Platynereis Dumerilii Research Articles

Where is the difference between the genomes of humans and annelids?

The first systematic investigation of an annelid genome has revealed that the genes of the marine worm Platynereis dumerilii are more closely related to those of vertebrates than to those of insects or nematodes.

Limited grazing pressure by native herbivores on the invasive seaweed Caulerpa taxifolia in a temperate Australian estuary

Caulerpa taxifolia is an invasive alga threatening biodiversity in invaded regions. Its proliferation in recipient communities will be due to several factors including limited grazing effects by native herbivores. However, little is known about grazing pressure exerted by native herbivores on C. taxifolia relative to native macrophytes or its attractiveness to them as habitat. The present study determined which herbivores co-occurred with invasive C. taxifolia in a temperate Australian estuary and documented their abundance, relative grazing effects, habitat preference and survivorship on C. taxifolia compared with native macrophytes. Four herbivores co-occurred with C. taxifolia and their densities were often low or zero at the sites studied. Feeding experiments showed that compared with C. taxifolia: the fish, Girella tricuspidata, preferred Ulva sp.; the sea-hare, Aplysia dactylomela, preferred Laurencia sp.; whereas the mesograzers, Cymadusa setosa and Platynereis dumerilii antipoda, both consumed Cystoseira trinodus and Sargassum sp. at higher rates. The two mesograzers also showed strong habitat preference for C. trinodus and Sargassum sp. Cymadusa setosa had poor survivorship on Caulerpa taxifolia whereas P. dumerilii antipoda had 100% survivorship on C. taxifolia after 41 days. We consider that the low diversity and abundance of native herbivores, their weak grazing pressure on C. taxifolia and its low attractiveness as habitat may facilitate further local spread in this estuary, and potentially in other invaded locations.

Pushing Back the Expansion of Introns in Animal Genomes

In a recent paper in Science, surveyed the position of introns in 30 genes of a marine annelid and showed that over 60% of the introns occupy positions identical to those in human homologs. In contrast, both human and marine annelid genes share only 30% of their introns with other invertebrates. These observations suggest that the common ancestor of most animal phyla had intron-rich genes and reinforce the notion that introns proliferated early in the evolutionary history of eukaryotes.

Caudal and even‐skipped in the annelid Platynereis dumerilii and the ancestry of posterior growth

In order to address the question of the conservation of posterior growth mechanisms in bilaterians, we have studied the expression patterns of the orthologues of the genes caudal, even-skipped, and brachyury in the annelid Platynereis dumerilii. Annelids belong to the still poorly studied third large branch of the bilaterians, the lophotrochozoans, and have anatomic and developmental characteristics, such as a segmented body plan, indirect development through a microscopic ciliated larva, and building of the trunk through posterior addition, which are all hypothesized by some authors (including us) to be present already in Urbilateria, the last common ancestor of bilaterians. All three genes are shown to be likely involved in the building of the anteroposterior axis around the slit-like amphistomous blastopore as well as in the patterning of the terminal anus-bearing piece of the body (the pygidium). In addition, caudal and even-skipped are likely involved in the posterior addition of segments. Together with the emerging results on the conservation of segmentation genes, these results reinforce the hypothesis that Urbilateria had a segmented trunk developing through posterior addition.

Pheromonal Communication in Nereids and the Likely Intervention by Petroleum Derived Pollutants

Nereis succinea and Platynereis dumerilii (Annelida, Polychaeta) are broadcast spawners and reproduce semelparously. The final events in reproduction, swarming and spawning are co-ordinated by sex pheromones.A water-soluble fraction of crude oil, the volatile fraction (C9-C16) of EKO FISK crude oil was found to induce release of gametes in male nereids at levels <0.3 ppm.Using vacuum distillation, column chromatography, preparative GC and GC-MS analysis we showed that C(5)-alkylated benzenes were most potent in inducing sperm release, of those n-butyl-4-methylbenzene and 1,4-diethyl-2-methylbenzene were found to induce release of gametes at concentrations ≥4 nM. This threshold is lower than those reported for natural pheromones (nereithione: 60 nM, uric acid: 600 nM) but higher than background levels of aromatic compounds of 0.05 nM and below.Other oil fractions showed additional effects, blocking pheromone reception or narcotising and intoxicating animals. Part of these effects could be assigned to naphthalenes at levels down to approx. 320 nM. In the original mixtures, their action was modified or compensated by the presence of gamete release inducing alkylated benzenes. Other highly paralysing substances remained elusive.

The polychaete Platynereis dumerilii (Annelida): a laboratory animal with spiralian cleavage, lifelong segment proliferation and a mixed benthic/pelagic life cycle.

Platynereis dumerilii, a marine polychaetous annelid with indirect development, can be continuously bred in the laboratory. Here, we describe its spectacular reproduction and development and address a number of open research problems. Oogenesis is easily studied because the oocytes grow while floating in the coelom. Unlike the embryos of other model spiralians, the Platynereis embryo is transparent giving insight into the dynamic structures and processes inside the cells that accompany the prevailing anisotropic cleavages. Functional studies on cell specification and differential gene expression in embryos, larvae, and later stages are underway. Lifelong proliferation of uniform trunk segments qualifies Platynereis as a model for the study of gene expression and of the functional circuitry of this process. Platynereis can also become a stepping stone in the comparison of segmentation between annelids and arthropods because it comes closer to the putative ancestral morphology and style of development than other model annelids.

Arthropod-like Expression Patterns of engrailed and wingless in the Annelid Platynereis dumerilii Suggest a Role in Segment Formation

The origin of animal segmentation, the periodic repetition of anatomical structures along the anteroposterior axis, is a long-standing issue [1] that has been recently revived by comparative developmental genetics [2–6]. In particular, a similar extensive morphological segmentation (or metamerism) is commonly recognized in annelids and arthropods. Mostly based on this supposedly homologous segmentation, these phyla have been united for a long time into the clade Articulata [7, 8]. However, recent phylogenetic analysis [9–10] dismissed the Articulata and thus challenged the segmentation homology hypothesis [11]. Here, we report the expression patterns of genes orthologous to the arthropod segmentation genes engrailed and wingless in the annelid Platynereis dumerilii. In Platynereis, engrailed and wingless are expressed in continuous ectodermal stripes on either side of the segmental boundary before, during, and after its formation; this expression pattern suggests that these genes are involved in segment formation. The striking similarities of engrailed and wingless expressions in Platynereis and arthropods may be due to evolutionary convergence or common heritage. In agreement with similarities in segment ontogeny and morphological organization in arthropods and annelids, we interpret our results as molecular evidence of a segmented ancestor of protostomes.

The role of chemical signals in the spawning induction of polychaete worms and other marine invertebrates

Extracts of gonad, body fluid and spawning water (into which gametes have been released by the process of spawning) were tested for the presence of spawning-inducing activity (SIA) on both sexes of the polychaetes Nereis succinea (Frey and Leuckhart) and Platynereis dumerilii (Audouin and Milne-Edwards). Gonadal and body fluid extracts from Asterias rubens (L.) and Echinus esculentus (L.) (echinoderms), Arenicola marina (L.) (polychaete), Clupea harengus (L.) (teleost) and body fluid and spawning water of Nereis virens (Sars) (polychaete) all exhibit SIA on male N. succinea. C. harengus extract from male gonads also had SIA on male P. dumerilii. Phytoplankton monoculture extracts were also tested. The cryptomonad ( Rhodomonas baltica) (Karsten) had SIA on male P. dumerilii, and the diatom Phaeodactylum tricornutum (Bohlin) had some activity on Mytilus edulis (L.). The active fraction of R. baltica is chromatographically similar to uric acid (the natural sperm-release pheromone produced by females of P. dumerilii) [Nature 382 (1996) 214], but has a different retention time and UV absorbance spectra on reverse phase HPLC. Conspecific extracts of spawning water and gonadal material did not have SIA on the same and opposite sex in A. marina and N. virens. The role of chemical signals in marine invertebrates is discussed in relation to their mode of spawning.

Phylogenetic Analysis of the Wnt Gene Family: Insights from Lophotrochozoan Members

The Wnt gene family encodes secreted signaling molecules that control cell fate specification, proliferation, polarity, and movements during animal development [1–3]. We investigate here the evolutionary history of this large multigenic family. Wnt genes have been almost exclusively isolated from two of the three main subdivisions of bilaterian animals [4], the deuterostomes (which include chordates and echinoderms) and the ecdysozoans (e.g., arthropods and nematodes). However, orthology relationships between deuterostome and ecdysozoan Wnt genes, and, more generally, the phylogeny of the Wnt family, are not yet clear. We report here the isolation of several Wnt genes from two species, the annelid Platynereis dumerilii and the mollusc Patella vulgata, which both belong to the third large bilaterian clade, the lophotrochozoans (which constitute, together with ecdysozoans, the protostomes). Multiple phylogenetic analyses of these sequences with a large set of other Wnt gene sequences, in particular, the complete set of Wnt genes of human, nematode, and fly [2], allow us to subdivide the Wnt family into 12 subfamilies. At least nine of them were already present in the last common ancestor of all bilaterian animals, and this further highlights the genetic complexity of this ancestor. The orthology relationships we present here open new perspectives for future developmental comparisons.

Genotoxic, cytotoxic and ontogenetic effects of tri- n-butyltin on the marine worm, Platynereisdumerilii (Polychaeta: Nereidae)

The genotoxic, cytotoxic and ontogenetic (embryo-larval) or developmental effects of tri- n-butyltin (TBT), were investigated in Platynereis dumerilii. Following the determination of maximum tolerated dose with regard to ontogenetic effects and mortality, early life stages of P. dumerilii were exposed to a range of TBT concentrations. Subsequently, the embryo-larvae were analysed for evidence of genotoxicity and cytotoxicity. Genotoxicity was assessed using cytogenetic endpoints that included the frequency of sister chromatid exchanges and chromosomal aberrations from metaphase spreads. Cytotoxicity was evaluated by determining the proliferative rate index of the growing embryo-larval cells using 5-bromodeoxyuridine labelling of the chromosomes or fluorescence plus Giemsa staining technique. TBT-exposed embryo-larvae of P. dumerilii exhibited sensitivity similar to that of other invertebrates, indicating that P. dumerilii is a suitable ecotoxicity test species. The results also suggested dose-dependent effects for genotoxic and cytotoxic end points in relation to TBT exposure. The present study highlights the need to elucidate the relative importance of direct genotoxic and indirect effects through production of genotoxic hormonal derivatives.

Development of pigment-cup eyes in the polychaete Platynereis dumerilii and evolutionary conservation of larval eyes in Bilateria.

The role of Pax6 in eye development in insects and vertebrates supports the view that their eyes evolved from simple pigment-cup ocelli present in their last common ancestors (Urbilateria). The cerebral eyes in errant polychaetes represent prototype invertebrate pigment-cup ocelli and thus resemble the presumed ancestral eyes. We have analysed expression of conserved eye specification genes in the early development of larval and adult pigment-cup eyes in Platynereis dumerilii (Polychaeta, Annelida, Lophotrochozoa). Both larval and adult eyes form in close vicinity of the optic anlagen on both sides of the developing brain ganglia. While pax6 is expressed in the larval, but not in the developing, adult eyes, expression of six1/2 from trochophora stages onwards specifically outlines the optic anlagen and thus covers both the developing larval and adult eyes. Using Platynereis rhabdomeric opsin as differentiation marker, we show that the first pair of adult eye photoreceptor cells is detected within bilateral clusters that transitorily express ath, the Platynereis atonal orthologue, thus resembling proneural sensory clusters. Our data indicate that--similar to insects, but different from the vertebrates--polychaete six1/2 expression outlines the entire visual system from early developmental stages onwards and ath-positive clusters generate the first photoreceptor cells to appear. We propose that pax6-, six1/2- and ath-positive larval eyes, as found in today's trochophora, were present already in Urbilateria.

Effect of environmental factors on the spatial variation of the epifaunal polychaetes of the alga Halopteris scoparia in Algeciras Bay (Strait of Gibraltar)

The effect of environmental factors on spatial variation of the polychaete community of the alga Halopteris scoparia in Algeciras Bay (Spain) was investigated. Environmental gradients (outer and inner areas) were detected, based fundamentally on hydrodynamism, solids in suspension,% of organic matter in the sediment, and structural complexity of the plant. Polychaetes can give information on strong environmental gradients, especially pollution, but showed little discrimination among stations, due mainly to the great homogeneity generally showed by these communities. This homogeneity was the result of the quantitative importance of ubiquitous species, such as Platynereis dumerilii, Sphaerosyllis hystrix, Syllis prolifera, and Amphiglena mediterranea, among others. The outer zone, however, included a great number of species with few individuals and low dominance, among which the most characteristic was the terebellid polychaete Nicolea venustula. This species seems to have strong hydrodynamic requirements and may have been limited by excess of accumulated sediment on the alga. More of the collected species were exclusive to the outer areas, and did not penetrate into the inner bay, while most of the inner species were also found in the outer zone. As a whole, the great majority of the species were located in intermediate environmental conditions, indicating a generalist character of the polychaete species.

Local recruitment differences in Platynereis dumerilii (Polychaeta, Nereididae) and their consequences for population structure

The population structure of Platynereis dumerilii (Annelida, Polychaeta, Nereididae) was investigated for 18 months (February 1997‐August 1998) in two sites (Gargano and Otranto), located 400 km from each other, along the Adriatic coast of Apulia (Italy). Samples were collected in three replicates by scraping off 100‐cm2 quadrats in a fringe of the brown alga Cystoseira amentacea. At the beginning of the study period, a recruitment event was observed in both sites. Despite the great difference in recruitment rates, at the end of the study period, local population density was similar in the two sites, suggesting the importance of post‐recruitment factors in controlling population density. Intra‐ and interspecific competition, predation, and physical stress are discussed in the light of the different ecological conditions of the two sites. Recruit distribution appeared relatively homogeneous in space with recruitment rates not being different among quadrat replicates. Variability in size class distribution among quadrat replicates was lower during the recruitment period, suggesting that the observed patchy patterns of adult distribution were a product of post‐recruitment events.

On the ecology of the Nereididae (Polychaeta: Annelida) in the Bay of İzmir, Aegean Sea

Distribution patterns of nereidid species were studied in the Bay of İzmir and its vicinity by sampling various habitats and by applying ecological indices. 15 species were identified, with Platynereis dumerilii, Nereis zonata and Ceratonereis costae being the most abundant species. Peculiar habitats such as brackish water, polluted water and the sponge community were characterized by a high dominance level of Hediste diversicolor, Neanthes caudata and Ceratonereis costae respectively. A cluster analysis to distinguish species and habitat associations was used.

Evolution of the bilaterian larval foregut.

Bilateria are subdivided into Protostomia and Deuterostomia. Indirect development through primary, ciliary larvae occurs in both of these branches; however, the closing blastopore develops into mouth and anus in Protostomia and into anus only in Deuterostomia. Because of this important difference in larval gut ontogeny, the tube-shaped guts in protostome and deuterostome primary larvae are thought to have evolved independently. To test this hypothesis, we have analysed the expression of brachyury, otx and goosecoid homologues in the polychaete Platynereis dumerilii, which develops by means of a trochophora larva-the primary, ciliary larva prototypic for Protostomia. Here we show that brachyury expression in the ventral portion of the developing foregut in Platynereis and also otx expression along ciliated bands in the mouth region of the trochophora larva parallels expression in primary larvae in Deuterostomia. In addition, goosecoid expression in the foregut of Platynereis mirrors the function in higher Deuterostomia. We present molecular evidence for the evolutionary conservation of larval foreguts and mouth regions of Protostomia and Deuterostomia. Our data indicate that Urbilateria, the common bilaterian ancestors, developed through a primary, ciliary larva that already possessed a tripartite tube-shaped gut.

Feeding ecology ofplatynereis dumerilii(audouin &amp; milne-edwards) in the seagrassposidonia oceanicasystem: The role of the epiphytic flora (Polychaeta, nereididae)

Abstract The feeding ecology and the ecological role of the herbivorous polychaete Platynereis dumerilii (Audouin & Milne-Edwards) (Nereididae) in the epiphytic community of the Mediterranean seagrass Posidonia oceanica (L.) Delile was investigated under natural and laboratory conditions. Experiments were devised to define the preferred items, their consumption rate and degree of assimilation of chlorophylls. Results of faecal pellets analyses, food-choice experiments and photosynthetic pigment analyses demonstrated that P. dumerilii feeds preferentially on erect filamentous algae. Worms of length above 10 mm may graze also on living tissue of Posidonia leaves, when starved. This behaviour has rarely been reported for invertebrates, and especially for poly-chaetes in Posidonia ecosystems. Small individuals had a lower feeding rate on large macroalgae (e.g., Cystoseira), but higher digestive efficiency. Platynereis dumerilii thus feeds preferentially on erect micro- and macroalgae which are more easily cut...

ʟ-Ovothiol A: The Egg Release Pheromone of the Marine Polychaete Platynereis Dumerilii: Annelida: Polychaeta

Sex pheromones, released with the coelomic fluid by male Platynereis dumerilii initiate egg release in swarming females. The egg release pheromone, isolated from the coelomic fluid of sexually mature males, was identified as ʟ-Ovothiol A, which was found in male marine invertebrates for the first time. Isolation was obtained by reversed-phase high-performance liquid chromatography in the biologically inactive disulfide form.

Assessment of developmental effects, cytotoxicity and genotoxicity in the marine polychaete ( Platynereis dumerilii) exposed to disinfected municipal sewage effluent

While sodium hypochlorite is widely used as a disinfectant for municipal sewage effluents and power station cooling waters discharged into coastal environments, there is limited information on the potential in vivo genotoxicity of such disinfection procedures to marine organisms. Using a recently developed test system based on the marine polychaete Platynereis dumerilii, we have evaluated impacts based on embryo–larval development, cytotoxicity and genotoxicity following exposure to disinfected settled (primary) effluent from a municipal sewage treatment works (STW). Sewage samples were collected from Newton Abbot STW, Devon, UK and then disinfected with sodium hypochlorite based on standard operational procedures. Exposure of polychaetes to dilutions of disinfected sewage in seawater (20±1°C) led to a marked reduction in normal embryo–larval development (7 h EC 50 from 0.57–1.88% (v/v), n=4), with a simultaneous increase in cytotoxicity. Following the calculation of the Maximum Tolerated Dose (MTD), based on developmental and cytotoxic effects, the organisms were also analysed for the induction of chromosomal aberrations. This investigation demonstrated the absence of genotoxicity in polychaetes exposed in vivo to sewage disinfected with sodium hypochlorite. These observations extend our previously published studies in which polychaetes exposed to non-disinfected sewage, while showing developmental toxicity and cytotoxicity, did not exhibit any evidence of cytogenetic damage.

Uric Acid: The Sperm-Release Pheromone of the Marine Polychaete Platynereis dumerilii

In the marine polychaete, Platynereis dumerilii, reproductive behavior in the two sexes is synchronized by the consecutive discharge of male and female sex-specific pheromones. After the female releases the eggs into the free water column, immediate fertilization is achieved by several males circling around the eggs emitting sperm clouds. We report the isolation and identification of the sperm-release pheromone present in the coelomic fluid of sexually mature females. Each step in isolation was guided by bioassay. Isolation methods included extraction and solvent partitioning and separation methods included ultrafiltration and high-performance liquid chromatography. Uric acid was identified as the sperm-release pheromone that is discharged by the female with release of the eggs. The threshold concentration for sperm release by males was determined as 0.6 μM.

Timing of reproduction in marine polychaetes: The role of sex pheromones

In many marine invertebrates, such as the nereid polychaetes, sex pheromones ensure the coordinated release of gametes by both sexual partners. The question of species-specificity of chemical cues and the scale of their distribution in the marine environment evolves when one considers the wide overlap in multispecies and multiphyla spawning. Behavioural and electrophysiological assays with several nereid species, such as Platynereis dumerilii, Nereis succinea, N. virens and N. japonica, confirm the existence of heterospecific activity of coelomic fluid. The nuptial dance, as well as the release of gametes, are elicited when individuals are exposed to coelomic fluid of another nereid species. We, therefore, discuss the function of sex pheromones in nereid polychaetes and their role in the timing of reproduction in relation to other environmental cues.