4 páginas, 3 figuras. ; Intraorganism genetic stability is assumed in most organisms. However, here we show for the first time intraorganism genetic heterogeneity in natural populations of marine sponges. A total of 36 different multilocus genotypes (MLGs) were detected in 13 individuals of Scopalina lophyropoda sampled at 4 distant points within each sponge. All genotypes (showing a mosaic distribution), were transmitted to the progeny, thus contributing to the high genetic diversity and low clonality reported for this species, although its populations are small and structured and show high fission rates. There did not seem to be intraindividual genotype conflicts; on the contrary, chimeric individuals are expected to show low mortality thanks to the differential mortality of their different MLGs. This novel mechanism may also counterbalance genetic constraints in other benthic invertebrate species. The presence of sponge chimerism also suggests that results from previous population genetics studies could have been misinterpreted. ; This work was supported by the Spanish Government (CICYT) (BENTHOMICS CTM2010-22218) to M.J.U. ; Peer reviewed
9 pages, 3 figures, 5 tables. ; [Background] Rare species have seldom been studied in marine habitats, mainly because it is difficult to formally assess the status of rare species, especially in patchy benthic organisms, for which samplings are often assumed to be incomplete and, thus, inappropriate for establishing the real abundance of the species. However, many marine benthic invertebrates can be considered rare, due to the fragmentation and rarity of suitable habitats. Consequently, studies on the genetic connectivity of rare species in fragmented habitats are basic for assessing their risk of extinction, especially in the context of increased habitat fragmentation by human activities. Sponges are suitable models for studying the intra- and inter-population genetic variation of rare invertebrates, as they produce lecitotrophic larvae and are often found in fragmented habitats. ; [Results] We investigated the genetic structure of a Mediterranean sponge, Scopalina lophyropoda (Schmidt), using the allelic size variation of seven specific microsatellite loci. The species can be classified as "rare" because of its strict habitat requirements, the low number of individuals per population, and the relatively small size of its distribution range. It also presents a strong patchy distribution, philopatric larval dispersal, and both sexual and asexual reproduction. Classical genetic-variance-based methods (AMOVA) and differentiation statistics revealed that the genetic diversity of S. lophyropoda was structured at the three spatial scales studied: within populations, between populations of a geographic region, and between isolated geographic regions, although some stochastic gene flow might occur among populations within a region. The genetic structure followed an isolation-by-distance pattern according to the Mantel test. However, despite philopatric larval dispersal and fission events in the species, no single population showed inbreeding, and the contribution of clonality to the population makeup was minor (only ca. 4%). ; [Conclusions] The structure of the S. lophyropoda populations at all spatial scales examined confirms the philopatric larval dispersal that has been reported. Asexual reproduction does not seem to play a relevant role in the populations. The heterozygote excess and the lack of inbreeding could be interpreted as a hitherto unknown outcrossing strategy of the species. The envisaged causes for this strategy are sperm dispersal, a strong selection against the mating of genetically related individuals to avoid inbreeding depression or high longevity of genets combined with stochastic recruitment events by larvae from other populations. It should be investigated whether this strategy could also explain the genetic diversity of many other patchy marine invertebrates whose populations remain healthy over time, despite their apparent rarity. ; This research was supported by an I3P predoctoral fellowship from CSIC to AB and funded by project CMT2007-66635-C02-01 of the Spanish Government (CICYT) to MJU. ; Peer reviewed
8 páginas, 3 figuras, 1 tabla. ; This study was financed by INTERGEN CTM-2004-05265-CO2/MAR (Spanish Government). A.B. was granted with an I3P fellowship from the CSIC. ; Peer reviewed
Este artículo contiene 18 páginas, 8 figuras. ; Sponges are key organisms in the marine benthos where they play essential roles in ecological processes such as creating new niches, competition for resources, and organic matter recycling. Despite the increasing number of taxonomical studies, many sponge species remain hidden, whether unnoticed or cryptic. The occurrence of cryptic species may confound ecological studies by underestimating biodiversity. In this study, we monitored photographically growth, fusions, fissions, and survival of two morpho- logically cryptic species Hemimycale mediterranea Uriz, Garate & Agell, 2017 and H. columella (Bowerbank, 1874). Additionally, we characterized the main environmental factors of the corresponding species habitats, trying to ascertain whether some abiotic factors were correlated with the distribution of these species. Sponge monitoring was performed monthly. Seawater samples were collected the same monitoring days in the vicinity of the target sponges. Results showed contrasting growth and survival patterns for each species: H. mediterranea totally disappeared after larval release while 64% of individuals of H. columella survived the entire two years we monitored. The species also differed in the number of fissions and fusions. These events were evenly distributed throughout the year in the H. mediterranea population but concentrated in cold months in H. columella. No measured environmental factor correlated with H. mediterranea growth rates, while temperature and dissolved organic nitrogen were negatively correlated with H. columella growth rates. The strong differences in depth distribution, survival, growth, fusions, and fissions found between these two cryptic species, highlights the importance of untangling cryptic species before ecological studies are performed in particular when these species share geographical distribution. ; MJU has received research grants from MarSymbiOmics from the Ministry of Economy and Competitivity (MINECO, I+D+I of Excellence, CTM2013-43287-P), the Benthic Ecology Consolidate Team (2014-SGR-120) from the Generalitat of Catalonian, and the BluePharm Train (FP7 People-INT) from the European Union. LG benefited from a fellowship (FPI BES-2011-049132) associated to the Benthomics' Project (ref. CTM2010-22218-C02-01) from the Ministry of Science and Innovation to MJU. ; Peer reviewed
7 páginas, 9 figuras. ; Marine biodiversity is difficult to assess accurately in part because of the existence of sibling species, which are difficult to discern. This is particularly tricky when sibling species live in sympatry. We investigated biological and ecological traits in 2 sympatric sibling sponge species inhabiting the shallow north-western Mediterranean: Scopalina lophyropoda Schmidt, 1862 and S. blanensis Blanquer & Uriz, 2008. Growth, fissions, fusions, and survival were monitored twice monthly for 2 yr. S. lophyropoda slightly increased in area over the 2 yr period, whereas S. blanensis did not show effective growth, since gains in autumn to winter were offset by losses in spring to summer. Survival was significantly different in both species. By the end of the study (24 mo), 74% of the individuals of S. lophyropoda and 34% of S. blanensis survived. All individuals of S. lophyropoda and all but 5 of S. blanensis underwent fissions or fusions at least once during the study. The frequencies of multiple fissions and fusions were higher in S. blanensis than in S. lophyropoda. These 2 sympatric sibling species share common traits such as a high dynamism (higher than any other previously studied encrusting sponge species) and intra-species variability in growth. However, they showed contrasting ecological strategies (conservative in S. lophyropoda vs. opportunistic in S. blanensis), which favours species coexistence. This example shows for the first time how seasonality promotes the co-existence of sibling sponge species in the Mediterranean, and may represent an important step towards understanding species coexistence mechanisms. ; This study was funded by grants INTERGEN CTM2004- 05265-C02-02/MAR and MARMOL CMT2007-66635-C02 from the Spanish Government (CICYT) to M.J.U. and an I3P fellowship to A.B. ; Peer reviewed
8 páginas, 2 figuras, 2 tablas. ; Insight from the spatial genetic structure (SGS) of a species is fundamental to understanding the patterns of effective dispersal and gene flow among its populations. Despite the ecological importance of sponges and the variety of reproduction and dispersal strategies they present, which can strongly influence SGS, there is only 1 study assessing small-scale SGS in sponges. That species had a continuous distribution and relatively wide-scale larval dispersal. Here we study the contribution of sexual and asexual reproduction, and the breeding and mating system to the SGS of a sponge species, Scopalina lophyropoda, with a patchy distribution and more limited larval dispersal. All individuals from 3 populations were mapped and genetically characterised for 7 microsatellite loci. The extent of clonality was minor (ca. 7%), possibly caused by a balance between fissions and fusions. The scarce clonality did not contribute to the SGS, which was analysed by autocorrelation statistics at both the ramet (including clones) and the genet (excluding clones) levels. The spatial autocorrelation analyses elicited a pattern of strong SGS at the small scale, confirming the predictions of philopatric larval dispersal, which fosters isolation by distance. All these patterns, however, contrast with the conspicuous lack of inbreeding detected in the populations, which is in agreement with recent data on other marine modular invertebrates and confirms that strong SGS does not necessarily imply inbreeding. ; This study was funded by grant CTM2007-66635-CO2 from the Spanish Government to M.J.U. and an I3P fellowship to A.B ; Peer reviewed
