Phylogeography of the freshwater red alga Sirodotia (Batrachospermales,Rhodophyta) in Brazil

Considering the lack of knowledge on genetic variation on members of the freshwater red algal of the order Batrachospermales in tropical regions, phylogeographic patterns in Sirodotia populations were investigated using two mitochondrial regions: the cox2‐3 spacer and partial cox1 gene (barcode). Individuals identified as Sirodotia delicatula were analyzed from 14 stream segments across its distribution in Brazil. Phylogenetic analyses based on the ribulose‐1,5‐bisphosphate carboxylase/oxygenase large sub‐unit gene showed three clades, one representing S. delicatula, from all locations in southeastern Brazil and other regions from Brazil. The remaining samples formed two clades, which were highly divergent and distantly positioned from those of S. delicatula: 2.5–2.7% and 3.4–3.7%. This level of variation would warrant the species split of these taxa from mid‐western Brazil. A total of eight cox2‐3 spacer and nine cox1 haplotypes were observed among the 122 individuals studied. One location had two cox2‐3 haplotypes and three locations had two cox1 haplotypes; all others had a single dominant haplotype each. The existence of high intraspecific genetic variation among individuals of distinct locations (several haplotypes), but little variation within a location seems to be a pattern for the Batrachospermales. Haplotype networks showed low variation among the haplotypes from southeastern Brazil (10 locations with divergence of 0.3–1.1% for cox2‐3, 0.1–0.3% for cox1) and high variation among the haplotypes from the mid‐west region (four locations, 4.0–9.3% for cox2‐3, 6.2–8.4% for cox1). Thus, the present data clearly suggest the existence of cryptic species in Sirodotia in Brazil.     

The introduction to Japan of the Titan barnacle,Megabalanus coccopoma (Darwin, 1854) (Cirripedia: Balanomorpha) and the role of shipping in its translocation

The Titan Acorn barnacle, Megabalanus coccopoma, a native of the tropical eastern Pacific, has become established in the western Atlantic (Brazil and the northern Gulf of Mexico to the Carolinas), northwestern Europe and the western Indian Ocean (Mauritius), and therefore its dispersal capabilities are well known. This study reports its introduction to Japan and confirms its occurrence in Australia. In an attempt to determine the source of this introduction, phylogeographic techniques, involving cytochrome c oxidase I sequences of various widely separate populations of M. rosa and M. volcano, were utilized. No significant genetic differentiation or haplotype patterns between widely separated populations of each of the three species were found. Lack of such differentiation indicates recent geographical isolation and thus negates a null hypothesis predicting that the occurrence of one of more of these species in Australia was natural.     

LOW GENETIC VARIABILITY OF SARGASSUM MUTICUM (PHAEOPHYCEAE) REVEALED BY A GLOBAL ANALYSIS OF NATIVE AND INTRODUCED POPULATIONS1

Sargassum muticum (Yendo) Fensholt is one of the most well‐known invasive species in the world. There have, however, been few genetic investigations on both its introduced and native populations. There are also some questions about the taxonomic status of this species. This study is the first to assess the genetic diversity of S. muticum on a global scale, by utilizing one marker each from the extranuclear genomes, namely, plastidial RUBISCO and mitochondrial TrnW_I spacers, as well as the nuclear internal transcribed spacer 2 (ITS2). Based on the markers investigated, both the invasive as well as the native populations of this species appeared very homogenous, when compared with other invasive and brown macroalgae. No variation in ITS2 and RUBISCO spacer was revealed in S. muticum populations, including those from its native ranges in Asia and the introduced ranges in Europe and North America. Two TrnW_I spacer haplotypes with a fixed two‐nucleotide difference were found between the populations of eastern Japan and the other 15 populations examined. This study confirms that there is no cryptic diversity in the introduced range of this species. All the materials collected globally are indeed S. muticum. Results depicting the distribution range of the two TrnW_I spacer haplotypes also support the earlier suggestion that the source of the introduced S. muticum populations is most likely western and central Japan (Seto Inland Sea), where the germlings of S. muticum were likely to have been transported with the Pacific oysters previously introduced for farming in Canada, UK, and France in earlier years.     

Phylogeography and phylogeny of the epineritic cosmopolitan bonitos of the genus Sarda (Cuvier): inferred patterns of intra‐ and inter‐oceanic connectivity derived from nuclear and mitochondrial DNA data

Aim To reconstruct the phylogenetic relationships of the four species of the genus Sarda (Sarda sarda, Sarda orientalis, Sarda australis and Sarda chilensis) and their phylogeographic history in the context of historical and ecological biogeography. Also, to reconstruct within‐species phylogenetic relationships to test whether the North Atlantic and Mediterranean populations of Atlantic bonito (S. sarda) warrant subspecies status, and the validity of the allopatric northern and southern populations of eastern Pacific bonito (S. chiliensis), recognized as S. chiliensis lineolata and S. chiliensis chiliensis. Location Representative samples of all four Sarda species collected world‐wide were analysed. Methods Phylogenetic inference was carried out with neighbour‐joining, maximum parsimony and maximum likelihood, employing nucleotide sequences of the mitochondrial DNA (mtDNA) control region I (CR‐I) and of the single‐copy nuclear DNA (nDNA) Tmo‐4c4 gene. Analysis of molecular variance was used on the mtDNA data to estimate the extent of geographic population structuring. Results Gene trees derived from mtDNA and nDNA data yielded concordant phylogenies that support the monophyly of the genus Sarda. The following sibling pairs received strong statistical support: striped bonito (S. orientalis) with Australian bonito (S. australis), and Atlantic bonito (S. sarda) with eastern Pacific bonito (S. chiliensis). Furthermore, the origin of S. sarda mtDNA is paraphyletic with respect to S. chiliensis, and these results are indicative of introgression. The analysis of Tmo‐4c4 sequences corroborates the ancestral hybridization between these allopatric species. Comparisons of north‐west Atlantic and Mediterranean populations of S. sarda using mtDNA CR‐I data revealed substantial genetic differentiation. By contrast, no differences between the putative northern and southern allopatric subspecies of S. chiliensis were detected. Main conclusions The monophyly of the genus Sarda as indicated by morphology is corroborated using both molecular markers. However, molecular phylogenies depicted a paraphyletic relationship between S. sarda and S. chiliensis. This phylogeographical relationship is better explained by an ancestral introgression facilitated by trans‐Arctic contact during the Pleistocene. The pronounced genetic differentiation between S. sarda samples from the north‐west Atlantic and the Mediterranean is consistent with the differentiation of these two regions, but not with the amphi‐Atlantic speciation hypothesis. Finally, the S. chiliensis lineolata and S. chiliensis chiliensis subspecies status is not supported by the molecular data.     

Phylogeography of the Northern Atlantic species Chondrus crispus (Gigartinales, Rhodophyta) inferred from nuclear rDNA internal transcribed spacer sequences

Eighteen isolates of the red algae Chondrus crispus were collected from Northern Atlantic sites, together with C. ocellatus, C. yendoi and C. pinnulatus from the North Pacific. The nuclear rDNA internal transcribed spacer (ITS) was sequenced and compared, spanning both the ITS regions and the 5.8S rRNA gene. Percentage of nucleotide variation for C. crispus ranged from 0.3% to 4.0%. Phylogenetic analyses were performed using maximum parsimony (MP), neighbor-joining (NJ) and minimum evolution methods. They showed that two main clades existed within the C. crispus samples examined and that suggested C. crispus had a single Atlantic origin. The clustering however did not follow the geographic origin. We hypothesized that the current distribution of C. crispus populations might be a result of three main factors: temperature boundaries, paleoclimate and paleoceanography. ITS data exhibited abundant molecular information not only for phylogeographical investigation but also for systematics studies. Handling editor: C. Sturmbauer     

A REASSESSMENT OF SPECIES BOUNDARIES IN CYSTOSEIRA AND HALIDRYS (PHAEOPHYCEAE,FUCALES) ALONG THE NORTH AMERICAN WEST COAST1

Application of phylogenetic species recognition to morphologically recognized species in the genera Cystoseira Agardh and Halidrys Lyngbye on North American west coasts revealed little genetic variation despite a remarkable degree of morphological variation currently used to recognize and delineate species. Whereas morphological characteristics allow recognition of two genera, four morphological species and three informal forms, maximum genetic variation among them was similar to that characteristic of the intraspecific level in European congeners and other Fucales. Among morphological species and forms, nucleotide variation in a combined 26S (large subunit (LSU)) and internal transcribed spacer (ITS) ribosomal DNA analysis was below 3% while it was 1% or less for the RUBISCO spacer of the chloroplast DNA. Comparison of the LSU data to available data for European congeners showed that the genera Cystoseira and Halidrys are not monophyletic and that the previously recognized Cystoseiraceae should be included within the family Sargassaceae. These observations suggest that the current taxonomy for the Sargassaceae fails to reflect evolutionary history because Atlantic and Pacific Cystoseira and Halidrys appear to have arrived at similar morphologies independently. Our results indicate a comparatively recent establishment on the west coast of North America of a sargassacean progenitor whose descendant taxa have experienced limited genetic divergence and are characterized by a high capacity for phenotypic variation despite their overall genetic similarity.     

GLOBAL PHYLOGEOGRAPHY OF THE LOGGERHEAD TURTLE (CARETTA CARETTA) AS INDICATED BY MITOCHONDRIAL DNA HAPLOTYPES

Restriction-site analyses of mitochondrial DNA (mtDNA) from the loggerhead sea turtle (Caretta caretta) reveal substantial phylogeographic structure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from eight nesting populations, most breeding colonies were distinguished from other assayed nesting locations by diagnostic and often fixed restriction-site differences, indicating a strong propensity for natal homing by nesting females. Phylogenetic analyses revealed two distinctive matrilines in the loggerhead turtle that differ by a mean estimated sequence divergence p = 0.009, a value similar in magnitude to the deepest intraspecific mtDNA node (p = 0.007) reported in a global survey of the green sea turtle Chelonia mydas. In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic–Mediterranean and Indian-Pacific samples. We attribute this aspect of phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. These results demonstrate how differences in the ecology and geographic ranges of marine turtle species can influence their comparative global population structures.     

Phylogeography of the marine macroalga Sargassum hemiphyllum (Phaeophyceae,Heterokontophyta) in northwestern Pacific

Sargassum hemiphyllum is commonly found in Japan and Korea, with a variety, var. chinense, that is found distributed in the southern Chinese coast. We previously reported distinct genetic differentiation between the two taxa based on the PCR‐RFLP data of plastid RubiscoL‐S spacer. The present study aims at elucidating the phylogeographic pattern of S. hemiphyllum based on more markers in the nuclear and extranuclear genomes, with a view to reveal the occurrence of hybridization. The two allopatrically distributed taxa were found to be genetically distinct in nuclear ITS2, plastidial Rubisco (Rbc) and mitochondrial TrnW_I (Trn) spacers. Their divergence was postulated to be attributable to the vicariant event which resulted from the isolation of the Sea of Japan during the late Miocene (6.58–11.25 Mya). Divergence within both S. hemiphyllum and the chinense variety was observed based on Trn spacer, while the divergence in S. hemiphyllum was further confirmed in Rbc spacer. This divergence appears to correspond to the separation of the Japanese populations between the Sea of Japan and the Pacific that occurred around 0.92–2.88 Mya (the early Pleistocene). The presence of an ITS2 clone resembling var. chinense sequences in a Japanese population of S. hemiphyllum (JpNS) raises the possibility of the introgression of var. chinense individuals into S. hemiphyllum population. Compared to that between S. hemiphyllum and the chinense variety, hybridization among the Japanese and Korean populations of S. hemiphyllum is highly probable as all these individuals share a pool of nuclear ITS2 sequences, possibly attributable to incomplete concerted evolution of ITS2.     

Deep phylogeographic structure may indicate cryptic species within the Sparid genus Spondyliosoma

Two geographically nonoverlapping species are currently described within the sparid genus Spondyliosoma: Spondyliosoma cantharus (Black Seabream) occurring across Mediterranean and eastern Atlantic waters from NW Europe to Angola and S. emarginatum (Steentjie) considered endemic to southern Africa. To address prominent knowledge gaps this study investigated range-wide phylogeographic structure across both species. Mitochondrial DNA sequences revealed deep phylogeographic structuring with four regionally partitioned reciprocally monophyletic clades, a Mediterranean clade and three more closely related Atlantic clades [NE Atlantic, Angola and South Africa (corresponding to S. emarginatum)]. Divergence and distribution of the lineages reflects survival in, and expansion from, disjunct glacial refuge areas. Cytonuclear differentiation of S. emarginatum supports its validity as a distinct species endemic to South African waters. However, the results also indicate that S. cantharus may be a cryptic species complex wherein the various regional lineages represent established/incipient species. A robust multilocus genetic assessment combining morphological data and detailing interactions among lineages is needed to determine the full diversity within Spondyliosoma and the most adequate biological and taxonomic status.     

Genetic structuring of the temperate gorgonian coral (Corallium rubrum) across the western Mediterranean Sea revealed by microsatellites and nuclear sequences

In the past decades, anthropogenic disturbance has increased in marine costal habitats, leading to dramatic shifts in population size structure of various marine species. In the temperate region, the gorgonian coral (Corallium rubrum) is one of the major disturbed species, mostly owing to the exploitation of its red skeleton for jewellery purposes. Red coral is a gonocoric species inhabiting subtidal rocky habitats in the Mediterranean and neighbouring Atlantic coasts. In order to investigate the spatial genetic structuring of C. rubrum, five microsatellite markers and the ribosomal internal transcribed spacer 1 (ITS-1) sequences were analysed in 11 samples from the northwestern Mediterranean Sea. Phylogenetic reconstructions obtained from ITS-1 sequences analysis showed that samples from Minorca and Sardinia islands were the most divergent while the three samples from the Tuscan archipelago (Argentario, Giannutri and Elba) appeared genetically homogeneous. Both markers revealed a strong structuring over large spatial scales (though to a different extent) with no isolation by distance pattern. Microsatellite-based F(ST) estimates appeared much smaller than ITS-based estimates and not significantly correlated, likely due to microsatellite allele size homoplasy typical of these highly polymorphic loci. Our study shows that the absence of clear patterns of genetic structuring over large spatial scales together with strong genetic structuring should be interpreted with caution because such patterns may hide underlying small-scale genetic structuring. Our results further confirm that effective larval dispersal in red coral is highly restricted in the northwestern Mediterranean Sea, suggesting that an increase of anthropogenic disturbance could aggravate the disappearance of red coral, not only along the Mediterranean coasts but also, and with more intensity, in the main Mediterranean islands.     

Phylogeny and biogeography of Muusoctopus (Cephalopoda: Enteroctopodidae)

Deep‐sea octopuses of the genus Muusoctopus are thought to have originated in the Pacific Northern Hemisphere and then diversified throughout the Pacific and into the rest of the World Ocean. However, this hypothesis was inferred only from molecular divergence times. Here, the ancestral distribution and dispersal routes are estimated by Bayesian analysis based on a new phylogeny including 38 specimens from the south‐eastern Pacific Ocean. Morphological data and molecular sequences of three mitochondrial genes (16S rRNA, COI and COIII) are presented. The morphological data confirm that specimens newly acquired from off the coast of Chile comprise two species: Muusoctopus longibrachus and the poorly described species, Muusoctopus eicomar. The latter is here redescribed and is clearly distinguished from M. longibrachus and other closely related species in the region. A gene tree was built using Bayesian analysis to infer the phylogenetic position of these species within the species group, revealing that a large genetic distance separates the two sympatric Chilean species. M. longibrachus is confirmed as the sister species of Muusooctopus eureka from the Falkland Islands; while M. eicomar is a sister species of Muusoctopus yaquinae from the North Pacific, most closely related to the amphi‐Atlantic species Muusoctopus januarii. Molecular divergence times and ancestral distribution analyses suggest that genus Muusoctopus may have originated in the North Atlantic: one lineage dispersed directly southward to the Magellan region and another dispersed southward along the Eastern Pacific to the Southern Ocean and Antarctica. The Muusoctopus species in the Southern Hemisphere have different phylogenetic origins and represent independent invasions of this region.     

Cryptic speciation and genetic structure of widely distributed brittle stars (Ophiuroidea) in Europe

Pérez‐Portela, R., Almada, V. & Turon, X. (2012). Cryptic speciation and genetic structure of widely distributed brittle stars (Ophiuroidea) in Europe. —Zoologica Scripta, 00, 000–000. The development of molecular techniques has led to the detection of numerous cases of cryptic speciation within widely distributed marine invertebrate species and important taxonomic revisions in all the major marine taxa. In this study, we analysed a controversial marine species complex in the genus Ophiothrix, a widespread taxon in European waters traditionally assigned to two nominal species, Ophiothrix fragilis and O. quinquemaculata. These species are important components of the rocky shores and deep marine benthos along the North Atlantic and Mediterranean littoral. Their status (including variants of both species) has remained contentious due to overlapping variability in morphological characters. In this study, we analysed the genetic and morphological differences of Ophiothrix lineages along the Atlantic and Mediterranean coasts. We also assessed population genetic structure in the Atlantic and Mediterranean basins by sequencing two mitochondrial genes, the 16S rRNA gene and COI gene, of 221 specimens from 13 locations. Phylogenetic analyses demonstrated the existence of two genetically distinct lineages, attributable to two different species although unrelated to previous taxonomic distinctions. Morphological differences could also be detected between these lineages. Samples from the Northeast Atlantic and one from the deep Mediterranean grouped within Lineage I, whereas Lineage II pooled together the southern Atlantic and rocky shallow Mediterranean samples. In the northern region of the Iberian Peninsula and at a deep locality in the Mediterranean, both lineages overlap. Speciation processes likely happened during the Mio–Pliocene transition (about 4.8–7.5 million years ago), when marine‐level oscillations led to the blockage of major marine corridors in Europe and promoted genetic isolation by vicariance. Secondary contact between lineages following sea‐level increases and recolonization during the refilling of the Mediterranean after the Miocene salinity crisis could explain the present‐day distribution of genetic variability. No barriers to gene flow along the Atlanto‐Mediterranean area were detected for Lineage II, and the lack of genetic structure could be caused by a mixture of several factors, such as wide dispersal potential, recent demographic expansion and large population size.     

Global mitochondrial DNA phylogeography and biogeographic history of the antitropically and longitudinally disjunct marine bryozoan Membranipora membranacea L. (Cheilostomata): another cryptic marine sibling species complex?

The origin of disjunct distributions in high dispersal marine taxa remains an important evolutionary question as it relates to the formation of new species in an environment where barriers to gene flow are not always obvious. To reconstruct the relationships and phylogeographic history of the antitropically and longitudinally disjunct bryozoan Membranipora membranacea populations were surveyed with mtDNA cytochrome oxidase 1 (COI) sequences across its cosmopolitan range. Maximum parsimony, maximum likelihood and Bayesian genealogies revealed three deep clades in the North Pacific and one monophyletic clade each in the southeast Pacific (Chile), southwest Pacific (Australia/New Zealand), North Atlantic and southeast Atlantic (South Africa). Human-mediated dispersal has not impacted M. membranacea’s large-scale genetic structure. M. membranacea did not participate in the trans-arctic interchange. Episodic long-distance dispersal, combined with climatic vicariance can explain the disjunct distribution. Dispersal led southward across the tropics perhaps 13 mya in the East Pacific and again northwards perhaps 6 mya in the Eastern Atlantic to colonize the North Atlantic from the south, and along the West Wind Drift to colonize Australia. The clades differentiated over evolutionary time in their respective ocean region, potentially forming a sibling species complex. The taxonomic status of the clades is discussed.     

Divergence and molecular variation in common whelk Buccinum undatum (Gastropoda: Buccinidae) in Iceland: a trans‐Atlantic comparison

The dispersal and history of species affects their genetic population structure at both small and large geographical scales. The common whelk, Buccinum undatum, is a widespread subtidal gastropod in the North Atlantic that has no planktonic larvae and has thus limited dispersal capacity. The snail, which has been harvested by humans for centuries, is highly variable in morphology. To evaluate the population structure in the rich fishing grounds in western Iceland and its divergence from samples across the Atlantic, genetic patterns based on sequence variation in two mitochondrial (mt)DNA genes (COI and 16S) and five microsatellites were studied and compared with variation in populations from both sides of the Atlantic. Significant differences in allele and haplotype frequencies were found among samples separated by short distances along the coast of Iceland. Partition of the variation showed larger variance among samples obtained from distant regions than from neighbouring sites and genetic distances were correlated with geographical distance among populations in Europe. Phylogeographic patterns in mtDNA reveal different monophyletic lineages on both sides of the Atlantic, which predate the onset of the Ice Age and which may constitute cryptic species. Similar micro‐ and macrogeographical patterns were observed for the mtDNA and microsatellite markers, despite high frequencies of null alleles. Bayesian skyline reconstructions of the demographic history and mismatch distributions suggest that, although sizes of some populations were unaffected by Ice Age glaciations, others show signs of expansion after the Last Glacial Maximum. These phylogeographical patterns are consistent with patterns expected for low dispersal species that have survived in allopatric glacial refugial populations on both sides of the Atlantic and in deep‐sea refugia within each continent. The observed genetic structure has implications for conservation and sustainable management of the harvested populations. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 145–159.     

PHYLOGENETIC RELATIONSHIPS WITHIN THE STYLONEMATALES (STYLONEMATOPHYCEAE,RHODOPHYTA): BIOGEOGRAPHIC PATTERNS DO NOT APPLY TO STYLONEMA ALSIDII1

The Stylonematales is the sole order of the Stylonematophyceae. The order consists of a mixture of filamentous or unicellular taxa that are small, grow on various surfaces, and are described from many floras, indicating that they may be cosmopolitan. Such ubiquity has been proposed to be due to properties of microorganisms, such as large population sizes, rather than human‐derived phenomena. While their small nature makes most records fortuitous, we targeted these red algae to get a better understanding of their global distribution, genetic variation, and phylogeographic relationships. Our results indicated that the genera are mostly well supported, except for the position of Stylonema cornu‐cervi with Goniotrichopsis reniformis, while intergeneric relationships are mostly unsupported. The most commonly isolated species was Stylonema alsidii. Within this species, several well‐supported clades were present. The phylogeographic relationships in S. alsidii showed no obvious biogeographic pattern, with supported clades containing samples from disparate locations, and multiple samples from the same area not grouping together. Some clades showed little genetic variation and wide distributions, possibly indicating human‐derived dispersal. Other clades, also with wide distribution, showed more genetic structure and could be candidates for groups formed by natural long‐distance dispersal. While all issues on ubiquity cannot be answered with this data set, it would appear that at least S. alsidii is a true ubiquitous taxon. The sister relationship of Rufusia pilicola to the remaining Stylonematophyceae, the presence of the carbohydrate floridoside, and this species’ unusual habitat indicate that it belongs to a new order, Rufusiales.     

Evolution of Nemertesia hydroids (Cnidaria: Hydrozoa,Plumulariidae) from the shallow and deep waters of the NE Atlantic and western Mediterranean

Moura, C. J., Cunha, M. R., Porteiro, F. M., Yesson, C. & Rogers, A. D. (2011) Evolution of Nemertesia hydroids (Cnidaria: Hydrozoa, Plumulariidae) from the shallow and deep waters of the NE Atlantic and Western Mediterranean. —Zoologica Scripta, 41, 79–96. Hydroid species from the genus Nemertesia develop some of the largest and most complex hydrozoan colonies. These colonies are abundant and ecologically important in both shallow and deep waters worldwide. Here, we analyse the systematics of most Nemertesia species from the NE Atlantic and Mediterranean using morphology and phylogenetic inferences of 16S rRNA haplotype data. Phylogeographical analysis revealed multiple movements of taxa to and from the Mediterranean after the Messinian salinity crisis through shallow and deep waters. The nominal species Nemertesia belini and Nemertesia antennina revealed multiple genetic lineages representing cryptic species diversity. Molecular phylogenetic evidence was supported by consistent phenotypic differences between lineages, and three and seven putative species were resolved within the N. belini and N. antennina complexes, respectively. Three putative species of the N. antennina complex found at different seamounts of Azores grouped in a clade clustered amongst the other four cryptic species present at neighbouring bathyal localities of the Gulf of Cadiz. These cryptic species, mostly from the deep sea, form a clade distantly related to the typical N. antennina from European coastal waters. Depth or environmental correlates of depth seem to influence the reproductive strategies of Nemertesia colonies and ultimately speciation. In particular, speciation of these hydroids must have been influenced by hydrography, habitat heterogeneity, isolation by distance and larval dispersal capacity. The deep sea is shown as an important environment in the generation and accumulation of lineages that may occasionally invade coastal waters in the NE Atlantic. Glacial cycles of cooling, along with changes in sea level, and eradication of some coastal faunas likely facilitated speciation and evolutionary transitions from deep to shallow waters.     

Molecular genetic delineation of Phaeocystis species (Prymnesiophyceae) using coding and non-coding regions of nuclear and plastid genomes

Sequence variation among 22 isolates representing a global distribution of the prymnesiophyte genus Phaeocystis has been compared using nuclear-encoded 18S rRNA genes and two non-coding regions: the ribosomal DNA internal transcribed spacer 1 (ITS1) separating the 18S rRNA and 5.8S rRNA genes and the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) spacer flanked by short stretches of the adjacent large and small subunits (rbcL and rbcS). 18S rRNA can only resolve major species complexes. The analysis suggests that an undescribed unicellular Phaeocystis sp. (isolate PLY 559) is a sister taxon to the Mediterranean unicellular Phaeocystis jahnii; this clade branched prior to the divergence of all other Phaeocystis species, including the colonial ones. Little divergence was seen among the multiple isolates sequenced from each colonial species complex. RUBISCO spacer regions are even more highly conserved among closely related colonial Phaeocystis species and are identical in Phaeocystis antarctica, Phaeocystis pouchetii and two warm-temperate strains of Phaeocystis globosa, with a single base substitution in two cold-temperate strains of P. globosa. The RUBISCO spacer sequences from two predominantly unicellular Phaeocystis isolates from the Mediterranean Sea and PLY 559 were clearly different from other Phaeocystis strains. In contrast, ITS1 exhibited substantial inter- and intraspecific sequence divergence and showed more resolution among the taxa. Distinctly different copies of the ITS1 region were found in P. globosa, even among cloned DNA from a single strain, suggesting that it is a species complex and making this region unsuitable for phylogenetic analysis in this species. However, among nine P. antarctica strains, four ITS1 haplotypes could be separated. Using the branching order in the ITS1 tree we have attempted to trace the biogeographic history of the dispersal of strains in Antarctic coastal waters.     

Analysis of meristic and mitochondrial DNA variation in Syngnathus abaster (Teleostea: Syngnathidae) from two western Mediterranean lagoons

Syngnathus abaster is a euryhaline pipefish distributed in the Mediterranean, Black Sea, and the north-eastern Atlantic. Although its populations are characterised by high morphological plasticity, neither congruent information about the morphological differentiation of S. abaster populations from the Mediterranean lagoons is available, nor population genetic surveys have been so far performed. In this context, the aims of our study were as follow: i) to describe the variation at nine meristic characters of S. abaster from two western Mediterranean brackish-water areas: the Tunis north lagoon (Tunisia) and the Mauguio lagoon (France); ii) to analyse sequences of four mitochondrial DNA regions in order to evaluate the occurrence of genetic variation between the two areas, if any. The morphological survey revealed a subdivision into two distinct groups: the first included the Tunisian specimens, the second the French ones. Genetic analysis evidenced the occurrence of a sharp genetic structuring with high levels of genetic differentiation between Tunisian and French S. abaster populations. Results suggest that the evolutionary forces driven by the different biogeographical and ecological conditions of the two Mediterranean brackish-water areas have boosted the morphological and genetic divergence of the populations here analysed. The scarce potential of long-distance dispersal of S. abaster may have also enhanced the divergence retrieved.