Echinoid Dendraster Research Articles

Variation in vertical distribution of sand dollar larvae relative to haloclines, food, and fish cues

Larvae of marine invertebrates may vertically position themselves in locations where conditions favor growth, development, and survival. Areas in stratified water columns with favorable salinities, concentrated food, or low predation may increase the probability for larvae to reach settlement. We examined the vertical distribution of three developmental stages of the echinoid Dendraster excentricus in response to haloclines, food cues, and predator cues in laboratory microcosms. Embryos, 4-arm plutei, and 8-arm plutei responded similarly to haloclines by swimming upward through haloclines when the bottom layer was at salinity 31 (ambient) and the top layer was at 27 or 23. The centers of larval mass for all stages were near the halocline when the top layer was at salinity 19 or 15. We tested the tolerance of each stage to prolonged exposure to each of these salinities and found sublethal effects under salinity 23, suggesting costs for concentrating in low salinity environments. To test the response of 4-arm larvae to food patches, we constructed a food layer composed of cells or supernatant of one of three species of algae (Dunaliella tertiolecta, Isocrysis galbana, Rhodomonas sp.). The larvae distributed above the food layer in the presence of two algal species, D. tertiolecta and Rhodomonas sp., but distributions were similar to controls when I. galbana was tested. Finally, larvae significantly changed their distributions in response to cues from a potential predator (juvenile perch), showing an avoidance behavior. The observed larval behaviors in response to haloclines, algae, and a potential predator suggest that D. excentricus plutei behaviorally respond to their environment and likely change position in response to environmental cues in the field.

Morphogenesis and organogenesis in the regenerating planktotrophic larvae of asteroids and echinoids.

In a previous study, we described complete body regeneration (with organogenesis) following surgical bisection in the planktotrophic larvae of the asteroids Luidia foliolata and Pisaster ochraceus. Here we present further detailed observations of these unique regenerative processes not presented in the previous paper. Furthermore, we describe for the first time complete regeneration following surgical bisection of planktotrophic larvae of the regular echinoid Lytechinus variegatus and the irregular echinoid Dendraster excentricus. Larvae of both asteroids and echinoids displayed a capacity for rapid regeneration regardless of their developmental stage. Within 48 h after bisection, aggregations of mesenchyme cells with pseudopodia were observed at the site of surgical bisection. These cellular aggregations were similar in appearance to the mesenchymal blastemas that form in adult echinoderms prior to their arm regeneration, and to those described in other deuterostomes that undergo regeneration. When asteroid larvae were surgically bisected in the early stages of their development, clusters of mesenchyme cells developed into completely new pairs of coelomic pouches located anterior to the newly regenerated digestive tract. This indicates that cell fate in regenerating asteroid larvae remains indeterminate during early development. In the larvae of P. ochraceus, regardless of the developmental stage at the time of bisection, both the anterior and posterior portions regenerated all their missing organs and tissues. However, the larvae of L. foliolata displayed differential regenerative capacity in bisected larval halves at the late bipinnaria stage. The differences observed may be due to differences in larval development (L. foliolata has no brachiolaria stage), and may have evolutionary implications. In the regular echinoid L. variegatus, both larval portions regenerated into morphologically and functionally normal larvae that were indistinguishable from non-bisected control larvae. The regenerative processes were similar to those we observed in planktotrophic asteroid larvae. Regenerating larvae readily metamorphosed into normal juveniles. In the irregular echinoid D. excentricus, posterior portions of larvae completed regeneration and metamorphosis, but anterior portions regenerated only partially during the 2-week study. Our observations confirm that asteroid and echinoid larvae provide excellent models for studies of regeneration in deuterostomes.

Evolution of egg target size: an analysis of selection on correlated characters.

In broadcast-spawning marine organisms, chronic sperm limitation should select for traits that improve chances of sperm-egg contact. One mechanism may involve increasing the size of the physical or chemical target for sperm. However, models of fertilization kinetics predict that increasing egg size can reduce net zygote production due to an associated decline in fecundity. An alternate method for increasing physical target size is through addition of energetically inexpensive external structures, such as the jelly coats typical of eggs in species from several phyla. In selection experiments on eggs of the echinoid Dendraster excentricus, in which sperm was used as the agent of selection, eggs with larger overall targets were favored in fertilization. Actual shifts in target size following selection matched quantitative predictions of a model that assumed fertilization was proportional to target size. Jelly volume and ovum volume, two characters that contribute to target size, were correlated both within and among females. A cross-sectional analysis of selection partitioned the independent effects of these characters on fertilization success and showed that they experience similar direct selection pressures. Coupled with data on relative organic costs of the two materials, these results suggest that, under conditions where fertilization is limited by egg target size, selection should favor investment in low-cost accessory structures and may have a relatively weak effect on the evolution of ovum size.

EVOLUTION OF EGG TARGET SIZE: AN ANALYSIS OF SELECTION ON CORRELATED CHARACTERS

In broadcast-spawning marine organisms, chronic sperm limitation should select for traits that improve chances of sperm-egg contact. One mechanism may involve increasing the size of the physical or chemical target for sperm. However, models of fertilization kinetics predict that increasing egg size can reduce net zygote production due to an associated decline in fecundity. An alternate method for increasing physical target size is through addition of energetically inexpensive external structures, such as the jelly coats typical of eggs in species from several phyla. In selection experiments on eggs of the echinoid Dendraster excentricus, in which sperm was used as the agent of selection, eggs with larger overall targets were favored in fertilization. Actual shifts in target size following selection matched quantitative predictions of a model that assumed fertilization was proportional to target size. Jelly volume and ovum volume, two characters that contribute to target size, were correlated both within and among females. A cross-sectional analysis of selection partitioned the independent effects of these characters on fertilization success and showed that they experience similar direct selection pressures. Coupled with data on relative organic costs of the two materials, these results suggest that, under conditions where fertilization is limited by egg target size, selection should favor investment in low-cost accessory structures and may have a relatively weak effect on the evolution of ovum size.Corresponding Editor: D. Wheeler

Localization of a SALMFamide Neuropeptide in the Larval Nervous System of the Sand Dollar Dendraster excentricus

AbstractUsing immunocytochemical methods we describe the localization of serotonin and the SALMFamide peptide, S1 (GFNSALMFamide), during embryonic and larval development of the echinoid Dendraster excentricus. Anti‐SI immunoreactivity first appears in the apical ganglion in late gastrulae at the same time as anti‐serotonin immunoreactivity. Initially, anti‐S1 immunoreactivity is restricted to fibres of the neuropile, but in later feeding stages, cell bodies are also immunoreactive. Anti‐S1 immunoreactivity appears as 2–4 cells in the oral ganglion of early prism stage larvae, whereas anti‐serotonin immunoreactivity does not occur in the oral ganglion until the 8‐arm stage. Anti‐S1 immunoreactivity also occurs in diffuse fibres in the oesophagus and in a single fibre encircling the pyloric sphincter of the gut. A reticular network associated with the apical surface of the epithelial cells of the vestibule of the adult rudiment was anti‐S1 immunoreactive. In double‐labelling experiments, anti‐serotonin and anti‐S1 immunoreactivity co‐localize in the neuropile of the apical ganglion. The distribution of S1, in association with putative sensory cells in the apical and oral ganglia and with muscles of the oesophagus and gut, suggests S1 may have diverse functions in the larval nervous system. The distribution of anti‐S1 immunoreactivity in echinoid embryos and larvae supports the proposal that SALMFamide‐like peptides are widely shared in echinoderms and potentially have a fundamental role in neural function.

THE BODY PLAN OF THE CYPHONAUTES LARVA OF BRYOZOANS PREVENTS HIGH CLEARANCE RATES: COMPARISON WITH THE PLUTEUS AND A GROWTH MODEL

The cyphonautes larva of bryozoans is anomalous among ciliary suspension feeders with upstream particle capture. This is because the length of the ciliated band that produces the feeding current does not increase disproportionately relative to body length during larval development and growth. Comparisons with previous studies of other upstream collectors (mostly the pluteus of the echinoid Dendraster excentricus or other echinoplutei) demonstrated a striking deficiency in feeding capabilities of the cyphonautes. (1) In comparison to the pluteus the ciliated band generating the feeding current of the cyphonautes was short both absolutely and relative to larval body size as protein. (2) During larval growth, the length of the ciliated band of the cyphonautes decreased relative to protein in the whole body whereas the length of ciliated band of the pluteus was nearly isometric with body protein. (3) The ratio of metabolic capacity (by electron transport system assay) to protein content was similar for the advanced stage pluteus and cyphonautes. If respiratory rate is proportional to metabolic capacity in these larvae, then the cyphonautes does not compensate for low feeding capacity by reduced respiratory rate. (4) The velocity of the current across the ciliated band and the length of lateral cilia was similar for the cyphonautes and pluteus. Therefore, maximum clearance rates per unit length of ciliated band were not unusually high for the cyphonautes. (5) The cyphonautes was inferior in rate of capture of small (2 µm) spheres relative to 10 µm spheres in comparison to plutei feeding on the same suspension. (6) The pluteus and cyphonautes were similar in the maximum sizes of spheres ingested. (7) In two experiments the cyphonautes was more selective of spheres flavored by incubation with the alga Dunaliella tertiolecta than was the pluteus. (8) Different patterns of allometric growth of ciliated bands were incorporated in a growth model based on the difference between allometry of gain in organic carbon through feeding and loss of organic carbon through respiration. The model predicted that a cyphonautes form required a much greater concentration of food than a pluteus form to gain the same organic material in the same time. Thus the cyphonautes proved inferior to the pluteus in quantitative measures of capacity for suspension feeding. The highly conservative differences in larval body plans result in differing capabilities for feeding that are likely to influence larval growth rates and the evolution of life histories.

A glycoprotein in the accessory cell of the echinoid ovary and its role in vitellogenesis.

A high-molecular-weight glycoprotein with a sedimentation coefficient of 22.6 has been isolated and characterized from the accessory cells in the previtellogenic ovary of the echinoid Dendraster excentricus. This glycoprotein is similar to the major yolk glycoprotein of the mature egg in its electrophoretic mobility under non-denaturing conditions, high mannose-type glycan, amino acid composition, constitutive glycopeptides, and immunological determinants. Previous histological and electron microscopical analyses led to the hypothesis that vitellogenesis involves a translocation of material from the accessory cell in the ovary to the oocyte. Because of the close similarities of the accessory cell glycoprotein to the yolk glycoprotein of the mature egg, we conclude that the glycoprotein in the accessory cell is a precursor to the major glycoprotein of the egg yolk. This conclusion is further supported by our additional finding that the accessory cell of another echinoid, Strongylocentrotus purpuratus, also contains a high-molecular-weight (24 S) glycoprotein which shows similarities to the yolk glycoprotein of the mature egg in the carbohydrate moiety and the constitutive glycopeptides.

Population dynamics in Dendraster, Merriamaster, and Anadara from the neogene of the Kettleman Hills, California

Samples of the echinoid Dendraster and the bivalve Anadara from the Neogene sedimentary rocks exposed in the Kettleman Hills of California contain few small specimens. The echinoid Merriamaster shows a more complete range of specimen sizes. Factors such as current winnowing, migration of adults to an area separate from juveniles, and mechanical, chemical, or biological destruction perhaps contributed to the lack of small specimens. However, rapid growth rate in juveniles and low juvenile mortality are probably the major reasons for the lack of small specimens. The adult portion of survivorship curves should be little affected by taphonomic processes and should thus contain useful information about population dynamics. The convex survivorship curves of Dendraster show low juvenile mortality followed by increasing mortality with age in adults. Dendraster specimens are always found in sediments indicating firm substrates and turbulent conditions. Convex survivorship curves for populations from this type of environment have been previously noted in other species. Merriamaster populations have linear to slightly convex survivorship curves. They probably lived in slightly less turbulent conditions than most Dendraster populations. Anadara populations lack small individuals, suggesting low juvenile mortality or taphonomic processes, but the post-juvenile portion of their survivorship curves range from linear to strongly convex. The linear pattern is frequently found in populations in sediments with a high proportion of mud, suggesting lower energy conditions.

Eccentricity in the clypeasteroid echinoid Dendraster: environmental significance and application in Pliocene paleoecology

Stanton, Robert J., Jr., Dodd, J. Robert & Alexander, Richard R. 1979 01 15: Eccentricity in the clypeasteroid echinoid Dendraster: environmental significance and application in Pliocene paleoecology. Lethaia. Vol. 12, pp. 75–87. Oslo. ISSN 0024–1164. The echinoid Dendraster lives in the northwest Pacific in environments ranging from open exposed coast to protected embayment. Water energy and the abundance and quality of food along this environmental gradient are correlated with test size and eccentricity of the apical area, so that larger and more eccentric specimens occur on the open coast than in bays. Study of Dendraster in Pliocene strata of the Coalinga California region indicates that these morphologic characteristics provide valuable information for paleoenvironmental reconstruction. Lateral and temporal environmental gradients within a broad Pliocene embayment and the location and size of the bay entrance can be determined on the basis of Dendraster eccentricity and size. Several species and subspecies of Dendraster in the Pliocene of the Coalinga region, described largely by differences in eccentricity, are probably not valid taxa but are merely ecophenotypic expressions of the laterally and temporally variable environment.

The Relation between Water Temperature and Morphology in Dendraster

An empirical correlation between mean water temperature and test weight in shallow-wrater forms of the living echinoid Dendraster excentricus (Eschscholtz) shows that sand dollars of a given size are heavier in cold water than in warm water. The correlation is interpreted as the result of phenotypic (non-heritable) adaptation to water temperature. Changes in test weight are accompanied by changes in several morphological characters that have been used to classify members of the genus Dendraster into species and subspecies. Investigation of the value of these characters as indicators of paleotemperatures in the fossil record of Dendraster indicates that the characters have evolved over time, thus eliminating their use as indicators of absolute temperatures. Furthermore, genetic or evolutionary differences in the same characters are recognized between certain geographically separated contemporaneous populations in the Pliocene. Thus only within a small geographic area and within a short range of time can morphology be used to deduce relative differences in temperature.

Developmental Pattern in the Starfish Patiria miniata, as Indicated by Indophenol

E ARLIER papers have shown that certain features of physiological developmental pattern can be rendered directly visible by differential intracellular formation, reduction, and reoxidation of the intensely blue indophenol in living, intact developmental stages of various forms. Data are at hand on early stages of the echinoid Dendraster excentricus (Child, I94Ib), embryonic development and gills, legs, and balancers of larval stages of the urodele Triturus (Child, 1942b; 1943a, c), embryonic stages of the teleost Oryzias latipes (Child, I942b, 1943d), and living ovaries of Drosophila hydei (Child, 1943b). The present paper is a study of those features of developmental pattern made visible by indophenol in Patiria miniata.