisions will take place before blockage occurs. 4. 4. The effect of mercaptoethanol is completely reversible. 5. 5. Roughly, the time required for the blocked eggs to complete division when mercaptoethanol is removed is equivalent to the normal time required for the eggs to pass to division from the stage at which the mercaptoethanol was applied.

The Modification of Developmental Patterns in the Sand Dollar by Sodium Selenite

E :PERIMENTS dealing with the modification of developmental pattern in the echinoderm egg by external agents are not new. Sixty years ago Herbst (1892) discovered that lithium would cause exogastrulation and vegetalization in the developing larva of the sea urchin. Child (1941a, pp. 197-246) reviewed the various agents that affect development differentially and pointed out that differential inhibition, differential recovery, and differential conditioning in a quantitatively graded physiological system may be largely responsible for modifications in development caused by external agents. Recently, others (Hbrstadius and Gustafson, 1947; see Hirstadius, 1949, for review) have found that certain substances (propanediol phosphate, phosphogluconic acid, lactate), which are thought to play a role in carbohydrate metabolism, cause an animalization in apical halves of the sea-urchin egg, while other substances (certain amino acids), which may tend to favor protein metabolism, cause vegetalization. Also recently, the author (Rulon, 1949; 1950a, b; 1951) has shown that in the developing egg of the sand dollar (Dendraster excentricus) certain enzyme inhibitors (azide, thiourea) promote vegetalization, while others (maleic acid, malonic acid) promote overdevelopment of the animal region. The different inhibitors also have other dissimilar effects. In continuation of this work and in an effort to learn more con-