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The two main types of theories for the evolution of the biphasic life cycles in marine invertebrates are discussed. The 'intercalation' theories propose that the larval stages (planktotrophic or lecithotrophic) have evolved as specializations from the ancestral, direct life cycle. The opposing 'terminal addition' theories propose that the ancestor was holopelagic and that the adult stage was added to the life cycle with the pelagic stage retained as a planktotrophic larva. It is emphasized that theories based on hypothetical ancestors that were unable to feed must be rejected. This applies to planula theories based on a compact planula. Various arguments against the theories that consider the feeding larvae as ancestral in the major eumetazoan lineages and in particular against the trochaea theory are discussed and found untenable. It is suggested that the 'Cambrian explosion' was actually a rapid Ediacaran radiation of the eubilaterians that was made possible by the evolution of a tubular gut with all the resulting possibilities for new body plans. We have irrefutable proof in support of the pelagic larval life as an original feature. ... This is so well documented that it would he superfluous to enter into the matter more closely, were it not for its great importance and the fact that there exist authors, who still assert that direct development is the original condition (Jagersten, 1972, p. 3)., Introduction In general, two main views have dominated recent discussions of animal life-cycle evolution, and specifically of that of the marine bilaterians. Either the ancestor was holopelagic (and therefore planktotrophic) [...]

Simultaneous hermaphrodites offer the chance to study antagonistic coevolution between the sexes when individuals function in both roles. Traumatic mating by hypodermic insemination has repeatedly evolved in hermaphroditic taxa, but evidence for the fitness costs of such male-advantage traits is lacking. When reared in isolation, specimens of the sea slug Alderia willowi (Opisthobranchia: Sacoglossa) initially laid clutches of unfertilized eggs but 4 days later began self-fertilizing; this is only the third report of selfing inan Alderia if penetration of the body wall bypasses internal mechanisms that promote outcrossing. Selfing specimens and slugs reared inpairs had reduced fecundity compared to isolated slugs laying unfertilized clutches, suggesting that hypodermic insemination imposes a cost of mating. Egg production increased for field-caught slugs separated after mating compared to slugs held in pairs, a further indication that accessibility to mates imposes a fitness cost to the female function. Such antagonism can confer a competitive advantage to slugs mating in the male role but diminish reproduction in the female role among hermaphrodites capable of long-term sperm storage. Alderia willowi is also a rare case of poecilogony, with adults producing either plankitotrophic or lecithotrophic larvae. Our rearing studies revealed that most slugs switched between expressed development models at some point; such reproductive flexibility within individuals is unprecedented, even among poecilogonous species., Introduction Sexually antagonistic traits that confer a male advantage are commonplace in animals (Rice, 1996; Partridge and Hurst, 1998; Arnqvist and Rowe, 2005). Physical features include genital armature and other [...]

Chemoautorophs that fix carbon by the reductive tricarboxylic acid cycle represent one of the dominant bacterial life forms that make a major contribution to bio-mass production. From the viewpoint of biogenesis, construction of a canonical chart of intermediary metabolism for this class of organisms may help us to understand early cellular evolution and point us to the last universal common ancestor. Data-mining the KEGG Pathways database enabled us to integrate required biosynthetic pathways and derive a chart that represents the complete anabolic network of a reductive chemoautotroph. Compounds of this metabolic network together constitute a representative minimal metabolome that comprises 287 metabolites. These compounds have been classified into different groups including those compounds that form nodes in the network. It can be seen that a relatively sparse set of organic chemical reactions dominate the anabolic synthesis in the assembly of the minimal autotrophic metabolome. Empirical generalizations that result from analyzing this metabolic network may aid in elucidating selection rules that govern its emergence and further evolution and may also help in delineating attributes that impart the observed robustness to these metabolites., Introduction Metabolic charts have been a central feature in the study of biochemistry since Donald Nicholson developed his first Metabolic Pathways Chart in 1955 (Nicholson, 2006). A printed version was [...]

Neuroecology unifies principles from diverse disciplines, scaling from biophysical properties of nerve and muscle cells to community-wide impacts of trophic interactions. Here, these principles are used as a common fabric, woven from threads of chemosensory physiology, behavior, and population and community ecology. The 'keystone species' concept, for example, is seminal in ecological theory. It defines a species whose impacts on communities are far greater than would be predicted from its relative abundance and biomass. Similarly, neurotoxins could function in keystone roles. They are rare within natural habitats but exert strong effects on species interactions at multiple trophic levels. Effects of two guanidine alkaloids, tetrodotoxin (TTX) and saxitoxin (STX), coalesce neurobiological and ecological perspectives. These molecules compose some of the most potent natural poisons ever described, and they are introduced into communities by one, or only a few, host species. Functioning as voltage-gated sodium channel blockers for nerve and muscle cells, TTX and STX serve in chemical defense. When borrowed by resistant consumer species, however, they are used either in chemical defense against higher order predators or for chemical communication as chemosensory excitants. Cascading effects of the compounds profoundly impact community-wide attributes, including species compositions and rates of material exchange. Thus, a diverse array of physiological traits, expressed differentially across many species, renders TTX and STX fully functional as keystone molecules, with vast ecological consequences at multiple trophic levels., Introduction A wide range of critical ecological interactions are mediated by chemistry. Biological responses to environmental chemical stimuli abound. Sensory perception of chemical signals, for example, strongly influences predation (Nevitt [...]

Given the current trends, it seems inevitable that all biological documents will eventually exist in a digital format and be distributed across the internet. New network services and tools need to be developed to increase retrieval rates for documents and to refine data recovery. Biological data have traditionally been well managed using taxonomic principles. As part of a larger initiative to build an array of names-based network services that emulate taxonomic principles for managing biological information, we undertook the digitization of a major taxonomic reference text, Nomenclator Zoologicus. The process involved replicating the text to a high level of fidelity, parsing the content for inclusion within a database, developing tools to enable expert input into the product, and integrating the metadata and factual content within taxonomic network services. The result is a high-quality and freely available web application (http://uio.mbl.edu/NomenclatorZoologicus/) capable of being exploited in an array of biological informatics services., Introduction In 1969, Raath described a new species of dinosaur with fused foot bones that he named 'Syntarsus,' (Raath, 1969), unaware that a hundred years earlier a beetle had been [...]

The vast majority of microorganisms in the environment remain uncultured, and their existence is known only from sequences retrieved by PCR. As a consequence, our understanding of the ecological function of dominant microbial populations in the environment is limited. We will review microbial diversity studies and show that these may have moved from an extreme underestimation to a potentially severe overestimation of diversity. The latter results from a simple PCR-generated artifact: the cloning of heteroduplex molecules followed by Escherichia coli mismatch repair, which may generate an exponential increase in observed sequence diversity. However, simple modifications to current PCR amplification protocols minimize such art if actual sequences and may bring within our reach estimation of bacterial diversity in environmental samples. Such estimates may spur new culture-independent approaches based on genomic and microarray technology, allowing correlation of phylogenetic identity with the ecological function of unculturable organisms. In particular, we are developing a DNA microarray that enables identification of individual populations active in utilization of specific organic substrates. The array consists of 16S and 23S rDNA-targeted oligonucleotides and is hybridized to RNA extracted from samples incubated with [14.sup.C-labeled] organic substrates. Populations that metabolize the substrate can be identified by the radiolabel incorporated in their rRNA after only one to two cell doublings, ensuring realistic preservation of community structure. Thus, the microarray approach may provide a powerful means to link microbial community structure with in situ function of individual populations., The last two decades have seen a radical shift in our understanding of microbial diversity. Previously the number of bacterial and archaeal species had been estimated to be in the [...]

Bacteria that live exclusively within eukaryotic host cells include not only well-known pathogens, but also obligate mutualists, many of which occur in diverse insect groups such as aphids, psyllids, tsetse flies, and the ant genus Camponotus (Buchner, 1965; Douglas, 1998; Moran and Telang, 1998; Baumann et al., 2000; Moran and Baumann, 2000). In contrast to intracellular pathogens, these primary (P) endosymbionts of insects are required for the survival and reproduction of the host, exist within specialized host cells called bacteriocytes, and undergo stable maternal transmission through host lineages (Buchner, 1965; McLean and Houk, 1973). Due to their long-term host associations and close phylogenetic relationship with well-characterized enterobacteria (Fig. 1), P-endosymbionts of insects are ideal model systems to examine changes in genome content and architecture that occur in the context of beneficial, intracellular associations. Since these bacteria have not been cultured outside of the host cell, they are difficult to study with traditional genetic or physiological approaches. However, in recent years, molecular and computational approaches have provided important insights into their genetic diversity and ecological significance. This review describes some recent insights into the evolutionary genetics of obligate insect-bacteria symbioses, with a particular focus on an intriguing association between the bacterial endosymbiont Blochmannia and its ant hosts., The specific functions of most insect P-endosymbionts remain unknown. However, the typically unbalanced diets of their hosts suggest these bacteria play a nutritional role. In fact, nutritional functions are well [...]

This review focuses on mycorrhizas, which are associations between fungi and the roots of 90% of terrestrial plants. These are the most common symbioses in the world; they involve about 6000 species of fungi distributed through all the fungal phyla and about 240,000 species of plants, including forest and crop plants. Thanks to mycorrhizal symbiosis and nutrient exchanges, regulated by complex molecular signals, the plant improves its vegetative growth, while the fungus accomplishes its life cycle. Molecular and cellular analyses demonstrate that during colonization the cellular organization of the two eukaryotes is completely remodeled. For example, in cortical cells, structural modifications involve both the host and the microbiont. Recent studies revealed that in arbuscular mycorrhizas (AM), system complexity is increased by the presence of a third symbiont: a bacterium living inside the fungus. The presence of this resident genome makes the investigation of the molecular dialogues among the symbiotic part ners even more complex. Molecular analysis showed that the bacterium has genes involved in the acquisition of mineral nutrients. The experimental data support the current view that mycorrhizal symbioses are often tripartite associations., Endosymbioses are excellent systems with which to investigate the dialog among genomes and cells. The aim of this short report is to demonstrate that mycorrhizas are of particular interest in [...]

Spain's Rio Tinto, or Red River, an example of an extremely acidic (pH 1.7-2.5) environment with a high metal content, teems with prokaryotic and eukaryotic microbial life. Our recent studies based on small-subunit rRNA genes reveal an unexpectedly high eukaryotic phylogenetic divershy in the river when compared to the relatively low prokaryotic diversity. Protists can therefore thrive in and dominate extremely acidic, heavy-metal-laden environments. Further, because we have discovered protistan acidophiles closely related to neutrophiles, we can hypothesize that the transition from neutral to acidic environments occurs rapidly over geological time scales. How have these organisms adapted to such environments? We are currently exploring the alterations in physiological mechanisms that might allow for growth of eukaryotic microbes at acid extremes. To this end, we are isolating phylogenetically diverse protists in order to characterize and compare ion-transporting ATPases from cultured acidophiles with those f rom neutrophilic counterparts. We predict that special properties of these ion transporters allow protists to survive in the Rio Tinto., Earth harbors many extreme environments. Previous investigations of the microbial diversity in these environments have been constrained by preconceived notions about the range of habitability for both eukaryotic and prokaryotic [...]

Symbiotic associations are fundamental to the survival of many organisms on Earth. The ability of the symbiont to perform key biochemical functions often allows the host to occupy environments that it would otherwise find inhospitable. This can have profound impacts upon the diversification and distribution of the host. Cellular organelles (chloroplasts and mitochondria) represent the final stages of integration of endosymbionts. These organelles were of critical importance to the evolution and success of eukaryotic lineages on our planet because they allowed the host cells to harness light energy and to thrive in the presence of oxygen. The marine photosymbiotic associations that we study represent an earlier stage in the process of symbiont integration--one in which the photobiont can still be removed from the host and exist on its own. These systems are of interest to us for two reasons. First, they are ecologically important in the marine environment where they occur. These organisms form zones of photosy nthetic production in oceanic regions typically low in nutrients. Second, investigation of these interactions may shed light on the molecular and evolutionary mechanisms involved in the integration of cells and their genomes., Associations between microbial symbionts and their hosts are fundamental trophic relationships that occur in both terrestrial and aquatic environments and depend upon regulated genomic communication between the interacting organisms. We [...]

Genomic markers for anaerobic microbial processes in marine sediments--sulfate reduction, methano genesis, and anaerobic methane oxidation--reveal the structure of sulfate-reducing, methanogenic, and methane-oxidizing microbial communities (including uncultured members); they allow inferences about the evolution of these ancient microbial pathways; and they open genomic windows into extreme microbial habitats, such as deep subsurface sediments and hydrothermal vents, that are analogs for the early Earth and for extraterrestrial microbiota., Sulfate reduction and methanogenesis are two terminal anaerobic bioremineralization pathways that convert low-molecular-weight products of other bacterial processes (degradation of polymers, fermentation) to [CO.sub.2] and methane. Sulfate-reducing bacteria are physiologically [...]

The goal of this project is to describe and understand the organismal composition, structure, and physiology of microbial ecosystems from hypersaline environments. One collection of such ecosystems occurs at North America's largest saltworks, the Exportadora de Sal, in Guerrero Negro, Baja California Sur. There, seawater flows through a series of evaporative basins with an increase in salinity until saturation is reached and halite crystallization begins. Several of these ponds are lined with thick (10 cm) microbial mats that have received some biological study. To determine the nature and extent of diversity of the microbial organisms that constitute these ecosystems, we are conducting a phylo genetic analysis using molecular approaches, based on cloning and sequencing of small subunit (SSU) rRNA genes (16S for Bacteria and Archaea, 18S for Eukarya). In addition, we report preliminary results on the microbial composition of a laminated community that occurs in a crystallized gypsum-halite matrix in near-satu rated salt water. Exposure of the interior of these large (kilogram) wet, endoevaporite crystals reveals a multitude of colors: layers of yellow, green, pink, and purple microbiota. To date, analyses of these two environments indicate the ubiquitous dominance of uncultured organisms of phylogenetic kinds not generally thought to be associated with hypersaline environments., The Endoevaporite Study The goals for this portion of the study were to examine the nature of life in the 'extreme' environment of an endoevaporite (endo-life within, evaporite-sedimentary rock of [...]

Biogeochemistry is the study of how living systems in combination with abiotic reactions process and cycle mass and energy on local, regional, and global scales (Schlesinger, 1997). Understanding how these biogeochemical cycles function and respond to perturbations has become increasingly important, as anthropogenic impacts have significantly altered many of these cycles (Galloway and Cowling, 2002; Houghton et al., 2002). Biogeochemistry is strongly governed by microbial processes, and it appears to closely follow thermodynamic constraints in that electron acceptor (02, [NO.sup.-.sub.3] [SO.sup.2-.sub.4], etc.) utilization closely follows a priori expectations based on energetics (Vallino et al., 1996; Hoehler et al., 1998; Jakobsen and Postma, 1999; Amend and Shock, 2001). Consortiums of microorganisms seem to have evolved to exploit chemical potentials wherever they exist in the environment, as manifested by the recent discovery of anaerobic methane oxidation by sulfate (Boetius et al., 2000) or sulfide ox idation by nitrate (Schulz et al., 1999). Three and a half billion years of natural selection have produced living systems capable of degrading most chemical potentials. We may therefore ask: If all ecosystem niche space is filled, is the biogeochemistry we observe in the environment dependent on the organisms that occupy that environment, or is the biogeochemistry determined by fundamental forces, with the evolution of living systems being the implementation of those forces? Recent developments in none quilibrium thermodynamics (NET) are beginning to support the latter alternative, and advances in genomics are allowing us to explore microbial consortiums in detail. Taking advantage of ideas being suggested by NET, we have developed a modeling framework that views microbial consortiums as an inter-species distributed metabolic network. When combined with experimental observations, the model should help us test hypotheses that govern how living systems function., The main challenge to understanding microbial biogeochemistry is understanding the complex, but mostly cooperative, metabolism that develops among organisms that orchestrate biogeochemical cycles. Consider, for example, the metabolism found in [...]

The deposition of four crystal types at the growth surface of the septa of several color morphs of the coral Galaxea fascicularis was investigated over a 24-h period. Results suggest that nanocrystals, on denticles at the apices of exsert septa, may be the surface manifestation of centers of calcification. These crystals were also found on the septa of the axial corallite of Acropora formosa. The deposition of nanocrystals appears to be independent of diurnal rhythms. Internally and proximal to the septal apices, distinct clusters of polycrystalline fibers originate from centers of calcification and form fanlike fascicles. Upon these fascicles, acicular crystals grow and extend to form the visible fasciculi at the skeletal surface. Deposition of aragonitic fusiform crystals in both G. fascicularis and A. formosa occurs without diurnal rhythm. Nucleation of fusiform crystals appears to be independent of centers of calcification and may occur by secondary nucleation. Formation of semi-solid masses by fusiform crystals suggests that the crystals may play a structural role in septal extension. Lamellar crystals, which have not been reported as a component of scleractinian coral skeletons before, possess distinct layers of polyhedral plates, although these layers also do not appear to be associated with daily growth increments. The relationship of lamellar crystals to other components of the scleractinian coral skeleton and their involvement in skeletal growth is unknown., Introduction The microstructural components of the [CaCO.sub.3] skeleton from a wide range of scleractinian corals have been well documented (see Wainwright, 1963; Vahl, 1966; Sorauf, 1970, 1972, 1974, 1980; Wise, [...]

Settlement and metamorphosis in most well-studied marine invertebrates are rapid processes, triggered by external cues. How this initial environmentally mediated response is transduced into morphogenetic events that culminate in the formation of a functional juvenile is still not well understood for any marine invertebrate. The response of larvae of the serpulid polychaete Hydroides elegans to inhibitors of mRNA and protein synthesis was examined to determine if metamorphosis requires these molecular processes. Competent larvae of H. elegans were induced to metamorphose by exposing them to a bacterial film or a 3-h pulse of 10 mM CsCl in the presence of the gene-transcription inhibitor DRB (5,6-dichloro- 1-jβ-D-ribofuranosylbenzimidazole) or the translation inhibitor emetine. When induced to metamorphose in the presence of either inhibitor, larvae of H. elegans progressed through metamorphosis to the point at which branchial radioles start to develop. DRB and emetine inhibited the incorporation of radiolabeled uridine into RNA and radiolabeled methionine into peptides, respectively, indicating that they were effective in blocking the appropriate syntheses. Taken together, these results indicate that the induction of metamorphosis in H. elegans does not require de novo transcription or translation, and that the form of the juvenile worm is achieved in two phases. During the first phase, larvae respond to the inducer by attaching to the substratum, secreting a primary tube, resorbing the prototroch cilia, undergoing caudal elongation, and differentiating the collar; once the collar is formed, they begin secreting the secondary, calcified tube. During the second phase, the small worm develops branchial radioles and begins to grow, requiring new mRNA and protein syntheses., Introduction Complex life histories in which a larval stage undergoes metamorphosis to achieve a juvenile form are common throughout the animal kingdom, including at least 15 phyla of marine invertebrates [...]

Photosynthetic microbial mats are remarkably complete self-sustaining ecosystems at the millimeter scale, yet they have substantially affected environmental processes on a planetary scale. These mats may be direct descendents of [...]

The movements of the basis of maxilla 2 in Palaemon adspersus were examined using macro-video recordings, and the morphology of its setae was examined using both scanning and transmission electron microscopy. The basis of maxilla 2 performs stereotypical movements in the latero-medial plane and gently touches the food with a frequency of 3-5 Hz. The medial rim of the basis of maxilla 2 carries three types of seta. Type 1 is serrate, type 2 and 3 are serrulate, and type 2 has a prominent terminal pore. Type 2 is innervated by 18-25 sensory cells whose cilia protrude through the terminal pore and are in direct contact with the external environment. The structure of type 2 setae indicates that they are mainly gustatory, although still bimodal due to their innervation by presumed chemosensory and mechanosensory neurons. Distally, the three types of setae have a complex arrangement of the cuticle involving water-filled canals, which may serve to improve flexibility. Type 1 and 3 setae have fewer sensory cells (4-9) but probably also have a bimodal sensory function. The function of type 1 setae is probably to protect type 2 setae, while type 3 setae might serve to groom the ventral side of the basis of maxilla 1., Introduction The decapod mouth apparatus comprises six pairs of limbs, which have as many as 40 parts capable of independent movement (Garm and H0eg, 2001). The parts, which are arranged [...]

Coral reef invertebrates that host phototrophic symbionts are thought to protect themselves and their symbionts with mycosporine-like amino acids (MAAs)--UV-absorbing substances that act as sunscreens (Dunlap, W. C., and J. M. Shick, 1998. J. Phycol. 34: 418-430). However, the histological distribution of MAAs in the host tissues has not yet been visualized. We have localized the U V-absorbing substances in the tissues of two colonial didemnid ascidians--Lissoclinum patella and Diplosoma sp.-that contain the symbiotic photo-oxygenic prokaryote Prochioron sp. Cross-sections of unfixed tissue from these ascidians were examined by U V-light microscopy at 320 or 330 nm, wavelengths at which UV light is absorbed by MAAs. Within the tunic, the gelatinous integument of the colony, UV light was exclusively absorbed by a particular type of cell, the tunic bladder cell. Tunic bladder cells with strong UV absorption were denser in the upper tunic, which lies over a colony's zooids, than in the basal tunic underlying the zooid. In the upper tunic, those cells with strong UV absorption were most dense near the surface. The tunic bladder cell is highly vacuolated, and the vacuole contains strong acid, which destabilizes MAAs. Furthermore, the UV-absorbing portion of tunic bladder cells seemed to be cup-shaped, indicating that the MAAs are not localized in the vacuole, but in the cytoplasm. These results strongly suggest that didemnid ascidians accumulate MAAs in tunic bladder cells as a protection against UV radiation., Ultraviolet (UV) radiation poses severe problems for organisms in tropical marine environments, because the path for sunlight through the atmosphere is shorter (1) and the seawater is clearer (2). Since [...]

Abstract. The copepod Acartia tonsa exhibits a vigorous escape jump in response to rapid decreases in light intensity, such as those produced by the shadow of an object passing above [...]

Abstract. Gelatinous zooplankton are the least understood of all planktonic animal groups. This is partly due to their fragility, which typically precludes the capture of intact specimens with nets or [...]

Abstract. Entamoeba histolytica and Spironucleus barkhanus have genes that encode short iron-dependent hydrogenases (Fe-hydrogenases), even though these protists lack hydrogenosomes. To understand better the biochemistry of the protist Fe-hydrogenases, we [...]

The freshwater eels have fascinated biologists because of their spectacular long-distance migrations between their freshwater habitats and their spawning areas far out in the ocean (1, 2, 3). Recent progress [...]

Abstract. Microscopic and cytological evidence suggest that many dinoflagellates possess a haploid nuclear phase. However, the ploidy of a number of dinoflagellates remains unknown, and molecular genetic support for haploidy [...]

Abstract. This study was meant to analyze the neural control of the branchial muscles of the clam Mercenaria mercenaria. Gills isolated from the animal contract in response to 5-hydroxytryptamine (5HT), [...]

Abstract. The lack of quantitative data on the environmental tolerances of the early life-history stages of invading species hinders estimation of their dispersal rates and establishment ranges in receptor environments. [...]

Abstract. Analyses of life-history data show that both the size-specific batch fecundities and the age-specific spawning frequencies differ for two halfbeak species, Hemiramphus brasiliensis, the ballyhoo, and H. balao, the [...]

Abstract. An important lipoprotein in the hemolymph of crustaceans is LpI. It transports lipid to peripheral tissues and also has a role in crustacean immune recognition. We employed a monoclonal [...]

Abstract. Limulus polyphemus, the American horseshoe crab, has a single type of circulating blood cell, the granular amebocyte, which is the horseshoe crab's primary cellular defense against microbial infection. On [...]

Abstract. The thermoregulatory behavior of Hemigrapsus nudus, the amphibious purple shore crab, was examined in both aquatic and aerial environments. Crabs warmed and cooled more rapidly in water than in [...]

Abstract. Previous workers have demonstrated that sessile filter feeders compete for food and space, but little is known about the relative strengths of these two processes. To determine this, the density and position of barnacles (Balanus improvisus) in a unidirectional current were manipulated to alter the amount of competition for space and food, respectively. Results indicated that competition for space significantly reduced growth, and marginally reduced survivorship. Competition for food was also detected, but only among uncrowded individuals; thus, it appears to be the weaker of the two interactions. However, under crowded conditions, downstream individuals actually grew more than those upstream. The most likely explanation for this result is that downstream individuals fed more efficiently because they were not exposed to the full force of the current. The results also suggest that since natural densities started high but continually decreased throughout the study, barnacles undergo an ontogenetic shi ft in the relative importance of these processes., Introduction Because all organisms need a place to live, it is not unreasonable for ecologists to consider competition for space a potentially important interaction. However, for some organisms access to [...]

Abstract. Two clades of marine bryozoans, cyclostomes and cheilostomes, exemplify the benefits of applying a multidisciplinary approach to the interpretation of long-term evolutionary patterns. The cyclostome bryozoans were dominant in the Mesozoic; since that era, they have decreased in absolute terms and the cheilostomes have come to exceed them in both abundance and diversity. Many studies of living assemblages of the encrusting members of these two clades indicate that cheilostomes are superior space competitors, but paleontological studies suggest that competition between the two taxa has not been escalating over geological time. Both clades occur throughout the world's oceans and seas, and recent work in the geographical extremes has shown that the relative success of the clades varies markedly from place to place. In this study, the importance of differential patterns of recruitment and cumulative space occupation in the two clades was evaluated over four years and in two environments, one temperate an d one polar. In both of these environments, peaks of recruitment and space occupation by the two clades were out of phase. The different strategies and outcomes of spatial competition are examined, largely using data from the literature. Only recently has it been realized that tied outcomes of competition are stable alternative results and not simply transitory phases. Many competitive encounters involving cyclostomes result in ties, implying that their strategy is based on persistence rather than dominance. When different indices and models are used to analyze competition data from the two clades, the interpretation varies markedly with methodology. The differences in patterns of recruitment, space occupation, and spatial competition have influenced both our understanding of how the two clades have persisted alongside each other and our perception of cheilostome superiority. Analysis of fluid dynamics has shown that small differences in the mechanical structure of typical members of each clade lead to fundam ental differences in water movement. For animals that rely on water motion for transport of nutritional and excretory elements (suspension feeders), small changes in current velocity and direction can have a major impact. Preliminary chemical analysis of the excurrent stream leaving cheilostome colonies has shown it to be laden with excretory products, which can interfere and mix with a neighbor's feeding currents. Clearly, spatial competition involves more than a simple mechanical 'showdown.', Introduction During the past two decades, taxon perseverance through geological time has been the center of much paleontological study, which has usually been focused on mass extinctions and radiations. Although [...]

Abstract. In a previous study, we described complete body regeneration (with organogenesis) following surgical bisection in the planktotrophic larvae of the asteroids Luidia foliolata and Pisaster ochraceus. Here we present further detailed observations of these unique regenerative processes not presented in the previous paper. Furthermore, we describe for the first time complete regeneration following surgical bisection of planktotrophic larvae of the regular echinoid Lytechinus variegatus and the irregular echinoid Dendraster excentricus. Larvae of both asteroids and echinoids displayed a capacity for rapid regeneration regardless of their developmental stage. Within 48 h after bisection, aggregations of mesenchyme cells with pseudopodia were observed at the site of surgical bisection. These cellular aggregations were similar in appearance to the mesenchymal blastemas that form in adult echinoderms prior to their arm regeneration, and to those described in other deuterostomes that undergo regeneration. When asteroid larvae were surgically bisected in the early stages of their development, clusters of mesenchyme cells developed into completely new pairs of coelomic pouches located anterior to the newly regenerated digestive tract. This indicates that cell fate in regenerating asteroid larvae remains indeterminate during early development. In the larvae of P. ochraceus, regardless of the developmental stage at the time of bisection, both the anterior and posterior portions regenerated all their missing organs and tissues. However, the larvae of L. foliolata displayed differential regenerative capacity in bisected larval halves at the late bipinnaria stage. The differences observed may be due to differences in larval development (L. foliolara has no brachiolaria stage), and may have evolutionary implications. In the regular echinoid L. variegatus, both larval portions regenerated into morphologically and functionally normal larvae that were indistinguishable from non-bisected control larvae. The regenerative proce sses were similar to those we observed in planktotrophic asteroid larvae. Regenerating larvae readily metamorphosed into normal juveniles. In the irregular echinoid D. excentricus, posterior portions of larvae completed regeneration and metamorphosis, but anterior portions regenerated only partially during the 2-week study. Our observations confirm that asteroid and echinoid larvae provide excellent models for studies of regeneration in deuterostomes., Introduction Regeneration has been described at both the cellular and the tissue level in many animals including planarians, crustaceans, reptiles, and amphibians (Goss, 1969; Mattson, 1976; Baguna et al., 1989; [...]

Abstract. Swimming in the nudibranch Melibe leonina consists of five types of movements that occur in the following sequence: (1) withdrawal, (2) lateral flattening, (3) a series of lateral flexions, (4) unrolling and swinging, and (5) termination. Melibe swims spontaneously, as well as in response to different types of aversive stimuli. In this study, swimming was elicited by contact with the tube feet of the predatory sea star Pycnopodia helianthoides, pinching with forceps, or application of a 1 M KC1 solution. During an episode of swimming, the duration of swim cycles (2.7 ± 0.2 s [mean ± SEM], n = 29) and the amplitude of lateral flexions remained relatively constant. However, the latency between the application of a stimulus and initiation of swimming was more variable, as was the duration of an episode of swimming. For example, when touched with a single tube foot from a sea star (n = 32), the latency to swim was 7.0 ± 2.4 s, and swimming continued for 53.7 ± 9.4 s, whereas application of KC1 resulted in a longer latency to swim (22.3 +/- 4.5 s) and more prolonged swimming episodes (174.9 ± 32.1 s). Swimming individuals tended to move in a direction perpendicular to the long axis of the foot, which propelled them laterally when they were oriented with the oral hood toward the surface of the water. The results of this study indicate that swimming in Melibe, like that in several other molluscs, is a stereotyped fixed action pattern that can be reliably elicited in the laboratory. These characteristics, along with the large identifiable neurons typical of many molluscs, make swimming in this nudibranch amenable to neuroethological analyses., Introduction Swimming is a common form of locomotion in marine gastropods. It has been described for at least 47 species (reviewed by Farmer, 1970), and the neural mechanisms underlying swimming [...]

Abstract. Spermatogenesis and mature sperm morphology have been described along with limited observations of the ovary in Methanoaricia dendrobranchiata, an orbiniid polychaete associated with dense populations of the mussel Bathymodiolus childressi at brine pools on the Louisiana slope, Gulf of Mexico. The species is gonochoric with gonads serially repeated in numerous segments and each associated with a nexus of blood vessels at the base of the parapodia. In the female, synchronous, intraovarian egg development occurs with the release from the ovary of large, yolky eggs into the coelom at first meiotic metaphase. Sperm develop in the coelom as free-floating, plasmodial clones interconnected via an anuclear cytophore. At the end of spermiogenesis, mature spermatozoa float freely in the coelom. The mature spermatozoon differs significantly from that of shallow-water orbiniid species by possessing an elongated nucleus and a greatly elongated and curved acrosome reaching 19.5 µm in length. The spermatozoo n resembles an ent-aquasperm and may not fertilize the eggs directly in seawater in the classical manner. We hypothesize that the unusual spermatozoon morphology in this species has evolved due to the hypoxic environment in which the adults live and that fertilization biology is likely modified in some way to minimize sperm exposure to high levels of hydrogen sulfide. An analysis of life-history features in shallow-water orbiniids is used to infer reproductive features in M. dendrobranchiata that could not be directly documented., Introduction The reproductive biology of invertebrates from deep-sea hydrothermal vents and cold methane seeps continues to receive a great deal of attention (Tyler and Young, 1999). Hydrothermal vents and cold-water [...]

Heterogeneous, 'aggregated' patterns in the spatial distributions of individuals are almost universal across living organisms, from bacteria to higher vertebrates. Whereas specific features of aggregations are often visually striking to human eyes, a heuristic analysis based on human vision is usually not sufficient to answer fundamental questions about how and why organisms aggregate. What are the individual-level behavioral traits that give rise to these features? When qualitatively similar spatial patterns arise from purely physical mechanisms, are these patterns in organisms biologically significant, or are they simply epi-phenomena that are likely characteristics of any set of interacting autonomous individuals? If specific features of spatial aggregations do confer advantages or disadvantages in the fitness of group members, how has evolution operated to shape individual behavior in balancing costs and benefits at the individual and group levels? Mathematical models of social behaviors such as schooling in fishes provide a promising avenue to address some of these questions. However, the literature on schooling models has lacked a common framework to objectively and quantitatively characterize relationships between individual-level behaviors and group-level patterns. In this paper, we briefly survey similarities and differences in behavioral algorithms and aggregation statistics among existing schooling models. We present preliminary results of our efforts to develop a modeling framework that synthesizes much of this previous work, and to identify relationships between behavioral parameters and group-level statistics., Types of Aggregations Aggregation occurs in the smallest organisms--bacteria--and the largest--whales--and spans virtually the entire extant diversity of taxon, habitat, trophic level, life-history strategy, degree of mobility, and many other [...]

Leaf-cutting ants cut vegetation into small fragments that they transport to the nest, where a symbiotic fungus cultivated by the ants processes the material. Since the harvested leaf fragments are incorporated into the fungus garden and not directly consumed by the workers, it is expected that foraging workers select plants by responding to those physical or chemical traits that promote maximal fungal growth, irrespective of the potential direct effects of these leaf features on them. In this paper I summarize experimental work focusing on the decision-making processes that occur at the individual level, and discuss to what extent individual complexity contributes to the emergence of collective foraging patterns. Although some basic features of self-organizing systems, such as the existence of regulatory positive and negative feedback loops, are expected to be involved in the collective organization of leaf-cutting ant foraging, I contend that they are combined with complex individual responses tha t may result from the integration of local information during food collection with an assessment of colony conditions., Social Foraging in Leaf-Cutting Ants: Self-Organized? Leaf-cutting ants are the dominant herbivores in the Neotropics. They cut vegetation into small fragments that they transport to the nest, which may contain [...]

Self-organization, or decentralized control, is widespread in biological systems, including cells, organisms, and groups. It is not, however, the universal means of organization. I argue that a biological system will be self-organized when it possesses a large number of subunits, and these subunits lack either the communicational abilities or the computational abilities, or both, that are needed to implement centralized control. Such control requires a well informed and highly intelligent supervisor. I stress that the subunits in a self-organized system do not necessarily have low cognitive abilities. A lack of preadaptations for evolving a system-wide communication network can prevent the evolution of centralized control. Hence, sometimes even systems whose subunits possess high cognitive abilities will be self-organized., Introduction Self-organization is widespread in biological systems. That is to say, it is common to find biological systems that function without guidance from an external controller, or even from an [...]

The numbers of brood cells in nests built by founding swarms of the Neotropical social wasp Polybia occidentalis closely correlate with the numbers of wasps in the swarms. We analyzed nests of different sizes to determine how they scale with respect to the allocation of brood cells among combs. Three patterns were evident: compared to smaller nests, larger nests have (1) more combs and (2) larger combs; and (3) among nests containing the same number of combs, the last two combs diverge in relative size as nest size increases. Taken together, these results suggest that members of a swarm somehow 'know' the size of the swarm they are in. This information feeds back to individual builders, which quantitatively modulate their responses to stigmergic cues in ways that result in the nest-size-scaled allocation of brood cells among combs. The patterns also suggest that swarms fine-tune the final size of their nests by making corrections as they build., Introduction The process of nest construction by a social wasp colony does not differ fundamentally from nest construction by a solitary wasp. In each case individuals construct the nest by [...]

Differences between related species are usually explained as separate adaptations produced by individual selection. I discuss in this paper how related species, which differ in many respects, may evolve by a combination of individual selection, self-organization, and group-selection, requiring an evolutionary adaptation of only a single trait. In line with the supposed evolution of despotic species of macaques, we take as a starting point an ancestral species that is egalitarian and mildly aggressive. We suppose it to live in an environment with abundant food and we put the case that, if food becomes scarce and more clumped, natural selection at the level of the individual will favor individuals with a more intense aggression (implying, for instance, biting and fierce fighting). Using an individual-centered model, called DomWorld, I show what happens when the intensity of aggression increases. In DomWorld, group life is represented by artificial individuals that live in a homogeneous world. Individuals are extremely simple: all they do is flock together and, upon meeting one another, they may perform dominance interactions in which the effects of winning and losing are self-reinforcing. When the intensity of aggression in the model is increased, a complex feedback between the hierarchy and spatial structure results; via self-organization, this feedback causes the egalitarian society to change into a despotic one. The many differences between the two types of artificial society closely correspond to those between despotic and egalitarian macaques in the real world. Given that, in the model, the organization changes as a side effect of the change of one single trait proper to an egalitarian society, in the real world a despotic society may also have arisen as a side effect of the mutat ion of a single trait of an egalitarian species. If groups with different intensities of aggression evolve in this way, they will also have different gradients of hierarchy. When food is scarce, groups with the steepest hierarchy may have the best chance to survive, because at least a small number of individuals in such a group may succeed in producing offspring, whereas in egalitarian societies every individual is at risk of being insufficiently fed to reproduce. Therefore, intrademic group selection (selection within an interbreeding group) may have contributed to the evolution of despotic societies., Introduction The assumption that evolution occurs through a single evolutionary process is no longer tenable (e.g., see Plotkin and Odling-Smee, 1981), and multiple-level selection theories have slowly become more accepted [...]

In this paper I ask questions about the evolution of self-organized activity cycles that are found in some ant colonies. I use a computer model that generates periodic activity patterns in interacting subunits and explore the parameters of this model using a genetic algorithm in which selecting on one aspect of the system produces the distinctive self-organized pattern. The general point that I explore, using the example of activity cycles, is that the observation of a self-organized pattern does not mean that the pattern is an adaptation. Self-organized patterns can represent nonadaptive correlated responses to selection, exaptations or even selectively disadvantageous traits. Evolution of selforganized patterns requires genetic feedback between the self-organized output and the subunits that produce the pattern. Without this necessary feedback, a self-organized system does not evolve., Introduction Many features of biological complexity result from self-organization. Biological systems are, in general, global patterns produced by local interactions. The biological structures that seem closest to the ideal of [...]

Self-organization is a concept and phenomenon whereby system-level patterns spontaneously arise solely from interactions among subunits of the system. Focusing on self-organization at the organismal level, I ask the question: are the boundaries to self-organization indistinct? After reviewing a number of published definitions of self-organization, I explore the conceptual boundaries among self-organization and two similar concepts, stigmergy and self-assembly. I highlight borderline cases that may blur the distinction among these and suggest that they may indeed be conceptually indistinct and difficult to separate in practice. Consequently, I propose a classification scheme based upon three aspects: whether the stimuli to which individuals respond are quantitative or qualitative, whether positive feedback is involved, and whether interindividual interactions are direct or indirect (stigmergic). In addition, I consider several other issues about self-organization, including (1) could a self-organized system use global information? (2) what is the role of the degree of correlation of activity among individuals? and (3) what is the role of positive feedback?, Introduction Ernst Mayr, that grand old father of evolutionary biology, claims that 'classifications are necessary wherever one has to deal with diversity' (Mayr, 1982: p. 147). In this essay, I [...]

In the eggs of a wide range of animal species, various factors that determine the blastomeres' presumptive fate are known to locate unevenly within the egg. In the embryos of these animals, cleavage occurs not just to increase cell numbers, but also to distribute the factors to the respective blastomeres, resulting in cell specialization at the later stages. In the early cleavage stages, before the establishment of a device such as desmosomes to directly join the blastomeres, some other means is needed to keep the blastomeres together and maintain the relative positions among them. In this study, we found that the embryos of the starfish Astropecten scoparius lack the hyaline layer seen in sea urchin embryos and that blastomeres adhere to the fertilization envelope (FE) via filamentous cellular projections (fixing processes). Electron microscopy revealed the fixing processes to be specialized microvilli formed, after the elevation of the FE, by the elongation of short microvilli that pre-exist in un fertilized eggs. After the first cleavage, the two blastomeres separate from each other and finally attach to the FE. In the subsequent cleavages, the blastomeres undergo repeated cell division without separating from the FE. Between the blastomeres and the FE, only shortened fixing processes were observed. Destruction of the fixing processes caused release of the blastomeres from the FE and disturbance of the relative positions of the blastomeres, resulting in abnormal development of the embryos. These observations suggest that the fixing process is a device to keep the egg placed centrally in the FE up to the first cleavage, and after the first cleavage and beyond to anchor the blastomeres to the FE so that the FE can be used as a scaffold for morphogenesis. Electron microscopy also suggests that the inner layer of the FE, which is derived from the contents of cortical granules, reinforces the adhesion of the fixing processes to the FE. Immuno-electron microscopy, using an antibody against sea urchin hyalin e layer, showed that the inner layer of the FE of starfish eggs and the hyaline layer of sea urchin eggs, which are both derived from cortical granules, contain some common elements., Introduction In mammals, 'compaction' of the embryo occurs at the 8-cell stage, leading to binding of the blastomeres together (Tarkowski and Wroblewska, 1967; Hillman et al., 1972; Fleming et al., [...]

In controlled laboratory experiments, colonies of Podocoryna carnea typically overgrow and kill colonies of Hydractinia symbiolongicarpus. Generally, these experiments have used colonies grown from tissue explants (clonal replicates) surgically removed from mature colonies taken from natural populations. In contrast, experiments involving interspecific bouts between small, sexually produced colonies reveal that both the characteristics and outcomes of competition differ from previous studies. During competition between small sexually produced colonies, H. symbiolongicarpus exhibits directional growth toward P. carnea and produces nematocyte-rich hyperplastic stolons more readily than P. carnea does. Nevertheless, P. carnea can still overcome H. symbiolongicarpus if it initially grows away from the contact zone and subsequently flanks H. symbiolongicarpus. Overall, sexually produced colonies of H. symbiolongicarpus destroyed their P. carnea counterparts in more than 35% of competitive bouts, whereas P. carnea dominated their H. symbiolongicarpus counterparts in all similar encounters between clonally produced colonies. In natural populations, competition between small sexually produced colonies of H. symbiolongicarpus may predominate, and these results support the hypothesis that this species is adapted to competition early in colony development. More generally, studies of competition between sexually produced colonies should complement similar studies of clonally produced colonies., Introduction Colonial animals can be described morphologically as a collection of iterated modules or ramets interconnected by a common vascular network. The arrangement of modules and vascular connections defines two [...]

An investigation of the feeding behavior of the acorn worm Harrimania planktophilus suggests a novel form of enteropneust feeding with significant phylogenetic implications. H. planktophilus is a holoinfaunal worm that feeds on deposited sediments, and filter feeds on suspended particles in interstitial pore water. To visualize the particle retention behavior involved in filter feeding, adult animals were held in chilled seawater under low light and fed food coloring and fluorescent particles. The behavior was recorded by videography. Most particles ingested were drawn into the mouth by an incurrent flow created by cilia on the pharyngeal bars and without the aid of mucus. Particles that passed freely through the gill pores averaged 3.04 µm, whereas particles retained in the gut and defecated in the feces averaged 13.9 µm. Food coloring entered the mouth and was pumped through the pharynx at a rate of 0.5-2.0 mm/s. There is no evidence of an endostyle or mucus-net capture mechanism in H. planktoph ilus, but instead particles are filtered and manipulated by a dense covering of cilia on the pharyngeal gill bars. This study suggests that the filter-feeding pharynx is not an innovation of the chordates, but evolved prior to the evolutionary divergence of the hemichordate-echinoderm clade from the chordates., Introduction The enteropneust worms and bryozoan-like pterobranchs constitute the small deuterostome phylum Hemichordata, which is generally regarded as an early offshoot from the chordate line of evolution (Ruppert and Barnes, [...]

Taxonomic accounts of octopodids frequently describe the spermatophore, the penis that releases the spermatophore from the internal organs, and the ligula and calamus that transfer it to a female. To explore relationships among these male features and body size, this study applies principal components analysis to data from 43 species of the family Octopodidae, or benthic octopuses. Covariation in penis and mantle length opposed by covariation in ligula and calamus lengths forms primary shape variation. Secondary shape variation is due to opposing variation between ligula and calamus lengths. Primary shape variation is greatest among shallow-water species. The calami and ligulae of diurnal and crepuscular shallow-water species are short compared to those of nocturnal shallow-water species. Because these structures contain heterogeneous collagen arrays and lack camouflaging chromatophore organs, they are white. Diurnal and crepuscular octopus species may minimize their lengths due to selection imposed by visual predators. Secondary shape variation is greater in deep-sea and high-latitude octopuses. Members of Voss's Eledoninae (except Eledone) and Graneledoninae and two species of Benthoctopus have exceptionally long calami and comparatively short ligulae; these lengths vary among members of the Bathypolypodinae. Variation in spermatophore length is independent of the structures considered., Introduction Male octopuses package sperm into spermatophores as it moves from the testis to the wholly internal penis, or terminal organ. To initiate sperm transfer, the muscular penis, which is [...]

The production of triploid shellfish has proven beneficial to the aquaculture industry since triploid organisms have reduced gonadal development, resulting in improved product quality and growth characteristics (1). Triploidization has been achieved for several molluscan species (2, 3, 4, 5, 6). In contrast, little is known about the effects of ploidy manipulation in decapod crustaceans. Triploidy has been induced in Penaeus chinensis and other penaeid shrimp using heat shock or cold shock, cytochalasin B, and 6-dimethylaminopurine (7, 8, 9, 10, 11). Triploidy was induced by suppression of polar body 2 in the shrimp Litopenaeus vannemei using cold shock, but resulted in poor survival for unknown reasons (11). One difficulty of ploidy manipulation in L. vannemei is the rapid sequence of meiotic events, since the polar bodies are produced at 8 and 15 min post-spawning at 28°C (12). In addition, the actual behavior of chromosomes and spindles was not addressed. Here I report that in the penaeoidean shrim p Sicyonia ingentis, inhibition of polar body 2 resulted in embryos that failed to undergo embryonic cleavage, while inhibition of polar body 1 produced oocytes with 'twin' meiosis 2 spindles followed by the simultaneous formation of two 'second' polar bodies., I performed a dose response study to determine the minimum level of cytochalasin D (CD) needed to inhibit cytokinesis in zygotes of Sicyonia ingentis. Embryonic cleavage was sensitive to CD [...]

S. M. Carr (1,*) H. D. Marshall (1) K. A. Johnstone (1) L. M. Pynn (1) G. B. Stenson (2) 'Either we do know all the varieties of beings which [...]

Brian S. T. Helmuth (1)(*) Gretchen E. Hofmann (2) Abstract. Thermal stress has been considered to be among the most important determinants of organismal distribution in the rocky intertidal zone. [...]

Sally P. Leys (1)(*) Bernard M. Degnan (2) Abstract. Ontogenetic changes in the photoresponse of larvae from the demosponge Reneira sp. were studied by analyzing the swimming paths of individual [...]

The efficiency of translational initiation depends upon the sequence context surrounding the AUG codon (1, 2, 3). A purine at position -3 contributes critically to context, but other neighboring nucleotides are also important. Nucleotide frequencies at these neighboring positions vary among distant taxa (4, 5). We have analyzed the translational initiation sites of cnidarian, echinoderm, molluscan, annelid, and crustacean sequences in nucleotide sequence databases. These taxa conform to the pattern of a strong preference for a purine at -3, but the frequencies of nucleotides at neighboring positions are characteristic for each taxon. The consensus translational initiation sequences of the marine invertebrate taxa are also different from those of vertebrates and single-celled eukaryotes. These consensus sequences are useful guides for predicting translational initiation sites in cDNA clones., The initiation of translation in eukaryotes requires the function of several complexes of proteins (6, 7, 8, 9, 10). In cap-dependent translation, a ternary complex of eukaryotic initiation factor 2B [...]