Showing papers in "The Biological Bulletin in 2004"
TL;DR: The ability of larvae to rapidly respond to brief encounters with dissolved settlement cues can enhance their rapid transport to the substratum, even in wave-driven turbulent flow.
Abstract: Larvae of the nudibranch Phestilla sibogae were used to study whether a natural dissolved settlement cue (from their prey, Porites compressa, an abundant coral on Hawaiian reefs) induces behavioral responses that can affect larval transport to suitable settlement sites. As cue and larvae are mixed in the turbulent flow over a reef, cue is distributed in fine-scale filaments that the larva experiences as rapid (seconds) on/off encounters. To examine larval responses in this setting, individual larvae were tethered in a small flume with flow simulating water velocity relative to a freely swimming larva, and their responses to realistic temporal patterns of cue encounter were videotaped. Competent larvae quickly ceased swimming in cue filaments and resumed swimming after exiting filaments. The threshold cue concentration eliciting a response was 3%–17% of concentrations within heads of P. compressa in nature. When moving freely in filtered seawater, competent larvae swam along straight paths in all direction...
108 citations
TL;DR: SLL-2 is described as the key chemical factor for arresting Symbiodinium in the cell-dividing, non-motile stage, while some nonsymbiotic microalgae were even destroyed by SLL- 2.
Abstract: Symbioses between zooxanthellae (Symbiodinium spp.) and marine invertebrates, including corals, are common in shallow marine environments. The zooxanthellae contribute to host nutrition by translocating photosynthetic products and enabling them to effloresce in oligotrophic conditions. Coral mainly acquire Symbiodinium spp. by capturing freeswimming cells from the environment (1). Cultured Symbiodinium cells show a diel growth cycle with alternation between motile and non-motile cell stages once a day (2, 3), and the cell divides only during the latter stage (2). When associated with a host, however, cells are arrested in a non-motile stage while healthy cell division is maintained (4). We deduced that host-directed and chemical-based mechanisms are responsible for this phenomenon since SLL-2, a lectin that binds to carbohydrate chains with a D-galactosyl moiety, produced by the octocoral Sinularia lochmodes, is localized on the cell surface of the Symbiodinium harbored in the host (5). Here we describe SLL-2 as the key chemical factor for arresting Symbiodinium in the cell-dividing, non-motile stage, while some nonsymbiotic microalgae were even destroyed by SLL-2. Symbiotic associations between photosynthetic dinoflagellates (Symbiodinium spp.) and invertebrate hosts such as corals are crucial for the survival of the host animals since Symbiodinium supplies organic compounds to them and enables them to prosper in the oligotrophic environment
88 citations
TL;DR: The histamine content of two host plants of H. purpurascens—D.
Abstract: Larvae of the Australian sea urchin Holopneustes purpurascens are induced to settle and metamorphose (termed settlement herein) by a water-soluble compound produced by the red alga Delisea pulchra,...
88 citations
TL;DR: The ability to tolerate significant chromosomal loss suggests that the modal karyotype of Pectinidae and possibly other bivalves with a haploid number of 19 is likely tetraploid; i.e., at least one genome duplication has occurred during the evolution of Bivalvia.
Abstract: Karyotype and chromosomal localization of major (18 -5.8 -28S) and minor (5S) ribosomal RNA genes were studied in two species of Pectinidae, zhikong (Chlamys farreri) and bay (Argopecten irradians irradians) scallops, using fluorescence in situ hybridization (FISH). C. farreri had a haploid number of 19 with a karyotype of 3m 4sm 7sm-st 4st 1st-t, and A. i. irradians had a haploid number of 16 with a karyotype of 5st 11t. In C. farreri, the major and minor rRNA genes had one locus each and were mapped to the same chromosome—Chromo- some 5. In A. i. irradians, the major rRNA genes had two loci, located on Chromosomes 4 and 8, and the 5S rRNA gene was found at a third chromosome—Chromosome 10. Results of this and other studies indicate that karyotype of A. i. irradians (n 16, 21 arms) is secondary and derived from an ancestral karyotype similar to that of C. farreri (n 19, 38 arms) through considerable chromosomal loss and rearrangements. The ability to tolerate significant chromo- somal loss suggests that the modal karyotype of Pectinidae and possibly other bivalves with a haploid number of 19 is likely tetraploid; i.e., at least one genome duplication has occurred during the evolution of Bivalvia.
85 citations
TL;DR: It is found that females and males use different (sex-specific) communicational cues during mate searching and assessment, and that the sexual communication of rock shrimp is similar to that of the American lobster, where females are first attracted to the dominant males by chemical cues emitted by these males.
Abstract: Mate searching in crustaceans depends on dif- ferent communicational cues, of which chemical and visual cues are most important. Herein we examined the role of chemical and visual communication during mate searching and assessment in the rock shrimp Rhynchocinetes typus. Adult male rock shrimp experience major ontogenetic changes. The terminal molt stages (named "robustus") are dominant and capable of monopolizing females during the mating process. Previous studies had shown that most fe- males preferably mate with robustus males, but how these dominant males and receptive females find each other is uncertain, and is the question we examined herein. In a Y-maze designed to test for the importance of waterborne chemical cues, we observed that females approached the robustus male significantly more often than the typus male. Robustus males, however, were unable to locate receptive females via chemical signals. Using an experimental set-up that allowed testing for the importance of visual cues, we demonstrated that receptive females do not use visual cues to select robustus males, but robustus males use visual cues to find receptive females. Visual cues used by the robustus males were the tumults created by agitated aggregations of subordinate typus males around the receptive females. These results indicate a strong link between sexual commu- nication and the mating system of rock shrimp in which dominant males monopolize receptive females. We found that females and males use different (sex-specific) commu- nicational cues during mate searching and assessment, and that the sexual communication of rock shrimp is similar to that of the American lobster, where females are first at- tracted to the dominant males by chemical cues emitted by these males. A brief comparison between these two species shows that female behaviors during sexual communication contribute strongly to the outcome of mate searching and assessment.
80 citations
TL;DR: It is demonstrated that acute exposure to hypercapnic hypoxia (HH) significantly impairs the ability of blue crabs to clear Vibrio from the hemolymph and suggests that HH alters the normal role of circulating hemocytes in the removal of an invading pathogen.
Abstract: Callinectes sapidus, the Atlantic blue crab, en- counters hypoxia, hypercapnia (elevated CO 2 ), and bacterial pathogens in its natural environment. We tested the hypoth- esis that acute exposure to hypercapnic hypoxia (HH) alters the crab's ability to clear a pathogenic bacterium, Vibrio campbellii 90 - 69B3, from the hemolymph. Adult male crabs were held in normoxia (well-aerated seawater) or HH (seawater with PO2 4 kPa; PCO2 1.8 kPa; and pH 6.7-7.1) and were injected with 2.5 10 4 Vibrio g 1 body weight. The animals were held in normoxia or in HH for 45, 75, or 210 -240 min before being injected with Vibrio, and were maintained in their respective treatment conditions for the 120-min duration of the experiment. Vibrio colony- forming units (CFU) ml 1 hemolymph were quantified be- fore injection, and at 10, 20, and 40 min afterward. Total hemocytes (THC) ml 1 of hemolymph were counted 24 h before (24 h), and at 10 and 120 min after injection. Sham injections of saline produced no change in the bacterial or hemocyte counts in any treatment group. Among the groups that received bacterial injections, Vibrio was almost com- pletely cleared within 1 h, but at 10-min postinjection, Vibrio CFU ml 1 hemolymph was significantly higher in animals held in HH for 75 and 210 -240 min than in those held in normoxia. Within 10 min after crabs were injected with bacteria, THC ml 1 significantly decreased in control and HH45 treatments, but not in the HH75 and HH210 -240 treatments. By 120 min after injection of bacteria, hemocyte counts decreased in all but the HH45 group. These data demonstrate that HH significantly impairs the ability of blue crabs to clear Vibrio from the hemolymph. These results also suggest that HH alters the normal role of circulating hemocytes in the removal of an invading pathogen.
74 citations
TL;DR: The appearance of the counterillumination was more affected by the visual acuity of the viewer than by the clarity of the water, even at relatively large distances, which has implications for the study of spatial resolution, contrast sensitivity, and color discrimination in deep-sea visual systems.
Abstract: Many deep-sea species, particularly crusta- ceans, cephalopods, and fish, use photophores to illuminate their ventral surfaces and thus disguise their silhouettes from predators viewing them from below. This strategy has several potential limitations, two of which are examined here. First, a predator with acute vision may be able to detect the individual photophores on the ventral surface. Second, a predator may be able to detect any mismatch between the spectrum of the bioluminescence and that of the background light. The first limitation was examined by modeling the perceived images of the counterillumination of the squid Abralia veranyi and the myctophid fish Cera- toscopelus maderensis as a function of the distance and visual acuity of the viewer. The second limitation was addressed by measuring downwelling irradiance under moonlight and starlight and then modeling underwater spec- tra. Four water types were examined: coastal water at a depth of 5 m and oceanic water at 5, 210, and 800 m. The appearance of the counterillumination was more affected by the visual acuity of the viewer than by the clarity of the water, even at relatively large distances. Species with high visual acuity (0.11° resolution) were able to distinguish the individual photophores of some counterilluminating signals at distances of several meters, thus breaking the camouflage. Depth and the presence or absence of moonlight strongly affected the spectrum of the background light, particularly near the surface. The increased variability near the surface was partially offset by the higher contrast attenuation at shallow depths, which reduced the sighting distance of mismatches. This research has implications for the study of spatial resolution, contrast sensitivity, and color discrimina- tion in deep-sea visual systems.
69 citations
TL;DR: It is indicated that temperature and salinity influence the rate of crab development, but only the extremes of these conditions have an effect on survival.
Abstract: The horseshoe crab Limulus polyphemus spawns in the mid- to upper intertidal zone where females deposit eggs in nests below the sediment surface. Although adult crabs generally inhabit subtidal regions of estuaries with salinities from 5 to 34 ppt, developing embryos and larvae within nests are often exposed to more extreme conditions of salinity and temperature during summer spawning periods. To test whether these conditions have a negative impact on early development and survival, we determined development time, survival, and molt cycle duration for L. polyphemus embryos and larvae raised at 20 combinations of salinity (range: 30-60 ppt) and temperature (range: 25-40 degrees C). Additionally, the effect of hyperosmotic and hypoosmotic shock on the osmolarity of the perivitelline fluid of embryos was determined at salinities between 5 and 90 ppt. The embryos completed their development and molted at salinities below 60 ppt, yet failed to develop at temperatures of 35 degrees C or higher. Larval survival was high at salinities of 10-70 ppt but declined significantly at more extreme salinities (i.e., 5, 80, and 90 ppt). Perivitelline fluid remained nearly isoosmotic over the range of salinities tested. Results indicate that temperature and salinity influence the rate of crab development, but only the extremes of these conditions have an effect on survival.
68 citations
TL;DR: The data indicate that B. schlosseri sperm have a functional life span that is considerably longer than those of the sperm of many other marine invertebrate taxa, are able to fertilize eggs at extremely low external sperm concentrations, and have a longevity that varies with temperature.
Abstract: Many benthic marine invertebrates reproduce by releasing sperm into the sea (free-spawning), but the amount of time that sperm are viable after spawning may have different consequences for fertilization, depending on the type of free-spawner. In egg-broadcasting marine organisms, gamete age is usually assumed to be irrelevant because of the low probability of contact between dilute sperm and egg. However, direct dilution effects might be reduced in egg-brooding free-spawners that filter dilute sperm out of the water column, and sperm longevity may play a role in facilitating fertilization in these taxa. We investigated the effects of time, temperature, and mixing on the viability of naturally released sperm of the colonial ascidian Botryllus schlosseri. Our data indicate that B. schlosseri sperm have a functional life span that is considerably longer than those of the sperm of many other marine invertebrate taxa (half-life of ∼16 to 26 h), are able to fertilize eggs at extremely low external sperm concent...
53 citations
TL;DR: Differences in size and shape of the rDNA-bearing chromosome represent a major divide between Asian-Pacific and Atlantic species of Crassostrea and suggest that chromosomal divergence can occur under seemingly conserved karyotypes and may play a role in reproductive isolation and speciation.
Abstract: Karyotype and chromosomal location of the major ribosomal RNA genes (rDNA) were studied using fluorescence in situ hybridization (FISH) in five species of Crassostrea: three Asian-Pacific species (C. gigas, C. plicatula, and C. ariakensis) and two Atlantic species (C. virginica and C. rhizophorae). FISH probes were made by PCR amplification of the intergenic transcribed spacer between the 18S and 5.8S rRNA genes, and labeled with digoxigenin-11-dUTP. All five species had a haploid number of 10 chromosomes. The Atlantic species had 1-2 submetacentric chromosomes, while the three Pacific species had none. FISH with metaphase chromosomes detected a single telomeric locus for rDNA in all five species without any variation. In all three Pacific species, rDNA was located on the long arm of Chromosome 10 (10q)-the smallest chromosome. In the two Atlantic species, rDNA was located on the short arm of Chromosome 2 (2p)-the second longest chromosome. A review of other studies reveals the same distribution of NOR sites (putative rDNA loci) in three other species: on 10q in C. sikamea and C. angulata from the Pacific Ocean and on 2p in C. gasar from the western Atlantic. All data support the conclusion that differences in size and shape of the rDNA-bearing chromosome represent a major divide between Asian-Pacific and Atlantic species of Crassostrea. This finding suggests that chromosomal divergence can occur under seemingly conserved karyotypes and may play a role in reproductive isolation and speciation.
53 citations
TL;DR: Data indicate that increased ROS scavenging capacity is a part of winter acclimatization; however, only trends in ascorbate content support the hypothesis that greater levels of antioxidants underlie the relatively greater winter tolerance of M. stellatus.
Abstract: Mastocarpus stellatus and Chondrus crispus are red macroalgae that co-dominate the lower rocky inter- tidal zones of the northern Atlantic coast. M. stellatus is more tolerant than C. crispus of environmental stresses, particularly those experienced during winter. This differ- ence in tolerance has been attributed, in part, to greater contents or activities of certain antioxidants in M. stellatus. We compared the photosynthetic capacities and activities of three antioxidant enzymes—superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR)—as well as the contents of ascorbate from fronds of M. stellatus and C. crispus collected over a year. Photosyn- thetic capacity increased in winter, but did not differ be- tween species in any season. The activities of the three antioxidant enzymes and the contents of ascorbate were significantly greater in tissues collected during months with mean air and water temperatures below 7.5 °C ("cold" months; December, February, March, April) than in months with mean air temperatures above 11 °C ("warm" months; June, July, August, October). Overall, C. crispus had sig- nificantly greater SOD and APX activities, while M. stella- tus had higher ascorbate contents. Species-specific differ- ences in GR activity depended upon mean monthly temperatures at the time of tissue collection; C. crispus had higher activities during cold months, whereas M. stellatus had higher activities during warm months. Taken together, these data indicate that increased ROS scavenging capacity is a part of winter acclimatization; however, only trends in ascorbate content support the hypothesis that greater levels of antioxidants underlie the relatively greater winter toler- ance of M. stellatus in comparison to C. crispus.
TL;DR: Alkylphenols at high concentrations are toxic to crustaceans and may contribute significantly to lobster mortality; at lower concentrations, they are likely to have endocrine-disrupting effects.
Abstract: We have identified, by gas chromatography/ mass spectrometry, four alkylphenols that are present in the hemolymph and tissues of the American lobster Homarus americanus and in marine sediments. These alkylphenols are used industrially in antioxidant formulations for plastic and rubber polymer manufacturing, and are similar in struc-
TL;DR: It is shown that the radular tooth is not pushed directly by the muscles of the proboscis but rather is propelled by a high-speed ballistic mechanism that causes tetanus of the body musculature, resulting in a rigid paralysis in Conus catus.
Abstract: Conus catus, a fish-hunting cone snail (Fig. 1A), delivers venom into its prey by means of a single-use radular tooth (Fig. 1B). The venom is composed of a potent mix of bioactive peptides that, when injected into a fish through the hollow harpoon-shaped tooth, causes tetanus of the body musculature, resulting in a rigid paralysis (1). Although peptide toxins in the venom have been extensively studied (2), the biomechanical mechanisms of tooth insertion and venom ejection have not been determined. Anatomical observations have led to the suggestion that the radular tooth is pushed into prey by muscles surrounding the proboscis lumen (3). In this paper we show that the radular tooth is not pushed directly by the muscles of the proboscis but rather is propelled by a high-speed ballistic mechanism. Small specimens of Conus catus (Hwass, 1792; 3 cm shell length) have a translucent proboscis allowing radular tooth movements to be visualized in situ by using a combination of transmitted-light microscopy with water-immersion optics and high-speed video. Figure 1A illustrates the experimental arrangement. A fish was positioned at the end of a trough where video observations were made. The snail sought the prey by extending its proboscis down a narrow trough in a recording chamber. As the proboscis approaches the fish, hairlike sensory papillae are visible at its tip (Fig. 1C, SP in top panels). Prior to stinging prey, the radular tooth is not held at the end of the proboscis but is positioned with its point 730 ms (about half the length of the tooth) from the end of the proboscis. The tip of the proboscis then contacts the fish, sensing potential prey (Fig. 1C, second panel). The delay between the proboscis first touching the fish and tooth ejection ranged from 240 to 295 ms. With the proboscis held stationary against the fish, the radular tooth is propelled against a constriction of the proboscis lumen (Fig. 1C, arrowheads in the third panels), presumably by pressurization of the fluid space behind the tooth. The slight movements of the radular tooth against the constriction during this “priming” step peak during the 4–5 ms prior to release of the tooth into the fish (Fig. 2). Priming was a consistent feature with a similar time course in 10 feeding sequences captured by high-speed video. During the final millisecond, the radular tooth is explosively propelled into the fish (Fig. 1C, fourth panels). This release step propels the base of the tooth (Fig. 1B, asterisk) to the tip of the proboscis, where it is tightly held by a ring of muscles. The minimum velocity of the tooth during release is approximately 3 ms , but the actual time course of tooth movement is clearly faster than the maximum recording rate employed (1000 frames per second, shutter speed 1/2000). This extremely rapid event exceeds the maximum velocity (2 ms ) for discharge of the cnidarian nematocyst (4). Radular tooth release is one of the fastest known prey capture events and has a time course similar to that of the trap jaw response (0.33 to 1 ms) of the ant Odontomachus (5). Immediately following impalement, the end of the proboscis loses its taper and swells with fluid, especially near the tip where a noticeable bulge appears (Fig. 1C, fourth panels). This fluid, which contains the venom peptides, enters an opening at the base of the tooth and is ejected from both the tip of the tooth and the beginning of the largest radular barb (data not shown and ref. 6, 7). Onset of tetanus in the fish prey is seen within 50 ms of impalement. By gripping the base of the radular tooth, the proboscis is Received 28 April 2004; accepted 19 July 2004. * To whom correspondence should be addressed at Department of Biology M-3, Occidental College, Los Angeles, CA 90041-3314. E-mail: jschulz@oxy.edu Reference: Biol. Bull. 207: 77–79. (October 2004) © 2004 Marine Biological Laboratory
TL;DR: The sensitivity of blue crabs to inter-pulse intervals in the range of several seconds indicates that larger-scale mixing processes, which create odor variation on comparable scales, may exert a significant impact on foraging success in nature.
Abstract: The ability of animals to track through chemical plumes is often related to properties of evanescent odor bursts and to small-scale mixing process that determine burst properties. However, odor plumes contain variation over a range of scales, and little is known about how variation in the properties of the odor signal on the scale of one to several seconds affects foraging performance. We examined how flux and pulse rate interact to modulate the search behavior of blue crabs, Callinectes sapidus, locating odor sources in controlled flume flows. Experimental treatments consisted of continuous plumes and plumes with discrete odor pulses at intervals of 2.5 s and 4 s at two fluxes. Crabs experienced diminished search success and reduced search efficiency as flux decreased and the inter-pulse interval lengthened. There often were significant interactions between flux and pulse length, and neither property completely determined search behavior. Thus, over the time span of several seconds, the blue crab chemosensory system is not a simple flux detector. The sensitivity of blue crabs to inter-pulse intervals in the range of several seconds indicates that larger-scale mixing processes, which create odor variation on comparable scales, may exert a significant impact on foraging success in nature.
TL;DR: It is reported here that locomotor activity in adult individuals of L. polyphemus is endogenously modulated on both a circatidal and a circadian basis and that when the animals are subjected to a light-dark (LD) cycle, most activity occurs at night.
Abstract: The nocturnal increases in the sensitivity of the lateral eye of Limulus polyphemus, the species of horseshoe crab found along the Atlantic coast, have been firmly established as being controlled by an endogenous circadian clock (1, 2, 3) located in the brain (4). Virtually nothing is known, however, about the control of the animal’s behavioral rhythms of mating and spawning that are observed in the intertidal zone during high tides in late spring (5, 6, 7). Many other marine species, especially intertidal crabs, exhibit similar rhythmic behaviors that have been demonstrated to be under the control of endogenous clocks that are circatidal (8, 9, 10, 11, 12), circadian (10, 12), or both. While there is some evidence that the activity of juvenile horseshoe crabs is primarily nocturnal (13, 14), and possibly controlled by a circadian clock (14), we know of no published work showing that locomotor activity in the adult is endogenously controlled on either a 12.4-h (circatidal) or 24-h (circadian) basis. We report here that locomotor activity in adult individuals of L. polyphemus is endogenously modulated on both a circatidal and a circadian basis and that when the animals are subjected to a light-dark (LD) cycle, most activity occurs at night. The locomotor activity of individual adult horseshoe crabs was recorded using activity chambers located in recirculating aquaria. Animals were exposed to three conditions: a 12:12 LD cycle, at 11–14 °C (“fall” conditions, LD1), a 14:12 LD cycle, at 17–21 °C (“summer” conditions, LD2), and constant darkness (DD). Typical records of the locomotor activity of three horseshoe crabs exposed to these three different photoperiods are presented in Figure 1. Circatidal rhythms were observed in all animals. While significant activity rhythms (15) in the tidal range (12.4 h) were found in only 3 of 6 animals (tau 12.83 0.78 h [mean SEM]) during LD1, in LD2, significant tidal rhythms (12.2 0.1 h) were observed in all animals. In some cases in LD2 (4 of 6 animals), clear free-running rhythms were sometimes apparent, (Fig. 1; middle, bottom panels), while in other cases the activity appeared to synchronize to the LD cycles (Fig. 1; top). In DD, circatidal rhythms (12.6 0.2 h) were found in 5 of 6 animals (Fig. 1; all panels). Most animals (5 of 6 in LD1; 6 of 6 in LD2) exhibited significant rhythms in the circadian range (tau 24.29 0.14 h). Periodogram analyses (15) and visual inspection indicated that 5 of the 6 animals tested synchronized their activity to the initial 12:12 LD cycle (LD1). The single animal that did not thus synchronize had a very low level of activity. Significantly more activity occurred during the dark phase than the light phase in 4 of 6 animals (Fig. 1; top and bottom [but not middle] panels). The average period (tau) for these animals in the daily (24-h) range in LD1 was 24.12 0.09 h. Upon subsequent exposure to “summer” conditions (LD2), 3 (of 6) animals remained synchronized to the LD cycle (Fig. 1; top panel). In others (2 of 6), this apparent synchronization was not stable (Fig. 1; middle, days 10–18 and days 29–42) and, in still another animal, the synchronization, if any, was unclear (Fig. 1; bottom). Animals that both synchronized and showed a clear onset of activity initiated their activity a significant amount of time (1.7 0.1 h; P 0.005) before the lights went out during LD2 but not LD1 (1.1 0.5 h; P 0.15). Significantly more activity occurred during D versus L periods in 3 of 6 animals (Fig. 1; top panel only). In constant darkness (DD), all animals also expressed significant circadian rhythms (25.27 0.69 h; Fig. 1, all panels). In addition, the activity patterns of 3 of 6 animals in DD exhibited evidence of entrainment based on the similarity of phasing with the previous LD cycle (Fig. 1; top, middle). L. polyphemus was significantly more active overall during LD2 than during LD1 and DD (P 0.03). Neither circatidal (P 0.78) nor Received 12 February 2004; accepted 7 June 2004. * To whom all correspondence should be addressed. E-mail: chrisc@mail.plymouth.edu Reference: Biol. Bull. 207: 72–75. (August 2004) © 2004 Marine Biological Laboratory
TL;DR: Tentacles from representatives of all four classes of the phylum Cnidaria were examined using antibodies against the neuropeptides FMRFamide and RFamide to reveal the organization of neurons and nerve nets associated with cnidocytes, and it is proposed that this peptidergic innervation may be involved in the chemosensory regulation of cNidocyte discharge.
Abstract: Tentacles from representatives of all four classes of the phylum Cnidaria were examined using antibodies against the neuropeptides FMRFamide and RFamide to reveal the organization of neurons and nerve nets associated with cnidocytes. The tentacles of all species examined contained FMRFamide- or RFamide-immunoreactive neurons, in varying densities. In representatives from the Scyphozoa, Hydrozoa, and Cubozoa, the FMRFamide-immunoreactive neurons formed plexuses at the base of the cnidocyte assemblages; in anthozoans, the absence of discrete assemblies of cnidocytes precluded visual co-localization of cnidocytes and immunoreactive neurons. In all four classes, immunoreactive sensory cells connected these peptidergic nerve nets to the surface of the tentacle. These findings suggest that members of all four cnidarian classes share a common organizational pattern, and it is proposed that this peptidergic innervation may be involved in the chemosensory regulation of cnidocyte discharge.
TL;DR: Mussels have maintained the ability to filter-feed, which apparently allows them to occupy a wider range of environmental conditions and better tolerate declining hydrothermal vent activity than the tubeworms, and post-settlement factors, such as physical overgrowth and resource competition.
Abstract: In the basalt-hosted hydrothermal vent habitat around 9°50 N on the East Pacific Rise, the vestimentiferan tubeworms Tevnia jerichonana and Riftia pachyptila (Polychaeta: Siboglinidae) commonly settle before the mussel Bathymodiolus thermophilus (Bivalvia: Mytilidae). We removed six aggregations of R. pachyptila and deployed mussels on the cleared sources of diffuse flow to test the effect of the B. thermophilus on the subsequent colonization by the tubeworms. None of the transplanted mussels persisted on the cleared sources of diffuse flow; however, aggregations of R. pachyptila grew in half of the clearances. We collected one of the aggregations of R. pachyptila along with the associated fauna for determination of relative abundance and biomass in this one-year-old community. This aggregation consisted of 647 specimens of R. pachyptila that hosted individuals of 24 species, including small individuals of T. jerichonana and B. thermophilus. The abundance of the associated fauna was numerically dominated by gastropods, and the biomass was dominated by the Alvinellid polychaete Paralvinella grasslei. Following an eruption, the vestimentiferan tubeworms Tevnia jerichonana and Riftia pachyptila (Polychaeta: Siboglinidae) quickly colonize the basalt-hosted hydrothermal vents around 9°50 N (East Pacific Rise) and soon grow to visually dominate these habitats (1, 2, 3). Colonization by the vent mussel Bathymodiolus thermophilus often follows shortly, and the mussels eventually overgrow the tubeworms at most sites (2, 4, 5). Both tubeworms and mussels harbor sulfur-oxidizing chemoautotrophic endosymbionts, which provide the bulk of their nutrition (6, 7). However, mussels have also maintained the ability to filter-feed (8), which apparently allows them to occupy a wider range of environmental conditions and better tolerate declining hydrothermal vent activity than the tubeworms (9). The mechanism of ecological succession in these hydrothermal vent habitats is not fully understood, but may be regulated by a combination of pre-settlement factors, such as the use of biogenic cues (3) and the response to geochemical changes (2), and post-settlement factors, such as physical overgrowth (4) and resource competition (5). We conducted a manipulative experiment to test the hypothesis that the mussel B. thermophilus prevents further colonization of a vent by tubeworms. In May 1998, six aggregations of the giant tubeworm R. pachyptila were cleared from a site named Riftia Field (9°50.705 N 104°17.593 W). The original location and source of diffuse flow for each aggregation were marked and recorded on video. After the aggregations were cleared, the temperatures of the venting fluid were measured, using the low-temperature probe of the DSV Alvin, and ranged from 20–22 °C above ambient at the six locations. Then about 600 mussels were collected from a nearby site (“East Wall”, 9°50.614 N 104° 17.509 W) and about 200 were deployed over each of three cleared sources of diffuse flow (treatments). Mussels were not deployed on the three other cleared areas (conReceived 28 April 2004; accepted 4 October 2004. * To whom correspondence should be addressed. E-mail: breea@psu.edu † Present address: Department of Fisheries and Aquatic Sciences, University of Florida, Gainesville, FL 32653. Reference: Biol. Bull. 207: 177–182. (December 2004) © 2004 Marine Biological Laboratory
TL;DR: It is concluded that the velocity at which the plastic response occurs has an upper limit of 2–4 m/s, a velocity commonly exceeded within the typical habitat of this species.
Abstract: Phenotypic plasticity, the capacity of a given genotype to produce differing morphologies in response to the environment, is widespread among marine organisms (1). For example, acorn barnacles feed by extending specialized appendages (the cirral legs) into flow, and the length of the cirri is plastic: the higher the velocity, the shorter the feeding legs (2,3). However, this effect has been explored only for flows less than 4.6 m/s, slow compared to typical flows measured at sites on wave-exposed shores. What happens at faster speeds? Leg lengths of Balanus glandula Darwin, 1854, an acorn barnacle, were measured at 15 sites in Monterey, California, across flows ranging from 0.5 to 14.0 m/s. Similar to previous findings, a plastic response in leg length was noted for the four sites with water velocities less than 3 m/s. However, no plastic response was present at the 11 sites exposed to faster velocities, despite a 4-fold variation in speed. We conclude that the velocity at which the plastic response occur...
TL;DR: The phylogenetic position of the marine zoochlorellae inhabiting A. elegantissima is determined by comparing sequence data from two cellular compartments, the nuclear 18S ribosomal RNA gene region and the plastid-encoded rbcL gene, and the results support the inclusion of these zoochorellae in a clade of green algae that form symbioses with animal, fungal, and seed plant partners.
Abstract: At northern latitudes the sea anemones Anthopleura elegantissima and its congener A. xanthogrammica contain unidentified green chlorophytes (zoochlorellae) in addition to dinophytes belonging to the genus Symbiodinium. This dual algal symbiosis, involving members of distinct algal phyla in one host, has been extensively studied from the perspective of the ecological and energetic consequences of hosting one symbiotic type over the other. However, the identity of the green algal symbiont has remained elusive. We determined the phylogenetic position of the marine zoochlorellae inhabiting A. elegantissima by comparing sequence data from two cellular compartments, the nuclear 18S ribosomal RNA gene region and the plastid-encoded rbcL gene. The results support the inclusion of these zoochlorellae in a clade of green algae that form symbioses with animal (Anthopleura elegantissima), fungal (the lichen genus Nephroma), and seed plant (Ginkgo) partners. This clade is distinct from the Chlorella symbionts of Hydra...
TL;DR: Sexual dimorphism, the peculiar pairing behavior, and the close relationship with the host sand dollar may have evolved as distinct reproductive characteristics in this ophiuroid with its typical ophiopluteus larvae.
Abstract: Ophiodaphne formata is a conspicuously dimorphic ophiuroid; the disk diameters are approximately 1 mm for males and 5 mm for females. The dwarf male clings to the larger female, with the oral surfaces and bursae of the paired ophiuroids closely appressed. Moreover, the female of each pair adheres aborally to the oral surface of a host sand dollar, Astriclypeus manni. Spawning and external fertilization occur in August, at Tsuruga Bay, Sea of Japan. Development of the dimorphic brittle star O. formata is described for the first time, from spawning through metamorphosis, with special attention to the formation of the skeletal system and the external morphology of early juveniles. Fertilized eggs are about 90 microm in diameter, pale pink, and negatively buoyant. The embryos undergo equal, total, and radial cleavage, and the larval skeleton first forms as a pair of tetraradiate spicules. Larval development proceeds to an 8-armed planktotrophic ophiopluteus, with skeletal elements that consist of a body rod and two recurrent rods. Three weeks after fertilization, all the pluteal arms, except for the postero-lateral arms, are absorbed, and the metamorphosing larvae sink to the bottom. Metamorphosis is completed 21.5 days after fertilization, and the resulting juvenile is pentagonal and approximately 270 microm in diameter. The smallest specimen (480 microm in disk diameter) collected by field sampling exhibited male features on the skeletal plates of the jaw and disk. Sexual dimorphism, the peculiar pairing behavior, and the close relationship with the host sand dollar may have evolved as distinct reproductive characteristics in this ophiuroid with its typical ophiopluteus larvae.
TL;DR: Differences between larvae of the two development modes may reflect fine-tuning by selection of traits important for dispersal and settlement into patchy adult habitats, including planktotrophic and lecithotrophic larvae.
Abstract: Specific effects of alternative developmental programs on swimming and settlement behavior for marine larvae have not been identified experimentally. A major impediment to this research has been the rarity of species with variable development. Here, we compared traits related to movement and habitat selection for different ontogenetic stages of long-lived, feeding larvae (planktotrophic) and short-lived, nonfeeding larvae (lecithotrophic) of the her- bivorous gastropod Alderia modesta. Newly hatched plank- totrophic larvae swam in meandering paths with equal rates of upward and downward movement. As planktotrophic larvae developed towards competence (physiological ability to metamorphose), their swimming paths became straighter, faster, and increasingly directed towards the bottom, traits shared by newly hatched lecithotrophic larvae. Despite dif- fering in developmental history, competent planktotrophic (32-d-old) and lecithotrophic larvae (competent upon hatch- ing) exhibited qualitatively similar swimming behaviors and substrate specificity. However, lecithotrophic larvae moved downward at twice the speed of competent planktotrophic larvae, potentially producing a 5-fold higher rate of contact with the bottom in natural flows. Competent larvae swam downwards rather than passively sinking, even though sink- ing rates were faster than swimming speeds; active swim- ming may allow larvae to keep the velum extended, permit- ting rapid response to chemical settlement cues and promoting successful habitat colonization. Differences be- tween larvae of the two development modes may reflect fine-tuning by selection of traits important for dispersal and settlement into patchy adult habitats.
TL;DR: Upogebia-conditioned seawater induced an exploratory swimming behavior in competent larvae of P. pallida in a dosage-dependent manner, and this behavior included a significant increase in swimming speed that was directed downward, along with the repeated probing of the bottom with the sensory portion of the oral hood.
Abstract: Phoronis pallida (Phoronida) occurs as a com- mensal within the burrow of Upogebia pugettensis (Deca- poda: Thalassinidea). Upogebia-conditioned seawater (UCSW) induced an exploratory swimming behavior in competent larvae of P. pallida in a dosage-dependent manner. This behavior included a significant increase in swimming speed that was directed downward, along with the repeated prob- ing of the bottom with the sensory portion of the oral hood. The waterborne cue from the shrimp was present in the gut effluent, and the swimming behavior was not the result of the elevated ammonia concentration. Molecular weight sep- aration of the UCSW estimated that the cue was between 10 and 50 kDa. Enzymatic treatments showed that the cue's activity could be eliminated by arginase and significantly reduced by lipase. Competent larvae were also induced to metamorphose when exposed to 20 mM CsCl for 30 min. Larvae did not respond to CsCl when cultured about 4 weeks past the onset of competence. Compared with acti- notroch larvae of other phoronid species, P. pallida larvae exhibit greater behavioral specificity and neuronal differ- ences within the hood sense organ. These anatomical and behavioral differences may have been maintained through a coevolutionary process among P. pallida and species of thalassinid shrimps that share Upogebia life-history charac- teristics.
TL;DR: The results suggest that caution must be used in extrapolating reported density effects on fertilization to all taxa of free-spawners; density effects may be reduced in brooders that have efficient sperm collection mechanisms.
Abstract: The possibility that free-spawning marine or- ganisms may be subject to fertilization failure at low pop- ulation density (due to the effects of sperm dilution) has sparked much interest, but these effects have been demon- strated only in a few species that broadcast their eggs. Some egg-brooding species may overcome dilution effects by filtering low concentrations of sperm from seawater and fertilizing eggs throughout an extended period of time. We examined the effects of population density and size on fertilization in Botryllus schlosseri, a hermaphroditic colo- nial ascidian that free-spawns sperm, but broods eggs. We experimentally manipulated the size and density of mating groups and surveyed fertilization levels in natural popula- tions that varied in density. Fertilization was not affected by variation in population size or density in either the experi- mental or natural populations. Near the end of the repro- ductive season, some eggs may have been fertilized too late to complete development, suggesting a temporal form of sperm limitation that has not been considered in other systems. We also detected greater variability in fertilization levels at lower population density. Nevertheless, these re- sults suggest that caution must be used in extrapolating reported density effects on fertilization to all taxa of free- spawners; density effects may be reduced in brooders that have efficient sperm collection mechanisms.
TL;DR: A general, mechanical explanation for microscaling of structural secretory cells and their secretions, including the cnidae is proposed, here, to suggest that cnida size, shape, and scaling patterns respond to natural selection.
Abstract: Scaling analysis provides a quantitative method for describing and comparing how qualities of organisms vary as a function of body size. However, cell level phe- nomena have been notoriously hard to analyze because animal cells and organelles have such irregular shapes. The intracellular cnidae make good models of scaling at the cell level because they are durable and easy to image and measure. The mean length of unfired tentacle cnidae (spi- rocysts) varies continuously, and reversibly, with body size for three macrophagous anemone species. Significant dif- ferences in spirocyst shape and size relative to body mass are related to differences in tissue functions and species ecologies, strongly suggesting that cnida size, shape, and scaling patterns respond to natural selection. Cnida scaling patterns can be treated as features of cnidarian life histories. Spirocyst scaling exponents (slopes of log cnida dimension vs. log body weight) are similar to each other (0.05-0.09) and to reported values for animal somatic cells (0.017- 0.17), but are much smaller than reported values for anem- one basal diameters (0.30-0.38). I propose, here, a general, mechanical explanation for microscaling of structural secre- tory cells and their secretions, including the cnidae. Larger bodies require thicker, pliant sheets of sluggishly respiring extracellular support materials such as mesoglea and base- ment membrane. Thicker mesoglea can support larger, taller epithelial cells, which in turn provide additional mainte- nance services for these progressively thicker acellular lay- ers. Ultimately, larger, taller cells can secrete and support larger, longer cnidae.
TL;DR: This study investigated whether mucus from the aeolid nudibranch Aeolidia papillosa would inhibit nematocyst discharge from four species of sea anemone prey and found that it did so, but only when the prey species was changed.
Abstract: Nudibranchs that feed on cnidarians must de- fend themselves from the prey's nematocysts or risk their own injury or death. While a nudibranch's mucus has been thought to protect the animal from nematocyst discharge, an inhibition of discharge by nudibranch mucus has never been shown. The current study investigated whether mucus from the aeolid nudibranch Aeolidia papillosa would inhibit nematocyst discharge from four species of sea anemone prey. Sea anemone tentacles were contacted with mucus- coated gelatin probes, and nematocyst discharge was quan- tified and compared with control probes of gelatin only. Mucus from A. papillosa inhibited the discharge of nema- tocysts from sea anemone tentacles. This inhibition was specifically limited to the anemone species on which the nudibranch had been feeding. When the prey species was changed, the mucus changed within 2 weeks to inhibit the nematocyst discharge of the new prey species. The nudi- branchs apparently produce the inhibitory mucus rather than simply becoming coated in anemone mucus during feeding. Because of the intimate association between most aeolid nudibranchs and their prey, an adaptable mucus protection could have a significant impact on the behavior, distribu- tion, and life history of the nudibranchs.
TL;DR: Results from subsequent experiments in which embryos were reared in low-oxygen environments suggest that any oxygen-absorption advantages of swimming have little, if any, effect on the development of D. excentricus embryos.
Abstract: Early embryonic swimming is widespread among marine invertebrates, but quantitative information about swimming behaviors is scarce. Swimming may affect encounters with predators, positioning in the water column, and nutrient absorption. Measured rates and patterns of swimming and sinking for blastulae of four eastern Pacific echinoid species show that sinking speeds equal or exceed swimming speeds. Swimming speed scaled negatively with embryo size, though sinking speed did not scale with size. Analysis of swimming paths of Strongylocentrotus fran- ciscanus revealed a temperature dependency in swimming pattern that affected speed of upward movement. Sinking speeds were significantly greater at 10 °C than at 14 °C for blastulae of all four species examined. In Dendraster ex- centricus, killing the blastulae annulled this temperature effect, indicating an active density regulation by these em- bryos. Finally, measurements of particle velocities around sinking and swimming D. excentricus blastulae show that swimming creates a more localized disturbance than sink- ing. Embryonic swimming may therefore decrease rather than increase encounters with pelagic predators. Results from subsequent experiments in which embryos were reared in low-oxygen environments suggest that any oxygen-ab- sorption advantages of swimming have little, if any, effect on the development of D. excentricus embryos.
TL;DR: It is suggested that the autumn cessation may maximize the fitness of N. virens, a spring-breeding semelparous organism, by reducing risk during gamete maturation, while spontaneous resurgence of activity after the winter solstice permits animals that are not physiologically competent to spawn to accrue further metabolic reserves.
Abstract: The locomotor activity of Nereis virens Sars associated with food prospecting was investigated in response to photoperiod and season using an actograph. Experimental animals which had been reared under natural photoperiods were exposed to two constant photoperiodic treatments, LD 16:8 and LD 8:16, in both the autumn and winter and in the absence of tidal entrainment. Autocorrelation analysis of rhythmicity showed that during the autumn, animals under the LD 16:8 photoperiod displayed a strong nocturnal rhythm of activity, whereas animals under the LD 8:16 photoperiod showed only a weak nocturnal activity rhythm. This is believed to represent an autumn feeding cessation that is triggered when the animals pass through a critical photoperiod LDcrit 12. Later in the winter, however, animals exposed to both photoperiodic treatments showed strong rhythms of foraging activity irrespective of the imposed photoperiod. It is suggested that the autumn cessation may maximize the fitness of N. virens, a spring-br...
TL;DR: The mouthparts of the spiny lobster Panulirus argus hold primarily two types of setae—simple setae and cuspidate setae; however, whether they were bend sensitive or displacement sensitive could not be determined, and they were thus called “tactile neurons.”
Abstract: The mouthparts of the spiny lobster Panulirus argus hold primarily two types of setae-simple setae and cuspidate setae. Mechanosensory neurons from these setae were examined by electrophysiological recordings. The population of simple setae contained two types of mechanosensory neurons: displacement-sensitive neurons, which responded to deflection at the setal base; and bend-sensitive neurons, which responded to bending of the setal shaft. Displacement-sensitive neurons, in general, responded phasically and only during actual displacement. Typically, their response changed with alteration of the direction, amplitude, and velocity/acceleration of the mechanical stimulus. Bend-sensitive neurons, in general, responded phaso-tonically and carried information on the direction and region of bending. This is the first experimental demonstration of bend sensitivity for arthropod setae. Cuspidate setae contain highly sensitive mechanosensory neurons; however, due to the rigid nature of these setae, whether they were bend sensitive or displacement sensitive could not be determined, and they were thus called "tactile neurons." Bend-sensitive neurons, but not displacement-sensitive neurons or tactile neurons, showed graded responses to changes in osmolarity. The osmosensitivity of these neurons could mediate behavioral responses to changes in the osmolarity of seawater or food.
TL;DR: It is argued that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecologically relevant results.
Abstract: Passive flow is believed to increase the gains and reduce the costs of active suspension feeding. We used a mixture of field and laboratory experiments to evaluate whether the unstalked intertidal ascidian Pyura stolonifera exploits passive flow. We predicted that its orientation to prevailing currents and the arrangement of its siphons would induce passive flow due to dynamic pressure at the inhalant siphon, as well as by the Bernoulli effect or viscous entrainment associated with different fluid velocities at each siphon, or by both mechanisms. The orientation of P. stolonifera at several locations along the Sydney-Illawarra coast (Australia) covering a wide range of wave exposures was nonrandom and revealed that the ascidians were con- sistently oriented with their inhalant siphons directed into the waves or backwash. Flume experiments using wax mod- els demonstrated that the arrangement of the siphons could induce passive flow and that passive flow was greatest when the inhalant siphon was oriented into the flow. Field exper- iments using transplanted animals confirmed that such an orientation resulted in ascidians gaining food at greater rates, as measured by fecal production, than when oriented perpendicular to the wave direction. We conclude that P. stolonifera enhances suspension feeding by inducing pas- sive flow and is, therefore, a facultatively active suspension feeder. Furthermore, we argue that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecolog- ically relevant results.
TL;DR: Results from the substrate sampling indicate that placozoans are present year-round at the study site, and large intermittent peaks in the number of animals collected at theStudy site occurred roughly once a year, between late summer and the beginning of winter.
Abstract: Long-term field studies on placozoans (Trichoplax adhaerens), including both substrate sampling and slide sampling, were carried out at a subtidal site near Shirahama, Japan. Samples of natural substrate materials from the field, such as stones, shells, or fragments of coral, were particularly useful for obtaining placozoans. Results from the substrate sampling indicate that placozoans are present year-round at the study site. Large intermittent peaks in the number of animals collected at the study site occurred roughly once a year, between late summer and the beginning of winter. Placozoans were present every year from 1989 through 2000. A seawater aquarium was also studied and provided a considerable number of placozoans for more than 1 year.