Showing papers in "The Biological Bulletin in 2005"
TL;DR: Although T. funebralis is more heat tolerant and eurythermal than its two lower-occurring congeners, it can encounter field body temperatures that exceed ABT, indicating that it faces a larger threat from heat stress, in situ.
Abstract: We analyzed the thermal limits of heart func- tion for congeneric species of the marine snail Tegula that have different patterns of vertical zonation. T. funebralis is found in the low to mid-intertidal zone, and T. brunnea and T. montereyi live in the low-intertidal or subtidally. As indices of thermal limits of heart function, we used the temperature at which heart rate initially decreased rapidly during heating (the Arrhenius break temperature, or ABT) and the temperature at which heart ceased to beat with either heating or cooling (the flatline temperature, or FLThot or FLTcold, respectively). These three indices provide an esti- mate of the thermal range within which Tegula heart func- tion is maintained. For field-acclimatized specimens, the thermal range of the high-intertidal T. funebralis was greater than those of its two lower-occurring congeners (higher ABT, higher FLThot, lower FLTcold). We also demonstrated the effects of constant thermal acclimation on the heart rate response to heat stress. Acclimation to 14 °C and 22 °C resulted in increases in ABT and FLT hot , with the largest changes in T. brunnea and T. montereyi. Although T. fune- bralis is more heat tolerant and eurythermal than its two lower-occurring congeners, it can encounter field body tem- peratures that exceed ABT, indicating that T. funebralis faces a larger threat from heat stress, in situ. These findings are consistent with recent studies on other taxa of marine invertebrates that have shown, somewhat paradoxically, that warm-adapted, eurythermal intertidal species may be more impacted by global warming than congeneric subtidal spe- cies that are less heat tolerant.
120 citations
TL;DR: The results suggest an evolutionary sequence: a homorhabdic filibranch gill structure with few symbionts among the epithelial cell microvilli eventually thickened abfrontally, and thereby offered a larger surface for colonization by Symbionts, which persisted and grew in vacuoles within epithelial cells.
Abstract: Among families of bivalves with chemoau- totrophic symbionts, the Thyasiridae may vary the most in their anatomical characters and in the extent of their nutri- tional reliance upon symbionts. Since only a fraction of thyasirid species are symbiotic, and the symbionts are mostly observed to be extracellular, this group may be representative of early stages in the evolution of bacterium- bivalve symbioses. To better understand the distribution of symbiosis among thyasirid genera, and the relationships between gill structure and symbiont occurrence, the gills of 26 thyasirid species were studied by light and electron microscopy. Observations revealed three gill types, which are generally constrained within genera or subgenera. Sym- bionts were found in two gill types: the most simple, ho- morhabdic filibranch morphotype, and the most derived and thickened morphotype, which resembles the gill structure of other chemosymbiotic bivalves. In all observable cases, the symbionts were located extracellularly among the microvilli of the bacteriocytes. Among individuals of the species Thyasira (Parathyasira) equalis, the quantity of symbionts varied. The results suggest an evolutionary sequence: a homorhabdic filibranch gill structure with few symbionts among the epithelial cell microvilli eventually thickened abfrontally, and thereby offered a larger surface for coloni- zation by symbionts. Eventually, the symbionts persisted and grew in vacuoles within epithelial cells.
108 citations
TL;DR: Stomach contents in Nectocarcinus tuberculosus (velvet crab) and Carcinus maenas (green crab) suggest that these species are omnivorous, and each species of crab studied had a complex suite of digestive enzymes, the relative activities of which reflected individual and very different species-specific dietary niches.
Abstract: The digestive physiology and stomach contents of six crab species from a variety of habitats were investigated to provide an indication of their digestive capability and dietary preferences. Stomach contents varied between species, but the key enzymes present were generally consistent with the types of dietary material being ingested. Nectocarcinus integrifons (red rock crab) consumed large quantities of seagrass and had high cellulase activity (0.02+/-0.004 units mg-1) to digest the constituent cellulose. Petrolisthes elongatus (porcelain crab) ingested brown and green phytoplankton and algae and had considerable laminarinase (0.35+/-0.08 units mg-1) and beta-glucosidase (0.025+/-0.005 units mg-1) activities to digest the laminarin in its diet. Leptograpsus variegatus (omnivorous swift-footed shore crab) had high activities of protease (1.2+/-0.02 units mg-1), alpha-glucosidase, and alpha-amylase and appeared well equipped to utilize both dietary protein and carbohydrate. Stomach contents in Nectocarcinus tuberculosus (velvet crab) and Carcinus maenas (green crab) also suggest that these species are omnivorous. N. tuberculosus had high cellulase and chitinase for digesting the cellulose in plants and the chitin in invertebrate shells respectively. C. maenas had intermediate digestive enzyme levels and may employ more of a generalist feeding strategy than other species. Plagusia chabrus (speedy crab) is carnivorous, consuming encrusting bryozoans, hydroids, crustaceans, and fish. It has high protease activity, particularly trypsin (0.73+/-0.12 units mg-1), to digest the protein in its animal prey. Each species of crab studied had a complex suite of digestive enzymes, the relative activities of which reflected individual and very different species-specific dietary niches.
91 citations
TL;DR: The detection of an endosymbiotic yeast in demosponges of the genus Chondrilla described here records the first such association within the phylum Porifera, and the fungal endosYmbiosis most likely evolved before or during the diversification of the species.
Abstract: The detection of an endosymbiotic yeast in demosponges of the genus Chondrilla described here records the first such association within the phylum Porif- era. The symbiont, interpreted as a yolk body in previous ultrastructural studies, is a chitinous-walled fission yeast. Chitin was detected by an immunocytochemical technique that labels its -1,4-N-acetyl-D-glucosamine residues. Abundant symbiotic yeast cells (4.4 2.3 cells per 10 m 2 ) transmitted from the soma through the oocytes to the fer- tilized eggs are directly propagated by vertical transmission in the female. Vertically transmitted yeast were detected in three Chondrilla species with disjunct biogeographical dis- tributions: the Mediterranean, the Caribbean, and the Aus- tralian Pacific. Apparently these yeasts are not present in other demosponge genera. Therefore, the fungal endosym- biosis most likely evolved before or during the diversifica- tion of the genus Chondrilla.
84 citations
TL;DR: The densities of chemoautotrophic and methanotrophic symbiont morphotypes were determined in life- history stages of two species of mussels from deep-sea chemosynthetic environments (the Lucky Strike hydrothermal vent and the Blake Ridge cold seep) in the Atlantic Ocean.
Abstract: The densities of chemoautotrophic and methanotrophic symbiont morphotypes were determined in life- history stages (post-larvae, juveniles, adults) of two species of mussels (Bathymodiolus azoricus ...
74 citations
TL;DR: The results show that, to evoke disruptive coloration in cuttlefish, visual information about the edges and contrast of objects within natural substrate backgrounds is required.
Abstract: Cuttlefish (Sepia officinalis Linnaeus, 1758) on mixed light and dark gravel show disruptive body patterns for camouflage. This response is evoked when the size of the gravel is equivalent to the area of the “White square,” a component of its dorsal mantle patterns. However, the features of natural substrates that cuttlefish cue on visually are largely unknown. Therefore, we aimed to identify those visual features of background objects that are required to evoke disruptive coloration. At first, we put young cuttlefish in a circular experimental arena, presented them with natural gravel and photographs of natural gravel, and established that the animals would show a disruptive pattern when presented either with three-dimensional natural gravel or its two-dimensional photographic representation. We then manipulated the digital photographs by applying (i) a low-pass filter to remove the edges of the fragments of gravel, and (ii) a high-pass filter to remove the contrast among them. The body patterns produced by the cuttlefish in response to these altered visual stimuli were then videorecorded and graded. The results show that, to evoke disruptive coloration in cuttlefish, visual information about the edges and contrast of objects within natural substrate backgrounds is required. Cephalopods have a remarkable ability to change the color and pattern of their skin, and research has demonstrated that visual input regulates these changes. Cuttlefish skin can show 20‐50 chromatophore patterns that are used
70 citations
TL;DR: The germinal epithelia of both sexes of Strongylocentrotus droebachiensis, the green sea urchin, throughout its annual gametogenic cycle are characterized using light and electron microscopy and cytochemistry to suggest proteins that may be important in the structural, phagocytic, and nutritive functions of NPs.
Abstract: Here we characterize the germinal epithelia of both sexes of Strongylocentrotus droebachiensis, the green sea urchin, throughout its annual gametogenic cycle, using light and electron microscopy and cytochemistry. In both sexes, germinal epithelia include two interacting cellular populations: nutritive phagocytes (NPs) and germ cells. After spring spawning, NPs accumulate nutrients; amitotic oogonia and often mitotic spermatogonia occur in clusters beneath NPs; and subsequent gametogenic stages are residual or absent. During the summer, NP nutrients are mobilized for use in vitellogenesis by residual primary oocytes or to support limited spermatogenesis. In addition, some residual primary oocytes may degenerate and be phagocytized by NPs. Significant nutrient mobilization from NPs and substantial gonial cell mitoses (indicative of new gametogenesis) occur in the fall. In both sexes, all of these changes are facilitated by NPs that form basal incubation chambers near the gonadal wall and within which germ ...
70 citations
TL;DR: The data suggest that differentiated cells of echinoderms are capable of transdifferentiation into other cell types, and this study provides an example of an alternative mechanism of tissue repair in the holothurian Eupentacta fraudatrix.
Abstract: It has recently been shown that the whole spectrum of cell types constituting a multicellular organism can be generated from stem cells. Our study provides an example of an alternative mechanism of tissue repair. Injection of distilled water into the coelomic cavity of the holothurian Eupentacta fraudatrix results in the loss of the whole digestive tract, except the cloaca. The new gut reforms from two separate rudiments. One rudiment appears at the anterior end of the body and extends posteriorly. The second rudiment grows anteriorly from the cloaca. In the anterior rudiment, the luminal epithelium (normally derived from endoderm) develops de novo through direct transdifferentiation of the coelomic epithelial cells (mesodermal in origin). In the posterior rudiment, the luminal epithelium originates from the lining epithelium of the cloaca. After 27 days, the two rudiments come into contact and fuse to form a continuous digestive tube lined with a fully differentiated luminal epithelium. Thus in this spec...
69 citations
TL;DR: The interaction between gametes of these closely related sea stars is consistent with the function of gamete recognition systems that are known to mediate fertilization success and speciation in other marine invertebrates.
Abstract: Gamete interactions may strongly influence speciation and hybridization in sympatric broadcast-spawn- ing marine invertebrates. We examined the role of gamete compatibility in species integrity using cross-fertilization studies between sympatric Asterias sea stars from a second- ary contact zone in the northwest Atlantic. In crosses be- tween single males and single females, gametes of both species were compatible and produced viable, fertile hybrid offspring, but with considerable variation in the receptivity of eggs to heterospecific sperm. Differential compatibility of heterospecific gametes was detected in sperm competi- tion studies in which we used a nuclear DNA marker to assign paternity to larval offspring. Several families showed conspecific sperm precedence in A. forbesi eggs, and one family showed competitive superiority of A. forbesi sperm fertilizing A. rubens eggs. Gametic interactions are an im- portant component of prezygotic reproductive isolation in sympatric Asterias. The interaction between gametes of these closely related sea stars is consistent with the function of gamete recognition systems that are known to mediate fertilization success and speciation in other marine inverte- brates.
61 citations
TL;DR: Evidence is presented demonstrating in the penaeid shrimp Litopenaeus vannamei that both Hypoxia and hypercapnic hypoxia affect the localization of bacteria, their conversion from culturable to non-culturable status (bacteriostasis), and their elimination from hemolymph and selected tissues, suggesting an overall decrease in bacteriostatic activity.
Abstract: Low oxygen (hypoxia) and elevated CO2 (hy- percapnia, are characteristic of estuarine environments. Al- though hypoxia and hypercapnic hypoxia decrease the re- sistance of shrimp to bacterial pathogens, their direct effects on the immune system are unknown. Here we present evi- dence demonstrating in the penaeid shrimp Litopenaeus vannamei that both hypoxia and hypercapnic hypoxia affect the localization of bacteria, their conversion from culturable to non-culturable status (bacteriostasis), and their elimina- tion from hemolymph and selected tissues. Shrimp were injected with a sublethal dose of a pathogenic strain of Vibrio campbellii expressing green fluorescent protein and resistance to kanamycin. Real-time polymerase chain reac- tion was used to determine the number of intact V. camp- bellii in hemolymph, gills, hepatopancreas, heart, and lym- phoid organ. Selective plating was used to quantify the injected bacteria that remained culturable. We found that both hypercapnic hypoxia and hypoxia increased the per- centage of culturable bacteria recovered from the hemo- lymph and tissues, suggesting an overall decrease in bacte- riostatic activity. Hypoxia and hypercapnic hypoxia generally increased the distribution of intact V. campbellii to the hepatopancreas and the gills, which are major targets for the pathogenic effects of Vibrio spp., without affecting the number of intact bacteria in the lymphoid organ, a main site of bacterial accumulation and bacteriostatic activity.
57 citations
TL;DR: This poster presents a probabilistic assessment of the phytochemical properties of E.coli found in response to the presence of carbon dioxide in the biota of the North Pacific Ocean.
Abstract: HENRY TRAPIDO-ROSENTHAL*, SANDRA ZIELKE, RICHARD OWEN, LUCY BUXTON, BRIAN BOEING, RANJEET BHAGOOLI, AND JESSICA ARCHER 1 Bermuda Biological Station for Research, Inc., Ferry Reach GE-01, Bermuda; 2 Environment Agency, Westbury-on-Trym, Bristol BS106BF, UK; 3 Department of Environmental Sciences, University of Technology, Sydney, New South Wales 2065, Australia; 4 Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822; 5 Department of Chemistry, Biology and Marine Sciences, University of the Ryukyus, Nishihara, Okinawa, 903-0213 Japan; and 6 Department of Biology, Evergreen State University, Olympia, Washington 98505
TL;DR: The effects of temperature, temperature-induced bleaching, and infection by Aspergillus sydowii, a fungal pathogen, on Symbiodinium types harbored by the sea fan Gorgonia ventalina in the Florida Keys are examined.
Abstract: Like most Caribbean octocorals, Gorgonia ven- talina, the common sea fan, harbors endosymbiotic dinoflagellates belonging to the genus Symbiodinium. When stressed, the host can lose these algal symbionts, a phenom- enon termed "bleaching." Many cnidarians host multiple types of algal symbionts within the genus Symbiodinium, and certain types of algae may be more tolerant of stress than others. We examined the effects of temperature, tem- perature-induced bleaching, and infection by Aspergillus sydowii, a fungal pathogen, on Symbiodinium types har- bored by the sea fan Gorgonia ventalina in the Florida Keys. Symbiont type, identified on the basis of variation in small subunit nuclear ribosomal genes or large subunit chloroplast ribosomal genes, did not vary with temperature treatment or infection status. Although allelic variation based on one microsatellite locus was found among samples and reef site, it did not consistently correlate with temper- ature, treatment, or disease status, suggesting that the sym- biont-host relationship is stable. An aberrant PCR product was found in samples collected at one site and could be used to differentiate Symbiodinium populations among sites in the Florida Keys.
TL;DR: This work uses maximum likelihood phylogenetic reconstruction methods to examine the nuclear 18S rDNA (SSU) gene and the mitochondrial cytochrome b gene and results strongly support the hypothesis that P. meseres is a highly derived flabelligerid annelid closely related to Therochaeta.
Abstract: Phylogenetic relationships among and within the more than 70 recognized families of Annelida are poorly understood. In some cases, such as the monotypic Poeobi- idae, derived morphology hinders the ability to find con- vincing synapomorphies that help elucidate evolutionary origins. In such cases, molecular data can be useful. Poeo- biidae consists of the holopelagic polychaete Poeobius meseres, which is typically found in midwater depths off California. Morphologists have speculated that it is close to or within Flabelligeridae, but definitive evidence was lack- ing. Herein we use maximum likelihood phylogenetic re- construction methods to examine the nuclear 18S rDNA (SSU) gene and the mitochondrial cytochrome b gene. Our results strongly support the hypothesis that P. meseres is a highly derived flabelligerid annelid closely related to Thero- chaeta. Thus, Poeobiidae is a junior synonym for Flabelli- geridae. This result raises interesting questions about the evolution of the holopelagic P. meseres from a benthic ancestral flabelligerid.
TL;DR: The hypothesis that crayfish bilaterally compare information from their antennae is supported, as well as the observation of the exploratory behavior of Cherax destructor in a T-maze under red light, which supports this hypothesis.
Abstract: Many crayfish species inhabit murky waters or have a crepuscular lifestyle, which forces them to rely on chemical and mechanical information rather than visual input. Information on how they use one form of mechanical information—tactile cues—to explore their local environ- ment is limited. We observed the exploratory behavior of the crayfish Cherax destructor in a T-maze under red light. Animals moved forward along the long arm of the maze and then moved equally in one of two available directions. The arm chosen by one crayfish did not affect that selected by a second crayfish tested immediately after in an unwashed maze. Previous experience in the maze also did not affect the choice. We found, however, that crayfish with one antenna denervated or splinted back to the carapace turned more often toward the unaltered side. Our data support the hypothesis that crayfish bilaterally compare information from their antennae.
TL;DR: Improved resolution reveals that material strength and stipe cross-sectional area are both positively correlated with drag, suggesting that individual blades or populations can adjust either or both of these parameters in response to their mechanical environment.
Abstract: Intertidal algae are exposed to the potentially severe drag forces generated by crashing waves, and several species of brown algae respond, in part, by varying the strength of their stipe material. In contrast, previous mea- surements have suggested that the material strength of red algae is constant across wave exposures. Here, we reexam- ine the responses to drag of the intertidal red alga Masto- carpus papillatus Kutzing. By measuring individuals at multiple sites along a known force gradient, we discern responses overlooked by previous methods, which com- pared groups of individuals between "exposed" and "pro- tected" sites. This improved resolution reveals that material strength and stipe cross-sectional area are both positively correlated with drag, suggesting that individual blades or populations can adjust either or both of these parameters in response to their mechanical environment. The combined effect of this variation is a stipe breaking force that is positively correlated with locally imposed drag. Owing to this response to drag, the estimated wave-imposed limit to thallus size in M. papillatus is larger than previously pre- dicted and larger than sizes observed in the field, indicating that factors other than wave force alone constrain the size of this alga on wave-swept shores.
TL;DR: It is shown experimentally that most eggs are inseminated internally, that fertilization rate is typically lower than 100%, that meiosis is completed after eggs are released from the female, and that the dispersal phase includes the entire embryonic period.
Abstract: Vestimentiferan tubeworms are ecologically important members of deep-sea chemosynthetic communi- ties, including hydrothermal vents and cold seeps. Some are community dominants and others are primary colonists of new vent sites; they include some of the longest living and fastest growing marine invertebrates. Their mechanisms of propagation, dispersal, and genetic exchange have been widely discussed. Direct sperm transfer from males to females has been documented in one species, Ridgeia piscesae, but others are known to discharge what are ap- parently primary oocytes. Brooding of embryos has never been observed in any vestimentiferan. These observations have led to the supposition that fertilization might be exter- nal in most species. Here we report sperm storage at the posterior end of the oviduct in five species, including tube- worms from both vents and seeps. We show experimentally that most eggs are inseminated internally, that fertilization rate is typically lower than 100%, that meiosis is completed after eggs are released from the female, and that the dis- persal phase includes the entire embryonic period.
TL;DR: Support for these hypotheses is robust to method of phylogenetic reconstruction and to outgroup selection, buttressing the argument that Stauromedusae should be recognized as the class Staurozoa.
Abstract: The deepwater stauromedusan Lucernaria janetae n. sp is described from adult and juvenile specimens collected from the East Pacific Rise. Lucernaria janetae is the first species in the genus recorded from the Pacific Ocean, and differs from its congeners in size and morphology. Mitochondrial (16S) and nuclear (SSU) ribosomal gene sequences from L. janetae were analyzed with those of representative stauromedusan taxa to evaluate stauromedusan monophyly. Both genes recovered a strongly monophyletic Stauromedusae that is the sister group to all other medusozoans. Support of these hypotheses is robust to method of phylogenetic reconstruction and to outgroup selection, buttressing the argument that Stauromedusae should be recognized as the class Staurozoa. The molecular markers used here favor the same topology of relationships among our samples and clearly distinguished between two species, Haliclystus sanjuanensis and H. octoradiatus, that have been considered synonymous by many workers. A stable systematic ...
TL;DR: It is found that pairs of L. dalli females quickly and readily form stable dominance relationships, with the dominant fish changing sex into a male, providing excellent opportunities to examine the early behavioral and morphological changes associated with dominance and sex change.
Abstract: In Lythrypnus dalli, the bluebanded goby, reproductive success is primarily determined by functional sex, and functional sex is determined largely by rank in the dominance hierarchy. In most natural social groups of L. dalli, one male is at the apex of the hierarchy, and 1 to 7 females are lower in rank. When a male exits the group, a female ascends to the top of the hierarchy and becomes a male. We have examined this process in a simplified environment—a pair of females—that allows us to identify behavior associated with the formation of a dominance relationship and any other phenotypic changes associated with dominance, sex change or both. We found that pairs of L. dalli females quickly and readily form stable dominance relationships, with the dominant fish changing sex into a male. This dominant animal also rapidly increases in body size and length of its dorsal fin. In summary, dominant L. dalli females change sex in this simplified environment, providing excellent opportunities to examine the early b...
TL;DR: Behavioral and electrophysiological observations suggest that in male helmet crabs, the outer flagellum of the antennule is the chemosensory organ that detects female sex pheromone.
Abstract: Sexually competent females of Telmessus cheiragonus (helmet crab) release two pheromones that elicit grasping and copulation behaviors in males (Kamio et al., 2000, 2002, 2003). Our study aimed to use behavioral and electrophysiological techniques to identify the site of reception of these sex pheromones. In behavioral experi- ments, either the inner or the outer flagella of the antennules were ablated bilaterally from male crabs, and responses of male crabs to female odor were examined. When the inner flagella were surgically ablated, the sexual response (i.e., grasping and copulation behavior) of male crabs was not significantly changed relative to control animals that had their second antennae ablated. In contrast, the sexual re- sponse was significantly reduced when the outer flagella of the antennules were ablated, suggesting that the outer fla- gellum is the receptor organ that detects the sex phero- mones. In electrophysiological experiments, urine, which in females contains the pheromone that elicits grasping behav- ior by males but does not contain the pheromone eliciting copulation, whose release site is not known, was tested. Female and male urine as well as shrimp extract evoked phasic responses of chemosensory afferents innervating aes- thetasc sensilla on the outer flagellum of male crabs. The response of the afferents had significantly higher magnitude and lower threshold when female urine was applied. Thus, behavioral and electrophysiological observations suggest that in male helmet crabs, the outer flagellum of the anten- nule is the chemosensory organ that detects female sex pheromone.
TL;DR: It was evident that sexual maturation had a significant effect upon the gonad energy content, but because the energy variation in the digestive gland and muscle was nonsignificant (P > 0.05), there was no evidence that storage reserves are transferred from tissue to tissue.
Abstract: The aim of this study was to investigate the biochemical changes that occur during sexual maturation of the squids Illex coindetii and Todaropsis eblanae. In both species, amino acids and protein content increased in the gonad throughout maturation, but the allocation of these nitrogen compounds from the digestive gland and muscle was not evident. A significant (P 0.05) increase in the content of lipids and fatty acids was observed in the gonad and digestive gland. It seems that both species take energy for egg production directly from food, rather than from stored products. Analyses for cholesterol revealed a signif- icant (P 0.05) increase in the gonad, and the lipid content differences between species are potentially related to differ- ent feeding ecologies. The glycogen reserves in the gonad increased significantly (P 0.05), suggesting that glycogen has an important role in the maturation process. It was evident that sexual maturation had a significant effect upon the gonad energy content, but because the energy variation in the digestive gland and muscle was nonsignificant (P 0.05), there was no evidence that storage reserves are trans- ferred from tissue to tissue.
TL;DR: The switch to viviparity was not accompanied by major change in gonad structure, indicating there were few or no anatomical constraints for evolution of a marsupial function for the gonad.
Abstract: Cryptasterina hystera has a highly derived life history with intragonadal development and juveniles that emerge from the parent’s reproductive tract. The gonads are ovotestes with developing eggs separated from sperm by follicle cells. C. hystera has typical echinosperm that must enter the gonoduct of conspecifics to achieve fertilization. During oogenesis, an initial period of yolk accumulation is followed by hypertrophic lipid deposition, the major contributor to the increase in egg size. 1-Methyladenine induces egg maturation and ovulation, but the spawning component of the hormonal cascade is suppressed. This is the major alteration in reproduction associated with evolution of viviparity in C. hystera. The switch to viviparity was not accompanied by major change in gonad structure, indicating there were few or no anatomical constraints for evolution of a marsupial function for the gonad. Despite their intragonadal habitat, the brachiolaria are equipped for a planktonic life, swimming in gonadal fluid....
TL;DR: It is demonstrated that non-self sperm outcompete self-sperm in fertilization competition assays and discussed the significance of this finding in the context of natural populations in the wild, where individuals of C. savignyi are typically found growing in large groups that spawn in unison and where self-fertilization would be expected to be very rare.
Abstract: Solitary ascidians are hermaphrodites that re- lease sperm and eggs simultaneously. However, many spe- cies are self-sterile, owing to a self/non-self recognition system operating at the outer surface of the chorion during sperm-egg interaction. In Ciona intestinalis, self-incompat- ibility is thought to have a genetic basis. Here, we report a survey of the self-fertilization potential of a Santa Barbara, California, population of Ciona savignyi, a close relative of C. intestinalis. We found that, in contrast to reports on C. intestinalis, C. savignyi is highly self-fertile. However, us- ing two nonlethal recessive mutant strains, aimless (aim) and immaculate (imc), and a stable transgenic strain that expresses green fluorescent protein (GFP) in the notochord to follow offspring genotype, we demonstrate that non-self sperm outcompete self-sperm in fertilization competition assays. When the chorion was removed, both self- and non-self sperm performed equally well in the competition assay. Thus the non-self/self gamete recognition in C. sav- ignyi is not absolute but relative, and is mediated by one or more components in the chorion. We discuss the signifi- cance of this finding in the context of natural populations in the wild, where individuals of C. savignyi are typically found growing in large groups that spawn in unison and where self-fertilization would be expected to be very rare.
TL;DR: High-amplitude pressure signals generated by infauna may provide a mechanism for prey detection, for predator avoidance, for competitor detection, and perhaps even for mate detection.
Abstract: Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We expected these activities to generate low-frequency pressure waves that would propagate through sediments and be detectable at some distance from the source. Pressure sensors in intertidal sediments recorded large-amplitude porewater pressure signals. Laboratory recordings of single individuals allowed us to identify characteristic signals of arenicolid and nereidid polychaetes and tellinid bivalves. In the bivalve Macoma nasuta, these high-amplitude signals were associated with burrowing, expulsion of pseudofeces, and siphon relocation. In the polychaetes Neanthes brandti and Abarenicola pacifica, the high-amplitude pressure signals were associated with burrowing, burrow construction, burrow ventilation, and defecation. These signals were detectable in the field at distances of at least 20 cm. Since the waveforms are species-specific as well as activity-specific, they may provide a mechanism for prey detection, ...
TL;DR: All aspects of the escape response showed a low dependence on temperature, with Q10 values below 2.5 consistent for escape parameters that involved neural as well as muscle components of the behavioral response, in contrast to other biological processes.
Abstract: Calanus finmarchicus, the dominant mesozoo- plankter of the North Atlantic, is an important food source for many fishes and other planktivores. This species, which has limited diel vertical migration, depends on its fast-start escape response to evade predators. It has myelinated neu- ronal axons, which contribute to its rapid and powerful escape response. The thermal environment that C. finmar- chicus inhabits ranges from below 0 °C to 16 °C. Previous studies have shown that respiration, growth, and reproduc- tive rates are strongly dependent on temperature, with Q10 2.5. A comparable dependence of the escape re- sponse could place the animal at higher risk for cold- compensated predators. Our work focused on the tempera- ture dependence of the behavioral response to stimuli that mimic predatory attacks. We found that in contrast to other biological processes, all aspects of the escape response showed a low dependence on temperature, with Q10 values below 2. This low temperature dependence was consistent for escape parameters that involved neural as well as muscle components of the behavioral response. These findings are discussed in the contexts of the predator-prey relations of copepods and the thermal dependence of behavior in other taxa.
TL;DR: The arrangement of striated muscle in the frenula suggests that these structures may function in directional nozzle formation of the velarium during turning and in hinge formation to aid bending of the pedalia and tentacles into the subumbrella during feeding and protective responses.
Abstract: The musculature of the cubomedusa Tripedalia cystophora was investigated using immunohistochemical staining with an anti-actin antibody and histochemical staining with fluorescent phalloidin. The subumbrella is lined with a sheet of circular, striated muscle that is interrupted at the perradii, and by the nerve ring. The sheet is continuous with circular, striated muscle of the velarium, which turns radially on each face of the four velarial frenula. Perradial strips of smooth muscle run radially from just above the level of the rhopalia into the manubrium and lips. The strips give off perpendicular offshoots that run a short distance in parallel with the circular swim muscle. Musculature of the tentacles and pedalia is longitudinal and limited to the oral side of the pedalia. The pedalial muscle connects with bundles of smooth muscle that runs circularly from the tentacle base well into the subumbrella. The arrangement of striated muscle in the frenula suggests that these structures may function in direc...
TL;DR: Assays of sequence diversity at a region of mitochondrial cytochrome oxidase I, combined with coalescent estimators of the time of separation for these two regions, suggest that a late Pleistocene event more than 100 thousand years ago may be responsible for the initial separation.
Abstract: A deep genetic cline between southern populations of the barnacle Balanus glandula (from about Monterey Bay southward) and northern populations (from northern California through Alaska) has recently been described. If this pattern is due to historical isolation and genetic drift, we expect it to have formed recently and represent a transient, nonequilibrium state. However, this cline appears to have formed well before the last glacial maximum. Our assays of sequence diversity at a region of mitochondrial cytochrome oxidase I, combined with coalescent estimators of the time of separation for these two regions, suggest that a late Pleistocene event more than 100 thousand years ago may be responsible for the initial separation. This suggests that either strong oceanographic mechanisms or natural selection have maintained the cline, because there has clearly been adequate time for this cline or polymorphism to resolve itself by genetic drift and migration. However, reliance on only a single mitochondrial marker for which the substitution rate has been estimated still limits the resolution of our analysis.
TL;DR: Evidence is presented for similar plasticity of skeletal growth in ophioplutei of the brittlestar genus Macrophiothrix that spanned a 3.8-fold range in egg size and if internal skeletons are independently derived in the two classes, then plasticity in the expression of this homoplastic trait may itself behomoplastic.
Abstract: The pluteus larval forms of sea urchins (echi- noids) and brittlestars (ophiuroids) use an internal skeleton to project arms that bear a long ciliated band used in swimming and feeding. The length of this ciliated band influences rates of maximum food clearance for larvae of both echinoderm classes and affects rates of growth and development in the plankton. Phylogenetic and morpholog- ical evidence, however, tend to support the view that the pluteus morphologies of the two classes are independently derived. Studies with echinoplutei have shown that invest- ment in skeletal growth and ciliated band length changes in response to food conditions, with poorly fed larvae invest- ing more in growth of the larval skeleton and arms either absolutely or in relation to other larval or developing post- larval structures. We present evidence for similar plas- ticity of skeletal growth in ophioplutei. We examined four species in the brittlestar genus Macrophiothrix that spanned a 3.8-fold range in egg size. Sibling larvae in 14 male-female crosses were reared with high (H) or low (L) food rations, and measurements were recorded for five skeletal arm rods and three non-arm body dimensions. The expression of adaptive plasticity (significantly longer arms in L versus H cultures on a given day) was apparent for most crosses in M. koehleri, the species with the smallest egg size. In the single cross for M. longipeda, larvae from L cultures had longer arms for their body length or stomach width than did larvae from H cultures. In these cases, plasticity was similar in timing, persistence, and magnitude to previously published results from echinoplutei. If internal skeletons are independently derived in the two classes, then plasticity in the expression of this homoplastic trait may itself be homoplastic.
TL;DR: These studies provide a framework for understanding how myelin proteins were recruited during evolution and how structural adaptations enabled them to play key roles in myelination.
Abstract: Several of the proteins used to form and maintain myelin sheaths in the central nervous system (CNS) and the peripheral nervous system (PNS) are shared among different vertebrate classes. These proteins include one-to-several alternatively spliced myelin basic protein (MBP) isoforms in all sheaths, proteolipid protein (PLP) and DM20 (except in amphibians) in tetrapod CNS sheaths, and one or two protein zero (P0) isoforms in fish CNS and in all vertebrate PNS sheaths. Several other proteins, including 2′, 3′-cyclic nucleotide 3′-phosphodiesterase (CNP), myelin and lymphocyte protein (MAL), plasmolipin, and peripheral myelin protein 22 (PMP22; prominent in PNS myelin), are localized to myelin and myelin-associated membranes, though class distributions are less well studied. Databases with known and identified sequences of these proteins from cartilaginous and teleost fishes, amphibians, reptiles, birds, and mammals were prepared and used to search for potential homologs in the basal vertebrate, Ciona intest...
TL;DR: Tubulin labeling associated with the apical ganglion in a variety of planktotrophic and lecithotrophic opisthobranch larvae is examined, with emphasis on the ampullary neurons, in which ciliary bundles within the ampulla are strongly labeled.
Abstract: This investigation examines tubulin labeling associated with the apical ganglion in a variety of planktotrophic and lecithotrophic opisthobranch larvae. Emphasis is on the ampullary neurons, in which ciliary bundles within the ampulla are strongly labeled. The larvae of all but one species have five ampullary neurons and their associated ciliary bundles. The anaspid Phyllaplysia taylori, a species with direct development and an encapsulated veliger stage, has only four ampullary neurons. The cilia-containing ampulla extends to the pretrochal surface via a long, narrow canal that opens to the external environment through a very small pore (0.1 μm diameter). Cilia within the canal were never observed to project beyond the opening of the apical pore. The ampullary canals extend toward and are grouped with the ciliary tuft cells and remain in this location as planktotrophic larvae feed and grow. If, as has been reported, the ciliary tuft is motile, the pores may be continually bathed in fresh seawater. Such a...
TL;DR: During the course of the study, snails became aroused by the presence of live fish more quickly, as evidenced by more rapid initiation of hunting behavior, and details of prey-capture techniques and effectiveness of stings remained similar over the same period.
Abstract: Most of the more than 500 species of predatory marine snails in the genus Conus are tropical or semitrop- ical, and nearly all are thought to be highly selective re- garding type of prey. Conus californicus Hinds, 1844, is unusual in that it is endemic to the North American Pacific coast and preys on a large variety of benthic organisms, primarily worms and other molluscs, and also scavenges. We studied the feeding behavior of C. californicus in cap- tivity and found that it regularly killed and consumed live prickleback fishes (Cebidichthys violaceus and Xiphister spp.). Predation involved two behavioral methods similar to those employed by strictly piscivorous relatives. One method utilized stings delivered by radular teeth; the other involved engulfing the prey without stinging. Both methods were commonly used in combination, and individual snails sometimes employed multiple stings to subdue a fish. Dur- ing the course of the study, snails became aroused by the presence of live fish more quickly, as evidenced by more rapid initiation of hunting behavior. Despite this apparent adaptation, details of prey-capture techniques and effective- ness of stings remained similar over the same period.