Is there potential for estradiol receptor signaling in lophotrochozoans?

Estrogen receptors (ERs) are thought to be the ancestor of all steroid receptors and are present in most lophotrochozoans studied to date, including molluscs, annelids, and rotifers. A number of studies have investigated the functional role of estrogen receptors in invertebrate species, although most are in molluscs, where the receptor is constitutively active. In vitro experiments provided evidence for ligand-activated estrogen receptors in annelids, raising important questions about the role of estrogen signalling in lophotrochozoan lineages. Here, we review the concordant and discordant evidence of estradiol receptor signalling in lophotrochozoans, with a focus on annelids and rotifers. We explore the de novo synthesis of estrogens, the evolution and expression of estrogen receptors, and physiological responses to activation of estrogen receptors in the lophotrochozoan phyla Annelida and Rotifera. Key data are missing to determine if de novo biosynthesis of estradiol in non-molluscan lophotrochozoans is likely. For example, an ortholog for the CYP11 gene is present, but confirmation of substrate conversion and measured tissue products is lacking. Orthologs CYP17 and CYP19 are lacking, yet intermediates or products (e.g. estradiol) in tissues have been measured. Estrogen receptors are present in multiple species, and for a limited number, in vitro data show agonist binding of estradiol and/or transcriptional activation. The expression patterns of the lophotrochozoan ERs suggest developmental, reproductive, and digestive roles but are highly species dependent. E2 exposures suggest that lophotrochozoan ERs may play a role in reproduction, but no strong dose-response relationship has been established. Therefore, we expect most lophotrochozoan species, outside of perhaps platyhelminths, to have an ER but their physiological role remains elusive. Mining genomes for orthologs gene families responsible for steroidogenesis, coupled with in vitro and in vivo studies of the steroid pathway are needed to better assess whether lophotrochozoans are capable of estradiol biosynthesis. One major challenge is that much of the data are divided across a diversity of species. We propose that the polychaetes Capitella teleta or Platyneris dumerilii, and rotifer Brachionus manjavacas may be strong species choices for studies of estrogen receptor signalling, because of available genomic data, established laboratory culture techniques, and gene knockout potential.

Polychaete Bioturbation Alters the Taxonomic Structure, Co-occurrence Network, and Functional Groups of Bacterial Communities in the Intertidal Flat.

Polychaetes are important benthic macrofauna that lives in sediments, usually in intertidal flats with high organic content and high sulfide. It has been suggested that polychaete bioturbation could perform environmental remediation. During the process, the microbial community plays important roles. Here, we used high-throughput sequencing technology to study the bioturbation effects on the bacterial community in the polychaete (Perinereis aibuhitensis) burrows at different tidal positions in intertidal flat. The results showed that the bacterial communities were dramatically influenced by the polychaete bioturbation. The ACE, Chao, and Shannon indices of the polychaete burrows increased in summer. Dominant phyla in the polychaete burrows were Proteobacteria, Campilobacterota, Desulfobacterota, Chloroflexi, and Bacteroidota, and the dominant bacterial families were Sulfurvaceae, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, Desulfobulbaceae, and Sulfurimonadaceae. Results of linear discriminant analysis effect size (LEfSe) showed that groups that include organic matter degraders, such as Bacteroidota, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, and groups that include sulfur oxidizers, such as Campilobacterota, Sulfurovaceae, Rhodobacteraceae, Desulfobulbaceae, and Sulfurimonadaceae, were significantly increased due to the polychaete bioturbation. The polychaete bioturbation reduced the complexity of the bacterial co-occurrence network while increased its modularity and homogeneity. The polychaete bioturbation also changed the functional groups, which significantly enhanced in functional groups of aerobic nitrite oxidation, nitration, dark thiosulfate oxidation, dark sulfur oxidation, and dark sulfite oxidation, while nitrogen respiration and nitrate respiration decreased. These results provide insight into the impact of bacterial communities under the intertidal polychaete bioturbation.

Thermal tolerance limits and physiological traits as indicators of Hediste diversicolor's acclimation capacity to global and local change drivers.

Global projections predict significant increases in ocean temperature and changes in ocean chemistry, including salinity variations by 2100. This has led to a substantial interest in the study of thermal ecophysiology, as temperature is a major factor shaping marine ectotherm communities. However, responses to temperature may be influenced by other factors such as salinity, highlighting the relevance of multiple stressor studies. In the present work, we experimentally evaluated the thermal tolerance of the marine ragworm Hediste diversicolor under predicted global change scenarios. Organisms were subjected to an experimental trial under control (24 °C), and two temperature treatment scenarios (ocean warming +3 °C - (27 °C) and heat wave +6 °C - (30 °C)), combined with salinity variations (20 and 30) in a full factorial design for 29 days. Environmental data from the field were collected during 2019 and 2020. At day 30 post exposure, upper thermal limits (Critical Thermal Maximum - CTMax), thermal safety margins (TSM) and acclimation capacity were measured. Higher acclimation temperatures led to higher thermal tolerance limits, confirming that H. diversicolor features some physiological plasticity, acclimation capacity and a positive thermal safety margin. This margin was greater considering in situ temperature data from 2019 than maximum temperatures for 2020 (CTMax > maximum habitat temperature-MHT). Moreover, smaller organisms displayed higher upper thermal limits suggesting that thermal tolerance is size dependent. Ragworms subjected to higher salinity also showed a higher CTMax than those acclimated to lower salinity. However, temperature and salinity showed an additive effect on CTMax, as no significant interaction was detected. We conclude that H. diversicolor can easily acclimate to increased water temperature, independently of salinity variations. Given the key role of ragworms in food webs in estuaries and coastal lagoons, substrate bioturbation and aquaculture, this information is relevant to support conservation actions, optimize culture protocols and identify thermal resistant strains.

Dominance of Sulfurospirillum in Metagenomes Associated with the Methane Ice Worm (Sirsoe methanicola).

Sirsoe methanicola, commonly known as the methane ice worm, is the only macrofaunal species known to inhabit the Gulf of Mexico methane hydrates. Little is known about this elusive marine polychaete that can colonize rich carbon and energy reserves. Metagenomic analysis of gut contents and worm fragments predicted diverse metabolic capabilities with the ability to utilize a range of nitrogen, sulfur, and organic carbon compounds through microbial taxa affiliated with Campylobacterales, Desulfobacterales, Enterobacterales, SAR324, Alphaproteobacteria, and Mycoplasmatales. Entomoplasmatales and Chitinivibrionales were additionally identified from extracted full-length 16S rRNA sequences, and read analysis identified 196 bacterial families. Overall, the microbial community appeared dominated by uncultured Sulfurospirillum, a taxon previously considered free-living rather than host-associated. Metagenome-assembled genomes (MAGs) classified as uncultured Sulfurospirillum predicted thiosulfate disproportionation and the reduction of tetrathionate, sulfate, sulfide/polysulfide, and nitrate. Microbial amino acid and vitamin B12 biosynthesis genes were identified in multiple MAGs, suggesting nutritional value to the host. Reads assigned to aerobic or anaerobic methanotrophic taxa were rare. IMPORTANCE Methane hydrates represent vast reserves of natural gas with roles in global carbon cycling and climate change. This study provided the first analysis of metagenomes associated with Sirsoe methanicola, the only polychaete species known to colonize methane hydrates. Previously unrecognized participation of Sulfurospirillum in a gut microbiome is provided, and the role of sulfur compound redox reactions within this community is highlighted. The comparative biology of S. methanicola is of general interest given research into the adverse effects of sulfide production in human gut microbiomes. In addition, taxonomic assignments are provided for nearly 200 bacterial families, expanding our knowledge of microbiomes in the deep sea.

The effects of teflubenzuron on mortality, physiology and accumulation in Capitella sp.

The chitin synthesis inhibitor teflubenzuron (TFB) is a feed antiparasitic agents used to impede molting of the salmon lice, an ecto-parasite that severely affects the salmon industry. Low absorption of oral administered TFB may cause elevated concentrations in the feces discharged from the salmon into the benthic environment. The polychaete Capitella sp. are often dominant in such habitats and consume organic waste deposited on the sediment. In the present study, Capitella sp. were exposed to doses of TFB in salmon feed of 1, 2 and 4 g TFB kg-1 (0 g TFB kg-1 in control group) over an experimental period of 32 days. Cumulative mortality was 12%-15% in both treatment groups with 1 and 2 g TFB kg-1 and reached 27% in the group with 4 g TFB kg-1. Only the highest dose (4 g TFB kg-1) negatively affected feed intake, growth and respiration of the polychaetes while food conversion efficiency was not affected. At the end of the experiment, the concentrations of TFB in the Capitella sp. were high, in the range of 9.24-10.32 µg g-1 for the three treatment groups. It was suggested that a maximum level of absorption rate was reached, also for the lowest dose. High concentrations of TFB in the Capitella sp. might pose a risk to crustaceans that forage for polychaetes in the vicinity of fish farms. We conclude that the effects of TFB on Capitella sp. may therefore primarily be to the predators rather than the Capitella sp.

Photoresponses in the radiolar eyes of the fan worm Acromegalomma vesiculosum.

Fan worms (Annelida: Sabellidae) possess compound eyes and other photoreceptors on their radiolar feeding tentacles. These eyes putatively serve as an alarm system that alerts the worm to encroaching threats, eliciting a rapid defensive retraction into their protective tube. The structure and independent evolutionary derivation of these radiolar eyes make them a fascinating target for exploring the emergence of new sensory systems and visually guided behaviours. However, little is known about their physiology and how this impacts their function. Here, we present electroretinogram recordings from the radiolar eyes of the fan worm Acromegalomma vesiculosum We examine their spectral sensitivity along with their dynamic range and temporal resolution. Our results show that they possess one class of photoreceptors with a single visual pigment peaking in the blue-green part of the spectrum around 510 nm, which matches the dominant wavelengths in their shallow coastal habitats. We found the eyes to have a rather high temporal resolution with a critical flicker fusion frequency around 35 Hz. The high temporal resolution of this response is ideally suited for detecting rapidly moving predators but also necessitates downstream signal processing to filter out caustic wave flicker. This study provides a fundamental understanding of how these eyes function. Furthermore, these findings emphasise a set of dynamic physiological principles that are well suited for governing a multi-eyed startle response in coastal aquatic habitats.

Diurodrilus kunii sp. nov. (Annelida: Diurodrilidae) and a Molecular Phylogeny of the Genus.

A new species of stygobiontic interstitial annelid, Diurodrilus kunii sp. nov., is described based on material collected from medium sand sediment (ϕ = 1.2-1.7) at groundwater level (40-100 cm in depth; 5-15 m inland from splash zone) in the intertidal beach slope on Ishikari Beach, facing the Sea of Japan, Hokkaido, Japan. The new species differs from six known congeners in the arrangement of the anterior-head ventral ciliophores, the degree of development in the primary and secondary toes, and the shape of the spermatozoa. We inferred the phylogenetic position of the new species among other congeners for which 18S rRNA, 28S rRNA, and COI gene sequences were available in public databases. This is the first representative of the genus from the Northwest Pacific.

Marine Bacterium Vibrio sp. CB1-14 Produces Guanidine Alkaloid 6-epi-Monanchorin, Previously Isolated from Marine Polychaete and Sponges.

Twenty-three bacterial strains were isolated from the secreted mucus trapping net of themarine polychaete Chaetopterus variopedatus (phylum Annelida) and twenty strains were identifiedusing 16S rRNA gene analysis. Strain CB1-14 was recognized as a new species of the genus Vibriousing the eight-gene multilocus sequence analysis (MLSA) and genome sequences of nineteen typeVibrio strains. This Vibrio sp. was cultured, and 6-epi-monanchorin (2), previously isolated from thepolychaete and two sponge species, was found in the cells and culture broth. The presence of the 6-epi-monanchorin was confirmed by its isolation followed by 1H NMR and HRESIMS analysis. Theseresults showed the microbial origin of the bicyclic guanidine alkaloid 2 in C. variopedatus.

Enhanced removal of sediment-associated total petroleum hydrocarbons under bioturbation by polychaete perinereis aibuhitensis.

Bioturbation processes could influence the physical, chemical and biological properties of aquatic sediments and improve the mineralization of organic matter in sediment. The influence of bioturbation by polychaete Perinereis aibuhitensis on the removal of sediment-associated total petroleum hydrocarbon (TPH) was evaluated through laboratory experiment with P. aibuhitensis cultured in crude oil contaminated coastal sediment. After 60 days, the TPH concentrations in the sediments were significantly decreased compared to the initial concentrations, in which the TPH concentrations in bioturbation experiments (with worms) were significantly lower than those in control experiments (without worms) for both low (1.48 ± 0.19g/kg dry wt) and high (2.67 ± 0.33 g/kg dry wt) TPH-contaminated groups, indicating bioturbation enhanced the removal of TPH in sediment. The TPH removal rates in high TPH group were significantly lower than those in low TPH group, suggested that petroleum pollution inhibited the degradation of petroleum hydrocarbons in sediment. However, the stimulation efficiency was higher in high TPH group than that in low TPH group, which may be the result of enhanced hydrocarbon's bioavailability by digestive fluid during gut transit.

Neurological Disorder Brain Model: A Lesson from Marine Worms (Annelida: Polychaeta).

The incidence of neurodegenerative diseases is directly proportional to age. The prevalence of non-communicable diseases, for example, Alzheimer's and Parkinson's, is expected to rise in the coming years. Understanding the etiopathology of these diseases is a crucial step that needs to be taken to develop drugs for their treatment. Animal models are being increasingly used to expand the knowledge and understanding on neurodegenerative diseases. Marine worms, known as polychaetes (phylum Annelida), which are abundantly and frequently found in benthic environments, possess a simple yet complete nervous system (including a true brain that is centralised and specialised) compared to other annelids. Hence, polychaetes can potentially be the next candidate for a nerve disease model. The ability to activate the entire nervous system regeneration (NSR) is among the remarkable features of many polychaetes species. However, the information on NSR in polychaetes and how it can potentially model neurodegenerative diseases in humans is still lacking. By exploring such studies, we may eventually be able to circumvent the developmental constraints that limit NSR in the human nervous system. This article is intended to briefly review responsible mechanisms and signalling pathways of NSR in marine polychaetes and to make a comparison with other established models of neurodegenerative disease.

Phylogeny, evolution and mitochondrial gene order rearrangement in scale worms (Aphroditiformia, Annelida).

Next-generation sequencing (NGS) has become a powerful tool in phylogenetic and evolutionary studies. Here we applied NGS to recover two ribosomal RNA genes (18S and 28S) from 16 species and 15 mitochondrial genomes from 16 species of scale worms representing six families in the suborder Aphroditiformia (Phyllodocida, Annelida), a complex group of polychaetes characterized by the presence of dorsal elytra or scales. The phylogenetic relationship of the several groups of scale worms remains unresolved due to insufficient taxon sampling and low resolution of individual gene markers. Phylogenetic tree topology based on mitochondrial genomes is comparable with that based on concatenated sequences from two mitochondrial genes (cox1 and 16S) and two ribosomal genes (18S and 28S) genes, but has higher statistical support for several clades. Our analyses show that Aphroditiformia is monophyletic, indicating the presence of elytra is an apomorphic trait. Eulepethidae and Aphroditidae together form the sister group to all other families in this suborder, whereas Acoetidae is sister to Iphionidae. Polynoidae is monophyletic, but within this family the deep-sea subfamilies Branchinotogluminae and Macellicephalinae are paraphyletic. Mitochondrial genomes in most scale-worm families have a conserved gene order, but within Polynoidae there are two novel arrangement patterns in the deep-sea clade. Mitochondrial protein-coding genes in polynoids as a whole have evolved under strong purifying selection, but substitution rates in deep-sea species are much higher than those in shallow-water species, indicating that purifying selection is relaxed in deep-sea polynoids. There are positive selected amino acids for some mitochondrial genes of the deep-sea clade, indicating they may involve in the adaption of deep-sea polynoids. Overall, our study (1) provided more evidence for reconstruction of the phylogeny of Aphroditiformia, (2) provided evidence to refute the assumption that mitochondrial gene order in Errantia is conserved, and (3) indicated that the deep-sea extreme environment may have affected the mitochondrial genome evolution rate and gene order arrangement in Polynoidae.

Kinematics of burrowing by peristalsis in granular sands.

Peristaltic burrowing in muds applies normal forces to burrow walls, which extend by fracture, but the kinematics and mechanics of peristaltic burrowing in sands has not been explored. The opheliid polychaete Thoracophelia mucronata uses direct peristalsis to burrow in beach sands, with kinematics consistent with the 'dual anchor system' of burrowing described for diverse organisms. In addition to expansions associated with a constrictive direct peristaltic wave, worms alternately expand the head region, which is separated by septa from the open body cavity, and expansible lateral ridges that protrude from the 10th setiger. Tracking of chaetae with fluorescent dye showed that the body wall advances while segments are thin, then stationary segments expand, applying normal forces to burrow walls. These normal forces likely compact burrow walls and serve as anchors. Perhaps more importantly, peristaltic movements minimize friction with the burrow wall, which would expand dilatant sands. Considerable slipping of worms burrowing in a lower-density sand analog suggests that this dual-anchor peristaltic burrowing may be limited to a narrow range of mechanical properties of substrata, consistent with the limited habitat of T. mucronata in a narrow swash zone on dissipative beaches.

A quantitative framework to estimate the relative importance of environment, spatial variation and patch connectivity in driving community composition.

Perhaps the most widely used quantitative approach in metacommunity ecology is the estimation of the importance of local environment vs. spatial structuring using the variation partitioning framework. Contrary to metapopulation models, however, current empirical studies of metacommunity structure using variation partitioning assume a space-for-dispersal substitution due to the lack of analytical frameworks that incorporate patch connectivity predictors of dispersal dynamics. Here, a method is presented that allows estimating the relative importance of environment, spatial variation and patch connectivity in driving community composition variation within metacommunities. The proposed approach is illustrated by a study designed to understand the factors driving the structure of a soft-bottom marine polychaete metacommunity. Using a standard variation partitioning scheme (i.e. where only environmental and spatial predictors are used), only about 13% of the variation in metacommunity structure was explained. With the connectivity set of predictors, the total amount of explained variation increased up to 51% of the variation. These results highlight the importance of considering predictors of patch connectivity rather than just spatial predictors. Given that information on connectivity can be estimated by commonly available data on species distributions for a number of taxa, the framework presented here can be readily applied to past studies as well, facilitating a more robust evaluation of the factors contributing to metacommunity structure.

Assessment of oxidative stress and bioaccumulation of the metals Cu, Fe, Zn, Pb, Cd in the polychaete Perinereis gualpensis from estuaries of central Chile.

The estuaries of the Aconcagua and Maipo Rivers of central Chile are receptors of residues that contain metals from anthropic activities including agriculture, mining and smelters, which have different levels in the two basins. This study postulates that the exposition to metals is different in the two estuaries and that their sediments contain bioavailable chemical agents that produce oxidative stress. The aim of the study was to evaluate the effect of estuarine sediments on the polychaete Perinereis gualpensis using oxidative stress biomarkers and to determine the metal concentrations in sediments and their accumulation in P. gualpensis. Sediments and organisms were collected in December 2015 and January 2016 in the estuaries. The Catapilco estuary was used as control, since its basin has little anthropic activity. The metal concentrations of Fe Cu, Pb, Zn and Cd were determined in tissues of the organisms and in sediments. The granulometry, conductivity, redox potential, pH and organic matter in sediments were determined, as well as catalase activity and lipid peroxidation. The results show that the concentrations of metals in sediments were higher in the estuary of the Aconcagua River: Cu: 48 ± 2µgg-1; Fe: 154 ± 19mgg-1, Pb: 20 ± 3µgg-1 and Zn: 143 ± 20µgg-1. In tissues, Pb and Fe were higher in the estuary of the Maipo River, while Cd was detected only in the Catapilco River mouth. Catalase activity was greater in the estuary of the Aconcagua River and lipid peroxidation in the estuary of the Catapilco River. Significant regressions were found between biomarkers of oxidative stress and metal concentrations in tissues of P. gualpensis. In conclusion, the sediments of the studied estuaries contain bioavailable chemical agents that provoke oxidative stress in P. gualpensis, which may be a risk for the benthic communities of these ecosystems. This species is proposed to monitor metals bioavailability and oxidative stress in estuarine sediments.

Respiratory Uptake and Depuration Kinetics of Perfluorooctanesulfonate (PFOS) in a Marine Sandworm Species.

We determined the respiratory uptake and depuration kinetics of perfluorooctanesulfonate (PFOS) in Perinereis wilsoni, a polychaete sandworm used as a model species to investigate the fate of chemical pollutants in coastal environments. The sandworms were kept in gravel-packed containers, and the water levels were varied cyclically to mimic the tides. We used seawater kept at 17.1°C. A 7-day exposure period was followed by a 9-day depuration period. The dissolved PFOS concentration averaged 28 ng/L during the exposure period. Sandworm samples were collected regularly for analysis of PFOS concentrations, and a first-order-kinetics model was applied to the concentrations. The respiratory absorption efficiency of PFOS was estimated to be 11% that of oxygen, which is higher than the corresponding estimates reported for several fish species. The estimated depuration half-life of 15 days was comparable to previously reported estimates for fish and oligochaete species. The bioconcentration factor was 470.

Articulating "Archiannelids": Phylogenomics and Annelid Relationships, with Emphasis on Meiofaunal Taxa.

Annelid disparity has resulted in morphological-based classifications that disagree with phylogenies based on Sanger sequencing and phylogenomic analyses. However, the data used for the latter studies came from various sources and technologies, involved poorly occupied matrices and lacked key lineages. Here, we generated a new Illumina-based data set to address annelid relationships from a fresh perspective, independent from previously generated data and with nearly fully occupied matrices. Our sampling reflects the span of annelid diversity, including two symbiotic annelid groups (Myzostomida and Spinther) and five meiofaunal groups once referred to as part of Archiannelida (three from Protodrilida, plus Dinophilus and Polygordius). As well as the placement of these unusual annelids, we sought to address the overall phylogeny of Annelida, and provide a new perspective for naming of major clades. Our results largely corroborate the phylogenomic results of Weigert et al. (2014; Illuminating the base of the annelid tree using transcriptomics. Mol Biol Evol. 31:1391-1401), with "Magelona + Owenia" and Chaetopteridae forming a grade with respect to all other annelids. Echiura and Sipuncula are supported as being annelid groups, with Sipuncula closest to amphinomids as sister group to Sedentaria and Errantia. We recovered the three Protodrilida terminals as sister clade to Phyllodocida and Eunicida (=clade Aciculata). We therefore place Protodrilida as part of Errantia. Polygordius was found to be sister group to the scaleworm terminal and the possibility that it is a simplified scaleworm clade, as has been shown for the former family Pisionidae, is discussed. Our results were equivocal with respect to Dinophilus, Myzostomida, and Spinther possibly owing to confounding long-branch effects.

Vanadium-Binding Ability of Nucleoside Diphosphate Kinase from the Vanadium-Rich Fan Worm, Pseudopotamilla occelata.

Polychaete fan worms and ascidians accumulate high levels of vanadium ions. Several vanadiumbinding proteins, known as vanabins, have been found in ascidians. However, no vanadium-binding factors have been isolated from the fan worm. In the present study, we sought to identify vanadiumbinding proteins in the branchial crown of the fan worm using immobilized metal ion affinity chromatography. A nucleoside diphosphate kinase (NDK) homolog was isolated and determined to be a vanadium-binding protein. Kinase activity of the NDK homologue, PoNDK, was suppressed by the addition of V(IV), but was unaffected by V(V). The effect of V(IV) on PoNDK precedes its activation by Mg(II). This is the first report to describe the relationship between NDK and V(IV). PoNDK is located in the epidermis of the branchial crown, and its distribution is very similar to that of vanadium. These results suggest that PoNDK is associated with vanadium accumulation and metabolism in P. occelata.

Exposure to low pH induces molecular level changes in the marine worm, Platynereis dumerilii.

Fossil fuel emissions and changes in net land use lead to an increase in atmospheric CO2 concentration and a subsequent decrease of ocean pH. Noticeable effects on organisms' calcification rate, shell structure and energy metabolism have been reported in the literature. To date, little is known about the molecular mechanisms altered under low pH exposure, especially in non-calcifying organisms. We used a suppression subtractive hybridisation (SSH) approach to characterise differentially expressed genes isolated from Platynereis dumerilii, a non-calcifying marine polychaeta species, kept at normal and low pH conditions. Several gene sequences have been identified as differentially regulated. These are involved in processes previously considered as indicators of environment change, such as energy metabolism (NADH dehydrogenase, 2-oxoglutarate dehydrogenase, cytochrome c oxidase and ATP synthase subunit F), while others are involved in cytoskeleton function (paramyosin and calponin) and immune defence (fucolectin-1 and paneth cell-specific alpha-defensin) processes. This is the first study of differential gene expression in a non-calcifying, marine polychaete exposed to low pH seawater conditions and suggests that mechanisms of impact may include additional pathways not previously identified as impacted by low pH in other species.

Acidification effects on biofouling communities: winners and losers.

How ocean acidification affects marine life is a major concern for science and society. However, its impacts on encrusting biofouling communities, that are both the initial colonizers of hard substrata and of great economic importance, are almost unknown. We showed that community composition changed significantly, from 92% spirorbids, 3% ascidians and 4% sponges initially to 47% spirorbids, 23% ascidians and 29% sponges after 100 days in acidified conditions (pH 7.7). In low pH, numbers of the spirorbid Neodexiospira pseudocorrugata were reduced ×5 compared to controls. The two ascidians present behaved differently with Aplidium sp. decreasing ×10 in pH 7.7, whereas Molgula sp. numbers were ×4 higher in low pH than controls. Calcareous sponge (Leucosolenia sp.) numbers increased ×2.5 in pH 7.7 over controls. The diatom and filamentous algal community was also more poorly developed in the low pH treatments compared to controls. Colonization of new surfaces likewise showed large decreases in spirorbid numbers, but numbers of sponges and Molgula sp. increased. Spirorbid losses appeared due to both recruitment failure and loss of existing tubes. Spirorbid tubes are comprised of a loose prismatic fabric of calcite crystals. Loss of tube materials appeared due to changes in the binding matrix and not crystal dissolution, as SEM analyses showed crystal surfaces were not pitted or dissolved in low pH conditions. Biofouling communities face dramatic future changes with reductions in groups with hard exposed exoskeletons and domination by soft-bodied ascidians and sponges.

Homeogenetic inductive mechanism of segmentation in polychaete tail regeneration.

Segmentation is a body-patterning strategy in which new segments are specified from a segment-addition zone containing uncommitted cells. However, the cell-recruitment process is poorly understood. Here we investigated in detail the segmentation in a polychaete annelid, Perinereis nuntia (Lophotrochozoa), in which new segments emerge at the boundary between the posterior end of the segmented region and the terminal pygidium. Cells at this border synchronously remodel their chromatin, enter the cell cycle, and undergo oriented cell division, before being added to new segments. wingless is expressed at the posterior edge of the pre-existing segment, abutted by hedgehog in the first row of the new segment. Overstimulation of Wingless signaling caused excess cells to enter the cell cycle, prolonging segmentation and widening the new segment. Thus, segment addition may occur by a homeogenetic mechanism, in which Wingless expressed in the differentiated segment coordinates the stepwise recruitment of undifferentiated cells from the segment/pygidium boundary.