Showing papers in "The Biological Bulletin in 2001"

Microhabitats, Thermal Heterogeneity, and Patterns of Physiological Stress in the Rocky Intertidal Zone

Abstract: Thermal stress has been considered to be among the most important determinants of organismal dis- tribution in the rocky intertidal zone. Yet our understanding of how body temperatures experienced under field condi- tions vary in space and time, and of how these temperatures translate into physiological performance, is still rudimen- tary. We continuously monitored temperatures at a site in central California for a period of two years, using loggers designed to mimic the thermal characteristics of mussels, Mytilus californianus. Model mussel temperatures were re- corded on both a horizontal and a vertical, north-facing microsite, and in an adjacent tidepool. We periodically measured levels of heat shock proteins (Hsp70), a measure of thermal stress, from mussels at each microsite. Mussel temperatures were consistently higher on the horizontal surface than on the vertical surface, and differences in body temperature between these sites were reflected in the amount of Hsp70. Seasonal peaks in extreme high temper- atures ("acute" high temperatures) did not always coincide with peaks in average daily maxima ("chronic" high tem- peratures), suggesting that the time history of body temper- ature may be an important factor in determining levels of thermal stress. Temporal patterns in body temperature dur- ing low tide were decoupled from patterns in water temper- ature, suggesting that water temperature is an ineffective metric of thermal stress for intertidal organisms. This study demonstrates that spatial and temporal variability in thermal stress can be highly complex, and "snapshot" sampling of temperature and biochemical indices may not always be a reliable method for defining thermal stress at a site.

Molecular Evidence for Cryptic Species of Aurelia aurita (Cnidaria, Scyphozoa)

Abstract: Morphological taxonomy suggests that marine faunas are species poor compared to terrestrial and freshwater faunas (1). This dichotomy has been attributed to the unique potential of marine plankters for distant dispersal across homogenous oceans with few barriers to gene flow (2). The relative scarcity of opportunities for allopatric divergence has resulted in depauperate marine faunas characterized by a high proportion of widespread or cosmopolitan species. Aurelia aurita (Linnaeus) has been considered a good example of such a cosmopolite (3, 4, 5, 6). However, recent molecular studies have revealed cryptic species in many marine taxa (7), suggesting that marine biodiversity is higher and opportunities for speciation have been more frequent than generally recognized. Here, we present nuclear and mitochondrial DNA sequence evidence of seven sibling species of Aurelia aurita and two additional species, A. limbata Brandt and A. labiata Chamisso & Eysenhardt. These sequence data indicate speciation events as early as the late Cretaceous or early Tertiary, consistent with the formation of well-recognized biogeographic barriers to gene flow in the seas. Traditionally, the genus Aurelia comprises two species: A. limbata, a polar species, and A. aurita, a common inhabitant of nearshore waters circumglobally between about 50 °N and 55 °S (3, 4, 5; Fig. 1). Perhaps due to its ubiquity, A. aurita has become a popular research organism for studies as diverse as protein chemistry, development, ecology, ethology, and hydrodynamics (6). A. aurita also is economically important because worldwide it preys on or competes with larvae of commercial fisheries and because swarms of medusae may impede trawling or block power-plant intakes (8). Furthermore, this “pest” has been introduced at least into San Francisco Bay (9) and possibly many other places (10). A. aurita is also familiar to nonspecialists because it is the most commonly displayed medusa in public aquaria. The systematics of A. aurita therefore is of considerable scientific, economic, and general interest. Aurelia has a typical bipartite scyphozoan life history in which benthic scyphopolyps asexually strobilate ephyrae that grow into sexual medusae, the females of which brood larvae that settle into the shallow coastal benthos within a few days of being released. Of these life stages, the medusa probably is the principal dispersal phase because only the medusa is both long-lived (several months to more than one year; 11) and planktonic (6). The potential of medusae for distant dispersal is consistent with the current classification of A. aurita as a circumglobal, almost cosmopolitan, species (4, 5). However, A. aurita medusae in Saanich Inlet, British Columbia, and perhaps elsewhere, migrate directionally (12), maintaining breeding aggregations within isolated inlets and probably limiting gene flow among populations. Consistent with limited gene flow, allozyme differences have been found between populations of A. aurita in the eastern and western Atlantic Ocean, the Gulf of Mexico, and the eastern and western Pacific Ocean (9, 13). In addition, one species, A. labiata, was recently recognized as native to Pacific North America and distinct from A. aurita (10). Novel DNA sequence data from nuclear internal transcribed spacer one (ITS-1) and mitochondrial cytochrome oxidase c subunit I (COI) reveal highly structured gene genealogies and at least nine distinct clades of Aurelia (Figs. 1, 2). Several lines of argument suggest that these clades warrant recognition as distinct species. First, the length of ITS-1 varies from 240 nucleotides (Charlestown, RI) to 360 nucleotides (Cananeia, Brazil). Such length variation is comparable to that found among congeneric species of Received 7 August 2000; accepted 19 October 2000. * To whom correspondence should be addressed at Coral Reef Research Foundation, Box 1765, Koror, PW 96940, Palau. Reference: Biol. Bull. 200: 92–96. (February 2001)

Zooxanthellae of the Montastraea annularis Species Complex: Patterns of Distribution of Four Taxa of Symbiodinium on Different Reefs and Across Depths

Abstract: Corals of the Montastraea annularis complex host several different dinoflagellates in the genus Symbiodinium. Here we address two questions arising from our previous studies of these associations on an offshore reef. First, do the same taxa and patterns of association (Symbiodinium A and B found in higher irradiance habitats than Symbiodinium C) occur on an inshore reef? Second, does M. franksi at the limits of its depth range host only Symbiodinium C, as it does at intermediate depths? In both surveys, a new Symbiodinium taxon and different patterns of distribution (assayed by analyses of small ribosomal subunit RNA genes [srDNA]) were observed. Inshore, a taxon we name Symbiodinium E predominated in higher irradiance habitats in M. franksi and its two sibling species; the only other zooxanthella observed was Symbiodinium C. Offshore, M. franksi mainly hosted Symbiodinium C, but hosted Symbiodinium A, B, C, and E in shallow water and Symbiodinium E and C in very deep water. Symbiodinium E may be stress-tolerant. Observed srDNA heterogeneity within samples of Symbiodinium B, C, and E is interpreted as variation across copies within this multigene family. Experimental bleaching of Symbiodinium C supported this interpretation. Thus sequences from natural samples should be interpreted cautiously.

The Adaptive Bleaching Hypothesis: Experimental Tests of Critical Assumptions

Abstract: Coral bleaching, the loss of color due to loss of symbiotic zooxanthellae or their pigment, appears to be increasing in intensity and geographic extent, perhaps re- lated to increasing sea surface temperatures. The adaptive bleaching hypothesis (ABH) posits that when environmen- tal circumstances change, the loss of one or more kinds of zooxanthellae is rapidly, sometimes unnoticeably, followed by formation of a new symbiotic consortium with different zooxanthellae that are more suited to the new conditions in the host's habitat. Fundamental assumptions of the ABH include (1) different types of zooxanthellae respond differ- ently to environmental conditions, specifically temperature, and (2) bleached adults can secondarily acquire zooxanthel- lae from the environment. We present simple tests of these assumptions and show that (1) genetically different strains of zooxanthellae exhibit different responses to elevated tem- perature, (2) bleached adult hosts can acquire algal symbi- onts with an apparently dose-dependent relationship be- tween the concentration of zooxanthellae and the rate of establishment of the symbiosis, (3) and finally, bleached adult hosts can acquire symbionts from the water column.

Repopulation of Zooxanthellae in the Caribbean corals Montastraea annularis and M. faveolata following experimental and disease-associated bleaching.

Abstract: Caribbean corals of the Montastraea annularis species complex associate with four taxa of symbiotic dinoflagellates (zooxanthellae; genus Symbiodinium) in ecologically predictable patterns. To investigate the resilience of these host-zooxanthella associations, we conducted field experiments in which we experimentally reduced the numbers of zooxanthellae (by transplanting to shallow water or by shading) and then allowed treated corals to recover. When depletion was not extreme, recovering corals generally contained the same types of zooxanthellae as they did prior to treatment. After severe depletion, however, recovering corals were always repopulated by zooxanthellae atypical for their habitat (and in some cases atypical for the coral species). These unusual zooxanthellar associations were often (but not always) established in experimentally bleached tissues even when adjacent tissues were untreated. Atypical zooxanthellae were also observed in bleached tissues of unmanipulated Montastraea with yellow-blo...

Hidden in plain sight: the ecology and physiology of organismal transparency.

Abstract: Despite the prevalence and importance of transparency in organisms, particularly pelagic species, it is a poorly understood characteristic. This article reviews the current state of knowledge on the distribution, ecology, and physical basis of biological transparency. Particular attention is paid to the distribution of transparent species relative to their optical environment, the relationship between transparency and visual predation, the physics of transparency, and what is known about the anatomical and ultrastructural modifications required to achieve this condition. Transparency is shown to be primarily a pelagic trait, uncommon in other aquatic habitats and extremely rare on land. Experimental and theoretical studies in terrestrial, freshwater, and marine ecosystems have shown that transparency is a successful form of camouflage, and that several visual adaptations seem to counter it. The physical basis of transparency is still poorly understood, but anatomical observations and mathematical models s...

Cytological basis of photoresponsive behavior in a sponge larva

Abstract: Ontogenetic changes in the photoresponse of larvae from the demosponge Reneira sp. were studied by analyzing the swimming paths of individual larvae exposed to diffuse white light. Larvae swam upward upon release from the adult, but were negatively phototactic until at least 12 hours after release. The larval photoreceptors are pre- sumed to be a posterior ring of columnar monociliated epithelial cells that possess 120-m-long cilia and pigment- filled protrusions. A sudden increase in light intensity caused these cilia to become rigidly straight. If the light intensity remained high, the cilia gradually bent over the pigmented vesicles in the adjacent cytoplasm, and thus covered one entire pole of the larva. The response was reversed upon a sudden decrease in light intensity. The ciliated cells were sensitive to changes in light intensity in larvae of all ages. This response is similar to the shadow response in tunicate larvae or the shading of the photore- ceptor in Euglena and is postulated to allow the larvae to steer away from brighter light to darker areas, such as under coral rubble—the preferred site of the adult sponge on the reef flat. In the absence of a coordinating system in cellular sponges, the spatial organization and autonomous behavior of the pigmented posterior cells control the rapid responses to light shown by these larvae.

Variable mate-guarding time and sperm allocation by male snow crabs (Chionoecetes opilio) in response to sexual competition, and their impact on the mating success of females

Abstract: Two laboratory experiments investigated mate guarding and sperm allocation patterns of adult males with virgin females of the snow crab, Chionoecetes opilio, in relation to sex ratio. Although females outnumbered males in treatments, operational sex ratios were male-biased because females mature asynchronously and have a limited period of sexual attractiveness after their maturity molt. Males guarded females significantly longer as the sex ratio increased: the mean time per female was 2.9 d in a 2 males:20 females treatment compared to 5.6 d in a 6 males:20 females treatment. Female injury and mortality scaled positively to sex ratio. Males that guarded for the greatest number of days were significantly larger, and at experiment's end had significantly smaller vasa deferentia, suggesting greater sperm expense, than males that guarded for fewer days. In both experiments, the spermathecal load (SL)--that is, the quantity of ejaculate stored in a female's spermatheca--was independent of molt date, except in the most female-biased treatment, where it was negatively related. The SL increased as the sex ratio increased, mainly because females accumulated more ejaculates. However, similarly sized males had smaller vasa deferentia and passed smaller ejaculates, such that, at a given sex ratio, the mean SL was 55% less in one experiment than in the other. Some females extruded clutches with few or no fertilized eggs, and their median SL (3-4 mg) was one order of magnitude smaller than that of females with well-fertilized clutches (31-50 mg), indicating sperm limitation. Males economized sperm: all females irrespective of sex ratio were inseminated, but to a varying extent submaximally; each ejaculate represented less than 2.5% of male sperm reserves; and no male was fully exhausted of sperm. Sperm economy is predicted by sperm competition theory for species like snow crab in which polyandry exists, mechanisms of last-male sperm precedence are effective, and the probability that one male fertilizes a female's lifetime production of eggs is small.

Plume-Tracking Robots: A New Application of Chemical Sensors

Abstract: Many animals have the ability to search for odor sources by tracking their plumes. Some of the key features of this search behavior have been successfully transferred to robot platforms, although the capabilities of animals are still beyond the current level of sensor technologies. The examples described in this paper are (1) incorporating into a wheeled robot the upwind surges and casting used by moths in tracking pheromone plumes, (2) extracting useful information from the response patterns of a chemical sensor array patterned after the spatially distributed chemoreceptors of some animals, and (3) mimicking the fanning behavior of silkworm moths to enhance the reception of chemical signals by drawing molecules from one direction. The achievements so far and current efforts are reviewed to illustrate the steps to be taken toward future development of this technology.

Development of host- and symbiont-specific monoclonal antibodies and confirmation of the origin of the symbiosome membrane in a cnidarian-dinoflagellate symbiosis.

Abstract: The “symbiosome membrane” as defined by Roth et al. (1988) is a single, host-derived membrane that surrounds an endosymbiotic organism, separating it from the cytoplasm of the host cell. However, in the case of cnidarian–dinoflagellate endosymbioses, clear identification of the symbiosome membrane is complicated by the fact that each algal symbiont is surrounded by multiple layers of apparent membrane. The origin and molecular nature of these membranes has been the subject of considerable debate in the literature. Here we report the development of host-specific (G12) and symbiont-specific (PC3) monoclonal antibodies that allow separation of the host and symbiont components of these multiple membranes. Using immunocytochemistry at both the light and the electron microscopic level, we present data supporting the conclusion that the definitive symbiosome membrane is a single, host-derived membrane, whereas the remainder of the underlying apparent membranes surrounding the algal cell are symbiont-derived. The...

NO/cGMP signaling and HSP90 activity represses metamorphosis in the sea urchin Lytechinus pictus.

Abstract: Nitric oxide (NO) signaling repressively regu- lates metamorphosis in two solitary ascidians and a gastro- pod. We present evidence for a similar role in the sea urchin Lytechinus pictus. NO commonly signals via soluble gua- nylyl cyclase (sGC). Nitric oxide synthase (NOS) activity in some mammalian cells, including neurons, depends on the molecular chaperone heat shock protein 90 (HSP90); this may be so in echinoid larvae as well. Pluteus larvae con- taining juvenile rudiments were treated with either radicicol L -o rD-nitroarginine-methyl-ester ( L-NAME and D-NAME), or IH-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), in- hibitors of HSP90, NOS, and sGC, respectively. In all instances, drug treatment significantly increased the fre- quency of metamorphosis. SNAP, a NO donor, suppressed the inductive properties of L-NAME and biofilm, a natural inducer of metamorphosis. NADPH diaphorase histochem- istry indicated NOS activity in cells in the lower lip of the larval mouth, the preoral hood, the gut, and in the tube feet of the echinus rudiment. Histochemical staining coincided with NOS immunostaining. Microsurgical removal of the oral hood or the pre-oral hood did not induce metamorpho- sis, but larvae lacking these structures retained the capacity to metamorphose in response to ODQ. We propose that the production of NO repressively regulates the initiation of metamorphosis and that a sensory response to environmen- tal cues reduces the production of NO, and consequently cGMP, to initiate metamorphosis.

Molecular Evidence that Sclerolinum brattstromi Is Closely Related to Vestimentiferans, not to Frenulate Pogonophorans (Siboglinidae, Annelida)

Abstract: Siboglinids, previously referred to as pogono- phorans, have typically been divided into two groups, frenu- lates and vestimentiferans. Adults of these marine proto- stome worms lack a functional gut and harbor endosymbiotic bacteria. Frenulates usually live in deep, sedimented reducing environments, and vestimentiferans inhabit hydrothermal vents and sulfide-rich hydrocarbon seeps. Taxonomic literature has often treated frenulates and vestimentiferans as sister taxa. Sclerolinum has traditionally been thought to be a basal siboglinid that was originally regarded as a frenulate and later as a third lineage of siboglinids, Monilifera. Evidence from the 18S nuclear rDNA gene and the 16S mitochondrial rDNA gene pre- sented here shows that Sclerolinum is the sister clade to vestimentiferans although it lacks the characteristic mor- phology (i.e., a vestimentum). The rDNA data confirm the contention that Sclerolinum is different from frenulates, and further supports the idea that siboglinid evolution has been driven by a trend toward increased habitat specialization. The evidence now available indicates that vestimentiferans lack the molecular diversity expected of a group that has been argued to have Silurian or possibly Cambrian origins.

Interspecific Relationships Between Egg Size and the Level of Parental Investment per Offspring in Echinoderms

Abstract: The relationship between the size of an egg and its energy content was analyzed using published data for 47 species of echinoderms. Scaling relationships were evalu- ated for all species, as well as for subsets of the species, based on mode of development. Regressions were calcu- lated using linear, power function, full allometric, and sec- ond-order polynomial models. The full allometric model is preferred because it is relatively simple and the most gen- eral. Among these species of echinoderms, larger eggs contain more energy. Egg energy content scales isometri- cally across a wide range of egg sizes both among and within different modes of development. The only exception is among species with feeding larval development, where there does not seem to be a clear scaling relationship. In most cases, the regressions were statistically significant and explained a very large proportion of the variance in energy content. However, there were wide confidence intervals around the estimated regression parameters. In all cases, the predictive power of the regression was poor, requiring large differences in egg size to yield significantly different pre- dictions of energy content. Consequently, egg size is of limited value for the quantitative prediction of egg energy content and should be used with caution in life-history studies.

Ecology and Behavior of Gecarcoidea natalis, the Christmas Island Red Crab, During the Annual Breeding Migration

Abstract: The terrestrial crab Gecarcoidea natalis is en- demic to the forests of Christmas Island but must migrate each year to the coast to breed. During 1993 and 1995, radio-tracking, mark and recapture, and counting methods were used to establish the routes, walking speeds, direction of travel, and destinations of migrating crabs, as well as crab numbers and distribution. The density of crabs ranged from 0.09 to 0.57 crabs per square meter, which gave a popula- tion estimate of 43.7 million adult crabs on the island. During the dry season the crabs were relatively inactive but on arrival of the wet season immediately began their mi- gration. The crabs generally walked in straight lines, and most crabs from around the Island traveled toward the northwest shore instead of simply walking toward the near- est shore. The maximum recorded distance walked by a red crab in one day was 1460 m, but the mean was 680 m per day in 1993 and 330 m in 1995. Comparing the 1993 and 1995 study seasons, there was a 3-week difference in the timing of the start of the migration, but the spawning date was fixed by the lunar phase and took place 17 to 18 days after mating. In 1993, late rain prompted a "rushed" migra- tion and crabs walked directly to their shore destinations; in contrast, in 1995 most crabs made stops of 1 to 7 days during the downward migration. By giving the crabs a chance to feed along the way and minimizing the time that the population was concentrated near the shore, these stops may be important in ensuring that the animals have enough food after the long dry season. Furthermore, this behavior implies that the crabs are able to judge how far away they are from the shore during the migration.

Fan Organs of Crayfish Enhance Chemical Information Flow

Abstract: Animals as well as autonomous robots need to acquire environmental signals in order to adjust their activ- ity in time and space. Some information is accessible to the sensors only as a result of specific behaviors for stimulus acquisition. Due to the slow rate of molecular diffusion, dispersal of chemical stimuli depends on fluid flow. Aquatic crustaceans can generate directed water currents by special- ized appendages. Here I describe the crayfish fan organs, which are feathered flagella of the mouthparts, and their activity in sending and receiving chemical signals in envi- ronments with stagnant flow conditions. During the power- stroke, the fan opens and displaces water; during the return stroke, it collapses and thereby minimizes drag. These or- gans can create a variety of flow fields including water jets, and in many different directions. Bilateral upward fanning draws water horizontally from all directions toward the anterior chemoreceptors. Unilateral upward fanning draws water from only one side towards the body. The versatility of the crayfish fan organ makes it a candidate for biomi- metic reconstruction and use in autonomous robots that can search chemical sources.

Invertebrate-Inspired sensory-motor systems and autonomous, olfactory-guided exploration.

Abstract: The localization of resources in a natural environment is a multifaceted problem faced by both invertebrate animals and autonomous robots. At a first approximation, locomotion through natural environments must be guided by reliable sensory information. But natural environments can be unpredictable, so from time to time, information from any one sensory modality is likely to become temporarily unreliable. Fortunately, compensating mechanisms ensure that such signals are replaced or disambiguated by information from more reliable modalities. For invertebrates and robots to rely primarily on chemical senses has advantages and pitfalls, and these are discussed. The role of turbulence, which makes tracking a single odor to its source a complex problem, is contrasted with the high-fidelity identification of stimulus quality by the invertebrate chemoreceptor and by artificial sensors.

Biogeography of Asterias: North Atlantic climate change and speciation.

Abstract: Fossil evidence suggests that the seastar genus Asterias arrived in the North Atlantic during the trans-Arctic interchange around 3.5 Ma. Previous genetic and morphological studies of the two species found in the Atlantic today suggested two possible scenarios for the speciation of A. rubens and A. forbesi. Through phylogenetic and population genetic analysis of data from a portion of the cytochrome oxidase I mitochondrial gene and a fragment of the ribosomal internal transcribed spacer region, I show that the formation of the Labrador Current 3.0 Ma was probably responsible for the initial vicariance of North Atlantic Asterias populations. Subsequent adaptive evolution in A. forbesi was then possible in isolation from the European species A. rubens. The contact zone between these two species formed recently, possibly due to a Holocene founding event of A. rubens in New England and the Canadian Maritimes.

Landing strategies in honeybees, and possible applications to autonomous airborne vehicles

Abstract: Insects, being perhaps more reliant on image motion cues than mammals or higher vertebrates, are proving to be an excellent organism in which to investigate how information on optic flow is exploited to guide locomotion and navigation. This paper describes one example, illustrating how bees perform grazing landings on a flat surface. A smooth landing is achieved by a surprisingly simple and elegant strategy: image velocity is held constant as the surface is approached, thus automatically ensuring that flight speed is close to zero at touchdown. No explicit knowledge of flight speed or height above the ground is necessary. The feasibility of this landing strategy is tested by implementation in a robotic gantry, and its applicability to autonomous airborne vehicles is discussed.

Why Do Animals Have So Many Receptors? The Role of Multiple Chemosensors in Animal Perception

Abstract: Many animals have an abundance and diverse assortment of peripheral sensors, both across and within sensory modalities. Multiple sensors offer many functional advantages to an animal's ability to perceive and respond to environmental signals. Advantages include extending the ability to detect and determine the spatial distribution of stimuli, improving the range and accuracy of discrimination among stimuli of different types and intensities, increasing behavioral sensitivity to stimuli, ensuring continued sensory capabilities when the probability of damage or other loss of function to some sensors is high, maintaining sensory func- tion over the entire sensory surface during development and growth, and increasing the richness of behavioral output to sensory stimulation. In this paper, we use the crustacean chemosensory system as the primary example to discuss these functions of multiple sensors. These principles may be applicable to the function of autonomous robots and should be considered in their design.

Competition for space among sessile marine invertebrates: changes in HSP70 expression in two Pacific cnidarians.

Abstract: The role of stress proteins— either constitutive (HSC) or inducible (HSP)— of the HSP70 family in intra- and interspecific competition for space was examined in two sessile Pacific cnidarians. Anthopleura elegantissima, an intertidal anemone, and Corynactis californica, a subtidal corallimorpharian, express HSP70 in the absence of appar- ent physical stress. HSP70 protein expression is concen- trated in the tentacles of A. elegantissima when the animal is exposed to contact with other benthic organisms. Under the same conditions, however, HSP concentrations are sim- ilar in the body and tentacles of C. californica. When two different clones of A. elegantissima interact in the field, the outside polyps (warriors) express more HSP70 than the inside ones (2.4 versus 0.6 ng HSP70/g Protein). When different C. californica clones interact, HSP70 expression in the outside and inside polyps is similar (1.5 versus 1.8 ng HSP70/g P) and is fairly constant in the corallimorpharian in the different interspecific encounters. HSP70 expression is related to the different kinds of aggression encountered by both cnidarians. HSP70 expression may be involved in the recovery of tissues damaged by the allelochemical, cyto- toxical, or corrosive substances produced by different ene- mies. C. californica clones appear prepared for war, as evidenced by the high constant expression of HSP70 in the polyps. A. elegantissimaexhibits differential HSP70 expres- sion depending on the identity of each neighboring intra- or interspecific sessile competitor. We propose that stress pro- teins can be used to quantify space competition or aggres- sion among sessile marine invertebrates.

Morula cells as the major immunomodulatory hemocytes in ascidians: evidences from the colonial species Botryllus schlosseri.

Abstract: Immunocytochemical methods were used to study the presence and distribution of IL-1-alpha- and TNF-alpha-like molecules in the hemocytes of the colonial ascidian Botryllus schlosseri. Only a few unstimulated hemocytes were positive to both the antibodies used. When the hemocytes were stimulated with either mannan or phorbol 12-mono-myristate, the phagocytes were not significantly changed in their number, staining intensity, or cell morphology. In contrast, stimulated morula cells were intensely labeled, indicating that these cells play an important immunomodulatory role.

Molecular Phylogeny of the Model Annelid Ophryotrocha

Abstract: Annelids of the genus Ophryotrocha are small opportunistic worms commonly found in polluted and nutrient- rich habitats such as harbors. Within this small group of about 40 described taxa a large variety of reproductive strategies are found, ranging from gonochoristic broadcast spawners to se- quential hermaphroditic brooders. Many of the species have a short generation time and are easily maintained as laboratory cultures. Thus they have become a popular system for explor- ing a variety of biological questions including developmental genetics, ethology, and sexual selection. Despite considerable behavioral, reproductive, and karyological studies, a phyloge- netic framework is lacking because most taxa are morpholog- ically similar. In this study we use 16S mitochondrial gene sequence data to infer the phylogeny of Ophryotrocha strains commonly used in the laboratory. The resulting mtDNA to- pologies are generally well resolved and support a genetic split between hermaphroditic and gonochoristic species. Although the ancestral state could not be unambiguously identified, a change in reproductive strategy (i.e., hermaphroditism and gonochorism) occurred once within Ophryotrocha. Addition- ally, we show that sequential hermaphroditism evolved from a simultaneous hermaphroditic ancestor, and that characters pre- viously used in phylogenetic reconstruction (i.e., jaw morphol- ogy and shape of egg mass) are homoplasic within the group.

Egg Longevity and Time-Integrated Fertilization in a Temperate Sea Urchin (Strongylocentrotus droebachiensis)

Abstract: Recent field experiments have suggested that fertilization levels in sea urchins (and other broadcast spawners that release their gametes into the water column) may often be far below 100%. However, past experiments have not considered the potentially positive combined effects of an extended period of egg longevity and the release of gametes in viscous fluids (which reduces dilution rates). In a laboratory experiment, we found that eggs of the sea urchin Strongylocentrotus droebachiensis had high viability for 2 to 3 d. Fertilization levels of eggs held in sperm-permeable egg baskets in the field and exposed to sperm slowly diffusing off a spawning male increased significantly with exposure from 15 min to 3 h. In a field survey of time-integrated fertilizations (over 24, 48, and 72 h) during natural sperm release events, eggs held in baskets accrued fertilizations over as much as 48 h and attained fairly high fertilization levels. Our results suggest that an extended period of egg longevity and the releas...

Development of Serotonin-like and SALMFamide-like Immunoreactivity in the Nervous System of the Sea Urchin Psammechinus miliaris

Abstract: The present immunocytochemical study utilizes serotonin and SALMFamide antisera, together with confocal laser scanning microscopy, to provide new information about the development of the nervous system in the sea urchin Psammechinus miliaris (Echinodermata: Echinoidea). Special attention is paid to the extent of the nervous system in later larval stages (6-armed pluteus to metamorphic competency), a characteristic that has not been well described in this and other species of sea urchin. An extensive apical ganglion appears by the 6-armed pluteus stage, forming a complex of 10-20 cells and fibers, including discrete populations of both serotonin-like and SALMFamide-like immunoreactive cells. At metamorphosis this complex is large, comprising at least 40 cells in distinct arrays. Serotonin-like immunoreactivity is also particularly apparent in the lower lip ganglion of 6- to 8-armed plutei; this ganglion consists of 15-18 cells that are distributed around the mouth. The ciliary nerves that lie beneath the c...

Drag, Drafting, and Mechanical Interactions in Canopies of the Red Alga Chondrus crispus

Abstract: Dense algal canopies, which are common in the lower intertidal and shallow subtidal along rocky coastlines, can alter flow-induced forces in their vicinity Alteration of flow-induced forces on algal thalli may ameliorate risk of dislodgement and will affect important physiological pro- cesses, such as rates of photosynthesis This study found that the force experienced by a thallus of the red alga Chondrus crispus(Stackhouse) at a given flow speed within a flow tank depended upon (1) the density of the canopy surrounding the thallus, (2) the position of the thallus within the canopy, and (3) the length of the stipe of the thallus relative to the height of the canopy At all flow speeds, a solitary thallus experienced higher forces than a thallus with neighbors A greater than 65% reduction in force occurred when the thallus drafted in the region of slower velocities that occurs in the wake region of even a single upstream neighbor, similar to the way racing bicyclists draft one behind the other Mechanical interactions between thalli were important to forces experienced within canopies A thallus on the upstream edge of a canopy experienced 6% less force than it did when solitary, because the canopy physically supported it A thallus in the middle of a canopy experienced up to 83% less force than a solitary thallus, and forces decreased with increasing canopy density Thus, a bushy morphology that increases drag on a solitary thallus may function to decrease forces experienced by that thallus when it is surrounded by a canopy, because that morphology increases physical support provided by neighbors

Cuttlefish Cue Visually on Area—Not Shape or Aspect Ratio—of Light Objects in the Substrate to Produce Disruptive Body Patterns for Camouflage

Abstract: Cephalopods have at least 20 body patterns for camouflage, yet these can be organized into four categories: uniform, stipple, mottle, and disruptive (1). Among them, disruptive coloration is probably the most striking because it breaks up the animal's body outline by visual deception (2). Cuttlefish produce (by direct neural control of chromatophores) an array of white skin components that produce a disruptive coloration on their bodies, and this helps them achieve camouflage as it is defined by Endler (3), "A colour or pattern is cryptic if it resembles a random sample of the visual background as perceived by the predator at the time and place at which the prey is most vulnerable to predation." The so-called "White square" on the dorsal mantle of cuttlefish represents a random sample of white background objects (Fig. 1) that are common in marine habitats, thereby distracting the attention of visual predators away from the body outline (2). How do cuttlefish "decide" to switch to disruptive coloration, and what sensory cues are involved? We developed a non-invasive assay that monitors motor output (i.e., the body pattern of the cuttlefish) resulting from different visual inputs (computer-generated artificial substrates). Although many aspects of cephalopod vision are known (4), little is known about the visual features of the substrate that elicit disruptive coloration. A recent study (5) of young cuttlefish, Sepia pharaonis, showed that the size, contrast, and number of white squares on a black background are the main visual features that cause cuttlefish to switch from general resemblance of the substrate to disruptive coloration. In this study, we examine the shapes and aspect ratios of white objects on black backgrounds that lead cuttlefish to show disruptive coloration. Five young cuttlefish, Sepia pharaonis (8-10 cm mantle length, 10 weeks old), were reared from eggs in the laboratory of the National Research Center for Cephalopods (University of Texas Medical Branch, Galveston) and were maintained in the Marine Resources Center at the Marine Biological Laboratory, Woods Hole, Massachusetts. Each animal was placed in a running seawater tank (25 cm X 40 cm X 10 cm) and was restricted by a four-wall divider (inside covered by black cloth to prevent light reflection) to an area (20 cm X 26 cm) where various computergenerated backgrounds (laminated to be waterproof) were presented as the substrate. Acclimation to the tank was gauged by the cessation of excessive swimming and hovering movements and by the chronic expression of a stable body pattern. A digital video camera was used to record the body patterning of S. pharaonis over a period of 30 min (i.e., record 2 s for every 1-min interval;

Metamorphosis of coeloblastula performed by multipotential larval flagellated cells in the calcareous sponge Leucosolenia laxa.

Abstract: The calcareous sponge Leucosolenia laxa releases free-swimming hollow larvae called coeloblastulae that are the characteristic larvae of the subclass Calcinea. Although the coeloblastula is a major type of sponge larva, our knowledge about its development is scanty. Detailed electron microscopic studies on the metamorphosis of the coeloblastula revealed that the larva consists of four types of cells: flagellated cells, bottle cells, vesicular cells, and free cells in a central cavity. The flagellated cells, the principal cell type of the larva, are arranged in a pseudostratified layer around a large central cavity. The larval flagellated cells characteristically have glutinous granules that are used as internal markers during metamorphosis. After a free-swimming period the larva settles on the substratum, and settlement apparently triggers the initiation of metamorphosis. The larval flagellated cells soon lose their flagellum and begin the process of dedifferentiation. Then the larva becomes a mass of dedifferentiated cells in which many autophagosomes are found. Within 18 h after settlement, the cells at the surface of the cell mass differentiate to pinacocytes. The cells beneath the pinacoderm differentiate to scleroblasts that form triradiate spicules. Finally, the cells of the inner cell mass differentiate to choanocytes and are arranged in a choanoderm that surrounds a newly formed large gastral cavity. We found glutinous granules in these three principal cell types of juvenile sponges, thus indicating the multipotency of the flagellated cells of the coeloblastula.

Parallel processing and image analysis in the eyes of mantis shrimps.

Abstract: The compound eyes of mantis shrimps, a group of tropical marine crustaceans, incorporate principles of serial and parallel processing of visual information that may be applicable to artificial imaging systems. Their eyes in- clude numerous specializations for analysis of the spectral and polarizational properties of light, and include more photoreceptor classes for analysis of ultraviolet light, color, and polarization than occur in any other known visual system. This is possible because receptors in different re- gions of the eye are anatomically diverse and incorporate unusual structural features, such as spectral filters, not seen in other compound eyes. Unlike eyes of most other animals, eyes of mantis shrimps must move to acquire some types of visual information and to integrate color and polarization with spatial vision. Information leaving the retina appears to be processed into numerous parallel data streams leading into the central nervous system, greatly reducing the ana- lytical requirements at higher levels. Many of these unusual features of mantis shrimp vision may inspire new sensor designs for machine vision.

Structure and Sequence Conservation of a Putative Hypoxia Response Element in the Lactate Dehydrogenase-B Gene of Fundulus

Abstract: Many aquatic habitats are characterized by periodic or sustained episodes of low oxygen concentration, or hypoxia, and organisms that survive in these habitats do so by utilizing a suite of behavioral, physiological and biochemical adjustments to low oxygen (1-3). In the killifish Fundulus heteroclitus, one response to prolonged exposure to hypoxia is an increase in the activity of lactate dehydrogenase-B (LDH-B), the terminal enzyme of anaerobic glycolysis, in liver tissue (4). An increase in glycolytic enzyme activity also occurs in mammalian cells during hypoxia, a process due, in part, to increased rates of gene transcription mediated by the hypoxia-inducible transcription factor, HIF-1 (5). Given that a homolog of HIF-1 has been identified in fish (6), we hypothesized that HIF might be involved in the observed up-regulation of LDH-B in F. heteroclitus. Herein, we describe the presence of DNA elements in intron 2 of the Ldh-B gene from F. heteroclitus that resemble hypoxia response elements (HRE) describedfor mammalian genes (7-10). Specifically, over a region of approximately 50 base pairs we identified two consensus HIF-1 binding sites, as well as DNA elements that may bind other transcription factors (e.g., cyclic AMP response elements; CRE). We found that these sites were perfectly conserved among geographically diverse populations of F. heteroclitus, as well as being highly conserved among multiple species in the genus Fundulus. The spacing, orientation, and sequence conservation of these putative regulatory elements suggest that they may be functionally involved in the hypoxic regulation of Ldh-B in these fish.

Multiple paternity in Littorina obtusata (Gastropoda, Littorinidae) revealed by microsatellite analyses.

Abstract: Parental identity for juvenile Littorina obtusata was determined from three egg masses by means of micro- satellite DNA markers. Results confirm that the attendant adult female in each case was the dam of the offspring and that at least 4 - 6 males contributed to each brood. This correlates with our behavioral observations that indicated multiple copulations between the female and several males in each experimental aquarium. A significant number of offspring from each brood were sired by non-sampled males (males that had copulated with females before capture) whose sperm had been stored by the female. This is the first direct evidence of multiple paternity in the Littorinidae. Results are discussed in reference to current theories of sperm competition, male precedence, and cryptic female choice.