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Este artículo contiene 6 páginas, 1 figura. ; Phylogeography is an integrative discipline that aims to understand the geographic ordination of genotypes. In recent decades, phylogeographic approaches have been used to enhance our understanding of both biogeography and landscape genetics across a variety of spatial and temporal scales. By definition, species studied using these approaches need to meet certain assumptions (e.g. mutation and drift need to be at equilibrium). However, artificially dispersed species (i.e. non-indigenous, naturalised and invasive species) often do not comply with these assumptions. Thus, the use of phylogeographic approaches to study these species may lead to erroneous interpretations. Considering that self-denominated phylogeographic studies of invasive species have proliferated in recent years and that genomic tools are now more accessible than ever before, kick starting this debate is particularly timely. We argue herein that invasion scientists must carefully use phylogeographic approaches when studying genomic data obtained from the introduced range. In addition, the assumptions of these phylogeographic approaches need to be explicitly considered when interpreting genomic patterns of invasive species. Finally, we suggest abandoning the use of the term 'phylogeography' for describing geographically contextualized genomic data from the introduced range to avoid both terminological and methodological confusion. ; The ideas developed in this opinion note were partly conceived during the development of the project CTM2017-88080 (MCIU/AEI/FEDER/UE) from the Spanish Government. ; Peer reviewed

1 página ; 1 Figura ; Research was funded by the Spanish Government project CTM2010-17755. ; Peer reviewed

16 Páginas ; 9 Tablas ; 3 Figuras ; We studied sequence variation in the mitochondrial gene cytochrome c oxidase subunit I (COI) for 135 individuals from eight Mediterranean populations of the colonial ascidian Pycnoclavella communis across most of its presently known range of distribution in the Mediterranean. Three haplotypes from Atlantic locations were also included in the study. Phylogenetic, phylogeographic and population genetic analyses were used to unravel the genetic variability within and between populations. The study revealed 32 haplotypes for COI, 29 of them grouped within two Mediterranean lineages of P. communis (mean nucleotide divergence between lineages was 8.55%). Phylogenetic and network analyses suggest the possible existence of cryptic species corresponding to these two lineages. Population genetic analyses were restricted to the five populations belonging to the main genetic lineage, and for these localities we compared the information gleaned from COI sequence data and from eight microsatellite loci. A high genetic divergence between populations was substantiated using both kinds of markers (COI, global Fst ¼ 0.343; microsatellite loci, global Fst ¼ 0.362). There were high numbers of private haplotypes (COI) and alleles (microsatellites) in the populations studied. Restricted gene flow and inbreeding occur in the present range of distribution of the species. Microsatellite loci showed a strong incidence of failed amplifications, which we attribute to the marked intraspecies variability that hampered the application of these highly specific markers. Our results show important genetic variability at all levels studied, from within populations to between basins, possibly coupled to speciation processes. This variability is attributable to restricted gene flow among populations due to short-distance dispersal of the larvae. ; The research was funded by the projects CTM2004-05265 and CTM2007-66635 of the Spanish Government and the ECIMAR project of the ''Agence Nationale de la Recherche'' (France). ; Peer reviewed

11 Páginas ; 4 Figuras ; 3 Tablas ; Bindin is a sea urchin gamete-recognition protein that plays an essential role in the specificity of egg– sperm interactions and thus may be evolving under sexual selection and be related to speciation. Bindin has been found to evolve under strong selection in some sea urchin genera and neutrally in others. In this study, we characterized bindin in the two extant species of the genus Paracentrotus: P. lividus from the Atlanto-Mediterranean region and P. gaimardi from Brazil. The structure of the bindin molecule in Paracentrotus is similar to that of other genera studied thus far, consisting of a conserved core flanked by two variable regions and an intron of variable length located at the same conserved position as in other genera. Polymorphism in P. lividus is caused mainly by point substitutions and insertions/deletions, and length variations are caused mainly by the number of repeated motifs in the flanking regions. There is no evidence of recombination. Positive selection is acting on amino acid sites located in two regions flanking the conserved core. ; This research was funded by Project No. CTM2007-66635 of the Spanish Government and by general research funds from the Smithsonian Tropical Research Institute. ; Peer reviewed

15 Páginas ; 8 tablas ; 4 Figuras ; Benthic marine invertebrates with long-lived larvae are believed to have dispersal capabilities that contribute to maintaining genetic uniformity among populations over large geographical scales. However, both hydrological and biological factors may limit the actual dispersal of such larvae. We studied the population genetic structure of the edible common sea urchin Paracentrotus lividus (Lamarck, 1816), to explore its dispersal patterns in the Atlanto-Mediterranean region and, more specifically, to ascertain the role of the Strait of Gibraltar in shaping the genetic structure of this species. For this purpose, we analysed 158 individuals for the mitochondrial 16S rRNA gene and 151 of these for the nuclear single-copy intron adenine nucleotide transporter (ANT) from 16 localities from the Atlantic and Mediterranean basins, spanning over 4,000 km. Mitochondrial 16S rRNA shows higher genetic diversity in the Mediterranean than in the Atlantic and reveals a sharp break between the populations of both basins, probably as a consequence of the barrier imposed by the Almerı´a–Ora´n hydrological front, situated east of the Strait of Gibraltar. Both markers suggest that a recent population expansion has taken place in both basins, most probably following the Messinian salinity crisis. ; This study was funded by projects CTM2004-05265 and CTM2007-66635 of the Spanish Government and by internal funds from the Museum of Comparative Zoology, Harvard University ; Peer reviewed

11 Páginas ; 3 Figuras ; 3 Tablas ; 1 Apéndice ; The spread of non-indigenous species into new marine habitats represents an increasing threat to global diversity. Genetic techniques provide basic understanding of the invasion processes. The ascidian Microcosmus squamiger is considered to be native to Australia, having been spread worldwide via transoceanic vessels. It has successfully invaded artificial and natural habitats where it has become a pest. We studied phylogeography and genetic structure of 12 M. squamiger populations, including samples from its native range (Australia) and introduced populations from the Indian, Pacific, and Atlantic oceans, as well as the Mediterranean Sea. We amplified 574 bp of the mitochondrial COI gene in 258 individuals and found a total of 52 haplotypes. A haplotype tree revealed two main groups of haplotypes. The relative frequency of each group of haplotypes, multidimensional scaling, and analysis of molecular variance showed important differences between the western Australia localities and the remaining ones (eastern Australia and introduced populations). Furthermore, we found that the colonization of the different areas by M. squamiger has not occurred independently, as many introduced populations shared some low frequency alleles. A nested clade analysis showed a global pattern of restricted gene flow with isolation by distance, although we found episodes of long-distance dispersal in some clades. A contiguous range expansion was detected between Australian populations. We conclude that M. squamiger is native to Australia and has most likely expanded its range of distribution sequentially through worldwide shipping, especially from the harbours of the more populated eastern Australia. In introduced populations, we found a high genetic diversity which suggests enhanced invasive potential. Consequently, there is a need to control this species, as it outcompetes local biota and is an economic threat. ; This research was funded by projects CTM2004-05265, CGL2006-13423, and CTM2007-66635 of the Spanish Government and a FPU scholarship to M. R. from the Spanish 'Ministerio de Educación y Ciencia'. ; Peer reviewed

Este artículo contiene 12 páginas, 3 figuras, 6 tablas. ; Spatial and temporal variation of environmental parameters can affect dispersal, recruitment and population persistence of marine benthic species. Studies including inter-annual comparisons of genetic structure often indicate high/moderate temporal heterogeneity in marine invertebrates, which may be a prevailing pattern. This suggests that temporal studies are necessary to understand the dynamics of marine metapopulations. In this study, we analyzed the spatio-temporal genetic structure of the ascidian Pyura chilensis, a low dispersal sessile marine species endemic from the Southeast Pacific coast and highly demanded for human consumption. We sequenced a fragment of the mitochondrial gene Cytochrome Oxidase I (COI) from 1,005 individuals of six locations (30–40 individuals per site and year) spanning a wide latitudinal range (24◦–42◦S) and sampled over 5 years (2012, 2014, 2015, 2016, and 2017). The genetic structure of COI indicates the presence of three monophyletic lineages (haplogroups 1–3) previously described for the species, being one of them highly divergent and geographically restricted (˜39◦S, Los Molinos). Considering the whole dataset, a picture of strong spatial differentiation but temporal stability emerged in Pyura chilensis. However, detailed studies of the two main lineages revealed important differences in the extent of spatio-temporal variation. Analyses using haplotype frequencies sorted by site and year showed that, for haplogroup 1, genetic variation was explained mainly by differences between sites, while for haplogroup 2 differences between years were prevailing. Haplogroup 3 was restricted to the most southern sites, and also showed inter-annual variability in its frequency. These results point to disparate patterns of genetic differentiation, which may reflect different adaptive scope or variation in reproductive and dispersal features and could be a response to extreme events such as El Niño (2015–2016). This work calls for caution when obtaining general trends in species clearly differentiated in lineages, and prompts instead for separate analyses of sub-specific genetic lineages whenever possible. ; This study was funded by the Chilean National Fund for Scientific and Technological Development through Grants FONDECYT 1140862, FONDECYT 3190482, Millennium Science Initiative Program—ICN2019_015, and partly funded by project PopCOmics CTM2017-88080 (MCIU/AEI/FEDER) of the Spanish Government. ; Peer reviewed

Este artículo contiene 8 páginas, 6 figuras. ; Sessile organisms are reliant on the use of refugia or chemical and physical defences to avoid or reduce attacks from predators. Many solitary ascidians possess a thick leathery outer tunic, sometimes reinforced with inorganic inclusions, that generally acts to deter predators. The genus Herdmania is remarkable among ascidians in possessing an abundance of barbed needle-like calcareous spicules in both the external tunic and the internal mantle. Our focus was on a habitat-forming subtidal ascidian – Herdmania grandis. We questioned why a large ascidian possessing a leathery test would possess spicules within the mantle – an apparent defence within a defence. We first quantified variation in spicule size and density within animals. Second, we examined the size and density of spicules for individuals of a range of sizes. Third, we incorporated these spicules at natural concentrations into feeding discs and tested their ability to deter gastropod predators that specialise in consuming ascidians and an asteroid that is considered a generalist consumer. Finally, we examined survivorship of lab-reared ascidian recruits when exposed to the starfish predator. Spicules constituted up to 30% dry weight (DW) of the tunic and an astounding 57% DW of the body wall (mantle). Spicules were significantly smaller in the contractile regions of the animal (the siphon and branchial basket) and were also found in lower densities, though not significantly. Mantle spicules were effective feeding deterrents; control feeding discs, lacking spicules, were consumed at three times the rate of discs with spicules (p < 0.05) by specialist ascidian predators, the Ranellid gastropods Cabestana spengleri and Ranella australasia. In contrast, we did not detect a significant difference in the consumption of feeding discs by the seastar Meridiastra calcar. In addition, the seastar reduced survivorship of 90 day old lab-reared recruits by four-fold. We contend that the primary defence mechanism of this ascidian is the leathery test and that this is effective against generalist consumers. The second line of defence – spicules in the mantle –is to thwart gastropod predators that bypass the tunic either by boring through it or by inserting their proboscis directly into soft tissues of their prey via the siphons. The presence of both a leathery tunic and spicules in H. grandis probably contributes to the dominance of this species on shallow subtidal reefs in southeastern Australia, where it is an important habitat-forming species. Our findings confirm the importance of considering a range of consumer strategies and life history stages in assessing potential control of engineering species by predation. ; We acknowledge financial support from the Centre for Sustainable Ecosystem Solutions, University of Wollongong. This work was completed while XT undertook sabbatical leave in Australia. Funding was provided by project CTM 2017-88080 from the Spanish Government. This represents contribution no. 318 from the Ecology and Genetics Group at UOW. ; Peer reviewed

12 páginas, 8 figuras, 1 tabla. ; The life-history traits of long-lived benthic littoral invertebrates remain poorly understood. In this study, we analysed patterns of growth in three abundant sublittoral sponges from the western Mediterranean Sea, chosen for their close phylogenetic relatedness, sympatric distribution, and contrasting amounts of photosymbionts: high in Ircinia fasciculata, lower in I. variabilis, and absent in I. oros. Sponge area, perimeter, number of oscula, and epibiont abundance were quantified from in situ digital images taken monthly for 1.5 years and volumetric growth rates were calculated from empirical area–volume relationships. Volumetric growth rates were different among species and coherent with the photosymbiont abundance: high in I. fasciculata (40.03 ± 4.81 % year-1, mean ± SE), low in I. variabilis (5.65 ± 6.11 % year-1), and almost nil in I. oros (-0.04 ± 3.02 % year-1). Furthermore, a marked seasonality was observed in the first two species, with greater growth during the warm season. The high growth rates of I. fasciculata were likely fuelled by symbiont-derived photosynthates and required to compete in the well-lit, algal-dominated habitats this species prefers. In contrast, I. variabilis and I. oros tended to dwell in shaded habitats, where competition from slow-growing invertebrates is intense, and featured lower growth rates. The flattened morphology and lower circularity of I. variabilis indicates a capacity for adaptation to any space that is freed, while I. oros had less oscula and was more massive and circular, suggesting a strategy of passive occupation and minimisation of biological interactions. The results show that even congeneric species living sympatrically can achieve important biomass using different growth and substrate occupation strategies. ; This research was supported by the US National Science Foundation under grant 0853089, the Spanish Government projects CTM2010-22218 and CTM2010- 17755, and the Catalan Government Grant 2009SGR-484 for Consolidated Groups. ; Peer reviewed

14 Páginas ; 10 Figuras ; 1 Tabla ; Marine introductions are a serious threat for biodiversity, especially in seas where shipping is intensive. Microcosmus squamiger is a widespread marine invader that can alter native biota and it is therefore imperative to understand its biology and ecology. We studied the population dynamics and reproductive cycles of M. squamiger over a 2-year period, as well as its settlement and colonization patterns, in a north-western Mediterranean (NE Spain) locality where M. squamiger has been introduced. All biological parameters showed a strong seasonal pattern that peaked in summer with a major spawning episode at the end of summer. Sizefrequency histograms indicated a 2-year cycle. Colonization experiments suggested that M. squamiger recruitment mortality is high and requires a well structured community. In addition, we monitored the abundance of the native predator Thais haemastoma, which showed a significant positive correlation with M. squamiger biomass, indicating its potential usefulness as a biological control. ; This study was funded by project CTM2007-66635 of the Spanish Government. ; Peer reviewed

10 Páginas ; 3 Figuras ; 5 Tablas ; Studies examining the eVects of invasive species have focussed traditionally on the direct/lethal eVects of the invasive on the native community but there is a growing recognition that invasive species may also have non-lethal eVects. In terrestrial systems, non-lethal eVects of invasive species can disrupt early life-history phases (such as fertilisation, dispersal and subsequent establishment) of native species, but in the marine environment most studies focus on adult rather than early life-history stages. Here, we examine the potential for an introduced sessile marine invertebrate (Styela plicata) to exert both lethal and non-lethal eVects on a native species (Microcosmus squamiger) across multiple early life-history stages. We determined whether sperm from the invasive species interfered with the fertilisation of eggs from the native species and found no eVect. However, we did Wnd strong eVects of the invasive species on the post-fertilisation performance of the native species. The invasive species inhibited the settlement of native larvae and, in the Weld, the presence of the invasive species was associated with a tenfold increase in the post-settlement mortality of the native species, as well as an initial reduction of growth in the native. Our results suggest that larvae of the native species avoid settling near the invasive species due to reduced postsettlement survival in its presence. Overall, we found that invasive species can have complex and pervasive eVects (both lethal and non-lethal) across the early life-history stages of the native species, which are likely to result in its displacement and to facilitate further invasion. ; This project was funded by projects DPO666147 of the Australian Research Council, and CTM2007- 66635 and PIE 200730I026 of the Spanish Government ; Peer reviewed

11 pages, 6 figures, 3 tables. ; [EN] The bioactivity of the most abundant sponges from three communities in a Mediterranean cave was assessed by Microtox® assay in two seasons, spring (June) and autumn (November). We quantified bioactivity as a proxy for the investment in production of biologically active substances, and we related sponge bioactivity to growth form, growth rates, and physical contacts of each species with other species. We established a threshold for classifying a species as bioactive based on a comparison between the results of the Microtox® and the sea urchin embryo toxicity bioassay. A total of 30 species were included in the study, of which 50% were bioactive in some community or season. Significant ecological (between communities) and seasonal variation in mean bioactivity was found. When sponge bioactivity was related to sponge growth shape, it was found that the encrusting species tended to be more toxic than the non-encrusting ones. There was a negative relationship between bioactivity and sponge growth, suggesting a trade-off in energy allocation to defence and to other biological functions. Furthermore, a negative correlation was found between bioactivity and positive associations with other species. These results highlight the important role of chemically-mediated interactions in cave communities. ; [ES] La bioactividad de las esponjas más abundantes en tres comunidades a lo largo de una cueva mediterránea fue cuantificada por medio del bioensayo Microtox® en dos estaciones, primavera (junio) y otoño (noviembre). La bioactividad medida se usó como una aproximación a la inversión en producción de sustancias bioactivas, y se relacionó la bioactividad de las esponjas con su morfología, tasas de crecimiento, y contactos de cada especie con otras. Se estableció un umbral para determinar si una especie es bioactiva mediante una comparación entre el test Microtox® y el test de biotoxicidad en embriones de erizo. En total se estudiaron 30 especies, de las que un 50% fue bioactivo en alguna comunidad o estación del año. Se encontraron importantes diferencias ecológicas (entre comunidades) y estacionales en la bioactividad media. Cuando se relacionó la bioactividad con la morfología de las esponjas se encontró que las esponjas incrustantes tendían a ser más tóxicas que las de otras morfologías. Se detectó una correlación negativa entre bioactividad y crecimiento, lo que sugiere un balance entre inversión de energía en defensa y en otras funciones. Por otro lado, se encontró una correlación negativa entre bioactividad y las asociaciones positivas con otras especies. Estos resultados ponen de manifiesto el importante papel de las interacciones mediadas por sustancias químicas en comunidades de cuevas. ; This research was funded by the project CTM2007-66635 of the Spanish Government, and the ECIMAR project of the Agence Nationale de la Recherche (France). ; Peer reviewed

13 páginas, 7 figuras, 4 tablas. ; The toxicity of crude extracts of 32 seaweed species from the western Mediterranean was analysed by Microtox® assay in spring and autumn of 1996 and 1997. The species analysed represented more than 76% of seaweed coverage in the 3 algal communities studied: photophilic and sciaphilic communities from the Cabrera Archipelago (Balearic Islands), and a hemisciaphilic community from the Medes Archipelago (northeastern Iberian Peninsula). Most species showed seasonal variation of toxicity, which was greater in species from Cabrera than in those from Medes. Both, intra and interspecies variation of toxicity were found. Moreover, comparison of mean toxicity of these communities showed that toxicity was higher in November than in June in all cases, and that the photophilic community had both the highest number and the most toxic species. To make an ecologically relevant interpretation of the toxicity detected by Microtox®, we compared the toxicity of extracts analysed by the Microtox® test and those analysed by the commonly used sea urchin embryo assay. In addition to seaweeds, some species of invertebrates (sponges and ascidians) were compared to ascertain whether the relationship between the 2 tests was applicable to species belonging to different phyla. These comparisons allowed us to establish that 0.5 gamma units in Microtox® assay is the threshold value between toxic and non-toxic species. Following a light gradient from the photophilic to the sciaphilic communities, the seaweed species that were occasionally toxic increased while the always-toxic seaweeds decreased. Rhodophyta and Phaeophyta had a higher percentage of toxic species than Chlorophyta. Non-encrusting seaweed forms were more toxic than the encrusting ones, and in contrast to most other seaweeds, the non-encrusting calcareous species that increased coverage from June to November simultaneously displayed a marked decrease in toxicity. We conclude that the temporal variation of toxicity observed in the seaweeds studied may be partially explained by intrinsic factors of the species (growth rates and growth shapes). ; This research was funded by projects Mar95-1764 and REN2001-2312 of the Spanish Government and by the Interreg IIIA-1-72-E project of the European Union. ; Peer reviewed

Este artículo contiene 10 páginas, 6 figuras, 1 tabla. ; The formation of chimeric entities through colony fusion has been hypothesized to favour colonisation success and resilience in modular organisms. In particular, it can play an important role in promoting the invasiveness of introduced species. We studied prevalence of chimerism and performed fusion experiments in Mediterranean populations of the worldwide invasive colonial ascidian Didemnum vexillum. We analysed single zooids by whole genome amplification and genotyping-by-sequencing and obtained genotypic information for more than 2,000 loci per individual. In the prevalence study, we analysed nine colonies and identified that 44% of them were chimeric, composed of 2–3 different genotypes. In the fusion experiment 15 intra- and 30 intercolony pairs were assayed but one or both fragments regressed and died in ~45% of the pairs. Among those that survived for the length of the experiment (30 d), 100% isogeneic and 31% allogeneic pairs fused. Fusion was unlinked to global genetic relatedness since the genetic distance between fused or non-fused intercolony pairs did not differ significantly. We could not detect any locus directly involved in allorecognition, but we cannot preclude the existence of a histocompatibility mechanism. We conclude that chimerism occurs frequently in D. vexillum and may be an important factor to enhance genetic diversity and promote its successful expansion. ; Funding was obtained from project PopCOmics (CTM2017- 88080, MCIU, AEI/FEDER/UE). This is a contribution from the Consolidated Research Group "Benthic Biology and Ecology" SGR2017-1120 (Catalan Government). ; Peer reviewed

11 páginas, 2 tablas, 7 figuras ; Background: 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 reviewed