Showing papers in "The Biological Bulletin in 1997"
TL;DR: The differences found between the effects of field acclimatization and laboratory thermal acclimation suggest that the stress response is modulated by environmental factors in addition to body temperature, and caution is required in extrapolating from laboratory acclimating studies to acclim atization effects in field populations.
Abstract: Heat-shock protein (hsp) expression was examined in gill of field-acclimatized and laboratory-acclimated mussels (Mytilus californianus) from the Oregon coast. Endogenous levels of heat-shock proteins in the 70-kDa class (hsp70 isoforms) and profiles of induction temperature for newly synthesized hsp 70 were measured in freshly field-collected specimens as functions of location height in the intertidal and season, and in mussels after 7 weeks of laboratory thermal acclimation. There were significant differences in endogenous levels of hsp70 as functions of season and collection height. Strong induction of new hsp70 synthesis occurred at body temperatures within the range measured in field specimens. Profiles of hsp70 thermal induction varied significantly with season, but not with height of collection. In contrast to the large differences in hsp70 expression between winter- and summer-acclimatized mussels, no differences related to temperature occurred in the differently acclimated mussels. The differences found between the effects of field acclimatization and laboratory thermal acclimation suggest that the stress response is modulated by environmental factors in addition to body temperature. Thus, caution is required in extrapolating from laboratory acclimation studies to acclimatization effects in field populations. The seasonal and tidal-height variations in the heat-shock response are discussed in the context of energy costs of protein turnover.
244 citations
TL;DR: Since strong locomotory abilities are not a priority in the deep sea, deeper-living cephalopods may rely more heavily on means of locomotion that are more efficient than jet propulsion via mantle contractions--means such as fin swimming or medusoid swimming utilizing the arms and extensive webbing present in many deep-living species.
Abstract: The metabolic rates of 33 species of pelagic cephalopods from California and Hawaii were measured and correlated with minimum depth of occurrence. Mean metabolic rates ranged from 0.07 {mu}mol O2g-1 h-1 for the deep-living vampire squid, Vampyroteuthis infernalis, to 8.79 {mu}mol O2 g-1 h-1 for Gonatus onyx, a vertically migrating squid. An individual of V. infernalis, which lives within the oxygen minimum layer off California, had the lowest mass-specific metabolic rate ever measured for a cephalopod (0.02 {mu}mol O2g-1 h-1, 1050 g wet weight). For species collected in sufficient quantity and size range, metabolism was related to body size. Critical partial pressures of oxygen (Pc) were determined for Hawaiian and Californian cephalopods. Pc values for Hawaiian animals were considerably higher than for those taken off California, a trend that corresponds to the higher levels of environmental oxygen in the Hawaiian waters. Buffering capacity ({beta}) of mantle muscle, assayed in eight cephalopod species, was used to estimate the capacity for glycolytic energy production. Mean {beta} ranged from 1.43 slykes for a bathypelagic octopod, Japetella heathi, to 77.08 slykes for an epipelagic squid. Sthenoteuthis oualaniensis. Significant declines with increasing depth of occurrence were observed for both metabolism and {beta}. The decline in metabolic parameters with depth is interpreted as a decreased reliance on locomotory abilities for predator/prey interactions in the light-limited deep sea. The decline in metabolism with depth observed for pelagic cephalopods was significantly steeper than that previously observed for either pelagic fishes or crustaceans. We suggest that since strong locomotory abilities are not a priority in the deep sea, deeper-living cephalopods may rely more heavily on means of locomotion that are more efficient than jet propulsion via mantle contractions--means such as fin swimming or medusoid swimming utilizing the arms and extensive webbing present in many deep-living species. The greater efficiency of deeper-living cephalopods may be responsible for the observation that the decline in metabolic rates with depth is more pronounced for pelagic cephalopods than for fishes or crustaceans.
152 citations
TL;DR: Characteristics of development that are common to hydra and triploblastic phyla are presented, including the time required to traverse each of the stages, and the changes that occur in the type and number of cells throughout the stages.
Abstract: Embryogenesis in hydra includes a variable period of dormancy; and this period, as well as subse- quent stages through hatching, takes place within a thick cuticle that hinders observation. Thus, although the early stages of development have been well-charac- terized qualitatively, the middle and later stages are only poorly understood. Here, we provide a detailed de- scription of the stages of embryogenesis, including the time required to traverse each of the stages, and the changes that occur in the type and number of cells throughout the stages. The events of cleavage and gas- trulation occur within the first 48 h. Cleavage is holo- blastic and unipolar and leads to a single-layered coe- loblastula. Gastrulation occurs by ingression and is fol- lowed by the deposition of the thick cuticle. Thereafter, during the variable period of dormancy ranging from 2-24 weeks, little occurs; the important events are the conversion of the outer layer into an ectoderm and the appearance of the interstitial cell lineage. During the last 2 days before hatching, the endoderm and gastric cavity form, while stem cells of the interstitial cell lin- eage proliferate and differentiate into neurons, nemato- cytes, and secretory cells. Finally, the cuticle cracks, and the hatchling enlarges and emerges from the cuticle as a functional animal. The formation of the gastric cavity and the hatching of the embryo are both explicable in terms of the osmotic behavior of the animal and the hy- drostatic forces generated by this behavior. Characteris- tics of development that are common to hydra and trip- loblastic phyla are presented.
146 citations
TL;DR: The results show that oxidative stress in A. pulchella is primarily an animal response, and suggest that the presence of symbiotic algae, although sufficient to cause hyperoxia, is not necessary for the appearance of oxidative Stress in these anemones at elevated temperature.
Abstract: Production of superoxide ions within tissues of the symbiotic sea anemone Aiptasia pulchella was de- tected using SOD-inhibitable cytochrome c reduction and quantified by SOD-inhibitable reduction of nitro blue tetrazolium (NBT). Intact aposymbiotic and sym- biotic specimens of A. pulchella produced superoxide in response to acute, sublethal thermal stress. Neither light nor inhibition of symbiont photosynthesis by (3,4-di- chlorophenyl)- 1,l -dimethylurea (DCMU) affected su- peroxide production. The time course of superoxide ion production strongly resembled the time course of in- creased dark respiration by intact anemones, suggesting that the effect of elevated temperature on host mitochon- dria may account for increased superoxide production. Interestingly, freshly isolated algae (FIZ) did not release superoxide ions in response to elevated temperature, and net oxygen production decreased greatly in both intact symbiotic anemones and in FIZ within 20 minutes after temperature elevation. These results show that oxidative stress in A. pulchella is primarily an animal response, and suggest that the presence of symbiotic algae, although sufficient to cause hyperoxia, is not necessary for the ap pearance of oxidative stress in these anemones at ele- vated temperature.
117 citations
TL;DR: The discontinuity between the zoogeographic distributions of these two species at about 40 {deg}-41{deg}N latitude in both the eastern and western Pacific suggests that temperature is a factor in determining their present distribution and limiting their dispersal to other regions.
Abstract: Diagnostic length differences in a PCR amplified fragment of the gene for byssal adhesive protein were used to study the zoogeographic distribution of Mytilus galloprovincialis and M. trossulus along the west coast of North America and in Japan. The distributions of M. galloprovincialis and M. trossulus are patchy, although an overall geographic pattern emerges. M. galloprovincialis was the only species found on either Kyushu or Honshu, and it was the most abundant mussel from Tomales Bay to San Diego, California. M. trossulus was the only bay mussel found on Hokkaido and in Alaska, and it was by far the most abundant mussel along the coasts of Washington and Oregon. Mytilus galloprovincialis and M. trossulus are sympatric and hybridize near Whidbey Island, Washington, in San Francisco Bay, and in San Diego Bay. A second diagnostic anonymous nuclear PCR marker was used to examine the extent of hybridization at Palo Alto, California. At this site, genotypes appeared to be a mixture of M. galloprovincialis, F1 hybrids between M. galloprovincialis and M. trossulus, and backcrosses between the F1's and M. galloprovincialis. The discontinuity between the zoogeographic distributions of these two species at about 40{deg}-41{deg}N latitude in both the eastern and western Pacific suggests that temperature is a factor in determining their present distribution and limiting their dispersal to other regions.
111 citations
TL;DR: Results provide the first direct evidence for myosin involvement in neuronal growth cone function and suggest that retrograde flow results from superimposition of two independent processes: actin assembly and myOSin-based filament retraction.
Abstract: Actin filaments assembled at the leading edge of neuronal growth cones are centripetally transported via retrograde F-actin flow, a process fundamental to growth cone guidance and other forms of directed cell motility. Here we investigated the role of myosins in retrograde flow, using two distinct modes of myosin inhibition: microinjection of NEM inactivated myosin S1 fragments, or treatment with 2,3-butanedione-2-monoxime, and inhibitor of myosin ATPase. Both treatments resulted in dose-dependent attenuation of retrograde F-actin flow and growth of filopodia. Growth was cytochalasin sensitive and directly proportional to the degree of myosin inhibition, suggesting that retrograde flow results from superimposition of two independent processes: actin assembly and myosin-based filament retraction. These results provide the first direct evidence for myosin involvement in neuronal growth cone function.
104 citations
TL;DR: The Xylophaga symbiosis suggests a mechanism for the conversion of terrestrially derived cellulosic carbon from wood into animal biomass in the deep sea.
Abstract: Bacterial endosymbionts found in gill tissues in several bivalve families convert otherwise unavailable energy sources (sulfide, methane, or cellulose) to forms readily metabolized by their hosts. We investigated the existence of such a symbiosis in two species of Xylophaga (family Pholadidae). The genus Xylophaga includes opportunistic species that are the predominant colonizers of wood at depths greater than 150 m. It has been hypothesized that, like their shallow-water counterparts the shipworms (family Teredinidae), species of Xylophaga utilize wood for nutrition. Results from transmission and scanning electron microscopy of X. atlantica and X. washingtona clearly demonstrate the presence of endosymbionts that resemble the shipworm endosymbionts both morphologically and in their anatomical location within the gills. Xylophaga and the teredinids both have a caecum packed with wood chips but lack the dense populations of microorganisms associated with cellulose digestion in termites or ruminants. These ...
91 citations
TL;DR: For the first time, 3-D, radio-linked acoustic positioning (RAP) is applied to this confusing process of mass spawning of squids, and early results now reveal a choreography that is, in fact, well organized in time and space.
Abstract: A mass spawning of squid resembles, at first glance, a chaotic "nuptial dance" (1). But for the first time, we have applied 3-D, radio-linked acoustic positioning (RAP) to this confusing process, and our early results now reveal a choreography that is, in fact, well organized in time and space. Remote tracking with RAP of individual Loligo vulgaris reynaudii off South Africa has provided insights into the daily sequence of behaviours that lead these animals to aggregate for sexual selection. Each dawn, the squid navigate for several kilometers, towards the shore, to small, well-defined zones near egg beds on the substrate. After several hours of circling above the egg beds, a pelagic, 3-D lek-like aggregation of large males forms: females are drawn in, and the aggregation condenses as the females and males pair, mate, and lay eggs. Smaller "sneaker males" remain on the periphery of the mating arena and, from this station, attempt extra-pair copulations (EPCs). The mating system of squids is thus unexpectedly complex, rivaling those of mammals and birds (2, 3). Commercial squid-jigging fishermen in South Africa have recently been attracted to the spawning grounds, and they have been successful. Moreover, their activities may be selective for large males. Thus, attention should be devoted to ensuring that such targeted fishing does not alter the characteristics of squid population genetics. Remote tracking and video observations, in combination with genetic analyses, may offer a new opportunity to monitor mating effort and reproductive success, and thus to manage the fishery.
88 citations
TL;DR: Experiments and field data on blue crab from mid-Chesapeake Bay between 1991 and 1994 were used to test whether large males have advantages over small males in accessing females and in sperm competition, suggesting that mating with large females may not be the primary determinant of male reproductive success.
Abstract: Experiments and field data on blue crab, Callinectes sapidus, from mid-Chesapeake Bay between 1991 and 1994 were used to test whether large males have advantages over small males in accessing females and in sperm competition. In the field, large males were paired more often, especially with large, more fecund females. However, the variance in the relationship between male and female size in mating pairs was high, suggesting that mating with large females may not be the primary determinant of male reproductive success. Large males had proportionately longer chelipeds, which may provide an advantage in aggressive interactions for females or in struggles to control females. Previous work indicates that sperm competition may occur in blue crabs and that ejaculate size may influence a male’s ability to compete during sperm competition. Large males stored more seminal fluid and spermatophores and passed a larger volume of ejaculate to each mate than did small males. Ejaculate volume averaged 47% of a male’s stored supply. However, ejaculate volume increased with the duration of copulation but decreased with successive matings, such that males needed about 15 days between matings to pass similar-sized ejaculates to successive mates. Pre-copulatory mate guarding may serve as a time to replenish ejaculate contents, and thus its duration also influences a male’s performance in sperm competition.
88 citations
TL;DR: Previous chromatographic evidence suggesting the presence of catecholamines in the larvae of bivalve molluscs is confirmed, but putative neuronal circuits that may control various larval behaviors are identified.
Abstract: Previous studies have suggested an involvement of catecholamines in the control of several larval behaviors, such as feeding, locomotion, and induction of settling and metamorphosis. In the present...
82 citations
TL;DR: Fertigation trials were conducted to determine the extent of reproductive isolation among the seven morphologically defined species of the scleractinian coral genus Platygyra, on the Great Barrier Reef, and reveal a discontinuity between reproductive and morphological species boundaries.
Abstract: In mass-spawning corals, potential exists for gametes of a number of species to mix in the water column. The existence of morphologically distinct sympatric coral populations despite such an event implies the presence of isolating mechanisms to prevent hybridization and maintain species boundaries. Over 380 fertilization trials were conducted to determine the extent of reproductive isolation among the seven morphologically defined species (morphospecies) of the scleractinian coral genus Platygyra, on the Great Barrier Reef. Results from these experiments demonstrate that fertilization between-morphospecies can occur at rates equivalent to within-morphospecies fertilizations, indicating that no gametic-level barriers to fertilization exist among these morphological species. Observations of spawning times both in the field and in the laboratory have shown that all seven morphospecies spawn on the same night and that there is considerable overlap in the hour of spawning among them. These data indicate that few, if any, temporal barriers to fertilization exist among morphospecies of Platygyra on the Great Barrier Reef. In addition, larvae resulting from between-morphospecies crosses are capable of settlement and subsequent growth equivalent to that of within-morphospecies larvae. Our results reveal a discontinuity between reproductive and morphological species boundaries within the scleractinian genus Platygyra and challenge species definitions within the Scleractinia. It is not yet clear what mechanisms might maintain morphological boundaries in Platygyra in the face of the clear potential for gamete mixing. The disjunct distributions of certain morphospecies along latitudinal and habitat boundaries, and the small levels of variation in reproduction may be two such mechanisms.
TL;DR: The interspecific comparison suggests that about half the metabolic expenditure for planktotrophic development goes toward building and operating the larval feeding apparatus and that the return on this investment is 400%-600% over the larva period.
Abstract: The energy required for development was measured in two closely related echinoids with differing modes of development. Heliocidaris tuberculata hatches from a 95-{mu}m egg (~0.1 {mu}g dry organic mass) and develops via a planktotrophic larva over 21-30 days into a juvenile (5.3-7.5 {mu}g). H. erythrogramma hatches from a ~400 {mu}m egg (11.6-19.0 {mu}g) and develops over 3.5-4 days via a lecithotrophic larva into a juvenile with a mass not detectably different from that of the egg. Oxygen consumption increased exponentially in H. tuberculata and peaked at about 200-500 pmol indiv-1 h-1, whereas the oxygen consumption of H. erythrogramma increased rapidly, reaching a plateau at about 800 pmol indiv-1 h-1 on the second day. Metabolic energy expenditure for development to metamorphosis was twofold higher for H. tuberculata (52-60 mJ indiv-1) than for H. erythrogramma (26-35 mJ indiv-1). The interspecific comparison suggests that about half the metabolic expenditure for planktotrophic development goes toward ...
TL;DR: The evolutionary relationships between the homeodomains of sea anemones and of bilaterian animals were assessed through database searches and phylogenetic analyses and suggests that the Hox gene complement of cnidarians is larger than previously expected.
Abstract: Homeobox genes belong to a phylogenetically widespread family of regulatory genes that play important roles in pattern formation and cell-fate specification in several model systems (e.g., Drosophi...
TL;DR: Traits such as highly synchronous spawning, high fecundity, large egg size, large polyps, and large colonies directly and indirectly enhance P. porosa gamete production and fertilization and reduce the importance of sperm limitation in the population dynamics of the gorgonian Pseudoplexaura porosa.
Abstract: in situ fertilization was examined in the gor gonian Pseudoplexaura porosa during 1994 and 1995 spawning events in the San Bias Islands, Panama, to as sess spatial and temporal variation in fertilization suc cess and to determine whether in situ fertilization was sperm limited. Fertilization rates did not differ signifi cantly between years (60% vs. 55%), but monthly means were significantly different, ranging from 22% to 66%. Fertilization rate varied among days, ranging from 0 to 85%; 80% ofthis variability was explained by daily van ation in the number of colonies that spawned. A weighted average ofin situ fertilization rates suggeststhat 67% or more of spawned eggs are fertilized in nature. Sperm limitation did not occur on the nights when most of the colonies synchronously spawned and when most of the eggs were released. Eggs collected downstream of the population often had higher fertilization rates than eggs collected either adjacent to their source colony or eggs collected in the middle ofthe population, which in dicates that in dense populations, eggs may have multiple opportunities to be fertilized. Traits such as highly synchronous spawning, high fecundity, large egg size, large polyps, and large colonies directly and mdi rectly enhance P. porosa gamete production and fertil ization. These life-history traits reduce the effects of ga mete dilution during spawning events and thus decrease the importance ofsperm limitation in the population dy namics ofP. porosa.
TL;DR: The small Hawaiian sepiolid Euprymna scolopes, with its symbiotic luminous bacterium Vibrio fischeri, was cultured through one complete life cycle in 4 months, indicating that the host organism of this symbiosis can soon be cultured with consistency through its brief life cycle, thus opening new avenues of research into developmental aspects ofThis symbiosis.
Abstract: The small Hawaiian sepiolid Euprymna scolopes, with its symbiotic luminous bacterium Vibrio fischeri, was cultured through one complete life cycle in 4 months. Paralarval squid hatchlings were acti...
TL;DR: It is argued that the apical ganglion, by virtue of its serotonergic cells, is well-suited to play important roles in the integration of sensory information to achieve proper motor adaptation to variable seawater conditions.
Abstract: The apical ganglion is a highly conserved structure present in various marine invertebrate larvae. Although one of the hallmarks of this ganglion is the presence of serotonergic cells, little is known about the structure and function of these cells. We have examined this ganglion in larvae of the marine mollusc Aplysia with light- and electron-microscopic immunocytochemistry. The results indicate that the cellular composition of the apical ganglion of Aplysia is very similar to that of other opisthobranchs. It consists of three classes of sensory cells (ampullary, para-ampullary, and ciliary tuft cells) and of other nerve cell types. Almost a third of the cells in the apical ganglion of Aplysia are serotonergic, and these can be divided into two classes: three para-ampullary and two interneuronal cells. All of the serotonergic cells extend an axon into the central nervous system. The variety of sensory and serotonergic cell types suggests that each type processes distinct attributes of the sensory environ...
TL;DR: It is demonstrated that genotypes in the colonial ascidian Botryllus schlosseri vary in sperm production, which is manifested as variation in testis size, and broad-sense heritabilities for a suite of life-history traits suggest a three-way tradeoff in resource allocation to asexual growth and sexual reproduction via male and female function.
Abstract: Intraspecific variation in life-history strategy provides a valuable opportunity for examining how natural selection acts on life-history variants to mold reproductive strategies. Evaluating the consequences of selection requires knowledge of the range of phenotypic variation in life histories, the extent to which variation is genetically based, and possible correlations among different traits that might constrain or promote the effect of selection on individual traits. We explored life-history variation in the colonial ascidian Botryllus schlosseri (a cyclical hermaphrodite) by growing clonal replicates of 18 genotypes in a common-garden experiment. Colonies of this species have previously been shown to vary in egg production and growth rate. We demonstrate that genotypes also vary in sperm production, which is manifested as variation in testis size. We then calculate broad-sense heritabilities for a suite of life-history traits and demonstrate correlations among traits that suggest a three-way tradeoff in resource allocation to asexual growth and sexual reproduction via male and female function. This correlation structure suggests that selection cannot act independently on individual life-history traits.
TL;DR: In palaemonid shrimps the pillar cells apparently play a dual role: ions move preferentially through ion transporters in the microvilli above the pillar cell perikaryon, while respiratory gases are exchanged through the fine flange regions in contact with the hemolymph.
Abstract: The ultrastructure of the pillar cells in the gill lamellae of the freshwater shrimp Macrobrachium olfersii was examined to evaluate the routes of salt and water movement across the gill epithelium and into the hemolymph. Alterations were morphometrically quantified in shrimp maintained in fresh water (FW, <0.5{permill} salinity) and after acclimation to saline media (21{permill} or 28{permill} salinity). The tissue interface between the hemolymph and the external medium consists exclusively of the thin apical flange regions of the pillar cells, the upper membrane of which is highly amplified by dense microvilli and overlain by a thin cuticle. The lower flange membrane, bathed by the hemolymph, is smooth and not invaginated. Contiguous flanges are strongly bound by junctional structures including desmosomes and septate junctions. The basal surface of the pillar cell perikaryon is linked to the adjacent septal cells through many basolateral junctions. The septal cell plasmalemma is abundantly and deeply invaginated, each infolding enclosing numerous mitochondria; these characteristics are typical of salt-transporting machinery. After shrimps were acclimated to saline media for 10 days, the thickness of the pillar cell flanges was significantly reduced (from 1.3 to {approx}0.4 {mu}m), as was the height (from 0.8 to 0.3 {mu}m) and density (from 4.0 to {approx} 1.8 microvilli/{mu}m) of the apical microvilli. This reduction in the apical surface area of the pillar cells appears to lead to decreased ionic permeability, concomitant with a reduction in Na+/K+-ATPase activity, thus limiting Na+ uptake. In contrast to the brachyurans, in which the respiratory and ion-transporting mechanisms are differentially located in the anterior and posterior gills, in palaemonid shrimps the pillar cells apparently play a dual role: ions move preferentially through ion transporters in the microvilli above the pillar cell perikaryon, while respiratory gases are exchanged through the fine flange regions in contact with the hemolymph.
TL;DR: The gastropod Ifremeria nautilei lives in high abundance around deep-sea hydrothermal vents of the Western Pacific and is the host partner in a thiotrophic chemoautotrophic bacterial symbiosis, which is underlined by the reduced size of the host's stomach.
Abstract: The gastropod Ifremeria nautilei lives in high abundance around deep-sea hydrothermal vents of the Western Pacific. The filaments of its ctenidium are very long and have a rigid axis with a hemocoelic vessel and a strongly ciliated epithelium. The flattened part of each filament largely consists of bacteriocytes that are distally filled with numerous gram-negative bacteria. The bacteria lie one by one in vacuoles that seem to be part of an interconnected tubular system. Some of the apical vacuoles regularly showed what could be openings to the ambient seawater. This special topological arrangement of the bacteria suggests that in a morphological series mirroring the supposed evolutionary pathway from extra- to intracellular symbioses, I. nautilei might correspond to an intermediate stage. The high sulfur content and the low stable carbon isotope values measured in this study, combined with corresponding data from the literature, indicate that I. nautilei is the host partner in a thiotrophic chemoautotroph...
TL;DR: Since long sclerites deter feeding by predatory snails, the increase in sclerite length in response to scarring of mid-branch regions may function as an inducible defense.
Abstract: The gorgonian coral Briareum asbestinum contains skeletal elements (sclerites) that vary in length and density within and among local populations. Data from previous work suggested that the sclerite compositions of colonies may be altered in response to environmental cues such as predator damage, water motion, and light level. To test these hypotheses, colonies from shallow reefs were transplanted to racks at a single location where the three environmental factors of interest were artificially manipulated. After 9-14 weeks of growth, sclerite morphologies and densities had not changed in response to shading or to water-motion reductions that mimicked deep-water conditions. However, colonies did respond significantly to two types of simulated predator damage. Following tip amputation, sclerites in the regenerated tips of damaged colonies were shorter and more dense than in the controls. In contrast, mid-branch scarring caused colonies to produce longer sclerites at lower densities. Since long sclerites deter feeding by predatory snails, the increase in sclerite length in response to scarring of mid-branch regions may function as an inducible defense.
Journal Article•
TL;DR: Measurements of transport rates of amino acids and sugars by these animals, and calculations of the energy input from these substrates, indicate that the cumulative transport of DOM from seawater during development to the early juvenile stage could supply an amount of energy equivalent to the initial maternal endowment of energy reserves to the oocyte of this lecithotrophic species.
TL;DR: Results contradict the hypothesis that sclerosponges are monophyletic and imply that a massive calcareous skeleton has evolved independently in several lineages of sponges.
Abstract: To test the competing hypotheses of poly- phyly and monophyly of "sclerosponges," sequences from the 5' end of 2% ribosomal RNA were obtained for Astrosclera willeyana, Acanthochaetetes wellsi, and six other demosponge species. Phylogenetic relationships deduced from parsimony and neighbor-joining analyses suggest that these sclerosponges belong to two different orders of Demospongiae: Astrosclera willeyana, being closely related to the Agelasidae, belongs to the Agela- sida, Acanthochaetetes wellsi, being closely related to the Spirastrellidae, belongs to the Hadromerida. These results contradict the hypothesis that sclerosponges are mono- phyletic and imply that a massive calcareous skeleton has evolved independently in several lineages of sponges.
TL;DR: Analysis of chromosome numbers suggests that C. leana, C. aff.
Abstract: Hermaphroditic freshwater clams in the genus Corbicula produce non-reductional spermatozoa. The DNA content of spermatozoa was almost identical with that of somatic cells in C. leana from Mie Prefecture, Japan. Hermaphroditic C. aff. fluminea from Saga Prefecture and C. fluminea from Taiwan also produce non-reductional spermatozoa. On the other hand, spermatozoa of the dioecious C. sandai had half the DNA found in somatic cells. Analysis of chromosome numbers suggests that C. leana (3n = 54 in somatic cells and 18 in meiotic cells) from Mie Prefecture and C. aff. fluminea (2n = 36 in gills and 18 bivalents in meiotic cells) from Saga Prefecture are triploids and diploids, respectively. C. leana, C. aff. fluminea, and C. fluminea may lack either first or second meiosis, resulting in non-reductional spermatozoa. We assume that gynogenetic reproduction occurs in both species; maternal chromosomes are also nonreductional, and spermatozoa activate development of the eggs, but do not contribute to the offspring.
TL;DR: The prediction of bimodality is tested in the holothuroid and ophiuroid echinoderms and it is shown that although the natural log-transformed egg size distributions are visually unimodal, the Holothurian egg size distribution is statistically composed of two discrete modes.
Abstract: Marine invertebrates can be categorized into species that reproduce by producing either large numbers of small, energetically inexpensive eggs that become planktotrophic larvae, or fewer, larger eggs with more yolk and lecithotrophic development (1). The selective advantages of these alternative strategies were considered in a series of simple mathematical models by Vance (2, 3). These models predicted that intermediate egg sizes should have lower reproductive efficiency, and that only extreme egg sizes should be evolutionarily stable (2, 3). Specifytally, Vance's models (2, 3) and later modifications (4-7), predict that eggs of marine invertebrates should have bimodal size distributions, rejecting the contrast between small egg/feeding and large egg/nonfeeding modes of development and the selection against intermediate egg sizes. Evidence for bimodality in egg size distributions is, however, equivocal, with unimodal distributions seen in the majority of comparative studies that are appropriate tests of t...
TL;DR: It is suggested that zooxanthellae from a range of host species and environments can establish symbioses with C. pedunculatus and that, over long periods under laboratory conditions, heterologous zooxanhellae may populate C. Pedunculatu to the same extent as homologous Zooxanthelae.
Abstract: The uptake and persistence of symbiotic dinoflagellates (zooxanthellae) were measured in the temperate sea anemone Cereus pedunculatus (Pennant). Aposymbiotic specimens of C. pedunculatus were inoculated with zooxanthellae freshly isolated from a range of temperate and subtropical Anthozoa. Each inoculate consisted of zooxanthellae from a single host species and was either homologous (zooxanthellae from a host of the same species as the one being inoculated) or heterologous (from a host of a different species than the one being inoculated). The densities of zooxanthellae in host tissues were determined at regular intervals. C. pedunculatus took up homologous and heterologous zooxanthellae to similar degrees, except for zooxanthellae from the temperate Anthopleura ballii, which were taken up to a lesser extent. The densities of all zooxanthellae declined between 4 hours and 4 days after uptake, indicating that zooxanthellae were expelled, digested, or both during this period. The densities of all zooxanthellae increased between 2 and 8 weeks after inoculation, indicating zooxanthella growth. Over the entire 8-week period after uptake, densities of homologous zooxanthellae were always greater than those of heterologous zooxanthellae. Between 8 and 36 weeks after infection, densities of homologous zooxanthellae declined markedly and densities of some heterologous zooxanthellae increased further, resulting in homologous and heterologous zooxanthella densities being the same at 36 weeks. These densities were the same as those in naturally infected C. pedunculatus of similar size. The results suggest that zooxanthellae from a range of host species and environments can establish symbioses with C. pedunculatus and that, over long periods under laboratory conditions, heterologous zooxanthellae may populate C. pedunculatus to the same extent as homologous zooxanthellae.
TL;DR: The palaemonid EC is a dynamic structure throughout embryonic development, and permeability of the EC during the 12-d incubation period is found to decrease between 0 and 5 d after oviposition, and then increase until hatching.
Abstract: The embryo of the grass shrimp, Palaemo- netes pugio, is surrounded during development by a protective extracellular coat designated as the embry- onic coat (EC). At hatching, this EC is composed of four embryonic envelopes (EE), each of which is composed of multiple layers. The outermost layer of the EC, the outer investment coat (OIC), is derived primarily, if not completely, from pleopods of the female. The first en- velope (EE1) forms as a bilayered envelope, EEla and EE 1b, immediately after oviposition. The OIC becomes closely associated with EE1 and remains in close con- tact with EE1 until hatching occurs. An additional layer, EE lc, is added to the inner side of EE 1 between 3 and 5 d after oviposition. Three more embryonic enve- lopes, EE2, EE3, and EE4, are formed between the embryo and EE 1 by 7 d after oviposition. Formation of embryonic envelopes continues until 10 d after ovipo- sition; by this time each envelope is morphologically distinct in composition, with "outer" and "inner" sides clearly identifiable. All but the innermost embryonic envelope (EE4) are shed by the embryo about 6 h before hatching. Permeability of the EC during the 12-d incu- bation period is found to decrease between 0 and 5 d after oviposition, and then increase until hatching. Flu- orescently labeled lectins react positively with the OIC,
TL;DR: Results showed that prey capture by M. senile is a function of both flow regime and polyp size, and different optimal flow regimes exist for different size classes, suggesting that small anemones are better at feeding in moderate- to high-flow habitats.
Abstract: The sea anemone Metridium senile is a quantitatively important passive suspension feeder in hard-bottom communities on the west coast of Sweden and occurs in aggregations with different size distribu- tions. This study tests the hypothesis that different polyp sizes have different optimal flow regimes maximizing prey capture. Results showed that prey capture by M. senile is a function of both flow regime and polyp size, and different optimal flow regimes exist for different size classes. Large anemones had a maximum feeding effi- ciency at the slowest flow, medium-sized anemones at moderate flow, and small anemones at moderate- to high-flow regimes. Small anemones showed consistently higher feeding rates (per unit of biomass and area of ten- tacle crown) at all velocities above 10 cm s-' and exhib- ited less flow-induced deformation of the tentacle crown, suggesting that small anemones are better at feeding in moderate- to high-flow habitats. Different vertical pro- jections of large and small anemones in the boundary layer could only partly account for differences in feeding success among size classes. Feeding rate was also a func- tion of upstream conspecifics, declining asymptotically to 30% of the maximum rate. The negative effects of neighbors on feeding in aggregations with clonal rather than polyp growth appear to be compensated for by the generally higher feeding efficiency of small polyps.
TL;DR: It is concluded that there may be a chiral specificity for the 5C compound, a-ketoglutarate, for the observed antimicrobial stimulation.
Abstract: may be used by marine microorganisms as an important reserduced antibiosis against both gram-positive and gram-negative test organisms, /I-ketoglutarate as a supplement was inactive against both test organisms. We conclude that there may be a chiral specificity for the 5C compound, a-ketoglutarate, for the observed antimicrobial stimulation. Low molecular weight carboxylic acids are produced and consumed during the TCA cycle and glycolysis, so these compounds are ubiquitous in marine organisms. Moreover, phytoplankton release a significant fraction of their fixed carbon into seawater as low molecular weight carboxylic acids; e.g., oxaloacetate and a-ketoglutarate (2). Therefore, these classes of or-