Showing papers in "The Biological Bulletin in 1999"
TL;DR: This study is the first to examine the onset of symbiosis between a motile cnidarian host and its algal symbiont in the scleractinian coral Fungia scutaria, which produces planula larvae that lack zooxanthellae.
Abstract: Many corals that harbor symbiotic algae (zooxanthellae) produce offspring that initially lack zooxanthellae. This study examined late larval development and the acquisition of zooxanthellae in the scleractinian coral Fungia scutaria, which produces planula larvae that lack zooxanthellae. Larvae reared under laboratory conditions developed the ability to feed 3 days after fertilization; feeding behavior was stimulated by homogenized Artemia. Larvae began to settle and metamorphose 5 days after fertilization. In laboratory experiments, larvae acquired experimentally added zooxanthellae by ingesting them while feeding. Zooxanthellae entered the gastric cavity and were phagocytosed by endodermal cells. As early as 1 h after feeding, zooxanthellae were observed in both endodermal and ectodermal cells. Larvae were able to form an association with three genetically distinct strains of zooxanthellae. Both zooxanthellate and azooxanthellate larvae underwent metamorphosis, and azooxanthellate polyps were able to ac...
165 citations
TL;DR: Gene sequences from an Atlantic sample matched sequences from the California chemotype M colonies, suggesting that this type may be cosmopolitan due to transport on boat hulls, and indicates that the chemotypes represent different species.
Abstract: Although the cosmopolitan marine bryozoan Bugula neritina is recognized as a single species, natural products from this bryozoan vary among populations. B. neritina is the source of the anticancer drug candidate bryostatin 1, but it also produces other bryostatins, and different populations contain different bryostatins. We defined two chemotypes on the basis of previous studies: chemotype O contains bryostatins with an octa-2,4-dienoate substituent (including bryostatin 1), as well as other bryostatins; chemotype M lacks bryostatins with the octa-2,4-dienoate substituent. B. neritina contains a symbiotic gamma-proteobacterium "Candidatus Endobugula sertula," and it has been proposed that bryostatins may be synthesized by bacterial symbionts. In this study, B. neritina populations along the California coast were sampled for genetic variation and bryostatin content. Colonies that differ in chemotype also differ genetically by 8% in the mitochondrial cytochrome c oxidase subunit 1 (CO I) gene; this difference is sufficient to suggest that the chemotypes represent different species. Each species contains a distinct strain of "E. sertula" that differs at four nucleotide sites in the small subunit ribosomal RNA (SSU rRNA) gene. These results indicate that the chemotypes have a genetic basis rather than an environmental cause. Gene sequences from an Atlantic sample matched sequences from the California chemotype M colonies, suggesting that this type may be cosmopolitan due to transport on boat hulls.
156 citations
TL;DR: High TMAO contents in muscles of other animals collected off the coast of Oregon may reflect diet, reduce osmoregulatory costs, increase buoyancy, or counteract destabilization of proteins by pressure.
Abstract: In muscles of shallow-living marine animals, the osmolyte trimethylamine N-oxide (TMAO) is reportedly found (in millimoles of TMAO per kilogram of tissue wet weight) at 30-90 in shrimp, 5-50 in crabs, 61-181 in skates, and 10-70 in most teleost fish. Recently our laboratory reported higher levels (83-211 mmol/kg), correlating with habitat depth, in deep-sea gadiform teleosts. We now report the same trend in muscles of other animals, collected off the coast of Oregon from bathyal (1800-2000 m) and abyssal plain (2850 m) sites. TMAO contents (mmol/kg +/- SD) were as follows: zoarcid teleosts, 103 +/- 9 (bathyal) and 197 +/- 2 (abyssal); scorpaenid teleosts, 32 +/- 0 (shallow) and 141 +/- 16 (bathyal); rajid skates, 215 +/- 13 (bathyal) and 244 +/- 23 (abyssal); caridean shrimp, 76 +/- 16 (shallow), 203 +/- 35 (bathyal), and 299 +/- 28 (abyssal); Chionoecetes crabs, 22 +/- 2 (shallow) and 164 +/- 15 (bathyal). Deep squid, clams, and anemones also had higher contents than shallow species. Osmoconformers showed compensation between TMAO and other osmolytes. Urea contents (typically 300 mmol/kg in shallow elasmobranchs) in skates were 214 +/- 5 (bathyal) and 136 +/- 9 (abyssal). Glycine contents in shrimp were 188 +/- 17 (shallow) and 52 +/- 20 (abyssal). High TMAO contents may reflect diet, reduce osmoregulatory costs, increase buoyancy, or counteract destabilization of proteins by pressure.
149 citations
TL;DR: The data show that dispersal by rafting is by far the most likely explanation for trans-Pacific range extension by this oyster, and reject competing hypotheses of vicariance, anthropogenic introduction, and dispersals by ancestral lineages with extended larval development.
Abstract: Stretches of deep ocean are potent barriers to the dispersion of nearshore, benthic marine taxa. Such obstacles can be overcome, however, by species that have either a protracted pelagic larval development or a benthic life-history stage that can be transported by rafting (1, 2). The oyster Ostrea chilensis lacks an extended pelagic larval phase and has discrete populations in New Zealand and Chile that are separated by one of the largest extents (>7000 km) of open ocean on the planet. We tested competing dispersal hypotheses for this species by using ontogenetically informative, dated fossil and sub-fossil shell material, as well as molecular phylogenetic analyses. Our data show that dispersal by rafting is by far the most likely explanation for trans-Pacific range extension by this oyster, and we reject competing hypotheses of vicariance, anthropogenic introduction, and dispersal by ancestral lineages with extended larval development. The presence of 0. chilensis in Chile is important because it clearly demonstrates that transoceanic range extension by rafting is potentially available to a significant fraction of nearshore marine biotas.
112 citations
TL;DR: The mucus used by the limpet Lottia limatula to form glue-like attachments was compared biochemically to the slippery mucus produced during other activities, such as suction adhesion, and three notable differences emerged.
Abstract: The mucus used by the limpet Lottia limatula to form glue-like attachments was compared biochemically to the slippery mucus produced during other activities, such as suction adhesion. Colorimetric assays revealed the protein content of the adhesive mucus to be 2.1 times greater than that of the non-adhesive form, and the carbohydrate content to be 1.9 times greater. Both forms of mucus contained roughly six times as much protein as carbohydrate, and there was no difference in their inorganic elemental compositions. Quantitative analysis of the protein content by SDS-PAGE and a scanning densitometer revealed a similar protein composition in both forms of mucus; but three notable differences emerged. First, the overall difference in protein concentration was confirmed. In addition, there was a 118 kD protein that was common only in the adhesive mucus, and a 68 kD protein that occurred only in the non-adhesive mucus.
99 citations
TL;DR: The results obtained provide interesting insights into the origins of AIDS, and have important practical implications for understanding.
Abstract: Acquired immune deficiency syndrome (AIDS) can be caused by either of two retroviruses, known as human immunodeficiency virus types 1 and 2 (HIV-l and HIV-2). Related viruses have been isolated from a number of other primate species; these have been termed simian immunodeficiency viruses (SIV), although in their natural hosts they do not appear to cause disease. Since complete or partial sequences have been determined for very large numbers of both HIVs and SIVs, and because they exhibit an extraordinary degree of sequence diversity, these viruses provide an interesting and challenging model system in which to study molecular evolution. Furthermore, the results obtained provide interesting insights into the origins of AIDS, and have important practical implications for understanding
99 citations
TL;DR: Evidence is presented that oxygen- and sulfur-centered free radicals are produced during the oxidation of sulfide in seawater, and a reaction pathway for sulfide oxidation that is consistent with observations is proposed, providing a possible mechanism for the unexplained light emission from hydrothermal vents.
Abstract: The discovery of symbioses between marine invertebrates and sulfide-oxidizing bacteria at deep-sea hydrothermal vents and in other high-sulfide marine environments has stimulated research into the adaptations of metazoans to potentially toxic concentrations of sulfide Most of these studies have focused on a particular action of sulfide-its disruption of aerobic metabolism by the inhibition of mitochondrial respiration-and on the adaptations of sulfidetolerant animals to avoid this toxic effect (I) We propose that sulfidic environments impose another, hitherto overlooked type of toxicity: exposure to free radicals of oxygen, which may be produced during the spontaneous oxidation of sulfide, thus imposing an oxidative stress Here we present evidence that oxygen- and sulfur-centered free radicals are produced during the oxidation of sulfide in seawater, and we propose a reaction pathway~for sulfide oxidation that is consistent with our observations We also show that chemiluminescence at visible wavelengths occurs during sulfide oxidation, providing a possible mechanism for the unexplained light emission from hydrothermal vents (2, 3) In the presence of molecular oxygen and trace metal catalysts, hydrogen sulfide spontaneously oxidizes Oxidation-reduction reactions frequently involve free-radical intermediates, and a metal-catalyzed pathway in which the initial reactions of sulfide oxidation form superoxide and sulfide radicals has been proposed (4) The proposed reaction begins with four steps:
93 citations
TL;DR: Comparisons of AFLP patterns obtained from DNA from sperm, somatic tissues, and zooxanthellae suggest that the technique routinely amplifies coral (animal) DNA, and analyses based on somatic tissue may be feasible, particularly after diagnostic differences have been established using sperm DNA.
Abstract: Analyses of DNA have not been widely used to distinguish coral sibling species. The three members of the Montastraea annularis complex represent an important test case: they are widely studied and dominate Caribbean reefs, yet their taxonomic status remains unclear. Analysis of amplified fragment length polymorphisms (AFLPs) and a microsatellite locus, using DNA from sperm, showed that Montastraea faveolata is genetically distinct. One AFLP primer yielded a diagnostic product (880 bp in M. faveolata 920 bp in M. franksi and M. annularis) whose homology was established by DNA sequencing. A second primer revealed a 630 bp band that was fixed in M. faveolata, and rare in M. franksi and M. annularis; in this case homologies were confirmed by Southern hybridizations. A tetranucleotide microsatellite locus with several alleles exhibited strong frequency differences between M. faveolata and the other two taxa. We did not detect comparable differences between M. annularis and M. franksi with either AFLPs (12 primers screened) or the microsatellite locus. Comparisons of AFLP patterns obtained from DNA from sperm, somatic tissues, and zooxanthellae suggest that the technique routinely amplifies coral (animal) DNA. Thus analyses based on somatic tissues may be feasible, particularly after diagnostic differences have been established using sperm DNA.
91 citations
TL;DR: It is hypothesized that schooling and diurnal activity may offset the disadvantage presented by increased visibility to predators, and the rapid changeability and the diversity of body patterns used for crypsis and communication are discussed in the context of the behavioral ecology of this species.
Abstract: Squids have a wide repertoire of body patterns; these patterns contain visual signals assembled from a highly diverse inventory of chromatic, postural, and loco motor components. The chromatic components reflect the activity of dermal chromatophore organs that, like the pos tural and locomotor muscles, are controlled directly from the central nervous system. Because a thorough knowledge of body patterns is fundamental to an understanding of squid behavior, we have compiled and described an etho gram (a catalog of body patterns and associated behaviors) for Loligo pea!ei. Observations of this species were made over a period of three years (440 h) and under a variety of behavioral circumstances. The natural behavior of the squid was filmed on spawning grounds off Cape Cod (northwest em Atlantic), and behavioral trials in the laboratory were run in large tanks. The body pattern componentsâ€"34 chro matic (including 4 polarization components), 5 postural, and 12 locomotorâ€"are each described in detail. Eleven of the most common body patterns are also described. Four of them are chronic, or long-lasting, patterns for crypsis; an example is Banded Bottom Sitting, which produces disrup tive coloration against the substrate. The remaining seven patterns are acute; they are mostly used in intraspecific communication among spawning squids. Two of these acute patternsâ€"Lateral Display and Mate Guarding Patternâ€"are used during agonistic bouts and mate guarding; they are visually bright and conspicuous, which may subject the squids to predation; but we hypothesize that schooling and diurnal activity may offset the disadvantage presented by
90 citations
TL;DR: It is determined that NO donors block pharmacologically induced metamorphosis in the mud snail Ilyanassa obsoleta, whereas injections of inhibitors of nitric oxide synthase (NOS) allow competent larvae to become juveniles.
Abstract: Metamorphosis is a crucial life-history event that can change an organism's form, function, behavior, and ecological interactions. In the Mollusca, several neurotransmitters and neuromodulators play inductive or inhibitory roles in the pathways that govern larval metamorphosis. Nitric oxide (NO) has been implicated in developmental processes in vertebrates and arthropods, but not previously in molluscs. We determined that NO donors block pharmacologically induced metamorphosis in the mud snail Ilyanassa obsoleta, whereas injections of inhibitors of nitric oxide synthase (NOS) allow competent larvae to become juveniles. We describe a new developmental role for NO, as an endogenous inhibitor of molluscan metamorphosis.
88 citations
TL;DR: It is concluded that the InsR-like molecules evolved in sponges prior to the "Cambrian Explosion" and contributed to the rapid appearance of the higher metazoan phyla.
Abstract: One autapomorphic character restricted to all Metazoa including Porifera (sponges) is the existence of transmembrane receptor tyrosine kinases (RTKs). In this study we screened for molecules from one subfamily within the superfamily of the insulin receptors. The subfamily includes the insulin receptors (InsR), the insulin-like growth factor I receptors, and the InsR-related receptors-all found in vertebrates-as well as the InsR-homolog from Drosoph- ila melanogaster. cDNAs encoding putative InsRs were isolated from the hexactinellid sponge Aphrocallistes vas- tus, the demosponge Suberites domuncula, and the calcar- eous sponge Sycon raphanus. Phylogenetic analyses of the catalytic domains of the putative RTKs showed that the sponge polypeptides must be grouped with the InsRs. The relationships revealed that all sponge sequences fall into one branch of this group, whereas related sequences from mam- mals (human, mouse, and rat), insects and molluscs, and polypeptides from one cephalochordate, fall together into a second branch. We have concluded that (i) the InsR-like
TL;DR: The results indicate that larvae of A. modesta metamorphose in response to both water-soluble and surface-associated carbohydrates of V. longicaulis, and that the soluble cue exists as both high and low molecular weight isoforms.
Abstract: Larvae of the specialist marine herbivore AIde na modesta (Opisthobranchia: Ascoglossa) metamorphose in response to a chemical settlement cue from the alga Vaucheria Iongicaulis, the obligate adult prey. Bioactivity coeluted with both high and low molecular weight carbo hydrates in solution, and with insoluble high molecular weight carbohydrates associated with the algal cell wall. Larvae metamorphosedin response to water conditioned by V. longicaulis, as well as to frozen and homogenized algal tissue. Tl@einducer was efficiently extracted from the algae with boiling water, but after all soluble activity was cx tracted, residual tissue still induced larval settlement. Etha nol precipitation of a boiled-water extract followed by gel filtration. chromatography showed that the precipitate con Wined carbohydrates of >100,000 Da molecular weight, while the supernatant contained only low molecular weight carbohydrates (<2,000 Da); in both cases all activity was associated with the carbohydrate peak. An aqueous-insolu ble 4% NaOH extract was chromatographedin 7 M urea to yield a bioactive high molecular weight carbohydrate peak. Activity was not affected by proteinase K or mild acid hydrolysis, but was significantly decreased by periodate treatment. The results indicate that larvae of A. modesta metamorphose in response to both water-soluble and sur face-assOciated carbohydrates of V. longicaulis, and that the soluble cue exists as both high and low molecular weight
TL;DR: The persistence of neurogenesis among the different neuronal types of the central olfactory pathway throughout adult life suggests an enormous structural plasticity of brain circuitry that may enable the longlived decapod crustaceans to adapt to changing olfaction environments.
Abstract: To examine the distribution of neurogenesis in the central olfactory pathway of adult decapod crustaceans, we labeled, in vivo, six species of decapod crustaceans representing most infraorders (shrimps, spiny lobsters, clawed lobsters, crayfish, hermit crabs, true crabs) with the proliferation marker 5-bromo-2'-deoxyuridine (BrdU). In all tested species a group of small, neuron-like nuclei in the lateral soma clusters of the brain was labeled; the lateral soma clusters are composed of the cell bodies of ascending olfactory projection neurons. In only a few instances did groups of BrdU-positive nuclei also occur in the other soma clusters of the central olfactory pathway. In the spiny lobster (Panulirus argus), a group of small neuron-like nuclei was labeled in the medial soma clusters containing the cell bodies of local interneurons of the olfactory deutocerebrum. In the hermit crab (Pagurus bernhardus), and the true crab (Cancer pagurus), a group of small neuron-like nuclei was labeled in soma clusters located in the eyestalks. These soma clusters probably contain the cell bodies of local interneurons of the hemiellipsoid bodies, to which the olfactory projection neurons ascend. These results indicate that neurogenesis occurs among olfactory projection neurons in the adult brain. Among the other neuronal types of the central olfactory pathway, however, neurogeneis is restricted to specific taxa. The persistence of neurogenesis among the different neuronal types of the central olfactory pathway throughout adult life suggests an enormous structural plasticity of brain circuitry that may enable the longlived decapod crustaceans to adapt to changing olfactory environments.
TL;DR: Faster-growing oysters feed more rapidly; invest more energy per joule ingested; show a higher net growth efficiency; and are able to allocate less energy per unit of tissue growth, than slower-growing individuals.
Abstract: Sydney rock oysters were sampled from a mass selection experiment for growth (the "selected" category) and from a control ("not selected") population and held in the laboratory at three ration levels. We evaluated three models to explain faster rates of growth by selected oysters. Selection resulted in oysters feeding at up to twice the rate and with greater metabolic efficiency than controls. A field experiment confirmed that selection leads to faster rates of feeding across a wide range of food concentrations. Selected oysters also grew more efficiently, at a smaller cost of growth (Cg): mean values for Cg were 0.43 J {middot} J-1 in selected individuals and 0.81 J {middot} J-1 in the controls. In contrast, oysters in both categories showed similar metabolic rates at maintenance, i.e., at a ration supporting zero growth. There was no evidence that differential energy allocation affected the balance between total metabolic requirements above and below zero net energy balance. By experimenting with select...
TL;DR: The results show that tunic morphology and cellulose composition are similar in ascidians and thaliaceans (pyrosomas, doliolids, and salps) and the tunic is considered to be a homologous tissue in these animals, and their most recent common ancestor would have possessed this tissue.
Abstract: The morphology and cellulosic composition of the tunic was studied in pelagic tunicates (3 pyrosomas, 2 doliolids, and 13 salps). The tunic is transparent and gelatinous, consisting of an electron-dense cuticular layer with a fibrous tunic matrix. The thickness and density of the cuticular layer and of the tunic matrix differ from species to species. In some salps, the cuticular layer has numerous minute protrusions that are structurally identical to those found in several ascidians. Free mesenchymal cells (tunic cells) are distributed in the tunic. Whereas the number of tunic cells in the pyrosomas is similar to that in ascidians, there are many fewer tunic cells in doliolids and salps. These differences may be caused by the different functions of the tunic in each group. The existence of cellulose in the tunic was confirmed using electron diffraction in all of the species studied thus far. Their diffractograms indicate that the cellulose microfibrils consist of nearly pure I{beta} of the allomorph. These results show that tunic morphology and cellulosic composition are similar in ascidians and thaliaceans (pyrosomas, doliolids, and salps). The tunic is considered to be a homologous tissue in these animals, and their most recent common ancestor would have possessed this tissue.
TL;DR: In this paper, the effects of extreme flow on the growth and morphology of a bryozoan, Membranipora membranacea, encrusting laminarian fronds in the Rapids of Lough Hyne (=Ine), County Cork, Ireland was described.
Abstract: We describe the effects of extreme flow on the growth and morphology of a bryozoan, Membranipora membranacea, encrusting laminarian fronds in the Rapids of Lough Hyne (=Ine), County Cork, Ireland. An ultrasonic current meter was used to characterize ambient flow regimes at the level of the algal canopy over a complete tidal cycle at three sites within the Rapids. Colonies collected from sites exposed to different flows showed a trend towards miniaturization with increased flow: the zooids were less elongate, the lophophores were smaller in diameter and had fewer tentacles, and the distances between excurrent jets were shorter. These morphological changes probably place feeding surfaces into slower flow regimes of the boundary layer. Similar growth rates of colonies at sites differing in flow provide evidence that this miniaturization is adaptive and that bryozoans are capable of adopting appropriate morphological responses to varying environmental regimes. Such plasticity should be considered when assessi...
TL;DR: The central nervous system of the cypris larva of Balanus amphitrite consists of a brain and posterior ganglion, and the antennular nerve is the major peripheral extension of the nervous system.
Abstract: The central nervous system of the cypris larva of Balanus amphitrite consists of a brain and posterior ganglion. The neuropil of the brain includes protocerebral and deutocerebral divisions, with nerve roots from the protocerebrum extending to the eyes and frontal filaments, and nerve roots from the deutocerebrum extending to the first antennae (antennules) and cement glands. The neuropil of the posterior ganglion includes subesophageal and thoracic divisions, with nerve roots from subesophageal divisions extending to the gut, and nerve roots from each of the six thoracic divisions extending to their corresponding thoracic appendage. The antennular nerve is the major peripheral extension of the nervous system and is composed in part by afferent fibers that innervate setae on the antennules. The cyprid nervous system is small, containing fewer than 2000 neurons, but is well organized for coordinating a response to settlement cues.
TL;DR: Retention of a large velum in Littorina that develop entirely within egg capsules may facilitate feeding on intracapsular protein, in the absence of specialized assimilative organs found in other species with encapsulated development.
Abstract: Many gastropod species develop within egg capsules within which larvae are provided with extraembryonic nutrients. Species with encapsulated development frequently have transitory embryonic organs, such as "larval kidneys," that may represent specializations for consumption of intracapsular nutrition. Larvae of Littorina species with nonplanktonic, encapsulated development consume intracapsular albumen, but they lack obvious morphological modifications for albumen consumption. To determine the mechanism and location of protein uptake, larvae of seven species of Littorina (L. keenae, L. littorea, L. plena, L. saxatilis, L. scutulata, L. sitkana, L. subrotundata) were exposed to solutions of either fluorescently labeled protein (FITC-bovine serum albumen) or ferritin. Under fluorescence microscopy, larvae of all species with encapsulated, nonplanktonic development displayed strong regional affinity for FITC in the ciliated cells of the velum, whereas hatched larvae of planktotrophic Littorina species did not. Transmission electron microscopy of epithelial cells of nonplanktotrophic veligers exposed to ferritin supported the interpretation that localized affinity for labeled protein indicated endocytotic protein uptake. Planktotrophic Littorina and Littorina with encapsulated, nonplanktonic development were shown to share equivalent velar width/larval length ratios during early embryonic development, whereas a literature search suggested that in other nonplanktotrophic prosobranchs the velum is relatively smaller than in planktotrophs. Retention of a large velum in Littorina that develop entirely within egg capsules may facilitate feeding on intracapsular protein, in the absence of specialized assimilative organs found in other species with encapsulated development.
TL;DR: Although tRNA is best known as a component of the translation apparatus, tRNA and tRNA-like molecules also play key roles-either as template or as primer-in a wide variety of replicative processes.
Abstract: Although tRNA is best known as a component of the translation apparatus, tRNA and tRNA-like molecules also play key roles-either as template or as primer-in a wide variety of replicative processes. These processes include replication of single-stranded RNA viruses of bacteria, plants, and possibly mammals; replication of duplex DNA plasmids of fungal mitochondria; replication of retroviral and pararetroviral genomes; and replication of modem chromosomal telomeres. Consider the following two obvious examples. First, the 3' end of many eubacterial and plant single-stranded RNA viruses resembles the "top half' (acceptor stem/loop) of tRNA, with a stem/loop structure immediately followed by the 3' terminal sequence CCA. This tRNA-like structure functions as the template for initiation of RNA replication. In fact, some of these tRNA-like structures are so similar to bona fide tRNA that they can be aminoacylated by the corresponding aminocyl-tRNA synthetases. Second, the replication of most retroviral RNA genomes begins with annealing of a mature tRNA to the primer binding site on genomic RNA; reverse transcriptase then uses the tRNA as primer to copy the RNA genome into the first strand of DNA. Thus in each case tRNA or a
TL;DR: Results suggest that in mediating this response, juvenile hormones may cause activation of PKC, leading to subsequent modulation of potassium and calcium channels.
Abstract: The signal transduction pathway by which juvenile hormone-active compounds induce settlement and metamorphosis of metatrochophore larvae of the polychaete annelid Capitella sp. 1 was investigated. The known protein kinase C (PKC) activator phorbol-12, 13-dibutyrate was an active inducer of settlement and metamorphosis, whereas H-7, an inhibitor of PKC, inhibited settlement and metamorphosis in response to juvenile hormone III (JH III). JH III and methyl farnesoate (MF) also directly activated, in vitro, both a PKC-like enzyme present in Capitella homogenates and PKC purified from rat brain. In addition, binding studies using the fluorescent PKC inhibitor RIM-1 revealed the presence of a PKC-like enzyme in intact Capitella larvae and juveniles. Settlement and metamorphosis of the larvae was also stimulated by membrane-depolarizing concentrations of KCI. This response to KCl was inhibited by tetraethylammonium. The potassium channel blocker 4-aminopyridine induced settlement and metamorphosis, whereas settl...
TL;DR: Analysis of larval anatomy and morphology through ontogeny reveals significant differences in the temporal sequence of segmentation, and in the character of segments formed, from the typical embryological pattern described for other polychaete families, such as nereidids or spionids.
Abstract: Seven post-gastrulation larval stages are described for the sedentary polychaete Chaetopterus. Analysis of larval anatomy and morphology through ontogeny reveals significant differences in the temporal sequence of segmentation, and in the character of segments formed, from the typical embryological pattern described for other polychaete families, such as nereidids or spionids. When compared in alternative phylogenetic schemes, these differences represent significant developmental heterochrony, among other evolutionary transitions, which has arisen in the chaetopterid lineage. The heterochrony is correlated with the extreme morphological regionalization along the anterior-posterior body axis, a feature that is also characteristic of chaetopterids.
TL;DR: Changes in locomotor activity in four species of crabs of differing osmoregulatory ability are described, with differences in behaviors between the species correlated closely with previously reported changes in cardiovascular function and hemolymph flow.
Abstract: Reports focusing on the behavioral responses of crabs to exposure to low salinity have involved choice chamber experiments or quantification of changes in activ- ity. In addition to describing changes in locomotor activity in four species of crabs of differing osmoregulatory ability, the present study describes six behaviors: increased move- ment of the mouthparts, cleaning of the mouthparts with the chelae, cleaning of the antennae and antennules with the maxillipeds, flicking of the antennae, retraction of the an- tennules, and extension of the abdomen. Callinectes sapidus and Carcinus maenas are classed as efficient osmoregula- tors, and in general, showed an increase in these behaviors with decreasing salinity. Cancer magister, a weak regulator, and Libinia emarginata, an osmoconformer, exhibited these behaviors to a lesser degree and became inactive in the lower salinities, tending to adopt an isolation-type response. The differences in behaviors between the species correlated closely with previously reported changes in cardiovascular function and hemolymph flow. These overt reactions are discussed in relation to the osmoregulatory physiology and ecology of each crab species.
TL;DR: Because the lower marsh is accessible at every high tide, differences in regularly flooded accessible marsh area may not be great enough to cause a large difference in mummichog growth.
Abstract: r A Sweeney o Club Head 1 enclosure experiments in which mummichogs were denied access to the marsh (4, 5), ail fish in our study could access the marsh, though the extent of this access differed among creeks. Thus, because the lower marsh is accessible at every high tide, differences in regularly flooded accessible marsh area may not be great enough to cause a large difference in mummichog growth. This work was funded by NSF Research Experience for Undergraduates through the Boston University Marine Program and the Plum Island Sound Long-term Ecological Research Program. We thank Simon Panall, Nate Tsao, Marc McDonnell, Susan Oleszko, Jo30 Salgado, Jaimie Champagne, and Jeff Hughes for their help with the project.
TL;DR: The temporal characteristics of the visual systems of eight species of mesopelagic crustaceans were studied using the electroretinogram (ERG), showing an unusually high flicker fusion frequency of the deeper living euphausiids, which may be correlated to their preference for bioluminescent prey.
Abstract: The temporal characteristics of the visual sys- tems of eight species of mesopelagic crustaceans were stud- ied using the electroretinogram (ERG). Experiments were conducted on shipboard, using dark-captured specimens collected off the south coast of Cuba. As one would expect based on the relative intensity differences in their light environments, the deepest living species, Systellaspis debi- lis and Sergia jilictum, have low maximum critical flicker fusion frequencies (CFFs) of 21-25 Hz, whereas the shal- lower living species Oplophorus gracilirostris and Janicella spinacaudu have higher maximum CFFs (31-32 Hz). One of the shallowest living species, Funchalia villosa, has an unusually low maximum CFF (24 Hz), which may be a function of working with a dark-adapted eye. Two of the bilobed euphausiid species, Nematobrachionfiexipes and N. sexspinosus, have very high maximum CFFs (44-57 Hz), comparable to those of surface-dwelling crabs, even though they live between 400 and 600 m. The maximum CFF of Stylocheiron maximum, a shallower living bilobed eu- phausiid, is only 36 Hz, indicating that maximum CFF among the euphausiids cannot be correlated with depth of occurrence. The unusually high flicker fusion frequency of the deeper living euphausiids may be correlated to their preference for bioluminescent prey.
TL;DR: The results indicate that the range for B. puteoserpentis extends from Snake Pit to Logatchev, and that an unnamed second species, B. n.
Abstract: Mussels were collected from deep-sea hydrothermal vents along the Mid-Atlantic Ridge Specimens from the Snake Pit site were previously identified genetically and anatomically as Bathymodiolus puteoserpentis, but the relationships of mussels from other sites (Logatchev and Lucky Strike) were unclear Molecular genetic and morphological techniques were used to assess differences among these mussel populations The results indicate that the range for B puteoserpentis extends from Snake Pit to Logatchev, and that an unnamed second species, B n sp, occurs at Lucky Strike Analysis of mitochondrial NADH dehydrogenase subunit 4 (ND4) revealed 13% sequence divergence between the two species Nei's genetic distance (D) based on 14 allozyme loci was 0112 A multivariate morphometric analysis yielded a canonical discriminant function that correctly identified individuals from these sites to species 95% of the time
TL;DR: A great variability and flexibility in blue crab courtship is demonstrated, with no evidence for stereotyped behavioral sequences, however, these behaviors appear regulated by urine- and nonurine-based redundant chemical signals emanating from both males and females.
Abstract: Behavioral flexibility and behavioral regulation through courtship signals may both contribute to mating success. Blue crabs (Callinectes sapidus) form precopulatory pairs after courtship periods that are influenced by female and perhaps male urine-based chemical signals. In this study, male and female crabs were observed in 1.5-m circular outdoor pools for 45 min while the occurrence and sequence of courtship behaviors and pairing outcomes were recorded. These results were then compared with trials in which males or females were blindfolded; lateral antennule (outer flagellum) ablated; blindfolded and lateral antennule ablated; or had received nephropore blocks. The relative importance of visual and chemical sensory systems during blue crab courtship were then determined and urine and non-urine based chemical signals for both males and females were examined. Courtship behaviors varied considerably in occurrence and sequence; no measured behavior was necessary for pairing success. Male or female blindfolding had no effect on any measured behavior. Males and females required chemical information for normal courtship behaviors, yet blocking male or female urine release did not affect courtship behaviors. Males required chemical information to initiate pairing or to maintain stable pairs. Male urine release was necessary for stable pairing, suggesting that male urine signals may be involved in pair maintenance rather than pair formation. Females that could not receive chemical information paired faster and elicited fewer male agonistic behaviors. The results demonstrate a great variability and flexibility in blue crab courtship, with no evidence for stereotyped behavioral sequences. However, these behaviors appear regulated by urine- and nonurine-based redundant chemical signals emanating from both males and females. Although urine-based signals play roles in blue crab courtship, chemical signals from other sites appear to carry sufficient information to elicit a full range of behavioral responses in males and females.
TL;DR: An array of experimental findings suggest that the simple molecules required for the origin of life may have been available on the primitive Earth, and the hydrothermal synthesis of reduced organics is a relatively new hypothesis that is just now undergoing experimental evaluation.
Abstract: An array of experimental findings suggest that the simple molecules required for the origin of life may have been available on the primitive Earth. The well-known MillerUrey electric discharge experiment yields HCN, amino acids, and carboxylic acids (1). Carbonaceous meteorites contain over 70 amino acids, some heterocyclic compounds, including purines, and carboxylic acids. Other organics may have been synthesized under the reducing conditions present in hydrothermal systems (2). Although some of these organics may have been present on the primitive Earth, there is no agreement on which was the most important for their formation. The Miller-Urey experiment requires the presence of either hydrogen gas or reduced carbon and hydrogen compounds, such as methane, carbon monoxide, and ammonia, in the atmosphere of the primitive Earth. Most geochemists believe that the Earth’s crust was not reducing when life originated, so the volcanic emissions that resulted in the primitive atmosphere were also not reducing. The notion that comets, meteorites, and asteroids delivered reduced organics to the surface of the primitive Earth is not favored by those who believe that, when these bodies hit the Earth’s atmosphere, the organic compounds present on them would have been pyrolyzed. The hydrothermal synthesis of reduced organics is a relatively new hypothesis that is just now undergoing experimental evaluation. Assuming that the requisite starting materials were available on the primitive Earth (2), and providing conditions that plausibly occurred at that time, I have undertaken to investigate how monomers, particularly mononucleotides,
TL;DR: The relationships between present-day prokaryotes and the ancestral eukaryotic lineage (those which existed before the LUCA) are thought to be more complex than previously thought.
Abstract: The concept of Archaea (formerly Archaebacteria), introduced by Carl Woese at the end of the seventies, raised the hope that studying this third form of life on earth would help to reconstitute the Last Universal Common Ancestor (LUCA) to all living organisms. In the years that followed, a consensus emerged within the community of archaeobiologists about early cellular evolution and the nature of LUCA. In the new paradigm, Archaea are the sister group of Eukarya (formerly eukaryotes), and LUCA was a simple prokaryote with features between those of Archaea and Bacteria (1, 2). In this scenario, the complex and specific molecular traits of the Eukarya, such as nuclear pores, mRNA splicing, or an elaborated cytoskeleton, are late inventions in the eukaryal lineage. This paradigm is usually justified by the rooting of the universal tree of life in the bacterial branch and the finding of eukaryal features in Archaea at the molecular level. In our opinion however, it is also based on the prejudice that “pro”karyotes predated “eu”karyotes in the course of early cellular evolution. Prokaryotes of course predate “modern” eukaryotes in the history of life since all present-day eukaryotes have probably descended from an ancestor that had already engulfed the bacterial endosymbiont which gave birth to mitochondria, (e.g., 3). We think, however, that the relationships between present-day prokaryotes and the ancestral eukaryotic lineage (those which existed before the
TL;DR: Data demonstrated that for small particles (< 2 microm) in the near field, movement of cirri was essential for successful capture either by direct contact or with water acting as a hydromechanical coupler.
Abstract: In this study we examined the mechanism of particle capture in Mytilus edulis, using radioactive-label clearance studies, progressive fixation, and scanning electron microscopy to visualize in detail the cirri and their range of motion. Confocal laser scanning microscopy was used to observe the interaction of cirri with 1 mucrom fluorescent latex particles on live strips of control and serotonin-treated isolated gill tissue. The gills of M. edulis possess large, complex latero-frontal cirri composed of 18-26 pairs of cilia. Particles that were intercepted by the cirri were transferred to the water current on the frontal surface of the filament where they were propelled toward the ventral particle groove. Clearance studies demonstrated that M. edulis removed Escherichia coli from 5 degrees C seawater bathing medium at 4.9 ml g(-1) dry tissue min(-1). When the gills were exposed to 10(-3) M serotonin, the latero-frontal cirri stopped moving and became fixed in a flexed position that partially blocked the frontal surface of the filament. Clearance studies demonstrated that removal of E. coli from the seawater bathing medium was reduced 90% to 0.5 ml g(-1) dry tissue min(-1) when 10(-3) M serotonin was present. These data demonstrated that for small particles (< 2 microm) in the near field, movement of cirri was essential for successful capture either by direct contact or with water acting as a hydromechanical coupler.
TL;DR: Time-lapse video microscopy and image analysis algorithms were used to generate high-resolution time series of the length and volume of a single hydrozoan polyp before and after feeding, compatible with the hypothesis that the presence of nutrients in the digestive cavity induces polyp oscillations and that release of nutrients into the gastrovascular system similarly induces unfed polyps to oscillate.
Abstract: Time-lapse video microscopy and image anal- ysis algorithms were used to generate high-resolution time series of the length and volume of a single hydrozoan polyp before and after feeding. A polyp of Podocoryne carnea prior to feeding is effectively static in length and volume. At 20°C feeding elicits 8-millihertz (mHz) oscillations in polyp length and volume. A polyp connected to a colony by a single stolon displayed an abrupt transition from low- amplitude, S-mHz oscillations to large-amplitude, 6-mHz oscillations at 1.5-2 h after feeding. The transition was preceded by a substantial decrease in polyp volume and increase in length which coincided with the export of food items from the digestive cavity of the polyp into the colonial gastrovascular system. In contrast, S-mHz oscillations of a polyp isolated from a colony continued for 12.7 h after feeding, at which time particulates from the digestive cavity were exported into the hydrorhiza and a 4-mHz subhar- monic became briefly dominant. Regular oscillatory behav- ior was terminated by regurgitation at comparable intervals post-feeding in coupled and isolated polyps. These obser- vations are compatible with the hypothesis that the presence of nutrients in the digestive cavity induces polyp oscilla- tions and that release of nutrients into the gastrovascular system similarly induces unfed polyps to oscillate, thereby distributing the contents of the fed polyp throughout the colony.