Showing papers in "The Biological Bulletin in 2008"

Consciousness as Integrated Information: a Provisional Manifesto

Abstract: The integrated information theory (IIT) starts from phenomenology and makes use of thought experi- ments to claim that consciousness is integrated information. Specifically: (i) the quantity of consciousness corresponds to the amount of integrated information generated by a complex of elements; (ii) the quality of experience is spec- ified by the set of informational relationships generated within that complex. Integrated information () is defined as the amount of information generated by a complex of elements, above and beyond the information generated by its parts. Qualia space (Q) is a space where each axis represents a possible state of the complex, each point is a probability distribution of its states, and arrows between points represent the informational relationships among its elements generated by causal mechanisms (connections). Together, the set of informational relationships within a complex constitute a shape in Q that completely and univo- cally specifies a particular experience. Several observations concerning the neural substrate of consciousness fall natu- rally into place within the IIT framework. Among them are the association of consciousness with certain neural systems rather than with others; the fact that neural processes un- derlying consciousness can influence or be influenced by neural processes that remain unconscious; the reduction of consciousness during dreamless sleep and generalized sei- zures; and the distinct role of different cortical architectures in affecting the quality of experience. Equating conscious- ness with integrated information carries several implications for our view of nature.

Heat-Shock Protein 70 (Hsp70) Expression in Four Limpets of the Genus Lottia: Interspecific Variation in Constitutive and Inducible Synthesis Correlates With in situ Exposure to Heat Stress

Abstract: Limpets of the genus Lottia occupy a broad vertical distribution on wave-exposed rocky shores, a range that encompasses gradients in the frequency and severity of thermal and desiccation stress bro...

Microbial Biofilms Facilitate Adhesion in Biofouling Invertebrates

Abstract: Much interest has focused on the role of mi- crobial layers— biofilms—in stimulating attachment of in- vertebrates and algae to submerged marine surfaces. We investigated the influence of biofilms on the adhesion strength of settling invertebrates. Larvae of four species of biofouling invertebrate were allowed to attach to test sur- faces that were either clean or coated with a natural biofilm. Measuring larval removal under precisely controlled flow forces, we found that biofilms significantly increased adhe- sion strength in the ascidian Phallusia nigra, the polychaete tubeworm Hydroides elegans, and the barnacle Balanus amphitrite at one or more developmental stages. Attach- ment strength in a fourth species, the bryozoan Bugula neritina, was neither facilitated nor inhibited by the pres- ence of a biofilm. These results suggest that adhesive strength and perhaps composition may vary across different invertebrate taxa at various recruitment stages, and mark a new path of inquiry for biofouling research.

Size-specific predation on marine invertebrate larvae.

Abstract: Predation on planktonic larval stages is fre- quently a major source of mortality for the offspring of benthic marine invertebrates. Mortality rate likely varies with larval size and developmental stage, but few experi- ments have measured how these factors affect predation rates. I used experimental reductions in egg size to test how variation in larval size affects the likelihood of predation during planktonic development. Blastomeres of the sand dollar Dendraster excentricus were separated at the two-cell stage to produce half-sized zygotes. Larvae resulting from this manipulation were tested for their susceptibility to predation relative to whole-sized siblings at four ages. In- dividuals from each size class were simultaneously pre- sented as prey items to five predators (crab zoeae, crab megalopae, chaetognaths, solitary tunicates, and postlarval fish) in the laboratory. Four predators consumed signifi- cantly more half-sized larvae than whole-sized larvae, but one predator type (postlarval fish) consumed more whole- sized larvae. Predators that consumed more half-sized lar- vae also preferentially consumed younger larvae. In con- trast, postlarval fish showed no significant prey preference based on larval age. These results suggest that assumptions of constant mortality rates during development should be modified to account for the effects of larval size and age.

Heat stress in the intertidal: comparing survival and growth of an invasive and native mussel under a variety of thermal conditions.

Abstract: In the rocky intertidal, organisms frequently experience a wide range of daily body temperatures depending on the stage of the tide and the time of day. In the intertidal, the thermal adaption of a species and its ability to invade a new region may be closely linked. In this research, the physiological effects of thermal stress in both low tide and high tide conditions are compared between Mytilus galloprovincialis, a worldwide mussel invader, and M. trossulus, a sibling species. In a seawater tank, mussels were exposed to one of three aerial temperature treatments (20, 25, 30 degrees C) in a cycle with one of two water temperatures (18, 12 degrees C). In 18 degrees C water, there was no effect of the aerial treatments on growth or survival in either species. In contrast, in 12 degrees C water, aerial exposure affected the survival and growth of both species. Growth and survival rates of M. galloprovincialis were higher in all conditions than the rates of M. trossulus, especially in the 18 degrees C water experiments and in the aerial exposure treatments of the winter 12 degrees C water experiment. M. galloprovincialis appears to be warm-adapted with regard to both low tide and high tide thermal stress. These results when paired with previous research suggest that as climates shift due to global warming, the temperatures favorable to M. galloprovincialis will become more common.

Genomic Survey of Candidate Stress-Response Genes in the Estuarine Anemone Nematostella vectensis

Abstract: Salt marshes are challenging habitats due to natural variability in key environmental parameters includ- ing temperature, salinity, ultraviolet light, oxygen, sulfides, and reactive oxygen species. Compounding this natural variation, salt marshes are often heavily impacted by an- thropogenic insults including eutrophication, toxic contam- ination, and coastal development that alter tidal and fresh- water inputs. Commensurate with this environmental variability, estuarine animals generally exhibit broader physiological tolerances than freshwater, marine, or terres- trial species. One factor that determines an organism's phys- iological tolerance is its ability to upregulate "stress- response genes" in reaction to particular stressors. Comparative studies on diverse organisms have identified a number of evolutionarily conserved genes involved in re- sponding to abiotic and biotic stressors. We used homology- based scans to survey the sequenced genome of Nema- tostella vectensis, the starlet sea anemone, an estuarine specialist, to identify genes involved in the response to three kinds of insult—physiochemical insults, pathogens, and in- jury. Many components of the stress-response networks identified in triploblastic animals have clear orthologs in the sea anemone, meaning that they must predate the cnidarian- triploblast split (e.g., xenobiotic receptors, biotransforma- tive genes, ATP-dependent transporters, and genes involved in responding to reactive oxygen species, toxic metals, osmotic shock, thermal stress, pathogen exposure, and wounding). However, in some instances, stress-response genes known from triploblasts appear to be absent from the Nematostella genome (e.g., many metal-complexing genes). This is the first comprehensive examination of the genomic stress-response repertoire of an estuarine animal and a member of the phylum Cnidaria. The molecular markers of stress response identified in Nematostella may prove useful in monitoring estuary health and evaluating coastal conser- vation efforts. These data may also inform conservation efforts on other cnidarians, such as the reef-building corals.

Cell-cell adhesion in the cnidaria: insights into the evolution of tissue morphogenesis.

Abstract: Cell adhesion is a major aspect of cell biology and one of the fundamental processes involved in the development of a multicellular animal Adhesive mechanisms, both cell-cell and between cell and

Reciprocal changes in calcification of the gastrolith and cuticle during the molt cycle of the red claw crayfish Cherax quadricarinatus.

Abstract: Mobilization of calcium during the molt cycle from the cuticle to transient calcium deposits is widely spread in crustaceans. The dynamics of calcium transport to transient calcium deposits called gastroliths and to the cu- ticle over the course of the molt cycle were studied in the crayfish Cherax quadricarinatus. In this species, calcium was deposited in the gastroliths during premolt and trans- ported back to the cuticle during postmolt, shown by digital X-ray radiograph analysis. The predominant mineral in the crayfish is amorphous calcium carbonate embedded in an organic matrix composed mainly of chitin. Scanning elec- tron micrographs of the cuticle during premolt showed that the endocuticle and parts of the exocuticle were the source of most of the labile calcium, while the epicuticle did not undergo degradation and remained mineralized throughout the molt cycle. The gastroliths are made of concentric layers of amorphous calcium carbonate intercalated between chiti- nous lamella. Measurements of pH and calcium levels dur- ing gastrolith deposition showed that calcium concentra- tions in the gastroliths, stomach, and muscle were about the same (10 to 11 mmol l 1 ). On the other hand, pH varied greatly, from 8.7 0.15 in the gastrolith cavity through 7.6 0.2 in muscle to 6.9 0.5 in the stomach.

Acquisition of Dwarf Male “Harems” by Recently Settled Females of Osedax roseus n. sp. (Siboglinidae; Annelida)

Abstract: After the deployment of several whale car- casses in Monterey Bay, California, a time-series analysis revealed the presence of a new species ofOsedax, a genus of bone-eating siboglinid annelids. That species is described here asOsedax roseusn. sp. It is the fifth species described since the erection of this genus and, like its congeners, uses a ramifying network of "roots" to house symbiotic bacteria. In less than 2 months,Osedax roseusn. sp. colonized the exposed bones of a whale carcass deposited at 1018-m depth, and many of the females were fecund in about 3 months post-deployment. As with otherOsedaxspp., the females have dwarf males in their tube lumens. The males accrue over time until the sex ratio is markedly male-biased. This pattern of initial female settlement followed by gradual male accumulation is consistent with the hypothesis that male sex may be environmentally determined inOsedax. Of the previously described species in this genus,Osedax ro- seusn. sp. is most similar toO. rubiplumus,but it has several anatomical differences, as well as much smaller females, dwarf males, and eggs.Osedax roseusn. sp. is markedly divergent (minimally 16.6%) for mitochondrial cytochrome oxidase subunit I (mtCOI) sequences from any otherOsedaxspecies.

Effect of Temperature on the Settlement Choice and Photophysiology of Larvae From the Reef Coral Stylophora pistillata

Abstract: To better understand the consequences of climate change for scleractinian corals, Stylophora pistillata was used to test the effects of temperature on the settlement and physiology of coral larvae. Freshly released larvae were exposed to temperatures of 23 degrees C, 25 degrees C (ambient), and 29 degrees C at light intensities of approximately 150 micromol photons m(-2) s(-1). The effects were assessed after 12 h as settlement to various substrata (including a choice between crustose coralline algae [CCA] and limestone) and as maximum quantum yield of PSII (F(v)/F(m)) in the larvae versus in their parents. Regardless of temperature, 50%-73% of the larvae metamorphosed onto the plastic of the incubation trays or in a few cases were drifting in the water, and 14% settled on limestone. However, elevated temperature (29 degrees C) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23 degrees C. Because temperature did not affect settlement on limestone or plastic, increased settlement on CCA reflected temperature-mediated choices by larvae that otherwise would have remained swimming. Interestingly, F(v)/F(m) was unaffected by temperature, but it was 4% lower in the larvae than in the parents. These results are important because they show that temperature can affect the settlement of coral larvae and because they reveal photophysiological differences between life stages that might provide insights into the events associated with larval development.

Marine invertebrate genome sequences and our evolving understanding of animal immunity.

Abstract: Animal immunity is under intense evolutionary pressure, and the mechanisms that carry out recognition and elimination of pathogens are among the most rapidly evolving genetic systems. It is increasingly apparent that this has led to the emergence of novel molecular mechanisms not only among vertebrates, where immunity is by far best characterized, but also across invertebrate phyla. This propensity for rapid divergence has been a serious obstacle for progress in the field of comparative immunology. The variety of recent genome sequences from marine invertebrates representing new phyla offers a means to move forward in this area. Genome sequences provide much improved sensitivity for the detection of gene homologs and a framework for unbiased computational and experimental searches for novel immune mediators. Furthermore, new genomes now offer a more complete and unbiased view of immunity across bilaterian phyla, especially among deuterostomes. In this review we summarize these findings with particular attention toward immunity in Strongylocentrotus purpuratus, the purple sea urchin, and outline the changing perspective on the evolution of deuterostome immunity.

Insights from a sea lamprey into the evolution of neural crest gene regulatory network.

Abstract: The neural crest is a vertebrate innovation that forms at the embryonic neural plate border, transforms from epithelial to mesenchymal, migrates extensively throughout the embryo along well-defined pathways, and differentiates into a plethora of derivatives that include elements of peripheral nervous system, craniofacial skeleton, melanocytes, etc. The complex process of neural crest formation is guided by multiple regulatory modules that define neural crest gene regulatory network (NC GRN), which allows the neural crest to progressively acquire all of its defining characteristics. The molecular study of neural crest formation in lamprey, a basal extant vertebrate, consisting in identification and functional tests of molecular elements at each regulatory level of this network, has helped address the question of the timing of emergence of NC GRN and define its basal state. The results have revealed striking conservation in deployment of upstream factors and regulatory modules, suggesting that proximal portions of the network arose early in vertebrate evolution and have been tightly conserved for more than 500 million years. In contrast, certain differences were observed in deployment of some neural crest specifier and downstream effector genes expected to confer species-specific migratory and differentiation properties.

Importance of time and place: patterns in abundance of Symbiodinium clades A and B in the tropical sea anemone Condylactis gigantea.

Abstract: The capacity of some corals and other cnidar- ians to form symbioses with multiple algae (Symbiodinium) is a candidate route by which these symbioses tolerate variable environmental conditions. On Bermuda, the coral reef dwelling anemone Condylactis gigantea bears Symbio- dinium of clades A and B. At thermally variable inshore and nearshore sites, clade A predominates (as sole symbiont or in mixed infection with clade B), whereas animals at off- shore sites with more uniform temperatures bear only clade B or mixed infections. Individual animals at one nearshore site monitored over a year by sampling tentacles showed increased prevalence of clade A in March-November, when sea waters were warm (average 26 °C), and increased clade B in November-March when cool waters prevailed (average 18.5 °C). In laboratory analyses of excised tentacles, the symbiosis with clade B, but not clade A, bleached at ele- vated temperature (32 o C), suggesting that thermal tolerance may contribute to the higher prevalence of clade A at inshore/nearshore sites and in the summer. The temporal changes in the algal complement were not accompanied by bleaching, and Symbiodinium density fluctuated in hosts with stable Symbiodinium composition but not in hosts with variable composition. This suggests that changes in the relative abundance of Symbiodinium clades do not require bleaching and may even protect the symbiosis from large fluctuations in algal density.

Flow Forces on Seaweeds: Field Evidence for Roles of Wave Impingement and Organism Inertia

Abstract: Hydrodynamic forces dislodge and kill large numbers of organisms in intertidal and subtidal habitats along rocky shores. Although this feature of wave-driven water motion is well recognized, the mechanics of force imposition on compliant organisms is incompletely understood. Here we undertake a field examination of two processes that are thought to impose many of the more dangerous forces that act on flexible benthic seaweeds: impingement of breaking waves directly on emergent organisms, and inertial effects tied to the rapid deceleration of mass that occurs when a passively moving but attached organism abruptly reaches the extent of its range of motion. We focus on two common and important seaweed species: one intertidal kelp (Egregia menziesii) and one subtidal kelp (Macrocystis pyrifera). Results support the concept that wave impingement and inertial effects produce intermittent force transients whose magnitudes commonly exceed values readily attributable to drag. Peak force transients are elevated by as much as a factor of 3 relative to drag in both small and large individuals, consistent with smaller seaweeds being more susceptible to brief impingement forces, and larger seaweeds being more vulnerable to inertial forces. Because both wave impingement and inertial effects vary with the size of an organism, they may have the potential to influence the demographics of physical disturbance in an array of flexible species.

Effects of cyclic hypoxia on gene expression and reproduction in a grass shrimp, Palaemonetes pugio.

Abstract: Cyclic changes in dissolved oxygen occur naturally in shallow estuarine systems, yet little is known about the adaptations and responses of estuarine organisms to cyclic hypoxia. Here we examine the responses of Palaemonetes pugio, a species of grass shrimp, to cyclic hypoxia (1.5-8 mg/l dissolved oxygen; 4.20-22.42 kPa) at both the molecular and organismal levels. We measured alterations in gene expression in hepatopancreas tissue of female grass shrimp using custom cDNA macroarrays. After short-term (3-d) exposure to cyclic hypoxia, mitochondrial manganese superoxide dismutase (MnSOD) was upregulated and 70-kd heat shock proteins (HSP70) were downregulated. After 7-d exposure, nuclear genes encoding mitochondrial proteins (ribosomal protein S2, ATP synthase, very-long-chain specific acyl-CoA dehydrogenase [VLCAD]) were downregulated, whereas mitochondrial phosphoenol pyruvate carboxykinase (PEP Cbk) was upregulated. After 14 d, vitellogenin and apolipoprotein A1 were upregulated. Taken together, these changes suggest a shift in metabolism toward gluconeogenesis and lipid export. Long-term (77-d) exposure to hypoxia showed that profiles of gene expression returned to pre-exposure levels. These molecular responses differ markedly from those induced by chronic hypoxia. At the organismal level, cyclic hypoxia reduces the number of broods and eggs a female can produce. Demographic analysis showed a lower estimated rate of population growth in grass shrimp exposed to both continuous and short-term cyclic hypoxia, suggesting population-level impacts on grass shrimp.

cDNA Sequences for Transcription Factors and Signaling Proteins of the Hemichordate Saccoglossus kowalevskii: Efficacy of the Expressed Sequence Tag (EST) Approach for Evolutionary and Developmental Studies of a New Organism

Abstract: We describe a collection of expressed sequence tags (ESTs) for Saccoglossus kowalevskii, a direct-developing hemichordate valuable for evolutionary comparisons with chordates. The 202,175 ESTs represent 163,633 arrayed clones carrying cDNAs prepared from embryonic libraries, and they assemble into 13,677 continuous sequences (contigs), leaving 10,896 singletons (excluding mitochondrial sequences). Of the contigs, 53% had significant matches when BLAST was used to query the NCBI databases (≤10−10), as did 51% of the singletons. Contigs most frequently matched sequences from amphioxus (29%), chordates (67%), and deuterostomes (87%). From the clone array, we isolated 400 full-length sequences for transcription factors and signaling proteins of use for evolutionary and developmental studies. The set includes sequences for fox, pax, tbx, hox, and other homeobox-containing factors, and for ligands and receptors of the TGFβ, Wnt, Hh, Delta/Notch, and RTK pathways. At least 80% of key sequences have been obtained...

Endosymbionts of Siboglinum fiordicum and the Phylogeny of Bacterial Endosymbionts in Siboglinidae (Annelida)

Abstract: Siboglinid worms are a group of gutless marine annelids that are nutritionally dependent upon endosymbiotic bacteria. Four major groups of siboglinids are known-vestimentiferans, moniliferans, Osedax spp. and frenulates. Although endosymbionts of vestimentiferans and Osedax spp. have been previously characterized, little is currently known about endosymbiotic bacteria associated with frenulate and moniliferan siboglinids. This is particularly surprising given that frenulates are the most diverse and widely distributed group of siboglinids. Here, we molecularly characterize endosymbiotic bacteria associated with the frenulate siboglinid Siboglinum fiordicum by using 16S rDNA ribotyping in concert with laser-capture microdissection (LCM). Phylogenetic analysis indicates that at least three major clades of endosymbiotic gamma-proteobacteria associate with siboglinid annelids, with each clade corresponding to a major siboglinid group. S. fiordicum endosymbionts are a group of gamma-proteobacteria that are divergent from bacteria associated with vestimentiferan or Osedax hosts. Interestingly, symbionts of S. fiordicum, from Norway, are most closely related to symbionts of the frenulate Oligobrachia mashikoi from Japan, suggesting that symbionts of frenulates may share common evolutionary history or metabolic features.

Articulated coralline algae of the genus Amphiroa are highly effective natural inducers of settlement in the tropical abalone Haliotis asinina.

Abstract: The initiation of metamorphosis in marine invertebrates is strongly linked to the environment. Plank- tonic larvae typically are induced to settle and metamor- phose by external cues such as coralline algae (Coralli- naceae, Rhodophyta). Although coralline algae are globally abundant, invertebrate larvae of many taxa settle in response to a very limited suite of species. This specificity impacts population structure, as only locations with the appropriate coralline species can attract new recruits. Abalone (Gas- tropoda, Haliotidae) are among those taxa in which closely related species are known to respond to different coralline algae. Here we identify highly inductive natural cues of the tropical abalone Haliotis asinina. In contrast to reports for other abalone, the greatest proportion of H. asinina larvae are induced to settle and metamorphose (92.8% to 100% metamorphosis by 48 h postinduction) by articulated coral- lines of the genus Amphiroa. Comparison with field distri- bution data for different corallines suggests larvae are likely to be settling on the seaward side of the reef crest. We then compare the response of six different H. asinina larval families to five different coralline species to demonstrate that induction by the best inductive cue (Amphiroa spp.) effectively extinguishes substantial intraspecific variation in the timing of settlement.

Nutritional Role of Two Algal Symbionts in the Temperate Sea Anemone Anthopleura elegantissima Brandt

Abstract: The intertidal sea anemone Anthopleura elegantissima in the Pacific Northwest may host a single type of algal symbiont or two different algal symbionts simultaneously: zooxanthellae (Symbiodinium muscatinei) and zoochlorellae (green algae; Trebouxiophyceae, Chlorophyta). A seasonal comparison of zooxanthellate and zoochlorellate anemones showed stable symbiont population densities in summer and winter, with densities of zoochlorellae about 4 times those of zooxanthellae. Photosynthesis-irradiance curves of freshly isolated symbionts show that the productivity (Pmax cell) of freshly isolated zooxanthellae was about 2.5 times that of zoochlorellae during July; comparable rates were obtained in other months. Models of algal carbon flux show that zoochlorellae may supply the host with more photosynthetic carbon per unit anemone biomass than zooxanthellae supply. Zooxanthellate anemone tissue was 2‰ (13C) and 5‰ (15N) enriched and zoochlorellate anemone tissue was 6‰ (13C) and 8‰ (15N) enriched over their resp...

Transitions in morphology, nematocyst distribution, fluid motions, and prey capture during development of the scyphomedusa Cyanea capillata.

Abstract: Like that of most scyphozoans, the ontogeny of Cyanea capillata medusae involves substantive alterations in feeding structures and mechanics. We used video and optical microscopy approaches to quantify these ontogenetic changes in morphology, flow, and feeding of C. capillata medusae. We found that alterations in gross morphology and nematocyst distributions coincided with a shift from prey capture on the manubrium or lappets of ephyrae (bell diameter 0.2-0.4 cm) to capture primarily on the tentacles in adult medusae (diameter >1.0 cm). These changes occurred within a hydrodynamic framework that itself changed due to medusan growth. Viscous forces were important in flows around small ephyrae (maximum Re 10(2)). The relative timing of these events indicates that ontogenetic processes are closely synchronized with alterations in the hydrodynamic environment within which C. capillata medusae develop.

Origin and expansion of foliated microstructure in pteriomorph bivalves.

Abstract: The ultrastructure of the calcitic prisms of the prismatic shell layers of pteriomorph bivalves was exam- ined by scanning electronic microscopy and diffraction techniques. Results indicate that the internal structure of the prisms is noticeably different among taxa. In species be- longing to the families Pinnidae, Pteriidae, and Isogno- monidae (Pterioida), prisms are built up with nanometric calcite crystals. On the other hand, Pectinidae, Propeamus- sliidae, Anomiidae (order Pectinoida) and the Ostreidae (Ostreoida) have prisms constituted by calcitic laths with micrometric size. These laths are indistinguishable from those constituting the foliated microstructure. In almost all cases, there is mineral continuity from the prisms to the underlying foliated layer, as confirmed by X-ray texture analyses. These findings corroborate a previous assumption that the foliated microstructure derived from calcitic prisms, particularly from those with internal foliated structure. The appearance of the foliated microstructure facilitated drastic mineralogical and microstructural changes in pteriomorph shells—for example, the development of rigid shell margins and the production of largely calcitic shells. Such changes have, no doubt, contributed to the evolutionary success of the groups, which have shown a pronounced diversification over time.

Patterns of Fluorescent Protein Expression in Scleractinian Corals

Abstract: Biofluorescence exists in only a few classes of organisms, with Anthozoa possessing the majority of spe- cies known to express fluorescent proteins. Most species within the Anthozoan subgroup Scleractinia (reef-building corals) not only express green fluorescent proteins, they also localize the proteins in distinct anatomical patterns.We ex- amined the distribution of biofluorescence in 33 coral spe- cies, representing 8 families, from study sites on Australia's Great Barrier Reef. For 28 of these species, we report the presence of biofluorescence for the first time. The dominant fluorescent emissions observed were green (480-520 nm) and red (580-600 nm). Fluorescent proteins were expressed in three distinct patterns (highlighted, uniform, and comple- mentary) among specific anatomical structures of corals across a variety of families. We report no significant overlap between the distribution of fluorescent proteins and the distribution of zooxanthellae. Analysis of the patterns of fluorescent protein distribution provides evidence that the scheme in which fluorescent proteins are distributed among the anatomical structures of corals is nonrandom. This tar- geted expression of fluorescent proteins in corals produces contrast and may function as a signaling mechanism to organisms with sensitivity to specific wavelengths of light.

Evolutionary and structural diversification of the larval nervous system among marine bryozoans.

Abstract: Regardless of the morphological divergence among larval forms of marine bryozoans, the larval nervous system and its major effector organs (musculature and cil- iary fields) are largely molded on the basis of functional demands of feeding, ciliary propulsion, phototactic behav- iors, and substrate exploration. Previously published ultra- structural information and immunohistochemical recon- structions presented here indicate that neuronal pathways are largely ipsilateral, with more complex synaptic connec- tions localized within the nerve nodule. Multiciliated sen- sory-motor neurons diversify structurally and functionally on the basis of their position along the axis of swimming largely due to the functional demands of photoklinotaxis and substrate exploration. Vesiculariform, buguliform, and ascophoran coronate larvae all have patches of sensory neurons bordering the pyriform organ's ciliated groove (juxtapapillary cells and border cells) that are active during substrate selection. Despite their simplified form, cyclo- stome larvae maintain swimming and probing behaviors with sensory-motor systems functionally similar to those of some parenchymella and planula larval types. Considering the evolutionary relationships among the morphological grades of marine bryozoans, particular lineages within the gymnolaemates have independently evolved larval traits that convey a greater range of sensory abilities and in- creased propulsive capacity. The larval nervous system of bryozoans may be evolutionarily derived from the pretro- chal region of a trochophore-like larval form.

Influence of conspecific and heterospecific aggregation cues and alarm odors on shelter choice by syntopic spiny lobsters.

Abstract: In spiny lobsters, conspecific scents (“aggregation cues”) may mediate gregarious diurnal sheltering, but scents from injured conspecifics (“alarm odors”) may elicit avoidance behavior. In laboratory experiments, individuals of two coexisting species, Panulirus guttatus (a reef-obligate) and P. argus (a temporary reef-dweller), significantly chose shelters emanating conspecific aggregation cues and responded randomly to shelters emanating heterospecific aggregation cues. However, despite evidence that the two species perceived each other's alarm odors to a similar extent, P. guttatus responded randomly to shelters emanating either conspecific or heterospecific alarm odors, whereas P. argus significantly avoided both. This differential influence of alarm odors likely reflects interspecific differences in life history, sociality, and behavior. The less social, reef-obligate P. guttatus lobsters forage close to their reef dens, into which they retract deeply upon perception of risk. This cryptic behavior may...

Rhythms of locomotion expressed by Limulus polyphemus, the American horseshoe crab: I. Synchronization by artificial tides.

Abstract: Limulus polyphemus, the American horseshoe crab, has an endogenous clock that drives circatidal rhythms of locomotor activity. In this study, we examined the ability of artificial tides to entrain the locomotor rhythms of Limu- lus in the laboratory. In experiments one and two, the activity of 16 individuals of L. polyphemus was monitored with activity boxes and "running wheels." When the crabs were exposed to artificial tides created by changes in water depth, circatidal rhythms were observed in animals exposed to 12.4-h "tidal" cycles of either water depth changes (8 of 8 animals) or inundation (7 of 8 animals). In experiment three, an additional 8 animals were exposed to water depth changes under cyclic conditions of light and dark and then monitored for 10 days with no imposed artificial tides. Most animals (5) clearly synchronized their activity to the im- posed artificial tidal cycles, and 3 of these animals showed clear evidence of entrainment after the artificial tides were terminated. Overall, these results demonstrate that the en- dogenous tidal clock that influences locomotion in Limulus can be entrained by imposed artificial tides. In the labora- tory, these tidal cues override the influence of light/dark cycles. In their natural habitat, where both tidal and photo- period inputs are typically always present, their activity rhythms are likely to be much more complex.

Can Salinity-Induced Mortality Explain Larval Vertical Distribution With Respect to a Halocline?

Abstract: For the larvae of two echinoderm species that coexist in Atlantic Canada (bipinnaria of the sea star Asterias rubens and 4- and 6-arm echinoplutei of the sea urchin Strongylocentrotus droebachiensis), we examined the effect of short- and long-term exposure to salinity (ranging from 18 to 35) on the probability of larval survival in laboratory experiments. We also related larval vertical distributions in response to sharp haloclines generated in the laboratory to survival probability in the salinity of different layers in the water column. For both species and developmental stages, survival probability decreased with decreasing salinity, and a salinity range of 24–27 emerged as the critical threshold for larval tolerance. The relationship between the proportion of larvae that crossed a halocline into the top water layer and the survival probability of larvae in the salinity of that layer was significant for both species. Interestingly, the shape of this response was species-specific but not stage-specific ...

Rhythms of Locomotion Expressed by Limulus polyphemus, the American Horseshoe Crab: II. Relationship to Circadian Rhythms of Visual Sensitivity

Abstract: In the laboratory, horseshoe crabs express a circadian rhythm of visual sensitivity as well as daily and circatidal rhythms of locomotion. The major goal of this investigation was to determine whether the circadian clock underlying changes in visual sensitivity also modulates lo- comotion. To address this question, we developed a method for simultaneously recording changes in visual sensitivity and locomotion. Although every animal (24) expressed con- sistent circadian rhythms of visual sensitivity, rhythms of locomotion were more variable: 44% expressed a tidal rhythm, 28% were most active at night, and the rest lacked statistically significant rhythms. When exposed to artificial tides, 8 of 16 animals expressed circatidal rhythms of loco- motion that continued after tidal cycles were stopped. How- ever, rhythms of visual sensitivity remained stable and showed no tendency to be influenced by the imposed tides or locomotor activity. These results indicate that horseshoe crabs possess at least two biological clocks: one circadian clock primarily used for modulating visual sensitivity, and one or more clocks that control patterns of locomotion. This arrangement allows horseshoe crabs to see quite well while mating during both daytime and nighttime high tides.

Patterns of Male Reproductive Success in Crepidula fornicata Provide New Insight for Sex Allocation and Optimal Sex Change

Abstract: The size-advantage model and sex-allocation theory are frequently invoked to explain the evolution and maintenance of sequential hermaphroditism in many taxa. A test of current theory requires quantitative estimates of reproductive success and knowledge of the relationship between reproduction and size for each gender. Reproductive success can be difficult to measure. In species where polyandry occurs, it can be quantified only by determining paternity of offspring. We employed microsatellite loci to establish paternity for 12 families of Crepidula fornicata, where a family is defined as a single female, her brood, and the males stacked on top of her. Genetic data were analyzed and paternity was assigned to a single potential father for more than 83% of the offspring tested. Estimates of reproductive success revealed that one male within the family fathered the majority of offspring and that he was usually the largest male and the one closest to the brooding female. The dominant male's success also tended...

Comparison of Gamete Compatibility Between Two Blue Mussel Species in Sympatry and in Allopatry

Abstract: Recent demonstrations of positive selection on genes controlling gamete compatibility have resulted in a proliferation of hypotheses concerning the sources of selec- tion. We tested a prediction of one prominent hypothesis, selection to avoid hybridization (i.e., reinforcement), by comparing heterospecific gamete compatibility in two Myti- lus edulis populations: one population in Cobscook Bay, Maine, in which the close congener, M. trossulus, is abun- dant (a region of sympatry), and one population in Kittery, Maine, in which M. trossulus is absent (a region of allo- patry). Three diagnostic nuclear DNA markers were used to identify mussels to species and to estimate the frequency of both species and their hybrids in the two populations. Con- trolled crosses were then conducted by combining eggs of M. edulis females with a range of M.edulis and M. trossulus sperm concentrations. Results were not consistent with the reinforcement hypothesis. M. edulis females collected from the region of sympatry were no more incompatible with M. trossulus males than were M. edulis females collected from the region of allopatry. A trend in the opposite direction, toward greater compatibility in sympatry, suggests that in- trogression of M. trossulus genes that control egg compat- ibility, such as those encoding receptors for sperm, may influence evolution of gametic isolation in hybridizing pop- ulations.

Phylogenetic analysis of caprellid and corophioid amphipods (Crustacea) based on the 18S rRNA gene, with special emphasis on the phylogenetic position of Phtisicidae.

Abstract: Members of the amphipod suborder Caprellidea exhibit degenerated abdomens and pereopods 3 and 4. Some genera of Podoceridae (Gammaridea, Corophioidea) such as Dulichia also show reduced abdomens and pereopods and thus are generally regarded as a sister group of the Caprellidea. In addition, one of the caprellid families, the Caprogammaridae, exhibits abdominal segments that are similar to those of the podocerids, as well as rudimentary pereopods 3 and 4, which are more consistent with those of other caprellids. Therefore, an evolutionary scheme has been suggested on the basis of the gradual degeneration of the pereopods and abdomen: [Dulichia, (caprogammarids, caprellids)]. However, the Phtisicidae (Caprellidea) contradict this hypothesis because they exhibit well-developed pereopods 3 and 4, along with degenerated abdomens. Therefore, previous studies have suggested that the Phtisicidae and other caprellids may be polyphyletic. We examined the phylogenetic position of the Phtisicidae and other caprellid ...