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Hypoxia at deep-sea hydrothermal vents represents one of the most basic challenges for metazoans, which then requires specific adaptations to acquire oxygen to meet their metabolic needs. Hydrothermal vent scale-worms (Polychaeta; Polynoidae) express large amounts of extracellular single- and multi-domain hemoglobins, in contrast with their shallow-water relatives that only possess intracellular globins in their nervous system (neuroglobins). We sequenced the gene encoding the single-domain (SD) globin from nine species of polynoids found in various vent and deep-sea reduced microhabitats (and associated constraints) to determine if the Polynoidae SD globins have been the targets of diversifying selection. Although extracellular, all the SD globins (and multi-domain ones) form a monophyletic clade that clusters within the intracellular globin group of other annelids, indicating that these hemoglobins have evolved from an intracellular myoglobin-like form. Positive selection could not be detected at the major ecological changes that the colonization of the deep-sea and hydrothermal vents represents. This suggests that no major structural modification was necessary to allow the globins to function under these conditions. The mere expression of these globins extracellularly may have been sufficiently advantageous for the polynoids living in hypoxic hydrothermal vents. Among hydrothermal vent species, positively selected amino acids were only detected in the phylogenetic lineage leading to the two mussel-commensal species ( Branchipolynoe). In this lineage, the multiplicity of hemoglobins could have lessened the selective pressure on the SD hemoglobin, allowing the acquisition of novel functions by positive Darwinian selection. Conversely, the colonization of hotter environments (species of Branchinotogluma) does not seem to have required additional modifications. [ABSTRACT FROM AUTHOR]

Deep-sea hydrothermal vents have now been reported along all active mid-ocean ridges and back-arc basins, but the boundaries of biogeographic entities remain questionable owing to methodological issues. Here we examine biogeographic patterns of the vent fauna along the East Pacific Rise (EPR) and determine the relative roles of regional and local factors on the distribution of biodiversity associated with mussel beds along a poorly explored zone, the southern EPR (SEPR). East Pacific Rise. A species list of macrobenthic invertebrates along the EPR was compiled from the literature and supplemented with data recovered during the French research cruise BIOSPEEDO carried out in 2004 along the SEPR. Biogeographic patterns were assessed by combining the identification of morphological species with a molecular barcoding approach. A multivariate regression tree (MRT) analysis was performed to identify any geographic breaks, and an empirical distribution of species richness was compared with predictions provided by a mid-domain effect model. Macrofaunal community structure associated with mussel beds along the SEPR was analysed in relation to environmental factors using cluster and canonical redundancy analyses. Sequencing of the cytochrome c oxidase subunit I gene revealed the occurrence of several cryptic species complexes along the EPR, with the equator separating the southern and northern clades. Furthermore, during the BIOSPEEDO cruise at least 10 still unnamed species were collected between 7°25′ S and 21°33′ S. The shift in community structure identified by MRT analysis was located south of 17°34′ S or south of 13°59′ S, depending on the data used, suggesting that the southern part of the SEPR (17°25′-21°33′ S) constitutes a biogeographic transition zone in the vent fauna along the EPR. At a regional scale, latitude combined with the type of venting was significantly correlated with the community structure associated with mussel beds. Together, the molecular data, in situ observations, and the distribution of species suggest that the high diversity of vent fauna species presently observed between 17°25′ S and 21°33′ S is probably a result of the overlap of several distinct biogeographic provinces. We argue that this area thus constitutes a biogeographic vent fauna transition zone along the EPR. [ABSTRACT FROM AUTHOR]

Hemoglobin is the most common respiratory pigment in annelids. It can be intra or extracellular, and this latter type can form large multimeric complexes. The hydrothermal vent scale worms Branchipolynoe symmytilida and Branchipolynoe seepensis express an extracellular tetra-domain hemoglobin (Hb) that is unique in annelids. We sequenced the gene for the single-domain and tetra-domain globins in these two species. The single-domain gene codes for a mature protein of 137 amino acids, and the tetra-domain gene codes for a mature protein of 552 amino acids. The single-domain gene has a typical three exon/two intron structure, with introns located at their typical positions (B12.2 and G7.0). This structure is repeated four times in the tetra-domain gene, with no bridge introns or linker sequences between domains. The phylogenetic position of Branchipolynoe globins among known annelid globins revealed that, although extracellular, they cluster within the annelid intracellular globins clade, suggesting that the extracellular state of these Hbs is the result of convergent evolution. The tetra-domain structure likely resulted from two tandem duplications, domain 1 giving rise to domain 2 and after this the two-domain gene duplicated to produce domains 3 and 4. The high O2 affinity of Branchipolynoe extracellular globins may be explained by the two key residues (B10Y and E7Q) in the heme pocket in each of the domains of the single and tetra-domain globins, which have been shown to be essential in the oxygen-avid Hb from the nematode Ascaris suum. This peculiar globin evolutionary path seems to be very different from other annelid extracellular globins and is most likely the product of evolutionary tinkering associated with the strong selective pressure to adapt to chronic hypoxia that characterizes hydrothermal vents. [ABSTRACT FROM PUBLISHER]

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A new species of vestimentiferan tubeworm belonging to the genus Escarpia is described from cold seeps off the western coast of Africa. The description is based on two collections (one of 180 animals, the other of 30 animals) using both morphological and molecular techniques. Morphologically, the African tubeworms are very similar to Escarpia laminata Jones, 1985 but differ from all other escarpids by the lack of branchial pinnules, a unique feature among vestimentiferans. Molecular evidence from sequences of the cytochrome-c oxidase subunit I gene places the species in the escarpid clade, closely related to E. laminata and Escarpia spicata Jones, 1985, but fails to discriminate among the three species. Four morphotypes are identified in the African species, corresponding to the four permutations of the following characters: presence or absence of an axial rod on the obturaculum and presence or absence of a split on the posterior ventral margin of the vestimentum. However, molecular data could not distinguish them as separate species. We suggest that the lack of an axial rod reflects predation. Biometrical data indicate a discontinuous recruitment period, as is known for other vestimentiferan species. Sex ratios are balanced, but females tend to be larger than males. We hypothesize that the males grow more slowly or die younger than the females. [ABSTRACT FROM AUTHOR]

During a research cruise in July 1997 in the Gulf of Mexico we discovered a gas hydrate approximately 1 m thick and over 2 m in diameter which had recently breached the sea floor at a depth of 540 m. The hydrate surface visible from the submarine was considerably greater than that of any other reported hydrate. Two distinct color bands of hydrate were present in the same mound, and the entire exposed surface of the hydrate was infested (2500 individuals/m2) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca methanicola, in the polychaete family Hesionidae (Desbruyères and Toulmond 1998). H. methanicola tissue stable isotope values are consistent with a chemoautotrophic food source. No evidence of chemoautotrophic symbionts was detected, but geochemical data support the presence of abundant free living bacteria on the hydrate. The activities of the polychaetes, grazing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution of hydrates in surface sediments. [ABSTRACT FROM AUTHOR]