Molecular population genetics of male and female mitochondrial genomes in European mussels <Emphasis Type="Italic">Mytilus</Emphasis>

The doubly uniparental system of mitochondrial inheritance (DUI) is best known in marine mussels Mytilus. Under DUI there are two types of mitochondrial DNA (mtDNA). The female type (F) is transmitted to offspring of both genders and the male type (M) exclusively to sons; consequently two distinct mtDNA lineages exist. The M lineage evolves under more relaxed selection than the F lineage resulting in higher polymorphism within the M lineage. Though this polymorphism is expected to make inferences on fine population structure easier using M instead of F data, no comprehensive comparative data exist to support this claim. We sequenced a 1,205 bp fragment of M and F mtDNA comprising parts of the COIII and ND2 genes, and analysed 204 individuals representing three Mytilus species: M. edulis, M. galloprovincialis and M. trossulus from 13 European sampling sites. A clear distinction between Mediterranean and Atlantic populations was found with both M and F data, but much better geographic differentiation was found within the Atlantic using F rather than M data. In particular, Atlantic M. galloprovincialis can be differentiated from Atlantic M. edulis, and further subdivision of Atlantic M. edulis is possible using the F data but not the M data. Multiple tests of selection were carried out to attempt to explain this paradox. We concluded that the overall pattern of polymorphism is consistent with strong purifying selection; not only is this selection relaxed in the M lineage in comparison with the F lineage, but it is also more frequently interrupted by periodic selective sweeps within the M lineage.     

Doubly uniparental transmission of mitochondrial DNA length variants in the mussel <Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">trossulus</Emphasis>

Doubly uniparental inheritance of mitochondrial DNA (mtDNA) is an unusual feature found in marine mussels and a few other bivalve species. In addition to a mitochondrial genome (F) inherited through the female line, heteroplasmic individuals (males) contain a second highly diverged genome (M) that is inherited through the paternal line. The Baltic mussel Mytilus trossulus is characterized by the presence of two phylogenetically close female and male genomes. We examined M. trossulus sampled from the Gulf of Gdansk, southern Baltic. Somatic tissues and gametes were surveyed for the presence of different types of mtDNA. Length variants were identified using PCR (polymerase chain reaction) amplification of the mtDNA fragment containing the major noncoding region. Seventeen length variants present in homo- and heteroplasmic individuals were found in a sample of 343 individuals analyzed. Two length variants of the major noncoding region (PCR product lengths: 1520 and 1370 bp) were the most frequent. Length heteroplasmy was found in 46.8% of males, and was mostly caused by the presence of the short length variant (PCR product length: 1370 bp) of the major noncoding region. MtDNA variants were also detected by restriction analysis of a 1.3 kb segment of coding region (ND2-COIII) amplified by PCR. This study provides evidence that the short length variant is always transmitted to sperm and has taken over the role of the M genome. The remaining length variants were present in both males and females. Longer length variants were transmitted mainly through the female line. A possibility of much higher incidence of genome role reversals in Baltic M. trossulus, in comparison with other populations of mussels is discussed.     

Distribution of male and female mtDNA lineages in populations of blue mussels,Mytilus trossulus and M. galloprovincialis,along the Pacific coast of North America

Geographic variation in mitochondrial large subunit (16S) ribosomal RNA haplotypes was examined for blue mussels, Mytilus trossulus Gould, 1850 and M. galloprovincialis Lamarck, 1819, sampled from ten sites along the Pacific coast of the USA in January of 1993. Using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assays we determined haplotype frequencies for both the male and female mussel mitochondrial DNA (mtDNA) lineages. Populations from Morro Bay south to San Diego, California, contained only M. galloprovincialis male and female haplotypes, while those from Arcata Bay, California, north to Port Orford, Oregon, were fixed for M. trossulus haplotypes. Populations from Monterey Bay to Bodega Bay, California, contained a mixture of M. trossulus and M. galloprovincialis haplotypes. Overall only 2 of 97 heteroplasmic individuals had a mixed M. trossulus/M. galloprovincialis mitochondrial genotype indicating that hybridization is uncommon in the populations sampled. Further, there was no evidence of extensive introgression between these mussel taxa at the level of mtDNA. This is in contrast to previously published results which suggested the significant introgression of M. trossulus haplotypes into southern populations containing primarily M. galloprovincialis nuclear genotypes. We feel the discrepancy lies in the ability of our assays to detect haplotypes corresponding to both the male and female mtDNA lineages. Potential explanations for the lack of mtDNA introgression include, low levels of backcrossing between hybrids and parental taxa, epistatic interaction between nuclear and mitochondrial genes and the breakdown of a sex-specific inheritance pattern for mtDNA in hybrids.     

Low variation in partial cytochrome oxidase subunit I (COI) mitochondrial sequences in the coralline demosponge Astrosclera willeyana across the Indo-Pacific

Partial sequences of the mitochondrial DNA (mtDNA) gene cytochrome oxidase subunit 1 (COI) were analysed from individuals of the coralline demosponge Astrosclera willeyana sensu lato out of ten Indo-Pacific populations from the Red Sea to the central Pacific. This taxon is widely distributed in cryptic coral reef habitats of the Indo-Pacific and is regarded as a modern representative of long-extinct, formerly reef-building stromatoporoid-type sponges. The aims were to clarify phylogeographic and taxonomic relationships in this “living fossil” and to explore mitochondrial DNA sequence variation over a wide geographic range. Very low variability was observed across the Indo-Pacific, as only three COI haplotypes were identified, with a maximum p-distance of 0.418% and low nucleotide diversity (π=0.00049). Very low genetic structure was revealed among populations: Haplotype 1 was found in all specimens from nine Pacific populations (N=45), separated by distances of more than 7,000 km; haplotype 2 was restricted to the Red Sea population (N=4); haplotype 3 was only found in the Tuamoto specimens (N=7). COI data presented here do not support the hypothesis of at least two sibling species belonging to genus Astrosclera in the Pacific. Considering the maximum geographic distance of more than 20,000 km between sampled populations, mtDNA COI sequence variation observed here is among the lowest reported to date for a diploblastic taxon and adds to the growing evidence of a general mtDNA conservation in sponges. It is argued that this low mtDNA variation in A. willeyana s.l. is due to a low rate of mtDNA evolution caused by a combination of long generation time and low metabolic rate.     

Introgression and mitochondrial DNA heteroplasmy in the Baltic populations of mussels Mytilus trossulus and M. edulis

A strong clinal change in salinity occurs between the Baltic Sea and the North Sea, Atlantic Ocean, in the Danish Straits, where hybridization zone between mussels Mytilus edulis and M. trossulus has been reported. Eleven samples of mussels were studied from the Danish Straits and the inner Baltic Sea. Extensive introgression of M. edulis alleles from the North Sea into populations throughout the Baltic was ascertained for mitochondrial DNA (mtDNA) and two nuclear markers (ME15–16 and ITS). In the opposite direction, introgression of M. trossulus alleles into the M. edulis background was observed at the EFbis nuclear marker in populations from Kattegat (Danish Straits). While only M. edulis F (female) mtDNA was present in the Baltic, there were still strong differences in frequencies in the control region length variants between the Danish Straits and the inner Baltic samples, and weaker variation in coding region ND2–COIII haplotype frequencies. In the assays of the two mtDNA regions, various patterns of heteroplasmy were detected in 32% of all the studied individual mussels; this includes the presence of distinct, independently inherited M and F mitochondria in males, as well as the presence of two different distinguishable F genomes. The male-inherited M mtDNA genomes are quite common in the mussels from the Danish Straits, but very rare in males from the inner Baltic. Instead, a recombined control region variant (1r), which seems to have taken over the role of the M genome, was present in a number of specimens in the Baltic. Observations of heteroplasmy for two F genomes in some females and males confirm disruptions of the doubly uniparental inheritance mechanism in the hybrid Baltic Mytilus.     

Molecular population genetics of male and female mitochondrial genomes in subarctic Mytilus trossulus

The doubly uniparental inheritance system allows for the use of two independent mitochondrial genomes for population history investigations. Under this system, two lineages of mitochondrial DNA (mtDNA) exist and males are typically heteroplasmic, having the additional, usually divergent, mitochondrial genome inherited from their male parent. This additional mtDNA typically evolves faster, potentially allowing for insight into more recent events in population history. Few studies did explore this possibility in marine mussels Mytilus showing its usefulness. Recent observations of the Mytilus trossulus mussels who have retained their native mtDNA in European waters posed the question of their origin. Are they part of a population present, but previously undetected, or is this a potentially human mediated, ongoing spread of an invasive species? To tackle this question, we amplified with species-specific primers and sequenced an approximately 1,200-bp-long fragment spanning COIII and ND2 genes from both mitochondrial genomes of mussels sampled at five locations worldwide, covering the whole M. trossulus range. The overall pattern of polymorphisms is compatible with the entirely postglacial history of the whole species, indicating a very deep bottleneck at last glacial maximum, with possible retention of the whole species in a single refugium, and the effective population size of no more than a few thousands. Both analyses of molecular variance and isolation with migration (IM) models point at the West Atlantic as the source of the European M. trossulus mussels, at least the ones who retained their native mtDNA. The hypothesis that this is an ongoing, human-mediated process was considered. To this end, comparison with the well-known case: the introduction of congeneric mussel, Mytilus galloprovincialis, from Mediterranean Sea to Asia was used. This introduction occurred within the last 100 years. The results inferred by the IM model suggest that the timing and structure of transatlantic migration of M. trossulus differs significantly from the M. galloprovincialis case: it is more than 1,000 years old and involves a much larger fraction of the ancestral population. Therefore, most likely, this invasion is not a human-mediated process.     

Mitochondrial DNA heteroplasmy in European populations of the mussel Mytilus trossulus

Mitochondrial DNA (mtDNA) of Mytilus trossulus from the Gulf of Gdansk (southern Baltic) and M. edulis from Swansea Bay, South Wales, UK, collected in 1991, was studied by restriction-enzyme analysis. These two species were more similar to each other in haplotype frequencies than either was to M. galloprovincialis from Britain. M. trossulus resembles M. edulis in having a high frequency of heteroplasmy restricted to males. However, in contrast to M. edulis where restriction-site heteroplasmy predominates, in M. trossulus heteroplasmic individuals possess two genomes which differ in length by up to 3 kilobases.     

Microsatellite data reveal fine genetic structure in male Guiana dolphins (<Emphasis Type="Italic">Sotalia guianesis)</Emphasis> in two geographically close embayments at south-eastern coast of Brazil

A large macrogeographic differentiation has been observed among Sotalia guianensis populations along the South American coast. However, no genetic structure has been detected so far in closely distributed populations of this species, even though it has been observed in other cetaceans. Here, we examined the fine scale population structure for the largest populations of S. guianensis inhabiting Sepetiba and Paraty embayments at the south-eastern coast of Rio de Janeiro, Brazil. Analysis of mitochondrial DNA (mtDNA) control region sequences failed to detect variability among sequences. Conversely, evidence of significant male population structure was found on the basis of ten nuclear microsatellite loci. Surprisingly, the microsatellite markers were able to distinguish between individuals from the two embayments located 60 km apart. The results suggest that differences in habitat type and behavioral specializations are likely to explain the patterns of genetic structure. These findings should provide baselines for the management of communities exposed to increasing human-driven habitat loss.     

Geographic and bathymetric patterns of mitochondrial 16S rRNA sequence divergence among deep-sea amphipods,Eurythenes gryllus

The physical uniformity of the deep sea suggests a lack of absolute barriers to faunal dispersal, and thus genetic homogeneity in broadly distributed species is expected. The deep-sea amphipod Eurythenes gryllus Lichtenstein (Crustacea: Lysianassoidea) is considered a panoceanic, cold-water stenotherm, with a vertical depth distribution from 184 to 6500 m. We surveyed mtDNA sequence diversity in E. gryllus to assess genetic diversity and population structure in different oceans and across traditionally defined bathyal and abyssal zones. DNA sequences (437 nucleotides length) from the mitochondrial large-subunit ribosomal RNA gene (16S rRNA) of 95 individuals, collected between 1982 and 1990 from 14 locations in the central North Pacific (including multiple samples on the slope of a seamount), castern and western North Atlantic, and the Arctic Ocean, were obtained. Our analysis of DNA sequence diversity indicates (1) genetic homogeneity among sites within the same depth zone at the scale of ocean basins; and (2) genetically divergent, cryptic taxa distributed at different depths, with the greatest diversity in the bathyal zone. These observations suggest that ecological and physical conditions are important isolating mechanisms that may lead to speciation in this group.     

Poecilogony in Polydora hoplura (Polychaeta: Spionidae) from commercially important molluscs in South Africa

Females of the polychaete Polydora hoplura (Claparède 1869) that produced planktotrophic and adelphophagic larvae were compared genetically to determine whether the different reproductive morphs represented sibling species or poecilogony. Worms were collected from Saldanha Bay, South Africa (33°0′37.71S, 17°56′59.74E), and cultured in a laboratory setting from November 2012 to April 2013. The results based on mitochondrial and nuclear DNA (Cyt b and ATPSα, respectively) showed shared haplotypes between reproductive morphs for both markers. Additionally, variation in mtDNA sequences was significantly higher within morphs than between morphs (95.8 and 4.2 %, respectively). A comparison of developmental modes found that broods of planktotrophic larvae were larger than broods of adelphophagic larvae, while the latter had larger eggs and larvae at hatching. Developmental time from oviposition to settlement for planktotrophic and adelphophagic larvae was 40.2 and 16.6 days, respectively. Polydora hoplura represents the fifth confirmed case of poecilogony in the Spionidae.     

Seeing stars: a molecular and morphological investigation into the evolutionary history of Odontasteridae (Asteroidea) with description of a new species from the Galapagos Islands

Odontasteridae (Asteroidea: Echinodermata) (Verrill in Am J Sci, 1899) is placed within Valvatida, a derived assemblage of sea stars. Odontasterids are found in the Southern, Atlantic, and Pacific Oceans and are concentrated in high southern latitudes. To date, the phylogenetic and evolutionary history of Odontasteridae as a whole has not been rigorously examined. We conducted molecular and morphological phylogenetic analyses of Odontasteridae to assess the interrelationships among and within recognized genera. We used mitochondrial 16S and cytochrome c oxidase subunit I molecular markers and 29 external morphological characters in an attempt to reconstruct the evolutionary history of the group. Generally, our results indicate that traditionally used external skeletal characters are not representative of phylogenetic history of Odontasteridae. We can conclude that species present in high latitudes in the Southern Hemisphere (i.e., Southern Ocean) are the most derived taxa. Additionally, mtDNA data suggest unrecognized lineages of odontasterids are present in high southern latitudes. A new species Odontaster cynthiae sp. nov. is described from the Galapagos Islands.     

Shell-boring versus tube-dwelling: is the mode of life fixed or flexible? Two cases in spionid polychaetes (Annelida, Spionidae)

Free crawling was an original life style, and the ability to build tubes and bore into shells evolved independently in various annelids and more than once within the family Spionidae. Absence of morphological differences between the shell-boring (SB) and tube-dwelling (TD) spionid worms and the innate ability of borers to build tubes raised a question whether the mode of life is fixed or flexible. Sequence data of three gene fragments of the mitochondrial 16S rDNA and nuclear 18S and 28S rDNA (in total 1,677 bp) have shown that SB and TD individuals of Dipolydora carunculata from the Sea of Japan were genetically identical, whereas those of Polydora triglanda from Taiwan were genetically distant and not conspecific. These data indicate that some species are constrained to a certain mode of life, while others are flexible and individuals can be either SB or TD depending on the place of settlement in the end of their larval development.     

Contrasting pattern of mitochondrial population diversity between an estuarine bivalve, the Kumamoto oyster Crassostrea sikamea, and the closely related Pacific oyster C. gigas

The Kumamoto oyster (Crassostrea sikamea) shows a spatially restricted distribution, favoring estuarine tideland environment. On the other hand, the Pacific oyster (C. gigas) has a broader range of habitat. The present study compared the mitochondrial population structure between the two closely related species. For accurate species identification of oysters sampled from Japanese and East Asian continental coasts, we performed sequencing analysis of the mitochondrial DNA (mtDNA) and PCR-RFLP assay of the first internal transcribed spacer of nuclear rRNA genes. Then, we estimated the extent of population differentiation within each of C. sikamea and C. gigas based on the mtDNA data. Few haplotypes were shared among the sites of sampling in C. sikamea, which contrasted with an extensive haplotype sharing among C. gigas samples. We discuss the mechanisms of elevated population differentiation observed in C. sikamea in light of the ecology and the ancient ocean geography around the present-day habitats.     

Phylogeography of the Southwestern Atlantic menhaden genus <Emphasis Type="Italic">Brevoortia</Emphasis> (Clupeidae,Alosinae)

Among pelagic fish, the Southwestern Atlantic menhaden genus Brevoortia (Clupeidae, Alosinae) constitutes an important species model to investigate the patterns of genetic differentiation. It is abundant in the Río de la Plata estuary and in the Atlantic coastal lagoons system from Uruguay and Southern Brazil. To access in the taxa discrimination and population structure in Brevoortia we perform a phylogeographic approach based on mitochondrial cytochrome b (cyt-b) sequences including 240 individuals from 16 collecting sites. Among the 720 bp cyt-b sequenced, 199 correspond to variables and 88 to phylogenetically informative sites. High values of haplotype diversity (h = 1.000) and nucleotide diversity (π = 0.061), as well as an average of 0.084 polymorphic segregating sites and 46 different haplotypes were found. Maximum likelihood analysis based on the GTR + I + G model and Bayesian inference strongly support the idea that B. aurea is the only species of the genus inhabiting the Southwestern Atlantic region. Our analyses revealed a complex population pattern characterized by the existence of long-term highly structured genetic assemblages of mixed stocks. Each monophyletic entity included individuals from different collecting sites, different age groups and collected in different years. Our data also suggest that the recruitment of unrelated mtDNA haplotypes carried out by individuals within schools could be occurring in the same nursery areas revealing the existence of many different maternal lineages. A scenario where different simultaneously and successively mixed mtDNA lineages remain historically connected through basal haplotypes among different clades could explains more accurately the complex and ordered metapopulation dynamic found in this pelagic fish.     

Genetic evidence of cryptic speciation within hammerhead sharks (Genus Sphyrna)

Surveys of genetic variation within cosmopolitan marine species often uncover deep divergences, indicating historical separation and potentially cryptic speciation. Based on broad geographic (coastal eastern North America, Gulf of Mexico, western Africa, Australia, and Hawaii) and temporal sampling (1991–2003), mitochondrial (control region [CR] and cytochrome oxidase I [COI]) and nuclear gene (lactate dehydrogenase A intron 6 [LDHA6]) variation among 76 individuals was used to test for cryptic speciation in the scalloped hammerhead, Sphyrna lewini (Griffith and Smith). CR and COI gene trees confirmed previous evidence of divergence between Atlantic and Indo-Pacific scalloped hammerhead populations; populations were reciprocally monophyletic. However, the between-basin divergence recorded in the mtDNA genome was not reflected in nuclear gene phylogenies; alleles for LDHA6 were shared between ocean basins, and Atlantic and Indo-Pacific populations were not reciprocally monophyletic. Unexpectedly, CR, COI, and LDHA6 gene trees recovered a deep phylogenetic partition within the Atlantic samples. For mtDNA haplotypes, which segregated by basin, average genetic distances were higher among Atlantic haplotypes (CR: D _HKY=0.036, COI: D _GTR=0.016) than among Indo-Pacific haplotypes (CR: D _HKY=0.010, COI: D _GTR=0.006) and approximated divergences between basins for CR (D _HKY=0.036 within Atlantic; D _HKY=0.042 between basins). Vertebral counts for eight specimens representing divergent lineages from the western north Atlantic were consistent with the genetic data. Coexistence of discrete lineages in the Atlantic, complete disequilibrium between nuclear and mitochondrial alleles within lineages and concordant partitions in genetic and morphological characters indicates reproductive isolation and thus the occurrence of a cryptic species of scalloped hammerhead in the western north Atlantic. Effective management of large coastal shark species should incorporate this important discovery and the inference from sampling that the cryptic scalloped hammerhead is less abundant than S. lewini, making it potentially more susceptible to fishery pressure.     

Present-day genetic composition suggests contrasting demographic histories of two dominant chaetognaths of the North-East Atlantic, <Emphasis Type="Italic">Sagitta elegans</Emphasis> and <Emphasis Type="Italic">S. setosa</Emphasis>

Sagitta elegans and S. setosa are the two dominant chaetognaths in the North-East (NE) Atlantic. They are closely related and have a similar ecology and life history, but differ in distributional ranges. Sagitta setosa is a typical neritic species occurring exclusively above shelf regions, whereas S. elegans is a more oceanic species with a widespread distribution. We hypothesised that neritic species, because of smaller and more fragmented populations, would have been more vulnerable to population bottlenecks resulting from range contractions during Pleistocene glaciations than oceanic species. To test this hypothesis we compared mitochondrial Cytochrome Oxidase II DNA sequences of S. elegans and S. setosa from sampling locations across the NE Atlantic. Both species displayed very high levels of genetic diversity with unique haplotypes for every sequenced individual and an approximately three times higher level of nucleotide diversity in S. elegans (0.061) compared to S. setosa (0.021). Sagitta setosa mitochondrial DNA (mtDNA) haplotypes produced a star-like phylogeny and a uni-modal mismatch distribution indicative of a bottleneck followed by population expansion. In contrast, S. elegans had a deeper mtDNA phylogeny and a multi-modal mismatch distribution as would be expected from a more stable population. Neutrality tests indicated that assumptions of the standard neutral model were violated for both species and results from the McDonald-Kreitman test suggested that selection played a role in the evolution of their mitochondrial DNA. Congruent with these results, both species had much smaller effective population sizes estimated from genetic data when compared to census population sizes estimated from abundance data, with a factor of ~10⁸–10⁹ difference. Assuming that selective effects are comparable for the two species, we conclude that the difference in genetic signature can only be explained by contrasting demographic histories. Our data are consistent with the hypothesis that in the NE Atlantic, the neritic S. setosa has been more severely affected by population bottlenecks resulting from Pleistocene range shifts than the more oceanic S. elegans.     

DNA sequence evidence for speciation,paraphyly and a Mesozoic dispersal of cancellothyridid articulate brachiopods

Because the classification of extant and fossil articulate brachiopods is based largely upon shell characters observable in fossils, it identifies morphotaxa whose biological status can, in practice, best be inferred from estimates of genetic divergence. Allozyme polymorphism and restriction fragment length polymorphism of mitochondrial DNA (mtDNA RFLP) have been used to show that nuclear and mitochondrial genetic divergence between samples of the cancellothyridid brachiopods Terebratulina septentrionalis from Canada and T. retusa from Europe is compatible with biological speciation, but the genetic distances obtained were biased by methodological limitations. Here, we report estimates of divergence in 12S rDNA mitochondrial sequences within and between samples of these brachiopods. The sequence-based genetic distance between these samples (5.98ǂ.07% SE) is at least 10 times greater than within them and, since they also differ in a complex life-history trait, their species status is considered to be securely established. Divergence levels between 12S rDNA genes of three other cancellothyridids, T. unguicula from Alaska, T. crossei from near Japan, and Cancellothyris hedleyi from near Australia are higher than between the two North Atlantic species, and the mean nucleotide distance between all these cancellothyrids is similar to the mean distance between species of Littorina (Mollusca: Gastropoda). Sequences of both 12S and 16S genes from cancellothyridids and other short-looped brachiopod species show neither saturation nor lineage-specific rate differences and, when analysed with different outgroups, either separately or together, yield one unexpected, but well-supported, tree with Alaskan T. unguicula basal and C. hedleyi nested within Terebratulina, i.e. these genera are paraphyletic. A geologically dated divergence between Antarctic and New Zealand species of the short-looped brachiopod Liothyrella is used to calibrate the rate of 12S divergence at ca. 0.1% per million years (MY), and this rate is used to infer that T. septentrionalis and T. retusa have been diverging for ca. 60 MY and that they and T. unguicula have been diverging from their last common ancestor for ca. 100 MY. This indicates a Mesozoic origin for the present-day distribution of cancellothyridids and the basal position of T. unguicula suggests a possible North Pacific centre of origin, with separate Atlantic and Pacific radiations. The inclusion of Cancellothyris within Terebratulina also shows that adult shell characters such as umbo, foramen and symphytium shape, whilst probably indispensible for the practical classification of fossils, are not reliable guides to genealogy.     

Phylogeography of Cerastoderma glaucum (Bivalvia: Cardiidae) across Europe: a major break in the Eastern Mediterranean

Molecular variation of the lagoon cockle Cerastoderma glaucum (Poiret, 1789) was examined across the species range along European coasts, from the northern Baltic to the Black Sea and the Caspian Sea. A major phylogeographic break in mitochondrial COI gene sequences (divergence 6.2%) separated a group of Ponto-Caspian and Aegean Sea haplotypes from those to the west of the Peloponnese peninsula in the Mediterranean and in the Atlantic-Baltic sector. A similar subdivision, yet not entirely geographically coincident, was found at 16 allozyme loci (Nei's distance D=0.15). The results imply a long-term isolation of populations in parts of the Eastern Mediterranean or Black Sea basins through the Pleistocene. The subdivision does not concur with previous views on the systematics of C. glaucum complex, but the pattern is notably similar to that described earlier from some fish species. Marked phylogeographic structuring was also found at lower level within the major Mediterranean-Atlantic phylogroup of C. glaucum, which was divided into six regional or local haplotype subgroups. Divergence of these groups may date back one or several major Pleistocene climatic cycles. Local mtDNA diversity was particularly high in a sample from the Ionian Sea, whose mitochondrial identity was of the Mediterranean-Atlantic type, while its nuclear characters were more strongly associated with the Ponto-Caspian type. Patterns of shallower, star-phylogeny type diversity within the Ponto-Caspian phylogroup and in the Baltic Sea area may represent more recent, post-glacial generation of variation.     

Cryptic species within the commercially most important lobster in the tropical Atlantic, the spiny lobster Panulirus argus

Panulirus argus (Latreille in Ann Mus Hist Nat Paris 3:388–395, 1804) is the lobster of greatest economic importance throughout its distribution. In this study, mitochondrial (Cytochrome Oxidase I and 16S ribosomal genes) and nuclear (Adenine Nucleotide Transporter gene) sequences were used to evaluate the taxonomic status of P. argus sampled from five sites in the Caribbean Sea and nine sites in the Southwest Atlantic. Phylogenetic analyses indicate that lobsters from the two regions form two monophyletic groups with a molecular divergence similar to that observed between distinct congeneric lobster species and much larger than that found between conspecific lobster populations. Therefore, the Caribbean and the Southwest Atlantic lobster populations originally attributed to P. argus belong to different species, with an estimated time of isolation of around 16 Million years. An important consequence of these findings is that the fisheries of spiny lobsters from the Caribbean and the Southwest Atlantic species must be managed separately.     

Four genes,morphology and ecology: distinguishing a new species of <Emphasis Type="Italic">Acesta</Emphasis> (Mollusca; Bivalvia) from the Gulf of Mexico

There is currently an active scientific debate about the most correct and efficient way to identify species. To date, few studies in the marine realm have combined the available taxonomic methods. In this study we have used morphology, ecology and molecular analyses to identify a new species within the bivalve genus Acesta. All four genes studied (12S, 16S, Cytb, COI) suggested that a common cold-seep species in the Gulf of Mexico, A. bullisi, should be divided into two distinct species. This conclusion was supported by morphological traits and by observations of ecological distribution. A. oophaga Järnegren, Schander and Young n. sp. is described here, and A. bullisi Vokes (Tulane Stud Geol 2:75–92, 1963) is re-described. This study shows that DNA barcoding in combination with traditional morphological and ecological analyses may be an important tools to identify hidden biodiversity among deep-water organisms such as bivalves.