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

Stable populations in unstable habitats: temporal genetic structure of the introduced ascidian Styela plicata in North Carolina

14 páginas, 3 tablas, 4 figuras.The analysis of temporal genetic variability is an essential yet largely neglected tool to unveil and predict the dynamics of introduced species. We here describe the temporal genetic structure and diversity over time of an introduced population of the ascidian Styela plicata (Lesueur, 1823) in Wilmington (North Carolina, USA, 34°08′24″N, 77°51′44″W). This population suffers important salinity and temperature changes, and in June every year we observed massive die-offs, leaving free substratum that was recolonized within a month. We sampled 12–14 individuals of S. plicata every 2 months from 2007 to 2009 (N = 196) and analyzed a mitochondrial marker (the gene cytochrome oxidase subunit I, COI) and seven nuclear microsatellites. Population genetic analyses showed similar results for both types of markers and revealed that most of the genetic variation was found within time periods. However, analyses conducted with microsatellite loci also showed weak but significant differences among time periods. Specifically, in the samplings after die-off episodes (August–November 2007 and 2008) the genetic diversity increased, the inbreeding coefficient showed prominent drops, and there was a net gain of alleles in the microsatellite loci. Taken together, our results suggest that recruits arriving from neighboring populations quickly occupied the newly available space, bringing new alleles with them. However, other shifts in genetic diversity and allele loss and gain episodes were observed in December–January and February–March 2008, respectively, and were apparently independent of die-off events. Overall, our results indicate that the investigated population is stable over time and relies on a periodic arrival of larvae from other populations, maintaining high genetic diversity and a complex interplay of allele gains and losses.This research was supported by a grant from the United States–Israel Binational Science Foundation (BSF), Jerusalem, Israel (number 2014025), the Spanish Government project CTM2013—48163—and the Catalan Government Grant 2014SGR-336 for Consolidated Research Groups.Peer reviewe

Too cold for invasions? Contrasting patterns of native and introduced ascidians in subantarctic and temperate Chile

10 páginas, 1 tabla, 2 figuras.We analysed the biodiversity of ascidians in two areas located in southern and northern Chile: Punta Arenas in the Strait of Magellan (53º latitude, subantarctic) and Coquimbo (29º latitude, temperate). The oceanographic features of the two zones are markedly different, with influence of the Humboldt Current in the north, and the Cape Horn Current System, together with freshwater influxes, in the Magellanic zone. Both regions were surveyed twice during 2013 by SCUBA diving and pulling ropes and aquaculture cages. Both artificial structures and natural communities were sampled. A total of 22 species were identified, three of them reported for the first time in Chilean waters: Lissoclinum perforatum, Synoicum georgianum, and Polyzoa minor. The first is an introduced species found here for the first time in the Pacific. No species occurred in both regions, highlighting the very different environmental conditions of subantarctic vs. temperate waters. In spite of exhaustive searches in aquaculture facilities and on artificial structures such as harbour docks and piers, no introduced species were found in the Punta Arenas area. Conversely, 5 out of 11 (45%) species found in northern Chile were introduced. The Coquimbo area has a history of ship traffic dating back at least 150 years, and cultures of native (e.g. scallop) as well as exotic species (e.g. abalone) have been deployed for ca. 35 years. Some of the introduced species, such as Ciona robusta (formerly C. intestinalis sp. A), constitute pests for scallop culture facilities in the area, causing serious losses to local farmers. It is surprising that the Punta Arenas zone, with a history of ship traffic dating back ca. 500 years and over 25 years of sustained mussel and salmon aquaculture activity, is apparently free from introduced species. The ascidian cover on artificial structures is high, but it is made up of native species such as Paramolgula sp., Cnemidocarpa verrucosa, or Polyzoa opuntia. It is hypothesized that cold waters (5 to 11ºC) are the determining factor hindering the development of introduced ascidians, which tend to be temperate-warm water species. The ongoing warming in the Southern Cone may change this picture and continued monitoring is strongly advised.This research was funded by CONICYT Chile (Grant 80122006). Additional funding was obtained by XT from the Spanish Government (project CHALLENGEN CTM2013-48163) and by JIC from University of Magallanes - UMAG/DI&P Grant PR-F2-01CRN- 12, CIMAR 18 & CIMAR 20 Fjords Chilean Navy, and GAIAAntarctic Project (MINEDUC-UMAG). RMR received a research grant from CNPq–National Counsel of Technological and Scientific Development (304768/2010-3).Peer reviewe

Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile

30 páginas, 15 figuras, 2 tablasWe studied the ascidian fauna from two zones located in subantarctic (Punta Arenas, latitude 53º) and temperate Chile (Coquimbo, latitude 29º). The different oceanographic features of the two zones, with influence of the Humboldt Current in the north and the Cape Horn Current System and freshwater inputs in the south, led to markedly different ascidian faunas. A total of 22 species were recorded, with no shared species across the two areas (11 species each). The new species Polyzoa iosune is described, Lissoclinum perforatum is found for the first time in the Pacific Ocean, and Synoicum georgianum and Polyzoa minor are new to the Chilean fauna. The populations of Ciona in the Coquimbo area (formerly attributed to Ciona intestinalis) correspond to the species Ciona robusta. A total of 35 Cytochrome oxidase (COI) sequences of the standard barcode region have been obtained for 17 of the 22 species reported.This research was funded by CONICYT Chile (Grant 80122006). Additional funding was obtained by XT from the Spanish Government (project CHALLENGEN CTM2013-48163) and by JIC from University of Magallanes: UMAG/DI&P Grant PR-F2-01CRN-12, CIMAR 18 & CIMAR 20 Fjords Chilean Navy, and GAIA-Antarctic Project (MINEDUC-UMAG). RMR received a research grant from CNPq–National Counsel of Technological and Scientific Development (304768/2010-3).Peer reviewe

Cyanobacterial Diversity and a New Acaryochloris-Like Symbiont from Bahamian Sea-Squirts

Symbiotic interactions between ascidians (sea-squirts) and microbes are poorly understood. Here we characterized the cyanobacteria in the tissues of 8 distinct didemnid taxa from shallow-water marine habitats in the Bahamas Islands by sequencing a fragment of the cyanobacterial 16S rRNA gene and the entire 16S–23S rRNA internal transcribed spacer region (ITS) and by examining symbiont morphology with transmission electron (TEM) and confocal microscopy (CM). As described previously for other species, Trididemnum spp. mostly contained symbionts associated with the Prochloron-Synechocystis group. However, sequence analysis of the symbionts in Lissoclinum revealed two unique clades. The first contained a novel cyanobacterial clade, while the second clade was closely associated with Acaryochloris marina. CM revealed the presence of chlorophyll d (chl d) and phycobiliproteins (PBPs) within these symbiont cells, as is characteristic of Acaryochloris species. The presence of symbionts was also observed by TEM inside the tunic of both the adult and larvae of L. fragile, indicating vertical transmission to progeny. Based on molecular phylogenetic and microscopic analyses, Candidatus Acaryochloris bahamiensis nov. sp. is proposed for this symbiotic cyanobacterium. Our results support the hypothesis that photosymbiont communities in ascidians are structured by host phylogeny, but in some cases, also by sampling location

Resilience to Disturbance Despite Limited Dispersal and Self-Recruitment in Tropical Barrel Sponges: Implications for Conservation and Management

While estimates of connectivity are important for effective management, few such estimates are available for reef invertebrates other than for corals. Barrel sponges are one of the largest and most conspicuous members of the coral reef fauna across the Indo-Pacific and given their large size, longevity and ability to process large volumes of water, they have a major role in reef functioning. Here we used a panel of microsatellite markers to characterise the genetic structure of two barrel sponge species, Xestospongia testudinaria and a currently undescribed Xestospongia species. We sampled across seven populations in the Wakatobi Marine National Park, SE Sulawesi (Indonesia) spanning a spatial scale of approximately 2 to 70 km, and present the first estimates of demographic connectivity for coral reef sponges. Genetic analyses showed high levels of genetic differentiation between all populations for both species, but contrasting patterns of genetic structuring for the two species. Autocorrelation analyses showed the likely dispersal distances of both species to be in the order of 60 and 140 m for Xestopongia sp. and Xestospongia testudinaria, respectively, which was supported by assignment tests that showed high levels of self-recruitment (>80%). We also found consistently high inbreeding coefficients across all populations for both species. Our study highlights the potential susceptibility of barrel sponges to environmental perturbations because they are generally long-lived, slow growing, have small population sizes and are likely to be reliant on self-recruitment. Surprisingly, despite these features we actually found the highest abundance of both barrel sponge species (although they were generally smaller) at a site that has been severely impacted by humans over the last fifty years. This suggests that barrel sponges exhibit environmental adaptation to declining environmental quality and has important implications for the management and conservation of these important reef species. © 2014 Bell et al

Increased Inter-Colony Fusion Rates Are Associated with Reduced COI Haplotype Diversity in an Invasive Colonial Ascidian Didemnum vexillum

Considerable progress in our understanding of the population genetic changes associated with biological invasions has been made over the past decade. Using selectively neutral loci, it has been established that reductions in genetic diversity, reflecting founder effects, have occurred during the establishment of some invasive populations. However, some colonial organisms may actually gain an ecological advantage from reduced genetic diversity because of the associated reduction in inter-colony conflict. Here we report population genetic analyses, along with colony fusion experiments, for a highly invasive colonial ascidian, Didemnum vexillum. Analyses based on mitochondrial cytochrome oxidase I (COI) partial coding sequences revealed two distinct D. vexillum clades. One COI clade appears to be restricted to the probable native region (i.e., north-west Pacific Ocean), while the other clade is present in widely dispersed temperate coastal waters around the world. This clade structure was supported by 18S ribosomal DNA (rDNA) sequence data, which revealed a one base-pair difference between the two clades. Recently established populations of D. vexillum in New Zealand displayed greatly reduced COI genetic diversity when compared with D. vexillum in Japan. In association with this reduction in genetic diversity was a significantly higher inter-colony fusion rate between randomly paired New Zealand D. vexillum colonies (80%, standard deviation ±18%) when compared with colonies found in Japan (27%, standard deviation ±15%). The results of this study add to growing evidence that for colonial organisms reductions in population level genetic diversity may alter colony interaction dynamics and enhance the invasive potential of newly colonizing species

CO I Barcoding Reveals New Clades and Radiation Patterns of Indo-Pacific Sponges of the Family Irciniidae (Demospongiae: Dictyoceratida)

DNA barcoding is a promising tool to facilitate a rapid and unambiguous identification of sponge species. Demosponges of the order Dictyoceratida are particularly challenging to identify, but are of ecological as well as biochemical importance.Here we apply DNA barcoding with the standard CO1-barcoding marker on selected Indo-Pacific specimens of two genera, Ircinia and Psammocinia of the family Irciniidae. We show that the CO1 marker identifies several species new to science, reveals separate radiation patterns of deep-sea Ircinia sponges and indicates dispersal patterns of Psammocinia species. However, some species cannot be unambiguously barcoded by solely this marker due to low evolutionary rates.We support previous suggestions for a combination of the standard CO1 fragment with an additional fragment for sponge DNA barcoding