ESTUDIO MORFOLÓGICO DE LAS ESPÍNULAS SIFONALES EN LAS ESPECIES DEL GÉNERO MICROCOSMUS (ASCIDIACEA) DEL LITORAL MEDITERRANEO ESPAÑOL

The morphology of the siphonal spines of the seven Microcosmus spicies present in the Spanish and scale-shaped. For their intraspecitic constancy and their readiness of observation, these spines can be used as a useful character in the classification of these species. They are specially helpful in the differentiation of some species of very similar external and internal apperance, such as M. vulgaris/M. subatieri or M. claudicans/M. savignyi.Se estudia la morfología de las espínulas sifonales de las siete especies del G. Microcosmus presentes en las costas mediterráneas españolas por medio del microscopio electrónico de barrido. Su forma varia ente escamosa y acicular. La constancia intraespecífica de estas espínulas, junto con la facilidad de su observación, hacen de ellas un carácter útil para la clasificación de estas especies. Son especialmente prácticas para la diferenciación de aquellas especies de apariencia externa e interna muy similar, como en los casos de M. vulgaris/M. sabatieri o M. claudicans/M. savignyi

The Microbiome of the Worldwide Invasive Ascidian Didemnum vexillum

All multicellular organisms, including ascidians, host diverse microbial communities that are essential for their evolution. The global invader Didemnum vexillum is a colonial species native to Japan with two main genetic clades, A (the only invasive) and B, which provides a unique opportunity to assess if the microbiome remains stable in the colonization process or shifts according to local environment. We have analyzed, using 16S amplicon sequencing, the microbiome of 65 D. vexillum colonies from 13 populations worldwide including the two clades in the native area, plus samples from a congeneric species and seawater from one of the localities. We found 3,525 zero-radius operational taxonomic units (ZOTUs) in D. vexillum, belonging to 36 bacterial and 3 archaeal phyla. The microbiome of this species had a markedly different composition from surrounding seawater and from the congeneric species. For the globally invasive clade A, we found 3,154 ZOTUs, and 8 of them were present in all colonies, constituting a core microbiome with high abundance (69.57% of the total reads) but low diversity (0.25% of the total number of ZOTUs). The variable component was quantitatively much less important but comprised a highly diverse assemblage. In a multiple regression model, global microbiome structure correlated with differences in temperature range across localities and also with geographic distances, pointing to horizontal acquisition of the symbionts. However, the ascidian may have a strong capacity to select and enrich its microbiome, as we found that the most abundant ZOTUs from tunic samples had low abundance in seawater samples from the same locality. The microbiome structure also correlated with the genetic distances between colonies obtained in a previous genome-wide analysis, suggesting some potential for vertical transmission. In geographically restricted comparisons, temperature and genetic makeup, but not geography, explained microbiome structure. The combination of a quantitatively dominant core component and a highly diverse variable fraction in the microbiome of D. vexillum can contribute to the success of this global invader in different environments

Estudio de las ascidias de las costas de Cataluña e Islas Baleares

[spa] La antedicha memoria constituye una contribución al conocimiento del grupo de las ascidias (tunicados) de las costas de Cataluña e Islas Baleares. Es este un grupo de animales marinos muy poco estudiado en nuestro país; y en el presente trabajo se realiza un completo estudio de la fauna de las costas catalano-baleares, incluyéndose también datos detallados del ciclo biológico y de la ecología del grupo. El material procede de 108 estaciones de la zona de estudio en las que se han efectuado 196 muestreos principalmente mediante el uso de escafandra autónoma. Los resultados faunísticos comprenden un catálogo de 100 especies, de las que se realiza una descripción, así como dibujos e imágenes fotográficas de las más interesantes. Dos especies (Cratostigma campoyi y Cratostigma vestigialis) se describen como nuevas para la ciencia. Igualmente, el trabajo aporta 32 especies no conocidas previamente en la zona de estudio. Se realiza también una completa descripción, mediante el uso del microscopio electrónico de barrido, de algunos caracteres de interés taxonómico poco utilizados hasta la fecha, como las espículas o las espínulas sifonales. En el apartado biológico, se han estudiado los ciclos reproductores de las poblaciones de ascidias de una localidad determinada a lo largo de un ciclo anual. Los resultados muestran que las especies solitarias aparecen de forma constante a lo largo del ciclo anual, mientras que muchas de las formas coloniales son estacionales. También los ciclos reproductores de estas últimas son marcadamente estacionales, correlacionándose bien las épocas reproductoras con el origen biogeográfico de las especies

Feeding cessation alters host morphology and bacterial communities in the ascidian Pseudodistoma crucigaster

11 páginas, 2 tablas, 7 figurasBackground: Ascidians can associate with abundant and diverse consortia ofmicrobial symbionts, yet these communities remain unexamined for the majority of host ascidians and little is known about host-symbiont interactions. Methods: We coupled electron microscopy and 16S rRNA gene tag pyrosequencing to investigate the bacterial communities associated with the colonial ascidian Pseudodistoma crucigaster, a species endemic to theMediterranean Sea that has a life cycle with two phases: actively-filtering (active) and non-filtering (resting) forms. Results: Resting colonies exhibited a reduced branchial sac (feeding apparatus) and a thickened cuticle. Electron microscope images also suggested higher abundance of colonizing microorganisms on surfaces of resting colonies. Accordingly, bacterial sequences associated with environmental sources (sediment and biofilms, >99 % similarity) were detected exclusively in resting colonies. Bacterial communities of P. crucigaster colonies (active and resting) were dominated by 3 core taxa affiliated (>94 % similarity) with previously described symbiotic Alphaproteobacteria in marine invertebrates. Shifts in rare bacteria were detected when ascidians entered the resting phase, including the appearance of strictly anaerobic lineages and nitrifying bacterial guilds. Conclusions: These findings suggest that physical (thickened cuticle) and metabolic (feeding cessation) changes in host ascidians have cascading effects on associated bacteria, where modified oxygen concentrations and chemical substrates for microbial metabolism may create anaerobic microhabitats and promote colonization by environmental microorganisms.This research was funded by the Marie Curie International Reintegration Grant FP7-PEOPLE-2010-RG 277038 within the 7th European Community Framework Program, the Spanish Government projects MARSYMBIOMICS CTM2013-43287-P and CHALLENGEN CTM2013-48163, and the Catalan Government grant 2014SGR-336 for Consolidated Research Groups.Peer reviewe

Microsatellite markers reveal shallow genetic differentiation between cohorts of the common sea urchin Paracentrotus lividus (Lamarck) in northwest Mediterranean

Temporal variability was studied in the common sea urchin Paracentrotus lividus through the analysis of the genetic composition of three yearly cohorts sampled over two consecutive springs in a locality in northwestern Mediterranean. Individuals were aged using growth ring patterns observed in tests and samples were genotyped for five microsatellite loci. No reduction of genetic diversity was observed relative to a sample of the adult population from the same location or within cohorts across years. FST and amova results indicated that the differentiation between cohorts is rather shallow and not significant, as most variability is found within cohorts and within individuals. This mild differentiation translated into estimates of effective population size of 90-100 individuals. When the observed excess of homozygotes was taken into account, the estimate of the average number of breeders increased to c. 300 individuals. Given our restricted sampling area and the known small-scale heterogeneity in recruitment in this species, our results suggest that at stretches of a few kilometres of shoreline, large numbers of progenitors are likely to contribute to the larval pool at each reproduction event. Intercohort variation in our samples is six times smaller than spatial variation between adults of four localities in the western Mediterranean. Our results indicate that, notwithstanding the stochastic events that take place during the long planktonic phase and during the settlement and recruitment processes, reproductive success in this species is high enough to produce cohorts genetically diverse and with little differentiation between them. Further research is needed before the link between genetic structure and underlying physical and biological processes can be well established

Benthic assemblages in two Mediterranean caves: species diversity and coverage as a function of abiotic parameters and geographic distance

16 páginas, 5 figuras, 4 tablasBenthic assemblages of two Mediterranean submarine caves were compared. Species coverage and number of species were lower in internal (dark) communities than external. This feature was specially marked in the less illuminated cave. Ordination analyses performed on species coverage per community for each cave separately, distinguished several benthic communities from the outermost to the innermost zone of each cave. Cluster analyses on species coverage, taking into account all communities in both the caves, established similarities among communities: algal-dominated communities clustered according to the level of light received independently of the cave they inhabited, while animal-dominated communities were more similar within each cave than between the caves. Moreover, among the abiotic parameters measured irradiance was the only factor that clearly diminished from the entrance to the innermost zone in both the caves. In contrast, water movement and particulate organic matter varied di¡erently in each cave. Results indicate that the di¡erent topography, depth and geographic location of the two caves determine water movement, light penetration and nutrient availability along the caves. These factors are responsible for determining species abundance and diversity, as well as species growth habit in each community.This research was partially supported by INTERREG-IIIA K115C n 0123 (EU) and CICYT (Comision Interdepartmental de Ciencia yTechnología) REN2001-2312-CO3/MAR grants. It also benefited from Governments of Catalonia and Spain fellowships to R. MartíPeer reviewe

Ultrastructure, molecular phylogenetics and chlorophyll a content of novel cyanobacterial symbionts in temperate sponge hosts

Marine sponges often harbor photosynthetic symbionts that may enhance host metabolism and ecological success, yet little is known about the factors that structure the diversity, specificity, and nature of these relationships. Here, we characterized the cyanobacterial symbionts in two congeneric and sympatric host sponges that exhibit distinct habitat preferences correlated with irradiance: Ircinia fasciculata (higher irradiance) and Ircinia variabilis (lower irradiance). Symbiont composition was similar among hosts and dominated by the sponge-specific cyanobacterium Synechococcus spongiarum. Phylogenetic analyses of 16S-23S rRNA internal transcribed spacer (ITS) gene sequences revealed that Mediterranean Ircinia spp. host a specific, novel symbiont clade ("M") within the S. spongiarum species complex. A second, rare cyanobacterium related to the ascidian symbiont Synechocystis trididemni was observed in low abundance in I. fasciculata and likewise corresponded to a new symbiont clade. Symbiont communities in I. fasciculata exhibited nearly twice the chlorophyll a concentrations of I. variabilis. Further, S. spongiarum clade M symbionts in I. fasciculata exhibited dense intracellular aggregations of glycogen granules, a storage product of photosynthetic carbon assimilation rarely observed in I. variabilis symbionts. In both host sponges, S. spongiarum cells were observed interacting with host archeocytes, although the lower photosynthetic activity of Cyanobacteria in I. variabilis suggests less symbiont-derived nutritional benefit. The observed differences in clade M symbionts among sponge hosts suggest that ambient irradiance conditions dictate symbiont photosynthetic activity and consequently may mediate the nature of host-symbiont relationships. In addition, the plasticity exhibited by clade M symbionts may be an adaptive attribute that allows for flexibility in host-symbiont interactions across the seasonal fluctuations in light and temperature characteristic of temperate environments