scispace - formally typeset
Search or ask a question

Showing papers in "The Biological Bulletin in 2011"


Journal ArticleDOI
TL;DR: The generation of endogenous EFs, the results of their alteration, and the mechanisms by which cells may sense these weak fields are reviewed to enable current and future therapeutic applications to be optimized.
Abstract: Endogenous DC electric fields (EFs) are important, fundamental components of development, regeneration, and wound healing. The fields are the result of polarized ion transport and current flow through electrically conductive pathways. Nullification of endogenous EFs with pharmacological agents or applied EFs of opposite polarity disturbs the aforementioned processes, while enhancement increases the rate of wound closure and the extent of regeneration. EFs are applied to humans in the clinic, to provide an overwhelming signal for the enhancement of healing of chronic wounds. Although clinical trials, spanning a course of decades, have shown that applied EFs enhance healing of chronic wounds, the mechanisms by which cells sense and respond to these weak cues remains unknown. EFs are thought to influence many different processes in vivo. However, under more rigorously controlled conditions in vitro, applied EFs induce cellular polarity and direct migration and outgrowth. Here we review the generation of endogenous EFs, the results of their alteration, and the mechanisms by which cells may sense these weak fields. Understanding the mechanisms by which native and applied EFs direct development and repair will enable current and future therapeutic applications to be optimized.

127 citations


Journal ArticleDOI
TL;DR: These recent studies on visceral regeneration in holothurians provide a unique view that complements regeneration studies in other animal phyla, which are mainly focused on whole-animal regeneration or appendage regeneration.
Abstract: Visceral regeneration in sea cucumbers has been studied since early last century; however, it is only within the last 15 years that real progress has been made in understanding the cellular and molecular events involved. In the present review, we bring together these recent studies, providing readers with basic information on the anatomy and histology of the normal gut and detailing the changes in tissue organization and gene expression that occur during the regenerative process. We discuss the nature and possible sources of cells involved in the formation of the intestinal regenerate as well as the role of cell death and proliferation in this process. In addition, we compare gut formation during regeneration and during embryogenesis. Finally, we describe the molecular studies that have helped advance regenerative studies in holothurians and integrate the gene expression information with data on cellular events. Studies on visceral regeneration in these echinoderms provide a unique view that complements regeneration studies in other animal phyla, which are mainly focused on whole-animal regeneration or appendage regeneration.

87 citations


Journal ArticleDOI
TL;DR: A mechanistic heat-budget model is used to compare the effects of behavioral and morphological traits on the body temperatures of five species of littorinid snails under natural weather conditions and indicates that, for all five species, the relative contribution of shell color or sculpturing to temperature regulation is small.
Abstract: For organisms living in the intertidal zone, temperature is an important selective agent that can shape species distributions and drive phenotypic variation among populations. Littorinid snails, which occupy the upper limits of rocky shores and estuaries worldwide, often experience extreme high temperatures and prolonged aerial emersion during low tides, yet their robust physiology— coupled with morphological and behavioral traits—permits these gastro- pods to persist and exert strong grazing control over algal communities. We use a mechanistic heat-budget model to compare the effects of behavioral and morphological traits on the body temperatures of five species of littorinid snails under natural weather conditions. Model predictions and field experiments indicate that, for all five species, the relative contribution of shell color or sculpturing to temper- ature regulation is small, on the order of 0.2-2 °C, while behavioral choices such as removing the foot from the substratum or reorienting the shell can lower body temper- atures by 2- 4 °C on average. Temperatures in central Cal- ifornia rarely exceeded the thermal tolerance limits of the local littorinid species during the study period, but at sites where snails are regularly exposed to extreme high temper- atures, the functional significance of the tested traits may be important. The mechanistic approach used here provides the ability to gauge the importance of behavioral and morpho- logical traits for controlling body temperature as species approach their physiological thresholds.

71 citations


Journal ArticleDOI
TL;DR: The results show that many ultrastructural characters are variable within this superfamily and could be useful for phylogeny and compared to the digenean spermatology literature.
Abstract: The ultrastructure of the mature spermatozoon of Gyliauchen sp., a parasite of the dusky rabbitfish Siganus fuscescens, was studied by transmission electron microscopy. The spermatozoon possesses two axonemes of the 9+"1" pattern of Trepaxonemata, four attachment zones, one mitochondrion, a nucleus, cortical microtubules, external ornamentation of the plasma membrane, and spine-like bodies. The main characteristics of this spermatozoon are the presence of one mitochondrion, spine-like bodies not associated with the external ornamentation, and a posterior extremity of type 3 that is characterized by the following sequence: posterior extremity of the nucleus then posterior extremity of the second axoneme. Numerous other ultrastructural features are also discussed and compared to the digenean spermatology literature. This is the first study of a member of the Gyliauchenidae and the fourth within the Lepocreadioidea. The results show that many ultrastructural characters are variable within this superfamily and could be useful for phylogeny.

49 citations


Journal ArticleDOI
TL;DR: Focusing on botryllid ascidians, the potential roles played by multipotent epithelia and multipotent/pluripotent stem cells as source of asexual propagation and regenerative plasticity in the different budding mechanisms are introduced.
Abstract: Regeneration is widely distributed among the metazoans. However, clear differences exist as to the degree of regenerative capacity: some phyla can only replace missing body parts, whereas others can generate entirely new individuals. Ascidians are animals that possess a remarkable regenerative plasticity and exhibit a great diversity of mechanisms for asexual propagation and survival. They are marine invertebrate members of the subphylum Tunicata and represent modern-day descendants of the chordate ancestor; in their tadpole stage they exhibit a chordate body plan that is resorbed during metamorphosis. Solitary species grow into an adult that can reach several centimeters in length, whereas colonial species grow by asexual propagation, creating a colony of genetically identical individuals. In this review, we present an overview of the biology of colonial ascidians as a paradigm for study in stem cell and regenerative biology. Focusing on botryllid ascidians, we introduce the potential roles played by mul...

48 citations


Journal ArticleDOI
TL;DR: An overview of adult and juvenile tissue regeneration models in small fish species, such as zebrafish and medaka, are given, and recent advances at the molecular level are highlighted.
Abstract: The multitude of cells constituting organisms are fragile and easily damaged day by day. Therefore, maintenance of tissue morphology and function is funda- mental for multicellular organisms to attain long life. For proper maintenance of tissue integrity, organisms must have mechanisms that detect the loss of tissue mass, activate the de novo production of cells, and organize those cells into functional tissues. However, these processes are only poorly understood. Here we give an overview of adult and juvenile tissue regeneration models in small fish species, such as zebrafish and medaka, and highlight recent advances at the molecular level. From these advances, we have come to realize that the epidermal and mesenchymal parts of the regenerating fish fin—that is, the wound epidermis and blastema, respectively—comprise heterogeneous popula- tions of cells with different molecular identities that can be termed "compartments." These compartments and their mu- tual interactions are thought to play important roles in promoting the proper progression of tissue regeneration. We further describe the current understanding of these compart- ments and discuss the possible approaches to affording a better understanding of their roles and interactions during regeneration.

47 citations


Journal ArticleDOI
TL;DR: It is concluded that spawning synchrony on a particular lunar night and specific time of night is a threshold response to differential periods of darkness after twilight that is primarily influenced by lunar photoperiod and secondarily by discrete optical components of early nocturnal illumination.
Abstract: Synchrony of spawning in many hermatypic corals, typically a few nights after the full moon, is putatively dependent on solar and lunar light cycles in conjunction with other possible cues such as tides and temperature. We analyze here the contributions of separate components of light dynamics, because the effects of twilight and lunar skylight on coral spawning synchrony have previously been conflated and the alternative hypothesis that these components have differential contributions as proximate cues has not been tested. Moonlight-dependent changes in spectra during twilight, rates of decreasing twilight intensities, and changes in lunar photoperiod were experimentally decoupled using programmed light-emitting diodes and compared for their separate effects on spawning synchrony in Acropora humilis. Effects on synchrony under the control of synthetic lunar cues were greatest in response to changes in lunar photoperiod; changes in light intensities and spectra had lesser influence. No significant differe...

40 citations


Journal ArticleDOI
TL;DR: X-ray micro-computed tomography is used to investigate the borings of Osedax mucofloris in bones of the minke whale, quantitatively detailing their morphological characteristics for the first time and hypothesizing a model of boring that is dependent on the density and microstructure of the bone.
Abstract: Osedax worms possess unique “root” tissues that they use to bore into bones on the seafloor, but details of the boring pattern and processes are poorly understood. Here we use X-ray micro-computed tomography to investigate the borings of Osedax mucofloris in bones of the minke whale (Balaenoptera acutorostrata), quantitatively detailing their morphological characteristics for the first time. Comparative thin-sections of the borings reveal how the bone is eroded at the sub-millimeter level. On the basis of these results we hypothesize a model of boring that is dependent on the density and microstructure of the bone. We also present evidence of acidic mucopolysaccharides in the mucus of the root tissue, and hypothesize that this plays an important role in the boring mechanism. We discuss the utility of these new data in evaluating Osedax trace fossils and their relevance for O. mucofloris ecology. Measured rates of bone erosion (6% per year) and evidence of enhanced sulfide release from the borings indicate...

40 citations


Journal ArticleDOI
TL;DR: Data suggest that the sphingosine rheostat may play a role in the balance between stability and dysfunction in cnidarian-dinoflagellate symbioses.
Abstract: The symbiosis between host cnidarians, such as corals and anemones, and their dinoflagellate symbionts is regulated by largely undescribed mechanisms that stabi- lize the symbiosis during normal conditions but lead to symbiosis breakdown, or cnidarian bleaching, during stress. Previous transcriptomic studies identified the sphingosine rheostat as a putative symbiosis regulatory pathway. The sphingosine rheostat, which includes the sphingolipids sphingosine (Sph) and sphingosine 1-phosphate (S1P), is a key homeostatic cell regulatory pathway known to function in cell fate and immunity in animals. This study explores the role of sphingosine rheostat components in the stability of the symbiotic partnership. The anemone Aiptasia pallida, host to the dinoflagellate Symbiodinium sp., was used to test the hypothesis that S1P promotes symbiosis stability whereas Sph increases bleaching induced by heat stress. Anemones pre-incubated in exogenous S1P and FTY720, a synthetic S1P analog, were partially rescued from heat- stress-induced bleaching. In addition, they displayed a de- crease in caspase activity, a measure of apoptosis, compared to controls. In contrast, when anemones were pre-incubated with Sph, both bleaching and caspase activity increased compared to untreated, heat-stressed controls. These data suggest that the sphingosine rheostat may play a role in the balance between stability and dysfunction in cnidarian- dinoflagellate symbioses.

38 citations


Journal ArticleDOI
TL;DR: Elliptical Fourier analysis quantifies morphological differences between species and measures colony variance in sclerite size and shape among colonies and species, which may be less useful in phylogenetic analyses.
Abstract: Species descriptions of most alcyonacean oc- tocorals rely heavily on the morphology of sclerites, the calcium carbonate spicules embedded in the soft tissue. Sclerites provide taxonomic characters for species delinea- tion but require qualitative descriptions, which introduce ambiguities in recognizing morphological features. Ellipti- cal Fourier analysis of the outline of sclerites was used to quantify the morphology of eight species of gorgoniid oc- tocoral in the genus Pseudopterogorgia. Sclerites from one to seven colonies of each species were compared. Scaphoids and spindles were examined separately; rods and octoradi- ates were excluded from the analyses because of their morphologic similarity across all species. Discriminant analysis of elliptical Fourier descriptors (EFDs) was used to determine whether the elliptical Fourier analysis could be used to identify the specimens. Sclerites were highly vari- able even within a single colony. Correct species assign- ments of individual sclerites were greater than 50% for both scaphoids and spindles. Species assignments based on av- erages of the EFDs for each colony approached 90%. El- liptical Fourier analysis quantifies morphological differ- ences between species and measures colony variance in sclerite size and shape among colonies and species. Phylo- genetic analysis based on EFDs did not capture monophy- letic groups. The quantification of complex shapes such as sclerites provides an important tool in alpha taxonomy but may be less useful in phylogenetic analyses.

37 citations


Journal ArticleDOI
TL;DR: Interspecific differences in anchor-ice formation and propagation characteristics for Antarctic benthic organisms show increased incidence of formation and accelerated spread of ice crystals compared to urchins and sea stars, and are consistent with, and provide a potential first step toward, an explanation for disturbance patterns observed in shallow polar benthics communities.
Abstract: Sea ice typically forms at the ocean's surface, but given a source of supercooled water, an unusual form of ice—anchor ice— can grow on objects in the water column or at the seafloor. For several decades, ecologists have considered anchor ice to be an important agent of distur- bance in the shallow-water benthic communities of Mc- Murdo Sound, Antarctica, and potentially elsewhere in po- lar seas. Divers have documented anchor ice in the McMurdo communities, and its presence coincides with reduced abundance of the sponge Homaxinella balfouren- sis, which provides habitat for a diverse assemblage of benthic organisms. However, the mechanism of this distur- bance has not been explored. Here we show interspecific differences in anchor-ice formation and propagation char- acteristics for Antarctic benthic organisms. The sponges H. balfourensis and Suberites caminatus show increased inci- dence of formation and accelerated spread of ice crystals compared to urchins and sea stars. Anchor ice also forms readily on sediments, from which it can grow and adhere to organisms. Our results are consistent with, and provide a potential first step toward, an explanation for disturbance patterns observed in shallow polar benthic communities. Interspecific differences in ice formation raise questions about how surface tissue characteristics such as surface area, rugosity, and mucus coating affect ice formation on invertebrates.

Journal ArticleDOI
TL;DR: The results of experiments suggest that FGFR signaling is required for lens regeneration in Xenopus, and reverse transcriptase–polymerase chain reaction analyses reveal that a number of FGF family members are expressed in cornea epithelium and retinal tissues both before and during the process of lens regeneration.
Abstract: In species of the frog genus Xenopus, lens regeneration occurs through a process of transdifferentia- tion, in which cornea epithelial cells presumably undergo dedifferentiation and subsequently redifferentiate to form a new lens. Experimental studies have shown that the retina provides the key signal required to trigger this process once the original lens is removed. A previous study showed that addition of an exogenous fibroblast growth factor (i.e., FGF1 protein) could initiate transdifferentiation of cornea epithelial cells in culture. To determine the role of FGF signaling in X. laevis lens regeneration, we have examined the presence of specific FGFs and their receptors (FGFRs) during this process and evaluated the necessity of FGFR signaling. Reverse transcriptase-polymerase chain reaction analyses reveal that a number of FGF family members are expressed in cornea epithelium and retinal tissues both before and during the process of lens regeneration. Of these, FGF1, FGF8, and FGF9 are expressed principally in retinal tissue and not in the cornea epithelium. Hence, these ligands could represent key signaling factors originating from the retina that trigger regeneration. The results of experiments using an in vitro eye culture system and an FGFR inhibitor (SU5402) suggest that FGFR signaling is required for lens regeneration in Xenopus.

Journal ArticleDOI
TL;DR: This work examines a cohort of cells conserved across all vertebrates, the reticulospinal neurons, which lend themselves well to experimental manipulations, and asks what characteristics a model system must have to support a GRN analysis.
Abstract: What gives an organism the ability to regrow tissues and to recover function where another organism fails is the central problem of regenerative biology. The challenge is to describe the mechanisms of regeneration at the molecular level, delivering detailed insights into the many components that are cross-regulated. In other words, a broad, yet deep dissection of the system-wide network of molecular interactions is needed. Functional genomics has been used to elucidate gene regulatory networks (GRNs) in developing tissues, which, like regeneration, are complex systems. Therefore, we reason that the GRN approach, aided by next generation technologies, can also be applied to study the molecular mechanisms underlying the complex functions of regeneration. We ask what characteristics a model system must have to support a GRN analysis. Our discussion focuses on regeneration in the central nervous system, where loss of function has particularly devastating consequences for an organism. We examine a cohort of ce...

Journal ArticleDOI
TL;DR: In laboratory experiments, the intertidal snail Chlorostoma funebralis was allowed to position itself on a temperature gradient, then measured its thermal preference and determined an index of how its performance varied with temperature, which resulted in a biased random walk along the temperature gradient.
Abstract: Evolutionary theory predicts that, in variable environments, it is advantageous for ectothermic organisms to prefer a body temperature slightly below the physiolog- ical optimum. This theory works well for many terrestrial organisms but has not been tested for animals inhabiting the hypervariable physical environment of intertidal shores. In laboratory experiments, we allowed the intertidal snail Chlorostoma funebralis to position itself on a temperature gradient, then measured its thermal preference and deter- mined an index of how its performance varied with temper- ature. Snails performed a biased random walk along the temperature gradient, which, contrary to expectations, caused them to aggregate where body temperature was 15 to 17 °C below their temperature of optimum performance and near the species' lower thermal limit. This "cold-biased" behavioral response may guide snails to refuges in shaded cracks and crevices, but potentially precludes C. funebralis from taking full advantage of its physiological capabilities.

Journal ArticleDOI
TL;DR: It is shown that the trophosome in Osedax is an apolar tissue composed of bacteriocytes and nonsymbiotic cells, and as in vestimentiferans, a specific cell cycle was identified; however, in this case it is directed from the posterior to the anterior end of the worms instead of from the center toward the periphery.
Abstract: The polychaete family Siboglinidae, which is currently construed as comprising the Frenulata, Monilifera (composed of Sclerolinum), Vestimentifera, and Osedax, has become known for its specialized symbiont-housing organ called the trophosome. This organ replaced the digestive system of the worms and is located in the elongated trunk region in Frenulata, Sclerolinum, and Vestimentifera. Currently two types of trophosomes have been described: in the taxa Frenulata and Sclerolinum the bacteriocytes originate from endoderm, and in Vestimentifera they originate from mesoderm. In Osedax, a trophosome was described as lacking (Rouse et al., 2004), but bacteriocytes are located in Osedax's characteristic root tissue. Here, we argue for a consistent name for the symbiont-housing tissue, namely trophosome, as in other siboglinids. In this study we provide morphological evidence that in Osedax the bacteriocytes are derived from somatic mesoderm. We show that the trophosome in Osedax is an apolar tissue composed of b...

Journal ArticleDOI
TL;DR: The results suggest that a wide range of bacteria could impair metabolism in C. sapidus and suggest that in general, gram-negative bacteria could stimulate hemocytopenia.
Abstract: In the blue crab Callinectes sapidus, injection with the bacterial pathogen Vibrio campbellii causes a de- crease in oxygen consumption. Histological and physiolog- ical evidence suggests that the physical obstruction of he- molymph flow through the gill vasculature, caused by aggregations of bacteria and hemocytes, underlies the de- crease in aerobic function associated with bacterial infec- tion. We sought to elucidate the bacterial properties suffi- cient to induce a decrease in circulating hemocytes (hemocytopenia) as an indicator for the initiation of hemo- cyte aggregation and subsequent impairment of respiration. Lipopolysaccharide (LPS), the primary component of the gram-negative bacterial cell wall, is known to interact with crustacean hemocytes. Purified LPS was covalently bound to the surfaces of polystyrene beads resembling bacteria in size. Injection of these "LPS beads" caused a decrease in circulating hemocytes comparable to that seen with V. campbellii injection, while beads alone failed to do so. These data suggest that in general, gram-negative bacteria could stimulate hemocytopenia. To test this hypothesis, crabs were injected with different bacteria—seven gram- negative and one gram-positive species—and their effects on circulating hemocytes were assessed. With one excep- tion, all gram-negative strains caused decreases in circulat- ing hemocytes, suggesting an important role for LPS in the induction of this response. However, LPS is not necessary to provoke the immune response given that Bacillus coral, a gram-positive species that lacks LPS, caused a decrease in circulating hemocytes. These results suggest that a wide range of bacteria could impair metabolism in C. sapidus.

Journal ArticleDOI
TL;DR: It is morphologically confirmed that N. nomurai podocysts have the capacity for long-term dormancy, an ability that should contribute to the periodic nature of the massive blooms of medusae of this species.
Abstract: Production of podocysts is the exclusive form of asexual reproduction by polyps of the giant jellyfish Nemopilema nomurai, which has been recurrently blooming in the East Asian seas in the last decade. Podocycts consist of a dome-shaped chitinous capsule with laminated struc- ture that encapsulates a mass of cyst cells filled with gran- ules containing nutrient reserves such as proteins, carbohy- drates, and lipids. Mitochondria, rough endoplasmic reticulum, and Golgi complexes are scarce in the cytoplasm of these cells, and the staining reaction for RNA is weak, indicating very low metabolic activity. Podocysts are capa- ble of dormancy for at least 5 years without significant change of internal structure or nutrient reserves. Integrated information about spontaneous and artificially induced metamorphosis suggests that the following processes occur during excystment: (1) nematocyst formation in the internal cell mass, (2) stratification of the cell mass into endoderm and ectoderm, (3) extrusion of the cell mass through a gradual opening of the capsule, (4) formation of primordial polyp mouth and tentacles, and (5) metamorphosis to a polyp. We morphologically confirmed that N. nomurai podocysts have the capacity for long-term dormancy, an ability that should contribute to the periodic nature of the massive blooms of medusae of this species.

Journal ArticleDOI
TL;DR: Results clearly showed that the stiffness changes in the starfish dermis were based on a non-muscular mechanism that was similar to that of other echinoderm connective tissues with mechanical mutability.
Abstract: Stiffness changes in response to mechanical and chemical stimulation were studied in muscle-free dermal samples from the body wall of the starfish Linckia laevigata. The ultrastructural study showed that the dermis was packed with collagen fibrils between which only a small number of cells were observed. Muscles were found only in the walls of coelomic extensions leading to papulae. Stress-strain tests were performed on isolated dermis containing no muscles. The tangent modulus was 27.5 MPa at 0.04% strain rate in the stress-strain tests. It was increased to 40.7 MPa by mechanical stimulation, which also increased the tensile strength and breaking-strain energy density. Dynamic mechanical tests showed that the increase in stiffness in response to mechanical stimulation was transient. Acetylcholine (10(-6)-10(-3) mol l(-1)) and artificial seawater with an elevated potassium concentration (KASW) stiffened the dermis. Mechanical stimulation caused a 12% mass loss. KASW also caused mass loss, which was inhibited by anesthesia. These results clearly showed that the stiffness changes in the starfish dermis were based on a non-muscular mechanism that was similar to that of other echinoderm connective tissues with mechanical mutability.

Journal ArticleDOI
TL;DR: This work examined changes in the bell morphology and swimming kinematics of the limnomedusa Liriope tetraphylla at different stages of development and compared the performance values of the different propulsive modes observed among juvenile medusae.
Abstract: Swimming animals may experience significant changes in the Reynolds number (Re) of their surrounding fluid flows throughout ontogeny. Many medusae experience Re envi- ronments with significant viscous forces as small juveniles but inertially dominated Re environments as adults. These different environments may affect their propulsive strategies. In particular, rowing, a propulsive strategy with ecological advantages for large adults, may be constrained by viscosity for small juvenile medu- sae. We examined changes in the bell morphology and swimming kinematics of the limnomedusa Liriope tetraphylla at different stages of development. L. tetraphylla maintained an oblate bell (fineness ratio 0.5-0.6), large velar aperture ratio (Rv 0.5- 0.8), and rapid bell kinematics throughout development. These traits enabled it to use rowing propulsion at all stages except the very smallest sizes observed (diameter 0.14 cm). During the juvenile stage, very rapid bell kinematics served to increase Re sufficiently for rowing propulsion. Other taxa that use rowing propulsion as adults, such as leptomedusae and scyphomedusae, typically utilize different propulsive strategies as small juveniles to function in low Re environments. We compared the performance values of the different propulsive modes observed among juvenile medusae.

Journal ArticleDOI
TL;DR: There is evidence that cortisol enhances glochidial metamorphosis on hosts by improving the retention of attached glochidia, and insights are given into the influence of host physiology on glchidial attachment and juvenile mussel transformation.
Abstract: The larvae of unionid freshwater mussels (i.e., glochidia) undergo a parasitic stage requiring their attachment to the external epithelia of fish hosts, where they metamorphose into free-living juveniles. We describe the physiological effects in bluegill sunfish (Lepomis macrochirus) of infection with glochidia from the paper pondshell (Utterbackia imbecillis). Glochidia accumulation on bluegill increased dramatically at concentrations of 2000 glochidia liter(-1) and above, reaching a maximum attachment density of about 30 glochidia g(-1) fish at 4000 glochidia liter(-1). Plasma cortisol was the most sensitive indicator of biological effect to glochidial exposure, increasing significantly in hosts exposed to 2000 glochidia liter(-1) or greater. Glochidia were 31% more likely to undergo successful juvenile metamorphosis when attached to bluegill with elevated plasma cortisol, largely due to the enhanced survivorship of these larvae during the first 48 h after infection. We tested the hypothesis that glochidial attachment and juvenile metamorphosis were stimulated directly by plasma cortisol in fish hosts. Bluegill were given an intraperitoneal injection of cortisol, then infected with 1000 glochidia liter(-1) at 48 h after hormone supplementation. Cortisol-injected fish had a 42% increase in the number of attached glochidia g(-1) fish and a 28% increase in larval metamorphosis compared to sham-injected and control fish. We provide evidence that cortisol enhances glochidial metamorphosis on hosts by improving the retention of attached glochidia. This study gives insights into the influence of host physiology on glochidial attachment and juvenile mussel transformation.

Journal ArticleDOI
TL;DR: The results suggest that as a consequence of acquiring CTA, the CS evokes conditioned fear in the conditioned snails, as evidenced by a change in the nervous system control of cardiac activity.
Abstract: In conditioned taste aversion (CTA) training performed on the pond snail Lymnaea stagnalis, a stimulus (the conditional stimulus, CS; e.g., sucrose) that elicits a feeding response is paired with an aversive stimulus (the unconditional stimulus, US) that elicits the whole-body withdrawal response and inhibits feeding. After CTA training and memory formation, the CS no longer elicits feeding. We hypothesize that one reason for this result is that after CTA training the CS now elicits a fear response. Consistent with this hypothesis, we predict the CS will cause (1) the heart to skip a beat and (2) a significant change in the heart rate. Such changes are seen in mammalian preparations exposed to fearful stimuli. We found that in snails exhibiting long-term memory for one-trial CTA (i.e., good learners) the CS significantly increased the probability of a skipped heartbeat, but did not significantly change the heart rate. The probability of a skipped heartbeat was unaltered in control snails given backward conditioning (US followed by CS) or in snails that did not acquire associative learning (i.e., poor learners) after the one-trial CTA training. These results suggest that as a consequence of acquiring CTA, the CS evokes conditioned fear in the conditioned snails, as evidenced by a change in the nervous system control of cardiac activity.

Journal ArticleDOI
TL;DR: Few sampling locations or individual anemones showed symbiont diversity at either organellar locus within the limits of the detection method, while sequence analysis of cloned nr18S polymerase chain reaction product suggests that nuclear pseudogenes may underlie intra-host diversity observed at that locus.
Abstract: Among temperate cnidarian symbioses, the partnership between the intertidal anemone Anthopleura elegantissima and its dinoflagellate and chlorophyte symbionts is one of the most well characterized. Biogeographic, reciprocal transplant, and physiological studies have convincingly demonstrated a relationship between environmental factors such as temperature and irradiance and the distribution of symbionts from both algal phyla. However, little is known about the fine-scale diversity or biogeographic distribution within symbiont lineages of this anemone. We used sequence information from the mitochondrial cytochrome b and chloroplast 23S ribosomal genes and restriction fragment length polymorphism data from the 18S nuclear ribosomal gene to characterize the Symbiodinium populations in tentacles clipped from 105 anemones at 14 sites along the entire California coast, spanning about 1200 km. Our results show the presence of at least three primary biogeographic regions with breaks around Cape Mendocino and Mont...

Journal ArticleDOI
TL;DR: In P. tuberculosa, larvae show a non-radial body plan and then metamorphose to almost-radian polyps after settlement, which may support a hypothesis that a common ancestor of Cnidaria had a bilateral body plan that has been secondarily lost in some extant cnidarians.
Abstract: The spawning behavior and early embryogenesis of Palythoa tuberculosa (Anthozoa, Zoantharia) were observed in August 2009 off Okinawa Island, Japan. P. tuberculosa released zygotes just after high tide around new moon nights. The mean diameter of zygotes was 365.6 ± s.d.14.8 μm, and zygotes did not contain any symbiotic algae (zooxanthellae). About 2 h after spawning, the first cleavage furrow appeared on one side of the zygotes, although it was uncertain when eggs were fertilized. After second cleavage, the arrangement of blastomeres was pseudospherical. At 9 h after spawning, the embryo became a concave-convex dish shape, then gastrulation occurred and the blastopore was formed. Seven-day old larvae were ellipsoid and about 700 μm long, with an open mouth at one end. Two weeks after spawning, the larvae developed a longitudinal band of long cilia (= ventral ciliate band) that is characteristic of zoanthella larvae. In P. tuberculosa, larvae show a non-radial body plan and then metamorphose to almost-rad...

Journal ArticleDOI
TL;DR: The results suggest that larval dispersal of spawning Acropora species may be on a more local scale than that of G. pectinata and most other reef coral species previously reported, and larval size is not a good estimator of larval lifespan in Reef coral species.
Abstract: Temporal dynamics of larval survival were examined in vitro in four broadcast-spawning reef coral species, Acropora hyacinthus, A. japonica, A. solitaryensis, and Goniastrea pectinata. Larval size was treated as an important characteristic that may relate to larval lifespan. Two patterns were observed in larval survival dynamics between the three Acropora species (mean initial larval size; 0.05-0.08 mm(3)) and G. pectinata (0.02 mm(3)), based on the timing of a sharp drop in larval survival rates (ca. > 50% reduction over a 1-2 week period). Consequently, the majority of larvae of the three Acropora species had a lifespan of less than 2-3 weeks, whereas those of G. pectinata were extended a further 2-3 weeks despite the smaller larval size. No significant relationship was detected between the initial larval size and larval lifespan in any of the four reef coral species. These results suggest that (1) larval dispersal of spawning Acropora species may be on a more local scale than that of G. pectinata and most other reef coral species previously reported, and (2) larval size is not a good estimator of larval lifespan in reef coral species.

Journal ArticleDOI
TL;DR: MYP accumulates in the agametogenic ovaries and testes during the non-reproductive season, playing a role as a carrier to transport zinc to the gonad.
Abstract: Sea urchins of both sexes store the nutrients necessary for gametogenesis in nutritive phagocytes of the agametogenic gonad. A zinc-binding protein termed the major yolk protein (MYP) is stored here as two isoforms: the egg-type (predominant in egg yolk granules) and the coelomic fluid-type (a precursor with greater zinc-binding capacity). MYP is used during gametogenesis as material for synthesizing gametic proteins and other components. We investigated its accumulation and relationship to zinc contents in gonads during the non-reproductive season in Pseudocentrotus depressus. MYP constituted most of the protein in coelomic fluid and gonads. Both ovaries and testes grew gradually, accumulating MYP and zinc during the year. Total zinc contents and the ratio of coelomic fluid-type to egg-type protein were higher in ovaries than in testes as gametogenesis approached. Most of the zinc in the coelomic fluid was bound to MYP, and the concentrations of MYP and zinc were elevated toward the onset of oogenesis in the female coelomic fluid. Thus, MYP accumulates in the agametogenic ovaries and testes during the non-reproductive season, playing a role as a carrier to transport zinc to the gonad. Transportation of zinc by MYP is more active in females than in males.

Journal ArticleDOI
TL;DR: It is demonstrated that extracts of egg jelly contain factors that extend the period of sperm motility as well as providing a chemoattractant activity as previously reported, and that jelly-derived factors regulate both the longevity and directionality of sperm propulsion.
Abstract: The motility of Xenopus sperm is initiated by the osmotic shock experienced when these cells are ejacu- lated into low-salinity pond water. Motility is brief and is required for the sperm to penetrate the jelly layers and fertilize the egg. In this study we demonstrate that extracts of egg jelly contain factors that extend the period of sperm motility as well as providing a chemoattractant activity as previously reported. Both activities are partially dependent on extracellular calcium. Time-lapse and video microscopy show that after activation of motility the number of motile sperm decreases rapidly, with a half-time of about 2 min. Addition of 10% v/v egg jelly extract ("egg water") in- creased the number of motile sperm 2-fold over controls at 20 s and about 4- to 10-fold over controls at 10 min after initiation of motility. Extension of motility lifetime was not mediated by a nonspecific protein or by allurin, the egg- water protein that has chemoattractant activity. The helical path of Xenopus sperm exhibited tight coupling between rotational and forward velocities in egg jelly, but coupling changed rapidly from moment to moment in low-salinity buffer. Our observations suggest that jelly-derived factors regulate both the longevity and directionality of sperm propulsion.

Journal ArticleDOI
TL;DR: The costs and benefits of fusion between juveniles are focused on, characterizing growth rates and patterns of somatic and germline chimerism after natural and controlled fusion events and finding that the majority of individual testes in a chimera were clonally derived.
Abstract: The colonial ascidian Botryllus schlosseri undergoes a histocompatibility reaction that can result in vascular fusion of distinct genotypes, creating a chimera. Chimerism has both potential benefits, such as an immediate increase in size that may enhance growth rates, and costs. For the latter, the presence of multiple genotypes in a chimera can lead to competition between genetically distinct stem cell lineages, resulting in complete replacement of somatic and germline tissues by a single genotype. Although fusion can occur at any point after metamorphosis, previous studies have focused on chimeras created from sexually mature adults, where no benefit to chimerism has been documented. Here we focus on the costs and benefits of fusion between juveniles, characterizing growth rates and patterns of somatic and germline chimerism after natural and controlled fusion events. We also compared outcomes between low- and high-density growth conditions, the latter more likely representative of what occurs in natural populations. We found that growth rates were density-dependent, and that only chimeras grew under high-density conditions. We also observed a positional component to a post-fusion event called resorption, indicating that extrinsic factors were important in this process. Patterns of germline and somatic chimerism and dominance in chimeras made from fused juveniles were equivalent to those after fusion of sexually mature adults, and there were no age-related differences in these processes. Finally, by using genetic markers that could retrospectively assign genotypes, we also found that the majority of individual testes in a chimera were clonally derived.

Journal ArticleDOI
TL;DR: It is shown that larvae of two species of sabellariid annelids, Sabellaria cementarium and Phragmatopoma californica, bear prototrochal and metatrochal cilia that beat in opposition to each other, confirming the presence of opposed bands in larvae of sabelariids.
Abstract: The larvae of marine annelids capture food using an unusual diversity of suspension-feeding mechanisms. Many of the feeding mechanisms of larval annelids are poorly known despite the abundance and ecological significance of both larvae and adults of some annelid taxa. Here we show that larvae of two species of sabellariid annelids, Sabellaria cementarium and Phragmatopoma californica, bear prototrochal and metatrochal cilia that beat in opposition to each other. For larvae of S. cementarium, we provide evidence that these opposed bands of cilia are used to capture suspended particles. In video recordings, captured particles were overtaken by a prototrochal cilium and then moved with the cilium to the food groove, a band of cilia between the prototroch and metatroch. They were then transported by cilia of the food groove to the mouth. Lengths of the prototrochal cilia, lengths of the prototrochal ciliary band, size range of the particles captured, and estimated rates of clearance increased with larval age ...

Journal ArticleDOI
TL;DR: It is found that prior to the third instar, larvae are unable to perform the characteristic “corkscrew-like roll” behavior and an avoidance behavior consistent with a nocifensive response that is present immediately after larval hatching is identified, representing a paradigm that may be useful in examining mutations with an early lethal phenotype.
Abstract: The ability to perceive and avoid harmful substances or stimuli is key to an organism's survival. The neuronal cognate of the perception of pain is known as nociception, and the reflexive motion to avoid pain is termed the nocifensive response. As the nocifensive re- sponse is an ancient and evolutionarily conserved behav- ioral response to nociceptive stimuli, it is amenable to study in relatively simple and genetically tractable model systems such as Drosophila. Recent studies have taken advantage of the useful properties of Drosophila larvae to begin eluci- dating the neuronal connectivity and molecular machinery underlying the nocifensive response. However, these studies have primarily utilized the third-instar larval stage, and many mutations that potentially influence nociception sur- vive only until earlier larval stages. Here we characterize the nocifensive responses of Drosophila throughout larval de- velopment and find dramatic changes in the nature of the behavior. Notably, we find that prior to the third instar, larvae are unable to perform the characteristic "corkscrew- like roll" behavior. Also, we identify an avoidance behavior consistent with a nocifensive response that is present im- mediately after larval hatching, representing a paradigm that may be useful in examining mutations with an early lethal phenotype.

Journal ArticleDOI
TL;DR: The relationship between neurogenesis and the regenerative ability of the brain is discussed, and also the evolutionary origin of thebrain structures in which adult Neurogenesis has been observed is discussed.
Abstract: Of all organs in mammals including humans, the brain has the most limited regenerative capacity after injury or damage. In spite of extensive efforts to treat ischemic/stroke injury of the brain, thus far no reliable therapeutic method has been developed. However, some molluscan species show remarkable brain regenerative ability and can achieve full functional recovery following injury. The terrestrial pulmonates are equipped with a highly developed olfactory center, called the procerebrum, which is involved in olfactory discrimination and odor-aversion learning. Recent studies revealed that the procerebrum of the land slug can spontaneously recover structurally and functionally relatively soon after injury. Surprisingly, no exogenous interventions are required for this reconstitutive repair. The neurogenesis continues in the procerebrum in adult slugs as in the hippocampus and the olfactory bulb of mammals, and the reconstitutive regeneration seems to be mediated by enhanced neurogenesis. In this review,...