Mineralization of Alvinella polychaete tubes at hydrothermal vents

Alvinellid polychaete worms form multilayered organic tubes in the hottest and most rapidly growing areas of deep‐sea hydrothermal vent chimneys. Over short periods of time, these tubes can become entirely mineralized within this environment. Documenting the nature of this process in terms of the stages of mineralization, as well as the mineral textures and end products that result, is essential for our understanding of the fossilization of polychaetes at hydrothermal vents. Here, we report in detail the full mineralization of Alvinella spp. tubes collected from the East Pacific Rise, determined through the use of a wide range of imaging and analytical techniques. We propose a new model for tube mineralization, whereby mineralization begins as templating of tube layer and sublayer surfaces and results in fully mineralized tubes comprised of multiple concentric, colloform, pyrite bands. Silica appeared to preserve organic tube layers in some samples. Fine‐scale features such as protein fibres, extracellular polymeric substances and two types of filamentous microbial colonies were also found to be well preserved within a subset of the tubes. The fully mineralized Alvinella spp. tubes do not closely resemble known ancient hydrothermal vent tube fossils, corroborating molecular evidence suggesting that the alvinellids are a relatively recent polychaete lineage. We also compare pyrite and silica preservation of organic tissues within hydrothermal vents to soft tissue preservation in sediments and hot springs.     

Spermiogenesis and modified sperm morphology in the "seepworm" Methanoaricia dendrobranchiata (Polychaeta: Orbiniidae) from a methane seep environment in the Gulf of Mexico: implications for fertilization biology

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 microm in length. The spermatozoon 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.     

The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography

Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than previously recognised.     

Male genital organs in the eulittoral meiofaunal polychaete <Emphasis Type="Italic">Stygocapitella subterranea</Emphasis> (Annelida,Parergodrilidae): ultrastructure,functional and phylogenetic significance

The marine interstitial polychaete Stygocapitella subterranea is characterized by aberrant morphological and biological traits resembling those of clitellates and Hrabeiella periglandulata, a terrestrial polychaete species. Although clearly related to the terrestrial Parergodrilus heideri, there are distinct differences in their morphology. An ultrastructural study of the male genital organs was undertaken to look for common apomorphic features in Parergodrilidae, to find structural evidence for clarifying their reproductive biology and mode of sperm transfer. Finally it should be elucidated whether a supposed sister-group relationship of Parergodrilidae and Orbiniidae based on molecular evidence can be supported by morphological characters as well. In S. subterranea the male organs consist of an unpaired seminal vesicle, a pair of sperm ducts and two large tube-like prostate glands. These glands constitute the distal parts of the gonoducts and open ventrally on a small genital papilla in chaetiger 9. True copulatory organs or organs for storage of mature sperm are lacking. The seminal vesicle is a coelomic cavity composed of two apposed coelomic linings supplied with blood spaces. The testes are found ventrally. The prostate glands are covered by a single layer of muscle fibres running in a longitudinal/spiral direction along the gland. There are no signs of spermatophore formation in any part of the male system. Since females always carry sperm, pseudocopulation can be excluded and the likelihood of either direct transfer of sperm or hypodermic injection is discussed. The structure of genital organs reveals similarities to those of P. heideri. Gonochorism, paired seminal vesicles and two pairs of male gonoducts opening in chaetigers 9 and 10 with a distal glandular part most likely belong to the ground pattern of Parergodrilidae. The observations confirm that consistencies with either clitellates or H. periglandulata are the result of convergent evolutionary events. On the other hand, the relationship of Parergodrilidae to an orbiniid/questid clade receives support from the present data. This paper is dedicated to our scientific teacher, Professor Wilfried Westheide, who made significant contributions to the reproductive biology of interstitial polychaetes, on the occasion of his 70th birthday.     

The anatomy of Lepetella sierrai (Vetigastropoda,Lepetelloidea): implications for reproduction,feeding, and symbiosis in lepetellid limpets

The Lepetelloidea, a clade of small limpet‐shaped gastropods, can be used as a case study in continental margin and deep‐sea diversification. Lineages in this clade have been found associated with a combination of different substrates, including hydrothermal vents, seeps, wood, whale carcasses, polychaete tubes, chondrichthyan egg cases, seagrass rhizomes, algal holdfasts, crab carapaces, and sponges. Members of one lepetelloidean family, Lepetellidae, live on or inside empty tubes of members of the polychaete genus Hyalinoecia. The detailed morphology of a Mediterranean species, Lepetella sierrai Dantart & Luque 1944, was reconstructed in three dimensions from serial semi‐thin sections and compared with that of eleven other members of Lepetellidae. The hermaphroditic lepetellid limpets possessed a ciliated seminal groove, distinct testis and ovary with a common distal gonoduct, and a seminal receptacle containing mature sperm. A unique alimentary tract, with huge esophageal pouches, no true stomach, an extensive multilobed midgut, and short intestine, was present. Additionally, a bacteriocyte system throughout the entire mantle rim was revealed via light and transmission electron microscopy. This is the first recognized evidence for intracellular microbial symbiosis in lepetelloidean limpets. Semi‐thin sections showed evidence of a parasite, potentially a chitonophilid copepod, penetrating the body wall of the limpet. Hypotheses about reproductive biology, feeding, and symbiosis are presented based on anatomical features and knowledge of the habitat described herein.     

Dispersal at hydrothermal vents: a summary of recent progress

The discovery of hydrothermal vents along the Galapagos Rift in 1977 opened up one of the most dynamic and productive research themes in marine biology. In the intervening 25 years, hydrothermal vent faunas have been described from the eastern, northeastern and western Pacific, the mid-Atlantic Ridge and the Indian Ocean in the region of the Rodriguez Triple Junction. In addition, there is evidence of hydrothermal signals from the Gakkel Ridge in the Arctic, the central and southwest Indian Ridges and the Scotia Arc in Antarctica. Although often perceived as a continuous linear structure, there are many discontinuities that have given rise to separate biogeographic provinces. In addition, the intervening 25 years have seen a massive increase in our understanding of the biological processes at hydrothermal vents. However, how vents are maintained, and how new vents are colonised has been relatively poorly understood until recently. This review addresses the known larval development of vent-endemic invertebrates. The distribution of larvae in relation to the hydrothermal plume, and the ocean ridge in general, are discussed and the experimental evidence of larval longevity and transport are discussed using such variables as gene flow and larval development rates. The concept of larval dispersal along the mid-ocean ridge is discussed in relation to dispersal barriers and relates the known biogeography of hydrothermal vent systems to both local and evolutionary processes.     

Sperm storage, internal fertilization, and embryonic dispersal in vent and seep tubeworms (Polychaeta: Siboglinidae: Vestimentifera)

Vestimentiferan tubeworms are ecologically important members of deep-sea chemosynthetic communities, including hydrothermal vents and cold seeps. Some are community dominants and others are primary colonists of new vent sites; they include some of the longest living and fastest growing marine invertebrates. Their mechanisms of propagation, dispersal, and genetic exchange have been widely discussed. Direct sperm transfer from males to females has been documented in one species, Ridgeia piscesae, but others are known to discharge what are apparently primary oocytes. Brooding of embryos has never been observed in any vestimentiferan. These observations have led to the supposition that fertilization might be external in most species. Here we report sperm storage at the posterior end of the oviduct in five species, including tubeworms from both vents and seeps. We show experimentally that most eggs are inseminated internally, that fertilization rate is typically lower than 100%, that meiosis is completed after eggs are released from the female, and that the dispersal phase includes the entire embryonic period.     

Oogenesis and oocytes

The morphological features of polychaete ovarian morphology and oogenesis are reviewed. Some basic information on ovarian structure and/or oogenesis is known for slightly more than half of recognized polychaete families although comprehensive studies of oogenesis have been conducted on 0.1 of described species. Relative to other major metazoan groups, ovarian morphology is highly variable in the Polychaeta. While some species appear to lack a defined ovary, most have paired organs that are segmentally repeated to varying degrees depending on the family. Ovaries vary widely in their location but are most frequently associated with the coelomic peritoneum, parapodial connective tissue, or elements of the circulatory system. The structural complexity of the ovary is correlated with the type of oogenesis expressed by the species. In some polychaetes, extraovarian oogenesis occurs in which previtellogenic oocytes are released into the coelom from a simple ovary where differentiation occurs in a solitary fashion or in association with nurse cells or follicle cells. In other species, intraovarian oogenesis occurs in which oocytes undergo vitellogenesis within the ovary, often in association with follicle cells that may provide nutrition. Vitellogenesis probably includes both autosynthetic and heterosynthetic processes; autosynthesis involves the manufacture of yolk bodies via the proteosynthetic organelles of the oocyte whereas heterosynthesis involves the extraovarian production of female-specific yolk proteins that are incorporated into the oocyte through a receptor-mediated process of endocytosis. Variation in the speed of egg production varies widely and appears to be correlated with the vitellogenic mechanism employed. Mature ova display a wide range of egg envelope morphologies that often show some intrafamilial similarities.     

Two apparently unrelated groups of symbiotic annelids,Nautiliniellidae and Calamyzidae (Phyllodocida,Annelida), are a clade of derived chrysopetalid polychaetes

Nautiliniellidae Miura and Laubier, 1989 is a small family of marine polychaetes with 20 currently described species in 11 genera, most of which are known to live symbiotically in the mantle cavity of bivalves, mainly from cold seeps and hydrothermal vents, while Calamyzidae (Hartmann‐Schröder, 1971) including only one described species, Calamyzas amphictenicola Arwidsson 1932 lives as an ectoparasite on ampharetid polychaetes in Swedish waters. Nautiliniellidae and Calamyzidae have both been considered to belong to Phyllodocida, but the few phylogenetic studies including these taxa have found their positions unstable. The internal relationships within Nautiliniellidae are also poorly understood. Using molecular information from both nuclear and mitochondrial genes and morphological data we assessed the systematic placement of Nautiliniellidae (seven species; collected from Pacific hydrothermal vents and cold seeps and one from Atlantic waters) and Calamyzas amphictenicola. Our results show that C. amphictenicola and Nautiliniellidae formed a well‐supported clade that is nested within Chrysopetalidae, a free‐living group of polychaetes. The chrysopetalid genus Vigtorniella Kiseleva 1992; a bacterial mat grazer found at methane seeps, anoxic basins and whalefalls, formed a paraphyletic grade with respect to the Nautiliniellidae–Calamyzas clade. The internal relationships within the Nautiliniellidae–Calamyzas clade as well as the relationships with their hosts are also examined. As a result we synonymize Calamyzidae and Nautiliniellidae with Chrysopetalidae, with the last as the oldest available family‐group name. Within Chrysopetalidae we refer to the subfamilies Chrysopetalinae Ehlers 1864; Dysponetinae Aguado, Nygren & Rouse, herein; and Calamyzinae Hartmann‐Schröder, 1971. Calamyzinae contains C. amphictenicola, all taxa formerly in Nautiliniellidae, and the chrysopetalid genus Vigtorniella.     

Development and cross‐amplification of nine polymorphic microsatellite markers in the deep‐sea hydrothermal vent polychaete Branchipolynoe seepensis

The hydrothermal vent polychaete Branchipolynoe seepensis lives commensally inside the mantel cavity of the bivalves Bathymodiolus azoricus and Bathymodiolus puteoserpentis that form dense mussel beds around hydrothermal vents on the Mid‐Atlantic Ridge. In order to study its dispersal capabilities and the way individuals develop and reproduce, nine microsatellite polymorphic markers were developed. Polymorphism was tested from three well‐separated populations ranging from 14°N to 35°N along the ridge and showed significant levels of genetic differentiation. Cross‐amplification tests in other polynoid species revealed that most loci could also be useful to study closely related species from both Atlantic and Pacific sites.     

Novel and diverse integron integrase genes and integron-like gene cassettes are prevalent in deep-sea hydrothermal vents

The lack of information about mobile DNA in deep-sea hydrothermal vents limits our understanding of the phylogenetic diversity of the mobile genome of bacteria in these environments. We used culture-independent techniques to explore the diversity of the integron/mobile gene cassette system in a variety of hydrothermal vent communities. Three samples, which included two different hydrothermal vent fluids and a mussel species that contained essentially monophyletic sulfur-oxidizing bacterial endosymbionts, were collected from Suiyo Seamount, Izu-Bonin, Japan, and Pika site, Mariana arc. First, using degenerate polymerase chain reaction (PCR) primers, we amplified integron integrase genes from metagenomic DNA from each sample. From vent fluids, we discovered 74 new integrase genes that were classified into 11 previously undescribed integron classes. One integrase gene was recorded in the mussel symbiont and was phylogenetically distant from those recovered from vent fluids. Second, using PCR primers targeting the gene cassette recombination site (59-be), we amplified and subsequently identified 60 diverse gene cassettes. In multicassette amplicons, a total of 13 59-be sites were identified. Most of these sites displayed features that were atypical of the features previously well conserved in this family. The Suiyo vent fluid was characterized by gene cassette open reading frames (ORFs) that had significant homologies with transferases, DNA-binding proteins and metal transporter proteins, while the majority of Pika vent fluid gene cassettes contained novel ORFs with no identifiable homologues in databases. The symbiont gene cassette ORFs were found to be matched with DNA repair proteins, methionine aminopeptidase, aminopeptidase N, O-sialoglycoprotein endopeptidase and glutamate synthase, which are proteins expected to play a role in animal/symbiont metabolism. The success of this study indicates that the integron/gene cassette system is common in deep-sea hydrothermal vents, an environment type well removed from anthropogenic disturbance.     

Experimental ecology at deep-sea hydrothermal vents: a perspective

In situ and laboratory experiments conducted over the past quarter of a century have greatly increased our understanding of the ecology of deep-sea hydrothermal systems. Early experiments suggested that chemosynthetic primary production constituted the principal source of organic matter for biological communities associated with vents, although subsequent studies have revealed many complexities associated with interactions between microbes and higher organisms inhabiting these ecosystems. A diversity of host-microbial symbiont relationships has been identified and experimental studies have revealed the exquisite physiological adaptations within the giant tubeworm, Riftia pachyptila, for the uptake, fixation, and assimilation of carbon. In vitro experiments demonstrated the unusual sulfide binding properties of tubeworm hemoglobin that prevent inhibition of the cytochrome-c oxidase enzyme system during transport of sulfide to symbiont-bearing tissues. Studies of respiration and growth of several species of vent organisms conducted over the past two decades transformed earlier views that low metabolism and slow growth are characteristics of all organisms inhabiting all deep-sea environments. Results of recent experiments suggest that metabolic rates correlate with the degree of mobility of the organisms rather than with any specific attribute of the deep-sea environment itself, and growth rates of certain vent organisms (e.g., R. pachyptila) were found to be among the highest in any marine environments. While extreme thermal tolerance has been suggested as characteristic of certain vent fauna (e.g., alvinellid polychaetes and alvinocarid shrimp), the majority of vent metazoans live at temperatures below 20 °C and additional experiments are necessary to reconcile field experiments documenting thermal tolerance in situ, thermal tolerance in vivo, and thermal sensitivity of biochemical constituents of vent organisms. Transplantation and clearance experiments, as well as in situ characterization of vent fluid chemistry, have greatly increased our understanding of organism–environment interactions. Early analyses of metazoan egg size and larval morphology, coupled with in vivo larval culture experiments, available physical oceanographic data, and genetic studies of gene flow, have contributed greatly to our understanding of mechanisms of dispersal between widely separated vent sites. The documentation of invertebrate colonization and succession of new vents following a volcanic eruption, and a series of manipulative field experiments, provide considerable insights into the relative roles of abiotic conditions and biotic interactions in structuring vent communities. Recent and emerging technological developments, such as in situ chemical analyzers, observatory approaches, and laboratory-based pressure culture systems, should provide invaluable new experimental tools for tackling many remaining questions concerning the ecology of deep-sea hydrothermal systems.     

Characterization of Bacterial Communities in Deep-Sea Hydrothermal Vents from Three Oceanic Regions

Deep-sea hydrothermal vents are considered to be one of the most spectacular ecosystems on Earth. Microorganisms form the basis of the food chain in vents controlling the vent communities. However, the diversity of bacterial communities in deep-sea hydrothermal vents from different oceans remains largely unknown. In this study, the pyrosequencing of 16S rRNA gene was used to characterize the bacterial communities of the venting sulfide, seawater, and tubeworm trophosome from East Pacific Rise, South Atlantic Ridge, and Southwest Indian Ridge, respectively. A total of 23,767 operational taxonomic units (OTUs) were assigned into 42 different phyla. Although Proteobacteria, Actinobacteria, and Bacteroidetes were the predominant phyla in all vents, differences of bacterial diversity were observed among different vents from three oceanic regions. The sulfides of East Pacific Rise possessed the most diverse bacterial communities. The bacterial diversities of venting seawater were much lower than those of vent sulfides. The symbiotic bacteria of tubeworm Ridgeia piscesae were included in the bacterial community of vent sulfides, suggesting their significant ecological functions as the primary producers in the deep-sea hydrothermal vent ecosystems. Therefore, our study presented a comprehensive view of bacterial communities in deep-sea hydrothermal vents from different oceans.     

Microbial colonization of metal sulfide minerals at a diffuse‐flow deep‐sea hydrothermal vent at 9°50′N on the East Pacific Rise

Metal sulfide minerals, including mercury sulfides (HgS), are widespread in hydrothermal vent systems where sulfur‐oxidizing microbes are prevalent. Questions remain as to the impact of mineral composition and structure on sulfur‐oxidizing microbial populations at deep‐sea hydrothermal vents, including the possible role of microbial activity in remobilizing elemental Hg from HgS. In the present study, metal sulfides varying in metal composition, structure, and surface area were incubated for 13 days on and near a diffuse‐flow hydrothermal vent at 9°50′N on the East Pacific Rise. Upon retrieval, incubated minerals were examined by scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM‐EDS), X‐ray diffraction (XRD), and epifluorescence microscopy (EFM). DNA was extracted from mineral samples, and the 16S ribosomal RNA gene sequenced to characterize colonizing microbes. Sulfur‐oxidizing genera common to newly exposed surfaces (Sulfurimonas, Sulfurovum, and Arcobacter) were present on all samples. Differences in their relative abundance between and within incubation sites point to constraining effects of the immediate environment and the minerals themselves. Greater variability in colonizing community composition on off‐vent samples suggests that the bioavailability of mineral‐derived sulfide (as influenced by surface area, crystal structure, and reactivity) exerted greater control on microbial colonization in the ambient environment than in the vent environment, where dissolved sulfide is more abundant. The availability of mineral‐derived sulfide as an electron donor may thus be a key control on the activity and proliferation of deep‐sea chemosynthetic communities, and this interpretation supports the potential for microbial dissolution of HgS at hydrothermal vents.     

Distribution, phylogenetic diversity and physiological characteristics of epsilon-Proteobacteria in a deep-sea hydrothermal field

Epsilon-Proteobacteria is increasingly recognized as an ecologically significant group of bacteria, particularly in deep-sea hydrothermal environments. In this study, we studied the spatial distribution, diversity and physiological characteristics of the epsilon-Proteobacteria in various microbial habitats in the vicinity of a deep-sea hydrothermal vent occurring in the Iheya North field in the Mid-Okinawa Trough, by using culture-dependent and -independent approaches. The habitats studied were inside and outside hydrothermal plume, and annelid polychaete tubes. In addition, we deployed colonization devices near the vent emission. The polychaete tubes harboured physiologically and phylogenetically diverse microbial community. The in situ samplers were predominantly colonized by epsilon-Proteobacteria. Energy metabolism of epsilon-Proteobacteria isolates was highly versatile. Tree topology generated from the metabolic traits was significantly different (P = 0.000) from that of 16S rRNA tree, indicating current 16S rRNA gene-based analyses do not provide sufficient information to infer the physiological characteristics of epsilon-Proteobacteria. Nevertheless, culturability of epsilon-Proteobacteria in various microbial habitats differed among the phylogenetic subgroups. Members of Sulfurimonas were characterized by the robust culturability, and the other phylogenetic subgroups appeared to lose culturability in seawater, probably because of the sensitivity to oxygen. These results provide new insight into the ecophysiological characteristics of the deep-sea hydrothermal vent epsilon-Proteobacteria, which has never been assessed by comparative analysis of the 16S rRNA genes.     

Spatial Variation in the Population Structure and Reproductive Biology of Rimicaris hybisae (Caridea: Alvinocarididae) at Hydrothermal Vents on the Mid-Cayman Spreading Centre

The dynamics and microdistribution of faunal assemblages at hydrothermal vents often reflect the fine-scale spatial and temporal heterogeneity of the vent environment. This study examined the reproductive development and population structure of the caridean shrimp Rimicaris hybisae at the Beebe and Von Damm Vent Fields (Mid-Cayman Spreading Centre, Caribbean) using spatially discrete samples collected in January 2012. Rimicaris hybisae is gonochoric and exhibits iteroparous reproduction. Oocyte size-frequency distributions (21-823 µm feret diameters) varied significantly among samples. Embryo development was asynchronous among females, which may result in asynchronous larval release for the populations. Specimens of R. hybisae from the Von Damm Vent Field (2294 m) were significantly larger than specimens from the Beebe Vent Field. Brooding females at Von Damm exhibited greater size-specific fecundity, possibly as a consequence of a non-linear relationship between fecundity and body size that was consistent across both vent fields. Samples collected from several locations at the Beebe Vent Field (4944–4972 m) revealed spatial variability in the sex ratios, population structure, size, and development of oocytes and embryos of this mobile species. Samples from the Von Damm Vent Field and sample J2-613-24 from Beebe Woods exhibited the highest frequencies of ovigerous females and significantly female-biased sex ratios. Environmental variables within shrimp aggregations may influence the distribution of ovigerous females, resulting in a spatially heterogeneous pattern of reproductive development in R. hybisae, as found in other vent taxa.     

Phylogeny of marine Gregarines (Apicomplexa)--Pterospora, Lithocystis and Lankesteria--and the origin(s) of coelomic parasitism

Gregarines constitute a large group of apicomplexans with diverse modes of nutrition and locomotion that are associated with different host compartments (e.g. intestinal lumena and coelomic cavities). A broad molecular phylogenetic framework for gregarines is needed to infer the early evolutionary history of apicomplexans as a whole and the evolutionary relationships between the diverse ultrastructural and behavioral characteristics found in intestinal and coelomic gregarines. To this end, we sequenced the SSU rRNA gene from (1) Lankesteria abbotti from the intestines of two Pacific appendicularians, (2) Pterospora schizosoma from the coelom of a Pacific maldanid polychaete, (3) Pterospora floridiensis from the coelom of a Gulf Atlantic maldanid polychaete and (4) Lithocystis sp. from the coelom of a Pacific heart urchin. Molecular phylogenetic analyses including the new sequences demonstrated that several environmental and misattributed sequences are derived from gregarines. The analyses also demonstrated a clade of environmental sequences that was affiliated with gregarines, but as yet none of the constituent organisms have been described at the ultrastructural level (apicomplexan clade I). Lankesteria spp. (intestinal parasites of appendicularians) grouped closely with other marine intestinal eugregarines, particularly Lecudina tuzetae, from polychaetes. The sequences from all three coelomic gregarines branched within a larger clade of intestinal eugregarines and were similarly highly divergent. A close relationship between Pterospora schizosoma (Pacific) and Pterospora floridiensis (Gulf Atlantic) was strongly supported by the data. Lithocystis sp. was more closely related to a clade of marine intestinal gregarines consisting of Lankesteria spp. and Lecudina spp. than it was to the Pterospora clade. These data suggested that coelomic parasitism evolved more than once from different marine intestinal eugregarines, although a larger taxon sample is needed to further explore this inference.     

Diversity in mussel beds at deep-sea hydrothermal vents and cold seeps

Remarkably little is known about fundamental distinctions (or similarities) between the faunas of deep‐sea hydrothermal vents and seeps. Low species richness at vents has been attributed to the transient nature of vent habitats and to toxic effects of hydrogen sulphide and heavy metals in vent effluents. Seeps are arguably more stable and more chemically benign than vents. They have also been regarded as more diverse, but until now there has not been a rigorous test of this hypothesis. We evaluated diversity indices for invertebrates associated with mussel beds at six vents and two seeps and found that invertebrate diversity was significantly higher at seeps than vents, although some vent mussel beds supported nearly the same diversity as seep mussel beds. Lower diversity at vents may be a consequence of a greater physiological barrier to invasion at vents than at seeps. Diversity was lowest where spacing between vents was greatest, suggesting that risks of extinction as a result of dispersal‐related processes may contribute to the pattern of diversity observed at vents.     

Anaerobic Respiration on Tellurate and Other Metalloids in Bacteria from Hydrothermal Vent Fields in the Eastern Pacific Ocean

This paper reports the discovery of anaerobic respiration on tellurate by bacteria isolated from deep ocean (1,543 to 1,791 m) hydrothermal vent worms. The first evidence for selenite- and vanadate-respiring bacteria from deep ocean hydrothermal vents is also presented. Enumeration of the anaerobic metal(loid)-resistant microbial community associated with hydrothermal vent animals indicates that a greater proportion of the bacterial community associated with certain vent fauna resists and reduces metal(loid)s anaerobically than aerobically, suggesting that anaerobic metal(loid) respiration might be an important process in bacteria that are symbiotic with vent fauna. Isolates from Axial Volcano and Explorer Ridge were tested for their ability to reduce tellurate, selenite, metavanadate, or orthovanadate in the absence of alternate electron acceptors. In the presence of metal(loid)s, strains showed an ability to grow and produce ATP, whereas in the absence of metal(loid)s, no growth or ATP production was observed. The protonophore carbonyl cyanide m-chlorophenylhydrazone depressed metal(loid) reduction. Anaerobic tellurate respiration will be a significant component in describing biogeochemical cycling of Te at hydrothermal vents.