Showing papers in "The Biological Bulletin in 1993"
TL;DR: It is suggested that the distribution of corals in areas of differential turbulence is related to the thickness of the diffusive boundary layers surrounding them, as well as the size of the polyp.
Abstract: The diffusive boundary layers surrounding sessile marine organisms have been implicated in controlling an organism's metabolism and growth. We studied boundary layers surrounding hermatypic corals by monitoring oxygen concentrations on a submillimetric scale. Oxygen concentration within the boundary layers varied from supersaturation during the day to anoxia at night, although the ambient water composition remained constant. Detailed mapping and oxygen measurements revealed diel oxygen fluctuations from supersaturation (373% air saturation) in the light to complete oxygen depletion at darkness in the massive coral Favia favus. Exposure to a 5-cm/s current reduced the boundary layer thickness from 2.44 mm to 1.90 mm, allowing more rapid oxygen exchange across the diffusive boundary layer. Similar patterns were found in the branching coral Stylophora pistillata. In massive corals, the thickness of the diffusive boundary layer was negatively correlated with the size of the polyp. We suggest that the distribution of corals in areas of differential turbulence is related to the thickness of the diffusive boundary layers surrounding them.
199 citations
TL;DR: Embryological development in sipunculans and mollusks shows a close relationship between them, and embryological development of the shell separates Aculifera and Conchifera, which supports the embryological and morphological relationships between Sipuncula and Mollusca.
Abstract: Evidence is presented in support of the following phylogenetic hypotheses: (1) Sipuncula are the sister taxon of Mollusca; (2) the two aplacophoran taxa, Neomeniomorpha (= neomenioids) and Chaetodermomorpha (= chaetoderms), are monophyletic with a common neomenioid-like ancestor, and of the two taxa, Chaetodermomorpha are more derived; (3) Aplacophora and Polyplacophora are sister taxa and form a clade, Aculifera; (4) Aculifera are the sister group of the remaining extant mollusks, Conchifera; and (5) Aplacophora are progenetic Aculifera. The evidence is based on homologies of early and late embryological development, adult morphologies, and molecular analyses. Embryological development in sipunculans and mollusks shows a close relationship between them, and embryological development of the shell separates Aculifera and Conchifera. Adult morphologies indicate: (1) monophyly of Aplacophora; (2) sister-group relationship between Aplacophora and Polyplacophora; (3) a molluscan plesiomorphy of nonsegmented se...
136 citations
TL;DR: Anatomical and ultrastructural observations of the light organ during embryogenesis indicate that the organ begins development as a paired proliferation of the mesoderm of the hindgut-ink sac complex of the sepiolid squid Euprymna scolopes.
Abstract: The sepiolid squid Euprymna scolopes maintains luminous bacterial symbionts of the species Vibrio fischeri in a bilobed light organ partially embedded in the ventral surface of the ink sac. Anatomical and ultrastructural observations of the light organ during embryogenesis indicate that the organ begins development as a paired proliferation of the mesoderm of the hindgut-ink sac complex. Three-dimensional reconstruction of the incipient light organ of a newly hatched juvenile revealed the presence of three pairs of sacculate crypts, each crypt joined to a pore on the surface of the light organ by a ciliated duct. The crypts, which become populated with bacterial symbionts within hours after the juvenile hatches, appear to result from sequential paired invaginations of the surface epithelium of the hindgut-ink sac complex during embryogenesis. A pair of anterior and a pair of posterior ciliated epithelial appendages, which may facilitate infection of the incipient light organ with symbiotic bacteria, develop by extension and growth of the surface epithelium. The ink sac and reflector develop dorsal to the crypts and together function to direct luminescence ventrally. These two accessory tissues are present at the time of hatching, although changes in their overall structure accompany growth and maturation of the light organ. A third accessory tissue, the muscle-derived lens, appears during post-hatch maturation of the light organ.
109 citations
TL;DR: Data strongly support a role for multixenobiotic transport as a mechanism of protection from environmental toxins and indicate an unsuspected mode of protection in invertebrate embryos.
Abstract: Urechis caupo is a marine worm that lives and reproduces in sediments containing a variety of potentially toxic environmental chemicals (xenobiotics) Its embryos have a multixenobiotic transporter, which is similar to the multidrug transporter in mammals, as indicated by their ability to transport a variety of moderately hydrophobic compounds such as dyes, drugs, and pesticides out of the cells The cell membranes of the embryos contain a protein of approximately 145 kD that is immunologically related to the mammalian multidrug transport protein and that can be cross-linked by a photoactivatable substrate of the mammalian multidrug transport protein The sediments in which the worm lives contain potential substrates for the transporter, indicating that this multixenobiotic transport activity may protect Urechis embryos from naturally occurring toxic compounds Embryos of a sea urchin from a pristine environment do not have this transport activity and are sensitive to hydrophobic toxins These data strongly support a role for multixenobiotic transport as a mechanism of protection from environmental toxins and indicate an unsuspected mode of protection in invertebrate embryos
106 citations
TL;DR: Strain CA2 may make a nutritional contribution to the growth of oyster larvae by enhancing larval survival and growth in comparison with control cultures that were fed only algae.
Abstract: Bacteria-free oyster larvae (Crassostrea gigas) were cultured under aseptic conditions; they were fed axenic algae (Zsochrysis galbana), and the medium was inoculated with isolated strains of marine bacteria. Twenty-one bacterial strains were tested, and most were detrimental to larval survival and growth. However, ad- ditions of strain CA2 consistently enhanced larval survival (2 l-22%) and growth ( 16-2 1%) in comparison with con- trol cultures that were fed only algae. Size-frequency dis- tributions of populations of larvae cultured for 10 days on axenic algae were skewed due to the poor growth of many individuals; whereas size-frequencies from popu- lations of larvae fed axenic algae supplemented with CA2 bacteria were distributed normally. Strain CA2 may therefore make a nutritional contribution to the growth of oyster larvae. I. galbana did not grow under the light intensities used for larval culture; thus the improvement in larval growth cannot be attributed to bacterial en- hancement of algal growth and, consequently, food avail- ability. Naturally occurring microflora from Yaquina Bay, Oregon, depressed survival or growth of larvae-fed live algae.
103 citations
TL;DR: The reproductive cycle of the sea cucumber Psolus fabricii was studied in a population from the St. Lawrence Estuary in eastern Canada from May 1988 through August 1989 and did not show a consistent relationship with either temperature or light conditions.
Abstract: The reproductive cycle of the sea cucumber Psolus fabricii was studied in a population from the St. Lawrence Estuary in eastern Canada from May 1988 through August 1989. The gonad consists of numerous germinal tubules which vary greatly in size. The mean diameter of the tubules and gonadal mass follow annual cycles, increasing from early winter through spring, and dropping abruptly during spawning in the summer. Ga- metogenesis is generally a prolonged process and begins in small tubules in January. By summer the ovarian tu- bules contain oocytes with a modal diameter of 400-600 pm, and the testicular tubules contain an abundance of early spermatogenic stages, but rarely spermatozoa. These small tubules of the gonad do not spawn until the follow- ing year, and there is little gametogenic activity within them until January, when oocyte growth and the pro- duction of later spermatogenic stages resumes. The latter production continues until summer and results in a marked increase in the diameter of the tubules. Then, during spawning, these now large fecund tubules are transformed into small tubules. Following spawning, the predominant activity within the spent tubules is phago- cytosis of the residual gametes. The active phase of ga- metogenesis (January to summer) coincides with an in- creasing photoperiod regime, and an accelerated game- togenesis occurs in March when temperature and food availability begin to increase. Spawning was one month later in 1989 than in 1988 and did not show a consistent relationship with either temperature or light conditions. However, in both years, spawning coincided with a de- crease in the freshwater run-off into the Estuary and with the predicted annual increase in phytoplankton.
95 citations
TL;DR: It is reported that leatherback sea turtle hatchlings orient to the geomagnetic field in complete darkness, a finding consistent with theoretical models proposing that magnetoreception involves a modulation of the response of retinal photoreceptors to light.
Abstract: Diverse animals can orient to the earth's magnetic field (1-6), but the mechanism or mechanisms undrlying magnetic field detection have not been determined. Behavioral (7-9) amd neurophysiological (10-12) results suggest that the transduction process underlying magnetic compass orientation in vertebrates is light-dependent, a finding consistent with theoretical models proposing that magnetoreception involves a modulation of the response of retinal photoreceptors to light (13, 14). We report, however, that leatherback sea turtle (Dermochelys coriacea) hatchlings orient to the geomagnetic field in complete darkness. Thus, light-dependence is not a universal feature of vertebrate magnetic compasses.
92 citations
TL;DR: It is argued that the ancestral asteroid life cycle involved pelagic larval development with both bipinnarian and brachiolarian stages and six types of evolutionary transitions in development that can account for the diversity of larval forms and developmental patterns in starfish.
Abstract: The diversity of larval forms and developmental patterns in asteroid echinoderms has become increasingly apparent over the past 10-15 years. However, the classification of developmental patterns has been ambiguous because the patterns have not been defined as unique sets of ecological and developmental character states. In addition, character states have not been defined consistently. Thus attempts to understand the evolutionary changes in development (e.g., heterochrony and heterotopy in morphogenesis) that underlie larval diversity have been hampered. We propose a multifactor classification of asteroid developmental patterns that uses an explicit set of characters that provide information on habitat (e.g., pelagic or benthic) and mode of nutrition (e.g., feeding or nonfeeding) of the developing young, as well as the type of morphological development (indirect = larval; direct = nonlarval). We conclude that direct development is exceptionally rare. All asteroids whose development has been studied, except...
92 citations
TL;DR: Results of the two experiments indicate that the growth response of animals to flow was most obviously related to the relative flow energy of the animal's natural habitat, whereas growth rates of animals from comparatively high-energy environments were relatively insensitive to flow speed.
Abstract: In separate experiments in 199 1 and 1992, the sensitivities of growth rates of six species of benthic suspension feeder to flow speed were tested in a series of turbulent pipe flows. Species examined were the cheilo- stome bryozoan Membranipora membranacea ( 199 1); the serpulid polychaete Pseudochitinopoma occidentalis (1991); and the barnacles Balanus glandula (1991), B. crenatus (1992), Semibalanus cariosus (1992), and Pollicipes polymerus ( 1992). In both experiments, animals were exposed to one of five constant, narrow ranges of speed that varied from about 2- 15 cm s-l. Growth rates of Membranipora and Pseudochitinopoma in 199 1 de- clined significantly and monotonically with increasing flow speed, despite evidence that at faster flows there were greater concentrations of suspended food available and higher particulate fluxes. In contrast, there was no de- tectable relationship between speed and growth of B. glandula over the same range of flow speeds in 199 1. Results of the 1992 experiment indicated variability in growth responses among three species of barnacle. Growth rates of S. cariosus and P. polymerus were insensitive to flow speed, whereas growth rates of B. crenatus increased from low speeds to a maximum at an intermediate speed of about 8 cm s-l, and then tended to decrease at higher speeds. Combined results of the two experiments indicate that the growth response of animals to flow was most obviously related to the relative flow energy of the animal's natural habitat. Growth rates of animals that typi- cally experience relatively weak flows (P. occidentalis, M. membranacea, and B. crenatus) were affected signifi- cantly by flow speed, whereas growth rates of animals from comparatively high-energy environments (B. glan- dula, S. cariosus, and P. polymerus) were relatively in- sensitive to flow speed. In contrast, animal morphology and behavior were not obviously related to growth re- sponses to flow. A key to understanding the impact of flow on a suspension-feeder's growth may be the animal's ability to handle and process particles that have impacted the feeding apparatus and to deliver them to the point of ingestion.
78 citations
TL;DR: Observations in larvae as disparate as oyster veligers and sea urchin plutei suggest that functionally similar examples of developmental plasticity in the growth of larval parts have evolved more than once and may be widespread.
Abstract: Veliger larvae of mollusks were predicted to develop a larger velum relative to the larval shell when reared with scarce food. The functional consequences of such developmental plasticity would be (1) greater max- imum capacity for capturing particles when food is scarce and (2) greater growth of structures retained in the post- larva when food is abundant. The hypothesis was tested by rearing veligers of the oyster Crassostrea gigas at high (near satiating) and low (growth limiting) concentrations of food. Veligers at the measured shell lengths (>200 ,m) had significantly larger velar lobes and longer prototrochal cilia than veligers reared in low concentrations of food. An analogous response to food levels (relatively longer ciliated band when food is scarce) has now been found for larvae as disparate as oyster veligers and sea urchin plutei. These observations suggest that functionally similar examples of developmental plasticity in the growth of lar- val parts have evolved more than once and may be wide- spread. An alternative interpretation is that differential mortality or growth in a genetically heterogeneous batch of oyster larvae results in advanced veligers of different forms at different concentrations of food. Both interpre- tations suggest an adaptive advantage to growing a larger
70 citations
TL;DR: The data indicate that the length-dependent variation in allozyme frequencies that characterizes sympatric populations can be attributed to a small but significant genotype-dependent difference in length-at-age values, but mostly to large and highly significant differences in viability.
Abstract: Mussels were collected at high and low shore locations from two Mytilus edulis/Mytilus galloprovincialis populations, Croyde Bay and Whitsand Bay, in S.W. England. Genotype-dependent length-at-age values were determined. At high and low shore locations at both sites, M. edulis-like mussels had significantly smaller length-at-age values than M. galloprovincialis-like and putative F1 hybrid individuals. The putative F1 hybrids exhibited length-at-age values between those of the parental types, but much closer to those of M. galloprovincialis-like rather than M. edulis-like individuals. Genotype frequencies as a function of age were determined and relative viability coefficients estimated from comparisons of genotype frequencies of young versus old mussels. At high and low shore locations at both sites, the relative viability coefficient of M. galloprovincialis-like individuals was greater than that of M. edulis-like mussels. Putative F1 hybrids at both sites had relative viability coefficients intermediate between those of the parental types. These data indicate that the length-dependent variation in allozyme frequencies that characterizes sympatric populations can be attributed to a small but significant genotype-dependent difference in length-at-age values, but mostly to large and highly significant differences in viability.
TL;DR: It is suggested that dietary protein contents below 40% w/w and dietary C/N ratios above 10 can qualitatively limit growth rates of juvenile M. trossulus.
Abstract: Juvenile mussels, Mytilus trossulus, were fed for 3 weeks on either low-protein (LP) algae, high-protein (HP) algae, or a combination of LP algae and protein microcapsules (PM). Growth rates of mussels fed a satiation ration of 27.5% body weight (bw; ash-free dry weight of algae/ash-free dry tissue weight of mussels) per day of LP algae (28% protein percent weight per weight) were significantly (P < 0.05) lower than growth rates of mussels fed a satiation ration (27.5% bw d-1) of HP algae (43% protein weight per weight). However, growth rates of mussels fed LP algae (27.5% bw d-1) supplemented with one of three different rations (6, 12 and 18% bw d-1) of PM increased proportionally to PM ration size. Mussels fed a diet containing LP algae with the highest level of PM supplementation grew at rates that were not significantly different from those of mussels fed a diet of HP algae alone. Growth rates of mussels fed LP algae alone were not improved if the ration of LP algae was increased (34.1% bw d-1), indic...
TL;DR: In addition to its hypothesized roles during insemination and sperm release, the mass of plug substance (mating plug) may act as a paternity assurance device that prevents subsequent inseminations by other males.
Abstract: Sperm are packaged into many small spermatophores of variable size in the median vas deferens (MVD) of the male. A substance is intermixed with sperm in the proximal coils of the MVD, separating groups of sperm that will be ejaculated as spermatophores. Most of the ejaculatory duct is occupied by a chamber filled with a transparent, viscous fluid termed the "plug substance." When males are artificially ejaculated, spermatophores are emitted, followed by plug substance that quickly solidifies. This latter material fills and stoppers a space on the female, the median pocket, which serves as an antechamber to the apertures of the internalized seminal receptacles, where sperm from ruptured spermatophores are stored. The slit-like openings to the receptacles are functionally divided into a posterior aperture, stoppered by plug substance after insemination, a closed mid-section, and an anterior exit for sperm release during spawning. Direct insemination by an everted male gonopore is considered more likely than transmission of spermatophores and plug substance via the male gonopod (petasma). In addition to its hypothesized roles during insemination and sperm release, the mass of plug substance (mating plug) may act as a paternity assurance device that prevents subsequent inseminations by other males.
TL;DR: The patterns of mineral composition of static bodies in the Mysidae reflect both anatomical and ecophysiological differences and with respect to population numbers in the different aquatic biota, vaterite prevails in freshwater species and fluorite is dominant among species in all brackish to marine environments.
Abstract: We studied the mineral composition of statoliths in 154 species belonging to 55 genera of Mysidae. Fluorite (CaF2) was found in 86% of Recent species, vaterite (CaCO3) in 9%, and no crystalline component in 5%. Seven samples of fossil statoliths from Upper Miocene deposits were exclusively calcite (CaCO3). Vaterite has the peak of occurrence in fresh water, fluorite in the photic zone of marine waters, and organic statoliths in oceanic deep waters. With respect to population numbers in the different aquatic biota, vaterite prevails in freshwater species and fluorite is dominant among species in all brackish to marine environments. The occurrence of CaCO3 in fresh to brackish waters coincides with fossil records and biogeographical observations. The Ponto-Caspian region is the center of abundance for Recent CaCO3-precipitating species. The rich brackish to freshwater fauna in this region probably has its roots in the brackish Paratethys, where a rich fossil material of calcareous mysid statoliths is known from Upper Miocene sediments. Morphological and scarce palaeontological evidence suggests that the earliest (Carboniferous to Jurassic) Mysidacea were mainly oceanic shrimps without statocysts; these were followed by (bentho) pelagic animals with nonmineralic organic statoliths. With the colonization of coastal to littoral areas by benthopelagic to benthic forms, mineralic statoliths were formed by precipitation of fluorite. Among the modern Mysidae, a special development occurred (in the Miocene) in the Ponto-Caspian region where CaCO3 statoliths appeared in brackish to freshwater forms. As in vertebrates, the patterns of mineral composition of static bodies in the Mysidae reflect both anatomical and ecophysiological differences.
TL;DR: It is suggested that in the absence of elevated levels of counteracting compounds, urea may reach toxic levels and may be one factor limiting the duration of estivation that is survived by these land snails.
Abstract: Biochemical changes occurring over 7 months of estivation were studied in two species of land snail, Oreohelix strigosa (Gould) and O. subrudis (Reeve), to determine whether differential mortality during estivation is related to different energetic strategies. Laboratory-maintained snails, which were fed ad libitum prior to estivation, were compared with snails collected from the field and induced to estivate without augmenting their energy reserves. In all groups, polysaccharide was catabolized early in estivation, and protein was the primary metabolic substrate after polysaccharide reserves were depleted. Lipid was catabolized at a low rate throughout estivation. Rates of catabolism were largely statistically equivalent between species. Urea and purine bases accumulated during estivation as a result of protein catabolism, with the former being quantitatively more important. In both laboratory-maintained and field-collected snails, the rate of urea accumulation was greater in O. subrudis, resulting in hi...
TL;DR: The pencil urchin Phyllacanthus imperialis as discussed by the authors was found to spawn synchronously with the mass spawning of scleractinian corals at Lizard Island, Australia, in two consecutive years.
Abstract: Information for understanding the evolution- ary shift from feeding to nonfeeding in echinoderm larvae can be gained from species whose larval development pattern appears to be intermediate between these ex- tremes. In this paper we report the development of one such species. The pencil urchin Phyllacanthus imperialis spawned synchronously with the mass spawning of scleractinian corals at Lizard Island, Australia, in two consecutive years. Their large yolky eggs (507 utm diameter) developed into nonfeeding echinopluteus larvae with two pairs of larval arms. The arms were identified as postoral and postero- dorsal, which are the first and third pairs in typical echi- noplutei. A larval skeleton was present, with skeletal rods extending the length of the arms. Five primary podia of the juvenile rudiment appeared at 2 days of age. Meta- morphosis of the larvae and settlement began 4 days after fertilization. Histological examination of 2-day-old larvae revealed the presence of a developing gut, but no mouth opened in what would be the oral region of a typical echinopluteus, or the oral surface of the juvenile rudiment in older larvae. Like other cidaroid larvae, this species showed no evidence of an amniotic invagination. The larva of P. imperialis appears to be a transitional form between the morphology of feeding and nonfeeding echinoid larvae. Traces of the ciliary band in the oral re- gion and the presence of arms typical of the echinopluteus larva indicate its evolutionary past, whereas the large egg size and absence of a mouth hint at its future. This larval form provides insights into developmental changes that
TL;DR: The reproduction and development of four species of terebellid polychaetes from the west coast of North America were studied and compared with several other tereBellid species to reveal the covariation of life history traits in the group, and assess any limitations on tere Bellid life history evolution that may be imposed by ancestry or body design.
Abstract: The reproduction and development of four species of terebellid polychaetes from the west coast of North America were studied and compared with several other terebellid species to reveal the covariation of life history traits in the group, and assess any limitations on terebellid life history evolution that may be imposed by ancestry or body design. The four species in the present study span the range of reproductive and developmental modes known for the family Terebellidae. Eupolymnia crescentis and Neoamphitrite robusta are both free spawners that reproduce during discrete 3-month breeding periods. In E. crescentis, oogenesis takes from 5 to 8 months and spawning occurs from July to September, maximum oocyte diameter is 210 {mu}m, and fecundity reaches {approx}128,500 during a single breeding period. The E. crescentis larva develops near the bottom for about 7 days before settling as a five-setiger juvenile. Neoamphitrite robusta reproduces from April to July after a 12-month oogenic cycle; oocytes in this species measure up to 180 {mu}m, and fecundity reaches ~830,000. The two brooders in the study, Ramex californiensis and Thelepus crispus, brood their larvae in the maternal tube. T. crispus reproduces continuously for at least 6 months, and has up to 51,500 larvae in a single brood. The oocytes in this species (400 {mu}m) give rise to larvae that are brooded to the one-setiger stage and then emerge to undergo a one-day planktonic period before the larvae settle and become juveniles at eight setigers. Ramex californiensis reproduces continuously year round; larvae are brooded in cocoons that are laid sequentially in the tube, with up to 44 larvae in a single cocoon. Development from the 410 {mu}m oocytes is direct, and juveniles have 11 setigers. Unlike E. crescentis and N. robusta, in which oogenesis is synchronized within individuals to produce a peak of large oocytes during the discrete spawning period, R. californiensis and T. crispus females have a wide range of oocyte sizes throughout the year. Correlation analysis and analysis of variance of reproductive and developmental traits of these and several other terebellid species revealed some expected trends. For example, egg size varies according to the mode of reproduction (free spawning, extratubular brooding, or intratubular brooding), and is also correlated with juvenile size. However, egg size does not predict fecundity in terebellids when body size is held constant, and brooding is not restricted to small-bodied species. Indeed, the largest and smallest species in the study brood their larvae intratubularly, suggesting that allometric constraints may not be important in determining mode of reproduction in these polychaetes. The Terebellidae is a diverse family found in all marine habitats, yet all known terebellid larvae are non-feeding; this contrasts with the occurrence of both planktotrophy and lecithotrophy in other polychaete families, and leads to the proposal that larval development in terebellids has been constrained during the evolution of the lineage. The results of this study demonstrate that generalizations regarding complex relationships among life history traits are often inappropriate. The need for more comparative studies of marine invertebrate reproduction and development, and the integration of phylogenetic analyses into the study of life history evolution in marine invertebrates is highlighted.
TL;DR: The Chilean oyster Ostrea chilensis broods its larvae within the mantle cavity, and in vivo observations have demonstrated that the female does not undergo gill modification before or during the brooding process, suggesting that the feeding mechanism functions normally during brooding.
Abstract: The Chilean oyster Ostrea chilensis broods its larvae within the mantle cavity. In vivo observations, made with an endoscope, have demonstrated that the female does not undergo gill modification before or during the brooding process. The veliger larvae move freely, have no physical connections with the tissues of the mother, and are often seen as an aggregation ("swarm") around the labial palps. The larvae show a distinct circulation pattern inside the mantle cavity of the mother. Sporadic but strong pallial currents eject larvae from the swarm and transport them between the demibranchs to the posterior region, from which some return anteriorly in the basal ciliated tracts of the gills, and others on the marginal ciliated grooves. Larvae frequently move from the basal to the marginal groove of a demibranch via the ordinary filaments, although they occasionally travel in the opposite direction, moving along the principal filaments from the marginal groove to the basal tract. The circulation of the larvae i...
TL;DR: It is suggested that the balance between growth and onset of reproduction in zooids is determined by the rate of translocate moving through each zooid, which is affected by the strength and proximity of sinks for that translocate, such as the growing edge of the colony.
Abstract: The control of reproduction and growth rate within colonies of marine invertebrates is often conditional and can be very localized. We demonstrate experimentally large and localized shifts in the timing and pattern of reproduction within colonies of a temperate bryozoan (Membranipora membranacea) in response to simulated damage by predators and crowding by conspecifics. In these protandrously hermaphrodite colonies, zooids on the damaged side of a colony reproduced sooner than in unmanipulated regions of the same colony. To examine the influence of the pattern of edge damage on localized reproduction, we damaged the perimeter of circular colonies in two patterns: (1) a continuous half of the edge was trimmed (1/2-Damage) and (2) the edge was trimmed in four alternating one-eighth sections (4/8-Damage). The 1/2-damage treatment triggered localized reproduction, and the more localized four-eighths-damage did not. These experiments demonstrate that the configuration rather than the total amount of edge damage affects the localization of reproduction. In parallel experiments, conspecifics were allowed to crowd half the perimeter of experimental colonies. This treatment also resulted in localized and accelerated reproduction near the contact zone adjacent to a conspecific. Not only do patterns of reproduction change in crowded or damaged colonies, but obstructed colonies also compensate for reduced growth at an obstructed edge by extending the adjacent unobstructed perimeter edge at a greater rate. One model to explain the sort of local cues governing the observed shifts in reproduction and growth rate is a source-sink model. A similar mechanism is proposed to underly growth and reproductive allocation in plants. We suggest that the balance between growth and onset of reproduction in zooids is determined by the rate of translocate moving through each zooid. The rate of translocate movement through zooids is, in turn, affected by the strength and proximity of sinks for that translocate, such as the growing edge of the colony. We propose a simple source-sink model of carbon flow to explain our experimental results. This model would account for the induction of localized reproduction in 1/2 damaged colonies and the lack of localization in 4/8 damaged colonies.
TL;DR: In this paper, levels of methyl farnesoate in the blood and in vitro rates of methyl Farnesoxide synthesis by the man-dibular organ were investigated to determine whether this compound is related to the differences in morphology and reproductive states of distinct types of male spider crabs described by Homola et al. (1992) in winter populations.
Abstract: Levels of methyl farnesoate in the blood and in vitro rates of methyl farnesoate synthesis by the man- dibular organ were investigated to determine whether this compound is related to the differences in morphology and reproductive states of distinct types of male spider crabs described by Homola et al. (1992) in winter populations. Three male types, selected from a summer population, were investigated in detail: ( 1) males with relatively large propoduses (claws) and worn exoskeletons (abraded), (2) males with relatively large propoduses and exoskeletons covered with epicuticle (unabraded), and (3) males with small propoduses and unabraded exoskeletons (small). All males examined had sperm, but abraded males, identical in propodus and body size to unabraded males, had a reproductive system that weighed twice as much. Large-clawed unabraded males had relatively small re- productive systems. Small-clawed males possessed a small reproductive system. Abraded males possessed larger mandibular organs, containing almost twice the total protein, and their man- dibular organs synthesized significantly more methyl far- nesoate in vitro than did the other types of males. Cir- culating levels of methyl farnesoate, in the hemolymph of the abraded males, were more then twice as high as the levels detected in any other type of male.
TL;DR: Comparisons of estimated lifetime reproductive investment made by the two developmental types of S. benedicti indicated that lecithotrophic development involved twice the C and N investment in reproduction, calling into question the use of embryo size as a predictor of parental investment in offspring.
Abstract: Per brood and per offspring C and N investment were examined in four developmental morphs of the spionid polychaete Streblospio: S. shrubsolii (direct development, D), S. benedicti (lecithotrophic, L), S. benedicti (planktotrophic, P), and Streblospio n. sp. (planktotrophic, P). Large differences were apparent among these morphs in fecundity and embryo size. S. shrubsolii (D) and S. benedicti (L) invested about 10 x more C and N in each brood in each offspring and 30% more C and N in each brood than did the morphs with planktotrophic development. C and N concentration (μg per unit volume) was significantly greater in S. benedicti (L) than in the other morphs, though no general relationship with embryo size was evident. The C:N ratio of offspring did not differ among the four morphs. Comparisons of estimated lifetime reproductive investment made by the two developmental types of S. benedicti indicated that lecithotrophic development involved twice the C and N investment in reproduction. Positive, significant regressions were evident between embryo C and N content and embryo volume at the intermorph level. Significant intra-morph regressions were evident in all morphs but Streblospio n. sp. (P). However, the large amount of variation unaccounted for by embryo volume calls into question the use of embryo size as a predictor of parental investment in offspring.
TL;DR: It is suggested that enhanced scope for activity (predator avoidance) may enhance survival of scallops at intermediate sizes, when they become too heavy to maintain elevation but have not yet attained effective refuge in size.
Abstract: Ontogenetic changes in the vertical distribu- tion of a cohort of juvenile bay scallops, Argopecten irradians, on eelgrass, Zostera marina, were followed throughout the summer and early fall in two Long Island embayments (New York, USA). Despite site-specific dif- ferences in eelgrass height and density, more than 95% of post-settlement scallops remained attached above the bottom until they reached a shell height of about 11 mm. Over a 5-week period, scallops gradually relocated until, at a mean size of 3 1 mm, all occurred on the bottom. The decline in percent attachment coincided with a 5-fold in- crease (from 16 to 84 pmoles min-' g muscle dry wt-') in the activity of octopine dehydrogenase (proposed here as an index of the scallops' capacity for burst swimming activity), and in maximum rate of increase in the shell aspect ratio. While attached to eelgrass, scallops were nonuniformly distributed, with greatest concentration at mid-canopy. Following disturbance, they rapidly regained above-ground position, attaining asymptotic heights within 3-10 h. This and prior studies suggest that the climbing behavior of the bay scallop is an adaptive re- sponse to high predation pressure at small sizes. Enhanced scope for activity (predator avoidance) may enhance sur- vival of scallops at intermediate sizes, when they become too heavy to maintain elevation but have not yet attained effective refuge in size.
TL;DR: Five neuropeptides isolated from CNS extracts of the horseshoe crab Limulus polyphemus are members of a novel family with virtually no relationship to FMRFamide, and at least one member of the novel family inhibits the isolated heart of Limulus.
Abstract: Five neuropeptides were isolated from CNS extracts of the horseshoe crab Limulus polyphemus by high pressure liquid chromatography (HPLC). The peptides were identified by radioimmunoassays (RIAs) based on two antisera raised to FMRFamide-related peptides (FaRPs). The purified peptides were analyzed by automated sequencing and mass spectrometry, and the following sequences were obtained: DEGHKMLYFamide, GHSLLHFamide, PDHHMMYFamide, DHGNMLYFamide, and GGRSPSLRLRFamide. The first four peptides are members of a novel family with virtually no relationship to FMRFamide. GGRSPSLRLRFamide, on the basis of structural similarity, becomes the second member of a class of FaRPs known previously only from a peptide isolated from mosquito heads. At least one member of the novel family (GHSLLHFamide) inhibits the isolated heart of Limulus.
TL;DR: The data suggest that metabolic rates are low in leptocephali, which implies that the demand for nutrients is also relatively low, and it is argued that the apparent diet of these larvae seems capable of providing a sufficient supply of nutrients under these conditions.
Abstract: The respiratory electron transport system (ETS) assay was used to estimate metabolic rates in four species of eel (Anguilliformes: Ophichthidae and Congridae) leptocephali (Myrophis punctatus, Ophichthus sp., Hildebrandia flava, and one unidentified congrid) and the bonefish (Albuliformes: Albulidae: Albula sp.). Wet-weight-specific ETS values in whole-body homogenates, assayed at physiological temperatures, ranged from 4-20 {mu}-at O h-1 (g wet wt)-1. Arrhenius activation energies (Ea) ranged from 11.0-15.7 kcal mole-1. Both wet-weight-specific ETS activity and oxygen consumption rate increased approximately fivefold during metamorphosis of leptocephali of Albula sp. Wet-weight-specific ETS activity showed little change as leptocephali of M. punctatus transformed into glass eels, but increased about fivefold as glass eels metamorphosed into elvers. No significant difference was found in ETS activity measured in fresh early metamorphic leptocephali of Albula sp. and leptocephali that had been stored frozen at -70{deg}C for up to 15 months. The data suggest that metabolic rates are low in leptocephali, which implies that the demand for nutrients is also relatively low. We argue that the apparent diet of these larvae seems capable of providing a sufficient supply of nutrients under these conditions.
TL;DR: The ultrastructural demonstration of Antho-RFamide immunoreactivity in interneuronal synaptic vesicles, together with the immunofluorescence and electrophysiological studies of other investigators, suggest thatAntho- RFamide plays a role in neurotransmission in sea anemones.
Abstract: Antho-RFamide is a neuropeptide isolated from the sea anemone Anthopleura elegantissima. Antho-RFamide immunoreactivity was localized in four different populations of neuronal vesicles in the tentacle nerve plexus of Anthopleura. Small, opaque, neuronal vesicles, averaging 49 nm in diameter, were gold-labeled at two-way synapses. Heterogranular vesicles, averaging 184 nm in diameter, were gold-labeled in a neuronal swelling adjacent to a muscle cell process. These vesicles were similar in size to a third class of gold-labeled dense-cored vesicles. A fourth class of immunogold-labeled vesicles observed in neuronal swellings had light cores and averaged 129 nm in diameter. Using 5-nm gold particles, we observed a heavy labeling of the granular cores of the dense-cored vesicles, suggesting that the immunoreactivity is specific to the vesicle core. The ultrastructural demonstration of Antho-RFamide immunoreactivity in interneuronal synaptic vesicles, together with the immunofluorescence and electrophysiological studies of other investigators, suggest that Antho-RFamide plays a role in neurotransmission in sea anemones.
TL;DR: Data suggest that, during normal development, induction of one or more ALDH-like proteins occurs simultaneously in both the lens and ciliated duct soon after the differentiation of lens cells, which begins approximately 7-10 days after hatching.
Abstract: We localized one or more aldehyde dehydrogenase (ALDH)-like proteins in the bacterially bioluminescent light organ of the sepiolid squid Euprymna scolopes, and determined the temporal changes in expression through normal light organ development. Our previous studies have revealed that 70% of the total protein in the light organ lens of adult animals is comprised of an ALDH-like protein, which we called L-crystallin. In the present study, antibodies raised to this protein were used in immunocytochemical analyses which showed that, in adult light organ lens cells, ALDH-like protein was localized to the cytoplasm, but not to the nuclei or mitochondria. Labeling in adult tissue was also found in moderate abundance in the ciliated duct epithelium, a tissue that is in direct contact with the bacterial symbionts. To determine the spatial and temporal onset of expression of ALDH-like protein(s), we examined light organs from juveniles at developmental stages before and after the differentiation of lens cells, whi...
TL;DR: Fertilized oyster eggs, treated with and without cytochalasin B (CB) at varying periods during meiotic maturation, were examined following 7-aminoactinomycin D (7-AAD) and anti-{beta} tubulin staining for DNA and microtubular patterns, respectively.
Abstract: Fertilized oyster (Crassostrea gigas) eggs, treated with and without cytochalasin B (CB) at varying periods during meiotic maturation, were examined following 7-aminoactinomycin D (7-AAD) and anti-{beta} tubulin staining for DNA and microtubular patterns, respectively. Electron microscopic observations of untreated fertilized eggs revealed the development of an extensive network of endoplasmic reticulum during germinal vesicle breakdown. Germinal vesicle breakdown was not accompanied by the disappearance of the nucleolus; the latter persisted morphologically unchanged throughout fertilization. The first meiotic spindle [12.4 +/- 1.0 {mu}m (1) x 5.4 +/- 0.55 {mu}m (diameter (d); metaphase plate)] was oriented with its long axis perpendicular to the egg's surface. In contrast, the second meiotic spindle was approximately one half the size of the first [7.4 +/- 0.65 {mu}m (1) x 2.91 +/- 0.29 {mu}m (d)] and initially oriented with its long axis parallel to the egg's surface. Just prior to anaphase II, the spindle rotated so that its long axis became perpendicular to the egg's surface. Following its incorporation into the egg cytoplasm, the sperm nucleus dispersed but did not form a nuclear envelope until the completion of polar body formation. Just prior to pronuclear migration, an array of microtubules assembled around the female pronucleus, and then regressed; concomitantly, a sperm aster formed in conjunction with the centrosome associated with the developing male pronucleus. Following their migration and apposition with one another, both pronuclei underwent prophase as independent structures. Chromosomes from the male and female pronuclei became organized on a mitotic spindle in preparation for first cleavage. In zygotes treated with CB continuously or for just meiosis I, anaphase I occurred; however, a polar body failed to form. Consequently, all the diads were retained within the zygote and became situated on a tripolar spindle. In such cases, anaphase II resulted in the production of a variable number of chromosomal aggregations that developed into pronuclei (3 to 6). In contrast, zygotes treated with CB during meiosis II developed spindles characteristic of untreated specimens; however, polar body formation was blocked, resulting in the development of usually two maternal pronuclei. Morphogenesis of C. gigas fertilized eggs is discussed in reference to similar processes in other species and with respect to strategies of triploid embryo production using CB.
TL;DR: The results suggest that microtubules are involved in the movement of some ooplasmic inclusions, including oil droplets, toward the vegetal pole; themovement of ooplasmic inclusions toward the animal pole; and pronuclear migration.
Abstract: Using time-lapse video microscopy, we found that ooplasmic inclusions in the fertilized medaka egg displayed two types of movement during ooplasmic segregation. The first manifested itself as the movement of many inclusions (diameter = 1.5-11 μm) toward the animal pole at about 2.2 μm min-1; this type of movement appeared to be streaming. The second type of movement was faster (about 44 μm min-1) and saltatory; inclusions displaying this type of movement were smaller (diameter ≤1.0 μm) and moved toward the vegetal pole. The movement of oil droplets toward the vegetal pole of the egg may represent a third type of motion. All these movements began only after a strong contraction of the ooplasm toward the animal pole, which at 25°C began 10-12 min after fertilization and <3 min after formation of the second polar body. In eggs treated with microtubule poisons--colchicine, colcemid, or nocodazole--oil droplets did not move toward the vegetal pole, saltatory motion toward the vegetal pole was absent, and the growth of the blastodisc was slowed. Eggs treated with β-lumicolchicine, an inactive derivative of colchicine, showed normal movements. Colchicine, while not inhibiting formation of the second polar body, did inhibit pronuclear migration. These results suggest that microtubules are involved in the movement of some ooplasmic inclusions, including oil droplets, toward the vegetal pole; the movement of ooplasmic inclusions toward the animal pole; and pronuclear migration.
TL;DR: These experiments suggest that there are at least two centers in the larva that control metamorphosis, and both substrate-induced and high K+ seawater-induced meetamorphosis may involve the function of voltage-dependent calcium channels.
Abstract: Larvae of Terebratalia will not undergo metamorphosis when maintained in a sterile environment unless they are 9-10 days old; under these conditions the frequency of normal metamorphosis is low. Four-day larvae are normally induced to metamorphose when they contact a suitable substrate. They will also undergo metamorphosis when they are treated with high K+ seawater in the presence of Ca2+. Additional experiments indicate that both substrate-induced and high K+ seawater-induced metamorphosis may involve the function of voltage-dependent calcium channels. Metamorphosis involves settlement of the larva followed by formation of the protegulum, the initial shell. In larvae that have been aged in a sterile environment and in larvae treated with high K+ in seawater with low Ca2+, partial metamorphosis takes place. Under these conditions the larva does not settle, however a protegulum forms. Substrate-induced metamorphosis does not occur in the absence of the distal end of the pedicle lobe of the larva which nor...