Sand Dollar Dendraster Excentricus Research Articles

Temperature and reduced pH regulate stress and biomineralization gene expression in larvae and post-larvae of the sand dollar Dendraster excentricus

ABSTRACT Seawater temperature, oxygen, salinity and pH are important abiotic factors, changes in which can generate stress in marine organisms. Subtidal and intertidal species, such as the sand dollar Dendraster excentricus, are daily exposed to stressors against which they have developed survival mechanisms to face environmental challenges. Analysing the expression of some key genes in response to stress factors due to changes in temperature and pH, especially in the early stages of development, opens a window of knowledge on the effect that these stressors have on benthic marine organisms. In the present work larvae and post-larvae of D. excentricus were exposed to high temperature and low pH scenarios. Survival, size and gene expression of five genes, involved in both stress response (hsp70 IV and hsp90 beta-like) and biomineralization for skeletogenesis (sm29, sm30A, carbonic anhydrase 14-like and mitochondrial proton/calcium exchanger protein LOC575637), were analysed in 4-, 6-, 8-arms, competent larvae and post-larvae. Survival of stressed larvae and post-larvae presented a significant decrease, up to 37% in some stages. A size reduction of almost 30 μm was observed when larvae were exposed to stressful conditions, except in competent larvae and in post-larvae where no significant changes were detected. After stress treatments, transcripts of hsp90 beta-like were up-regulated in all larval stages but hsp70 IV transcripts were not. Under tested stressful conditions sm29 and sm30A expression was down-regulated in larvae and post-larvae, while carbonic anhydrase 14-like and LOC575637 expressions were up-regulated. It is evident that tolerance to changes in seawater temperature and pH has a direct effect on metabolic functions of D. excentricus larvae and post-larvae, which depends on the developmental stage. If laboratory results are extrapolated to marine ecosystems, it is possible that populations of this structuring organism may be disturbed with subsequent damage to ecosystem balance, until resilient organisms acclimatize and adapt to their changing habitats.

Infrequent Fluctuations in Temperature and Salinity May Enhance Feeding in Pisaster ochraceus (Asteroidea) but Not in Dendraster excentricus (Echinoidea) Larvae.

AbstractIn recent years, low-salinity events characterized by high temperatures (18-23 °C) and low-salinity waters (20‰-22‰) have increased during late spring and summer, when many marine invertebrate larvae are developing. The present study examines the effects of low-salinity events on particle ingestion for larvae of two echinoderm species, the sea star Pisaster ochraceus and the sand dollar Dendraster excentricus. Larvae were exposed to high temperatures and low salinities for 24 hours, followed by feeding on the alga Isochrysis galbana in high or low salinity for another 10 minutes. Exposing Pisaster larvae to high temperatures and low salinities, followed by feeding in low salinity, did not impair ingestion rates. In fact, these larvae ingested particles at similar and sometimes higher rates than those in the controls. In sharp contrast, a 24-hour exposure to a high temperature and low salinity, followed by continued exposure to low salinity to feed, led to a decrease in the number of particles ingested by 8-arm Dendraster larvae. Larvae of both species captured very few particles when returned to 30‰ after a low-salinity event, indicating that continuous interruption of larval feeding by low-salinity events during development could be deleterious. Sand dollar larvae may have responded negatively to low-salinity events in our experiments because they are found in protected bays, where they may seldom experience these events.

Adaptive and Plastic Responses to Environmental Variation: Introduction to a Virtual Symposium in The Biological Bulletin.

Adaptive and Plastic Responses to Environmental Variation: Introduction to a Virtual Symposium in The Biological Bulletin.

Effects of Bisphenol-A on the morphology and survival of larvae of the sand dollar Dendraster excentricus (Echinodermata, Echinoidea)

ABSTRACT Bisphenol-A (BPA) is an ingredient used in phenol resins, epoxy resins, polyesters and polycarbonate plastics. BPA gets released into the aquatic environment through toxic waste disposal, groundwater, sewage runoff and plastic leaching. When BPA enters aquatic environments, it can affect the development and physiology of marine organisms. This study aimed to understand the effects of relatively low concentrations of BPA on the larvae of the sand dollar Dendraster excentricus. Embryos and larvae were exposed to four treatment solutions (no additives, vehicle control, 50 µg/L BPA, and 500 µg/L BPA) for 7 days. The two BPA treatment concentrations were higher than have usually been detected in coastal marine waters, but lower than those used in most other studies of BPA effects on echinoderm development. After exposure, larval midline body length, postoral arm length, frequency of normal development and survyivorship were measured. Midline body length, frequency of normal development and survivorship all decreased in the presence of BPA, in a dose-dependent manner. Relatively low concentrations of BPA can thus have strong effects on the development of sand dollar larvae.

Temporal variation in food limitation in larvae of the sand dollar Dendraster excentricus

Rates of development of the feeding larvae of marine invertebrates may often be limited by inadequate food, extending the length of the larval period and increasing overall larval mortality. A better understanding of the frequency and importance of this phenomenon requires knowledge of the food concentration below which larvae are limited, and above which they are not, as well as estimates of how strongly food supply affects length of the planktonic period. We addressed these issues using larvae of the sand dollarDendraster excentricusas a model and chlaconcentration as a metric of food abundance. We reared larvae in natural seawater collected from coastal southern California (USA), as well as in reduced and supplemented food treatments created from this natural seawater, 6 times from 2017 to 2019 to take advantage of temporal variation in chlaconcentration. Larvae showed morphological responses indicative of low food in nature in only 1 of 6 experiments and showed delayed time to 50% metamorphic competence in 2 of 6 experiments. Larvae appeared to be food limited below chlaconcentrations of ~2.4-3.0 µg l-1, but developed at maximal rates at higher food concentrations. Low natural food supplies delayed time to 50% competence by up to 1.25 d. An 11 yr record of chlaconcentration in waters of coastal southern California suggests that larvae ofD. excentricusare likely food limited in developmental rate throughout much of the year except for late winter to late spring.

Developmental Consequences of Temperature and Salinity Stress in the Sand Dollar Dendraster excentricus.

Animals that reside, reproduce, and develop in nearshore habitats are often exposed to strong fluctuations in abiotic conditions, including temperature and salinity. We studied the developmental response of the sand dollar Dendraster excentricus to increased temperature and reduced salinity at levels comparable to those induced by summer freshwater input into the San Juan Archipelago, Washington. We observed that embryos exposed to temperature and salinity stress exhibited polyembryony (the splitting of one embryo into multiple independent individuals), and we subsequently tested the competency of twin and normal embryos to reach metamorphosis. We found that twin embryos generated from a single egg are each capable of reaching metamorphosis. To begin investigating the mechanisms underlying polyembryony, we tested whether osmotic stress caused swelling of the fertilization envelope, thus allowing embryos the physical space to produce multiples within a single envelope. We also tested whether reduced calcium levels in low-salinity seawater reduced cell-cell adhesion and allowed cells to separate and develop as multiple embryos within a fertilization envelope. However, neither osmotic stress nor reduced calcium levels alone appear sufficient to induce polyembryony. We hypothesize that changes in the properties of the hyaline layer that lies beneath the fertilization envelope facilitate polyembryony.

Rethinking competence in marine life cycles: ontogenetic changes in the settlement response of sand dollar larvae exposed to turbulence.

Complex life cycles have evolved independently numerous times in marine animals as well as in disparate algae. Such life histories typically involve a dispersive immature stage followed by settlement and metamorphosis to an adult stage on the sea floor. One commonality among animals exhibiting transitions of this type is that their larvae pass through a ‘precompetent’ period in which they do not respond to localized settlement cues, before entering a ‘competent’ period, during which cues can induce settlement. Despite the widespread existence of these two phases, relatively little is known about how larvae transition between them. Moreover, recent studies have blurred the distinction between the phases by demonstrating that fluid turbulence can spark precocious activation of competence. Here, we further investigate this phenomenon by exploring how larval interactions with turbulence change across ontogeny, focusing on offspring of the sand dollar Dendraster excentricus (Eschscholtz). Our data indicate that larvae exhibit increased responsiveness to turbulence as they get older. We also demonstrate a likely cost to precocious competence: the resulting juveniles are smaller. Based upon these findings, we outline a new, testable conception of competence that has the potential to reshape our understanding of larval dispersal and connectivity among marine populations.

Effect of stress on the ecophysiological response of the sand dollar Dendraster excentricus from northwestern Mexico

In the Mexican Pacific, Dendraster excentricus, a common estuarine echinoderm, is subject to daily environmental variations in tidal fluxes. Little is known about its ecophysiological response when individuals are exposed to temperature and oxygen changes. This study evaluates their thermal stress response under normal and reduced oxygen conditions using the RNA/DNA ratio and hsp70 gene expression. We exposed sand dollars to different temperature and oxygen conditions. Three experimental temperatures were similar to the ones that organisms experience during one annual cycle and two were considered extreme. Reduced oxygen conditions were considered when levels dropped below 4 mg L–1. To estimate variations in the stress-induced RNA/DNA ratio, we determined the value for males and females during a daily cycle. We also analyzed the hsp70 expression. Under stress conditions, a significant decrease was observed in the RNA/DNA ratios. The lowest values were detected after 6 h under normoxic conditions and high temperatures seemed to induce a major effect on the RNA/DNA ratios during the first hour of stress. Analysis of the hsp70 expression showed significant differences. According to our results, thermal and reduced oxygen stress induces a reduction in the general metabolism of the organisms. These metabolic changes were observed by the decrease in the RNA/DNA ratios and expression levels of hsp70 (at high temperatures). We conclude that RNA/DNA ratios are a useful ecophysiological tool to evaluate the effect of particular stressors on the physiology of D. excentricus, and seem to be more sensitive to oxygen levels than to thermal stress, in contrast to the hsp70 expression, which was more sensitive to extreme temperatures.

Inhibition of Cell Division in Mouse B-Cell Hybridomas: An Overlooked Property of 2-Mercaptoethanol and Its Impact onin vitroAntibody Production

Thiol 2-mercaptoethanol (2-ME) has been reported to enhance growth in lymphocytes by various investigators. Some have used 50 μM for growing hybridomas in vitro. Concentrations of 50 and 5 μM in 5% FBS supplemented D-MEM were tested to determine their effects on the growth of 5 monoclonal antibody secreting mouse B cell hybridomas and the myeloma Sp2/O-Ag14. Viability after 24 and 48 h exposure was determined by Trypan blue exclusion. Analysis by one-way ANOVA confirmed that 50 μM 2-ME has a significant negative impact (p<0.05) on hybridoma as well as on myeloma growth, whereas no significant difference (p>0.05) between the control and the 5 μM treatment group was observed after 48 h. Also, no significant difference (p>0.05) in the mortality rates between the control and the treatment groups was found. When combined with the observed protracted doubling time in the 50 μM treatment group, these results indicate that the impact of 2-ME is due to inhibition of cell division. The degree of inhibition was observed to vary between the different hybridomas as well as the myeloma. Although the impact of 2-ME on mitosis has been demonstrated in organisms such as the ciliated protozoan Tetrahymena pyriformis, the yeast Saccharomycess cerevisiae, and the egg of the echinoid the sand dollar Dendraster excentricus, this work demonstrates for the first time that 2-ME impedes the growth of mouse B cell hybridomas. We conclude that adding 2-ME to mouse B cell hybridoma growth media may not be beneficial.

Gonad index and larval development of the sand dollar Dendraster excentricus (Echinodermata; Echinoidea) in Baja California, Mexico

The sand dollar Dendraster excentricus has been extensively used in diverse studies in Baja California (Mexico). This study shows annual variations in the gonad index and describes larval development under laboratory conditions of D. excentricus. Over a period of one year, adult sand dollars (6.73 ± 0.56 cm diameter and 23.22 ± 6.90 g) were collected monthly. Both the monthly analysis of the gonad index (male and female) and the measure of mature eggs were considered to estimate the reproductive period of the sand dollar in Punta Banda Estuary (Baja California). Our results suggest that D. excentricus has two maximum reproductive peaks, one during the early spring and another during the summer, although viable gametes were obtained in the laboratory year round. Larval development took 21–23 days from fertilization to metamorphosis under laboratory conditions (19 ± 2 ºC, salinity 33.5). The blastula stage was observed 5 h postfertilization, while four-armed echinopluteus larvae, with an average size of 387.00 ± 23.25 ?m (from aboral to dorsal arms), were observed two days after fertilization. A different larval stage was attained approximately every two days. Eight-armed echinopluteus larvae were 744.60 ± 69.45 µm in size. The completely developed juvenile rudiment was detected 18 days after fertilization and metamorphosed larvae were observed 72 h after induction. These results, while not new for the species, show the reproductive behavior and larval period for the D. excentricus populations associated with an estuary at the southern limit of its distribution, and will be useful to document variation in the response of species of ample geographic distribution in global change scenarios.

Effects of ocean-acidification-induced morphological changes on larval swimming and feeding

Reduction in global ocean pH due to the uptake of increased atmospheric CO(2) is expected to negatively affect calcifying organisms, including the planktonic larval stages of many marine invertebrates. Planktonic larvae play crucial roles in the benthic-pelagic life cycle of marine organisms by connecting and sustaining existing populations and colonizing new habitats. Calcified larvae are typically denser than seawater and rely on swimming to navigate vertically structured water columns. Larval sand dollars Dendraster excentricus have calcified skeletal rods supporting their bodies, and propel themselves with ciliated bands looped around projections called arms. Ciliated bands are also used in food capture, and filtration rate is correlated with band length. As a result, swimming and feeding performance are highly sensitive to morphological changes. When reared at an elevated P(CO2) level (1000 ppm), larval sand dollars developed significantly narrower bodies at four and six-arm stages. Morphological changes also varied between four observed maternal lineages, suggesting within-population variation in sensitivity to changes in P(CO2) level. Despite these morphological changes, P(CO2) concentration alone had no significant effect on swimming speeds. However, acidified larvae had significantly smaller larval stomachs and bodies, suggesting reduced feeding performance. Adjustments to larval morphologies in response to ocean acidification may prioritize swimming over feeding, implying that negative consequences of ocean acidification are carried over to later developmental stages.

Molecular Reproduction &amp; Development Volume 78, Issue 10–11 cover image

AbstractTopography map of Friday Harbor from 1895, part of the San Juan Islands off the coast of Washington state (courtesy of University of Washington Library). Photos are larvae of two native echinoderms found in the coastal waters of Friday Harbor, the sand dollar Dendraster excentricus (top) and sea star Pisaster spp (bottom) species. Larval photos taken by Dr. Mette Handberg‐Thorsager, a student in the 2010 “Comparative Invertebrate Embryology” class.

Swimming performance as a constraint on larval morphology in plutei

Understanding evolutionary mechanisms constraining larval morphology is challeng- ing, both because morphology has many potential functional consequences and because the impacts of morphological variation on most functions are difficult to quantify. We assessed the potential importance of swimming as a factor driving larval morphology by hypothesizing that larvae of the sand dollar Dendraster excentricus are at or near a local maximum in swimming performance as a function of their morphological characteristics. To test this hypothesis, we used a hydrodynamic model parameterized to represent the 4-armed larval stage to predict the consequences of morpho- logical changes on larval movement in still water and shear flows. We created 3 morphological fami- lies, consisting of series in which either larval body skeleton volume, relative arm length, or arm ele- vation angle were incrementally altered from observed morphologies, and used upward swimming velocity as a metric of performance. For each morphological family, a wide subset of alternate mor- phologies performed better than the observed morphology in still water. However, in shear flows, the observed morphology consistently fell within the narrow morphological range that minimized rapid downward velocities. These results suggest that larval swimming performance, especially perfor- mance in moving water, is a driving factor in the evolution of D. excentricus larval morphology. Fur- ther, our results suggest that small morphological changes resulting from environmental shifts, such as those predicted to result from ocean acidification, may have potentially large deleterious ecologi- cal consequences.

Temperature and diet modified swimming behaviors of larval sand dollar

Swimming behaviors of marine invertebrate larvae play key roles in larval dispersal and survival and, hence, have important consequences for adult population dynamics. However, to date, insufficient quantitative information exists on larval swimming to understand and predict swimming movements in most marine invertebrate species. Previous work suggests that larvae swim more slowly at lower temperatures and, consequently, might have difficulty regulating depth when experiencing temperature changes. Improved diet quality in terms of essential fatty acid composition has been suggested to increase cold tolerance in many organisms. We used non-invasive videotracking techniques to quantify swimming in larvae of the sand dollar Dendraster excentricus, raised on 4 algal diets differing in their fatty acid profiles and then exposed to an ecologically relevant temperature decrease from 20 to 12°C. Differences in diet quality led to significant morphological differences by the 8-arm larval stage, and there were significant diet-temperature interaction effects on swimming patterns. While larval swimming speeds decreased as temperature decreased across all diet treatments, net vertical velocities of larvae did not decrease. Changes in helical geometries of larval swimming trajectories suggest that larvae compensate for reduced swimming speeds by reducing horizontal movement, thus preserving their ability to regulate depth. The observed compensatory mechanism effectively circumvents constraints on swimming due to lowered temperatures. More generally, video-tracking of free-swimming larvae can yield quantitative data to inform biophysically coupled models that better predict consequences of larval dispersal for adult population dynamics under current and future environmental conditions.

Abrupt Change in Food Environment Induces Cloning in Plutei of Dendraster excentricus

Asexual reproduction, or cloning, of planktonic echinoderm larvae has been observed in the laboratory and in nature, but little is known about its ecology. Here we examine the effects of algal food density and of a change in food density on the incidence of cloning in larvae of the sand dollar Dendraster excentricus. Results indicate that a change in food concentration can induce cloning in plutei. Cultures transferred from a low to a high algal ration at the time when primary larvae were developing the third (posterodorsal) pair of larval arms showed decreased postoral arm length, unusual morphologies, and increased larval density in culture. These dense cultures of smaller plutei were produced within 48 h of the food pulse. The result is consistent with the occurrence of a burst of cloning, possibly through anterior autotomization. A second feeding experiment demonstrated that anterior autotomization does occur in 4- to 6-arm plutei. Rather than constituting a developmental rarity, cloning may happen early and often in D. excentricus cohorts when environmental conditions favor rapid growth.

Light influences feeding and growth of echinoplutei

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 404:69-78 (2010) - DOI: https://doi.org/10.3354/meps08488 Light influences feeding and growth of echinoplutei L. Milonas1, B. Pernet2, B. L. Bingham1,* 1Department of Environmental Sciences, Western Washington University, Bellingham, Washington 98225, USA 2Department of Biological Sciences, California State University, Long Beach, Long Beach, California 90840, USA *Corresponding author. Email: brian.bingham@wwu.edu ABSTRACT: Because planktonic invertebrate larvae may be food-limited, anything that increases feeding and digestive efficiency should increase the chances of larval survival to metamorphosis. As light directly enhances both feeding and digestion in some planktonic heterotrophic protists, we hypothesize that similar processes might occur in the larvae of marine invertebrates. We studied the direct effects of light on feeding and development in sea urchin larvae (Strongylocentrotus droebachiensis, S. franciscanus and sand dollar Dendraster excentricus). Larvae were placed in 12:12 h light:dark cycles or in complete darkness and ingestion rates were measured. We monitored larval morphology during the first 2 to 3 wk of development and tested for light-related differences. Short-term changes in light regime had no effect on feeding rates. However, larvae of all 3 species showed longer-term diel feeding patterns with ingestion rates generally higher during daylight hours. These patterns persisted in S. franciscanus larvae even when larvae were held in complete darkness for 3 d. Larvae of D. excentricus exposed to natural light cycles developed longer arms usually associated with food limitation; those held in darkness had significantly shorter arms. The developing juvenile structures (i.e., rudiments) of S. droebachiensis larvae exposed to light were significantly smaller than those of larvae held in continuous darkness, suggesting that light may have negative effects on larval growth and development. Measuring the effects of light on feeding and growth may clarify the behaviors of invertebrate larvae during their critically important planktonic period. KEY WORDS: Light effects · Larval feeding · Larval growth · Larval morphology Full text in pdf format PreviousNextCite this article as: Milonas L, Pernet B, Bingham BL (2010) Light influences feeding and growth of echinoplutei. Mar Ecol Prog Ser 404:69-78. https://doi.org/10.3354/meps08488 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 404. Online publication date: April 08, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Regulation of feeding mode by the sand dollar Dendraster excentricus in a shallow estuarine habitat

The sand dollar Dendraster excentricus is a facultative suspension feeder, which is relatively rare within the Order Clypeasteroida. Field studies of regulation of its feeding mode have been mostly conducted in exposed coastal habitats, where they are typically observed in an inclined position and oriented parallel to each other during suspension feeding. Physical (current speed and direction, reduction of drag and lift) and biological factors (increased efficiency of capture of particulates, and density) have been associated with regulation of its feeding mode in exposed coastal systems. We simultaneously measured the role of physical and biological factors in regulating the selection mode for feeding under varying tidal conditions in a shallow estuary in Baja California, Mexico. We used photographic records and direct sampling in fixed plots to determine the relationship between feeding behavior and environmental conditions. Current direction and speed, tidal level, density and content of organic matter in the water column and sediments were measured with respect to feeding mode (prone or inclined) and orientation relative to prevailing currents during spring and neap tides. Multiple regression analysis indicated that the percentage of inclined sand dollars was strongly and positively correlated only with tidal level at the densities found in the estuary (mean < 180 individuals m − 2 ); there was no relationship with current velocity, density, and organic matter content of the water. The prone position, indicative of deposit feeding, was largely limited to low tidal levels. We used circular statistics to determine whether the orientation of inclined sand dollars was correlated with current direction and speed. Sand dollars were only oriented parallel to the prevailing currents during the strongest currents of spring tides (> 20 cm s − 1 ). We did not observe the predominant oral:aboral configuration found in exposed coastal systems, which may be attributed to the relatively low densities of sand dollars in the exposed coastal environment (30–180 individuals m − 2 ), compared to protected coastal habitats (up to 1000 individuals m − 2 ). Our results suggest that regulation of the feeding mode of sand dollars in shallow and hydrodynamically complex estuarine systems differs from the feeding mode found in exposed coastal environments.

A comparison of the copper sensitivity of six invertebrate species in ambient salt water of varying dissolved organic matter concentrations

The copper sensitivity of four saltwater invertebrates (the mussel Mytilus galloprovincialis, the oyster Crassostrea virginica, the sand dollar Dendraster excentricus, and the sea urchin Strongylocentrotus purpuratus) was determined experimentally using chronic-estimator embryo-larval test procedures. The effect of sample dissolved organic matter (DOM) content on Cu bioavailability was determined for these species using commonly prescribed test procedures. Comparisons were made among these test results and test results reported previously for two other invertebrate species: the mussel Mytilus edulis and the copepod Eurytemora affinis. All six species exhibited a direct and significant relationship between the sample dissolved organic carbon (DOC; a surrogate measure of DOM) and either the dissolved Cu median lethal concentration (LC50) values or median effect concentration (EC50) values. This relationship is significant even when the DOM has different quality as evidenced by molecular fluorescence spectroscopy. Once normalized for the effects of DOM, the Cu sensitivity of these species from least to most sensitive were E. affinis < D. excitricus < C. virginica approximately S. purpuratus approximately M. edulis approximately M. galloprovincialis. This ranking of species sensitivity differs from the saltwater species sensitivity distribution proposed in 2003 by the U.S. Environmental Protection Agency. These results support the need to account for factors that modify Cu bioavailability in future saltwater Cu criteria development efforts. More specifically, Cu saltwater species sensitivity distribution data will need to be normalized by factors affecting Cu bioavailability to assure that accurate and protective criteria are subsequently developed for saltwater species and their uses.

About the Cover

Next article FreeAbout the CoverFull TextPDF Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverThe 30th plate from Ernst Haeckel's Kunstformen der Natur (Artforms of nature) (1904), pictured on the cover, depicts echinoids at various stages of development—planktonic larva, metamorphosed juvenile, and benthic adult. Echinoids, which include sand dollars and sea urchins, spend their earliest days as free-swimming larvae before metamorphosing and settling to the sea floor as juveniles. Larval mortality is estimated to be high in marine planktonic environments. Although the causes of mortality are poorly understood, predation is considered a significant source of mortality for the eggs, embryos, and larvae of marine organisms. With little protection and provisioning in an environment that cannot be accurately predicted from the mother's position on the sea floor, other mechanisms may have evolved to increase a larva's chance of surviving its time in the plankton. One mechanism that can counter the effects of “growing up” all alone in a risky and unpredictable environment is developmental plasticity, the ability to change in response to experience or environment. A particularly well-documented category of developmental plasticity is the defensive responses that exposure to predators can induce in prey organisms. Recent research documents an unusual predator-induced response in the pluteus larvae of the sand dollar Dendraster excentricus: cloning (asexual reproduction) and reduced larval size as consequence of cloning. The smaller than usual plutei are subsequently less vulnerable to some planktivorous predators. In this issue (pp. 103–114), Dawn Vaughn presents evidence that predator-induced cloning in D. excentricus plutei is influenced by maternity. Half-sibling plutei (three mothers, same father) were exposed to stimuli from predators (i.e., fish mucus) for 9 days during early development. Vaughn found that plutei of different mothers varied in the rate and frequency of cloning. Unexpectedly, all plutei exposed to fish mucus were smaller and developmentally delayed when compared to all plutei reared in the absence of mucus. The results from this study support the hypothesis that mothers have an influence on cloning of larval offspring; however, reduced larval size was a uniform response to fish mucus and did not indicate a maternal effect. The potential advantages conferred by successful larval cloning (i.e., the production of two larvae from one larva) may then differ among unrelated conspecifics, while the developmental effect of reduced size as a potential adaptation to predators is a consistent response shared by all larval conspecifics. Future research on cloning in echinoid larvae will benefit from further consideration of the influence of benthic mothers on their planktonic offspring and may provide additional insight into how developmental plasticity mediates the effects of developing in an unpredictable environment. Cover design: Beth Liles, Marine Biological Laboratory. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 217, Number 2October 2009 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv217n2cover Views: 71 © 2009 by Marine Biological Laboratory. All rights reserved. Crossref reports no articles citing this article.

Fatty acid composition of larvae of the sand dollar Dendraster excentricus (Echinodermata) might reflect FA composition of the diets

Fatty acid (FA) requirements of echinoderm larvae were examined by a study of the FA composition, growth, and development of Dendraster excentricus larvae fed a microencapsulated diet, and two algal diets. Larvae were assigned to three treatments with three replicates per treatment, a microencapsulated diet, a single algal diet of Dunaliella tertiolecta and a mixed algal diet of Isochrysis galbana and Dunaliella tertiolecta. The percentage of saturated fatty acids (SAFA), short and long chain polyunsaturated fatty acids (PUFA) differed significantly among the algal diets and the microencapsulated diet. Differences in dietary FA composition influenced larval tissue FA composition. Eight day-old sand dollar larvae fed the single and mixed algal diets had a significantly higher percentage of the SAFA myristic acid (14:0), while eight day-old larvae fed the microencapsulated diet had a significantly higher percentage of the SAFA palmitic acid (16:0). Sixteen day-old competent larvae fed all three diets did not differ significantly in the percentage of myristic or palmitic acid. The algal diets had a higher percentage of the short chain PUFAs linolenic (LNA, 18:3n-3) and stearidonic acid (SDA, 18:4n-3) while the microencapsulated diet had the highest percentage of the long chain PUFAs eicosapentanoic acid (EPA, 20:5n-3) docosahexanoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6). The percentage of short chain PUFAs, though high in the algal diets, was low in the larval tissues, while the percentage of long chain PUFAs, though low in the algal diets, was high in the larval tissues. Competent larvae fed the two algal diets had up to ten times the percentage of EPA and AA than those fed the microencapsulated diet. Unexpectedly, despite a high percentage of DHA and EPA in the microencapsulated diet, the percentage of these long chain PUFAs in the tissues of larvae fed this diet was extremely low. Eight day-old larvae fed the three diets did not differ significantly in total larval length. Competent larvae fed algal diets had significantly longer larval arms, bigger stomachs and larger rudiments than those fed the microencapsulated diet. This study indicates that early larval growth and development of Dendraster excentricus were not discernibly affected by differences in dietary FA composition of microencapsulated and algal diets but the competent larval stages were. Similar growth and development of competent echinoderm larvae fed microencapsulated or algal diets might be obtained by enriching the microencapsulated diets with the short chain PUFAs LNA and SDA, and the long chain PUFAs EPA and AA. This is an important research tool as microencapsulated feeds can be used to establish nutritional requirements of fatty acids for echinoderm larval development.