Morphological and meristic evaluation of the population structure of Anguilla marmorata across its range

The population structure of the giant mottled eel Anguilla marmorata was evaluated using statistical analysis of 21 morphological characters among 13 representative localities across the Indo-Pacific region and as far north as Japan. There were no clear differences in 15 proportional and six vertebral characters using principal component analysis. The total number of vertebrae ( N _V) of A . marmorata at these localities had the widest variation among the morphological and meristic characters examined. A statistical analysis of the N _V of 1238 specimens from 14 localities that included previously published data found significant differences among Micronesia, French Polynesia and other localities, and between localities in the North Pacific and South Pacific regions. Few differences were detected between specimens from the Indian Ocean and the North Pacific or South Pacific regions. The differences in N _V among some regions and the population genetic studies of this species indicate that there are at least four populations of A. marmorata (North Pacific, Micronesia, Indian Ocean and South Pacific), which appear to include metapopulation structures in the Indian Ocean and South Pacific. This population structure is consistent with the ocean current patterns in each region and the evolution of migration loops of each spawning population.     

Isolation by distance and vicariance drive genetic structure of a coral reef fish in the Pacific Ocean

We studied the genetic diversity of a coral reef fish species to investigate the origin of the differentiation. A total of 727 Acanthurus triostegus collected from 15 locations throughout the Pacific were analyzed for 20 polymorphic loci. The genetic structure showed limited internal disequilibrium within each population; 3.7% of the loci showed significant Hardy-Weinberg disequilibrium, mostly associated with Adh*, and we subsequently removed this locus from further analysis of geographic pattern. The genetic structure of A. triostegus throughout the tropical Pacific Ocean revealed a strong geographic pattern. Overall, there was significant population differentiation (multilocus F(ST) = 0.199), which was geographically structured according to bootstraps of neighbor-joining analysis on Nei's unbiased genetic distances and AMOVA analysis. The genetic structure revealed five geographic groups in the Pacific Ocean: western Pacific (Guam, Philippines, Palau, and Great Barrier Reef); central Pacific (Solomons, New Caledonia, and Fiji); and three groups made up of the eastern populations, namely Hawaiian Archipelago (north), Marquesas (equatorial), and southern French Polynesia (south) that incorporates Clipperton Island located in the northeastern Pacific. In addition, heterozygosity values were found to be geographically structured with higher values grouped within Polynesian and Clipperton populations, which exhibited lower population size. Finally, the genetic differentiation (F(ST)) was significantly correlated with geographic distance when populations from the Hawaiian and Marquesas archipelagos were separated from all the other locations. These results show that patterns of differentiation vary within the same species according to the spatial scale, with one group probably issued from vicariance, whereas the other followed a pattern of isolation by distance. The geographic pattern for A. triostegus emphasizes the diversity of the evolutionary processes that lead to the present genetic structure with some being more influential in certain areas or according to a particular spatial scale.     

The West Pacific diversity hotspot as a source or sink for new species? Population genetic insights from the Indo‐Pacific parrotfish Scarus rubroviolaceus

We used a population genetic approach to quantify major population subdivisions and patterns of migration within a broadly distributed Indo-Pacific parrotfish. We genotyped 15 microsatellite loci in Scarus rubroviolaceus collected from 20 localities between Africa and the Americas. A STRUCTURE model indicates the presence of four major populations: Eastern Pacific, Hawaii, Central-West Pacific and a less well-differentiated Indian Ocean. We used the isolation and migration model to estimate splitting times, population sizes and migration patterns between sister population pairs. To eliminate loci under selection, we used BayeScan to select loci for three isolation and migration models: Eastern Pacific and Central-West Pacific, Hawaii and the Central-West Pacific, and Indian Ocean and the Central-West Pacific. To test the assumption of a stepwise mutation model (SMM), we used likelihood to test the SMM against a two-phase model that allowed mutational complexity. A posteriori, minor departures from SMM were estimated to affect ≤2% of the alleles in the data. The data were informative about the contemporary and ancestral population sizes, migration rates and the splitting time in the eastern Pacific/Central-West Pacific comparison. The model revealed a splitting time ～17,000 BP, a larger contemporary N(e) in the Central-West Pacific than in the eastern Pacific and a strong bias of east to west migration. These characteristics support the Center of Accumulation model of peripatric diversification in low-diversity peripheral sites and perhaps migration from those sites to the western Pacific diversity hotspot.     

Population genetic structure of Bryde’s whales (<Emphasis Type="Italic">Balaenoptera brydei</Emphasis>) at the inter-oceanic and trans-equatorial levels

Bryde’s whales (Balaenoptera brydei) differ from other typical baleen whale species because they are restricted to tropical and warm temperate waters in major oceans, and frequent trans-equatorial movement has been suggested for the species. We tested this hypothesis by analyzing genetic variation at 17 microsatellite loci (N = 508) and 299 bp of mitochondrial DNA (mtDNA) control region sequences (N = 472) in individuals obtained from the western North Pacific, South Pacific, and eastern Indian Ocean. Combined use of microsatellite and mtDNA markers allowed us to distinguish between contemporary gene flow and ancestral polymorphism and to describe sex-specific philopatry. A high level of genetic diversity was found within the samples. Both nuclear and mtDNA markers displayed similar population structure, indicating a lack of sex-specific philopatry. Spatial structuring was detected using both frequency-based population parameters and individual-based Bayesian approaches. Whales in the samples from different oceanic regions came from genetically distinct populations with evidence of limited gene flow. We observed low mtDNA sequence divergence among populations and a lack of concordance between geographic and phylogenetic position of mtDNA haplotypes, suggesting recent separation of populations rather than frequent trans-equatorial and inter-oceanic movement. We conclude that current gene flow between Bryde’s whale populations is low and that effective management actions should treat them as separate entities to ensure continued existence of the species.     

Worldwide phylogeography of the blacktip shark (Carcharhinus limbatus) inferred from mitochondrial DNA reveals isolation of western Atlantic populations coupled with recent Pacific dispersal

Although many coastal shark species have widespread distributions, the genetic relatedness of worldwide populations has been examined for few species. The blacktip shark, (Carcharhinus limbatus), inhabits tropical and subtropical coastal waters throughout the world. In this study, we examined the genetic relationships of blacktip shark populations (n = 364 sharks) throughout the majority of the species' range using the entire mitochondrial control region (1067-1070 nucleotides). Two geographically distinct maternal lineages (western Atlantic, Gulf of Mexico, and Caribbean Sea clades, and eastern Atlantic, Indian, and Pacific Ocean clades) were identified and shallow population structure was detected throughout their geographic ranges. These findings indicate that a major population subdivision exists across the Atlantic Ocean, but not the Pacific Ocean. The historical dispersal of this widespread, coastal species may have been interrupted by the rise of the Isthmus of Panama. This scenario implies historical dispersal across the Pacific Ocean (supported by the recovery of the same common haplotype from the Philippines, Hawaii, and the Gulf of California reflecting recent/contemporary dispersal abilities) and an oceanic barrier to recent migration across the Atlantic. Genetic structure within the eastern Atlantic/Indo-Pacific (Phi(ST) = 0.612, P < 0.001) supports maternal philopatry throughout this area, expanding previous western Atlantic findings. Eastern Atlantic/Indo-Pacific C. limbatus control region haplotypes were paraphyletic to Carcharhinus tilstoni haplotypes in our maximum-parsimony analysis. The greater divergence of western Atlantic C. limbatus than C. tilstoni from eastern Atlantic/Indo-Pacific C. limbatus reflects the taxonomic uncertainty of western Atlantic C. limbatus.     

Microsatellite and mitochondrial haplotype diversity reveals population differentiation in the tiger shrimp (Penaeus monodon) in the Indo-Pacific region

The black tiger shrimp (Penaeus monodon) is an ecologically and economically important penaeid species and is widely distributed in the Indo-Pacific region. Here we investigated the genetic diversity of P. monodon (n = 355) from eight geographical regions by genotyping at 10 microsatellite loci. The average observed heterozygosity at various loci ranged from 0.638 to 0.743, indicating a high level of genetic variability in this region. Significant departures from Hardy-Weinberg equilibrium caused by heterozygote deficiency were recorded for most loci and populations. Pairwise F(ST) and R(ST) values revealed genetic differentiation among the populations. Evidence from the assignment test showed that the populations in the West Indian Ocean were unique, whereas other populations examined were partially admixed. In addition, the non-metric multidimensional scaling analysis indicated the presence of three geographic groups in the Indo-Pacific region, i.e. the African populations, a population from western Thailand and the remaining populations as a whole. We also sequenced and analysed the mitochondrial control region (mtCR) in these shrimp stocks to determine whether the nuclear and mitochondrial genomes show a similar pattern of genetic differentiation. A total of 262 haplotypes were identified, and nucleotide divergence among haplotypes ranged from 0.2% to 16.3%. Haplotype diversity was high in all populations, with a range from 0.969 to 1. Phylogenetic analysis using the mtCR data revealed that the West Indian Ocean populations were genetically differentiated from the West Pacific populations, consistent with the microsatellite data. These results should have implications for aquaculture management and conservation of aquatic diversity.     

Phylogeography of the green turtle, Chelonia mydas, in the Southwest Indian Ocean

Patterns of mitochondrial DNA (mtDNA) variation were used to analyse the population genetic structure of southwestern Indian Ocean green turtle (Chelonia mydas) populations. Analysis of sequence variation over 396 bp of the mtDNA control region revealed seven haplotypes among 288 individuals from 10 nesting sites in the Southwest Indian Ocean. This is the first time that Atlantic Ocean haplotypes have been recorded among any Indo-Pacific nesting populations. Previous studies indicated that the Cape of Good Hope was a major biogeographical barrier between the Atlantic and Indian Oceans because evidence for gene flow in the last 1.5 million years has yet to emerge. This study, by sampling localities adjacent to this barrier, demonstrates that recent gene flow has occurred from the Atlantic Ocean into the Indian Ocean via the Cape of Good Hope. We also found compelling genetic evidence that green turtles nesting at the rookeries of the South Mozambique Channel (SMC) and those nesting in the North Mozambique Channel (NMC) belong to separate genetic stocks. Furthermore, the SMC could be subdivided in two different genetic stocks, one in Europa and the other one in Juan de Nova. We suggest that this particular genetic pattern along the Mozambique Channel is attributable to a recent colonization from the Atlantic Ocean and is maintained by oceanic conditions in the northern and southern Mozambique Channel that influence early stages in the green turtle life cycle.     

Genetic diversity and structure of circumtropical almaco jack,Seriola rivoliana: tool for conservation and management

The almaco jack, Seriola rivoliana, is a circumtropical pelagic fish of importance both in commercial fisheries and in aquaculture. To understand levels of genetic diversity within and among populations in the wild, population genetic structure and the relative magnitude of migration were assessed using mtDNA sequence data and single nucleotide polymorphisms (SNPs) from individuals sampled from locations in the Pacific and Atlantic Oceans. A total of 25 variable sites of cytochrome c oxidase subunit 1 and 3678 neutral SNPs were recovered. Three genetic groups were identified, with both marker types distributed in different oceanic regions: Pacific-1 in central Pacific, Pacific-2 in eastern Pacific and Atlantic in western Atlantic. Nonetheless, the analysis of SNP identified a fourth population in the Pacific coast of Baja California Sur, Mexico (Pacific-3), whereas that of mtDNA did not. This mito-nuclear discordance is likely explained by a recently diverged Pacific-3 population. In addition, two mtDNA haplogroups were found within the western Atlantic, likely indicating that the species came into the Atlantic from the Indian Ocean with historical gene flow from the eastern Pacific. Relative gene flow among ocean basins was low with _rm < 0.2, whereas in the eastern Pacific it was asymmetric and higher from south to north (_rm > 0.79). The results reflect the importance of assessing genetic structure and gene flow of natural populations for the purposes of sustainable management.     

Genetic evidence for a single stock of the deep-sea teleost Beryx decadactylus in the North Atlantic Ocean as inferred from mtDNA control region analysis

Mitochondrial control region sequences of 141 alfonsino Beryx decadactylus sampled off the coast of South Carolina were compared with 164 sequences from B. decadactylus collected in the Azores for inferring population structure and demographic history of this deep-water teleost in the North Atlantic Ocean. Analysis of molecular variance showed that 100% of the genetic variation was found within populations, indicating an absence of population structure (Φ(ST) = -0· 003). Neutrality tests and mismatch distribution analyses of pooled sequences suggested that B. decadactylus in the North Atlantic Ocean have undergone population expansion. These results may indicate that transatlantic gene flow occurs, possibly through passive drift of larvae or adult migration. The potential of a shared stock between the eastern and western North Atlantic Ocean will need to be considered if a directed fishery for B. decadactylus were to develop in the U.S.A.     

Present and past genetic connectivity of the Indo‐Pacific tropical eel Anguilla bicolor

Aim The objective of this study was to reveal the present population structure and infer the gene‐flow history of the Indo‐Pacific tropical eel Anguilla bicolor. Location The Indo‐Pacific region. Methods The entire mitochondrial control region sequence and the genotypes at six microsatellite loci were analysed for 234 specimens collected from eight representative localities where two subspecies have been historically designated. In order to infer the population structure, genetic differentiation estimates, analysis of molecular variance and gene‐tree reconstruction were performed. The history of migration events and population growth was assessed using neutrality tests based on allelic frequency spectrum, coalescent‐based estimation of gene flow and Bayesian demographic analysis using control region sequences. Results Population structure analysis showed genetic divergence between eels from the Indian and Pacific oceans (F_ST = 0.0174–0.0251, P < 0.05 for microsatellites; Φ_ST = 0.706, P < 0.001 for control region), while no significant variation was observed within each ocean. Two mitochondrial sublineages that do not coincide with geographical regions were found in the Indian Ocean clade of a gene tree. However, these two sublineages were not differentiated at the microsatellite markers. The estimation of mitochondrial gene‐flow history suggested allopatric isolation between the Indian and Pacific oceans, and a possible secondary contact within the Indian Ocean after an initial population splitting. Bayesian demographic history reconstruction and neutrality tests indicated population growth in each ocean after the Indo‐Pacific divergence. Main conclusions Anguilla bicolor has diverged between the Indian and Pacific oceans, which is consistent with the classical subspecies designation, but is apparently genetically homogeneous in the Indian Ocean. The analysis of gene‐flow and demographic history indicated that the two mitochondrial sublineages observed in the Indian Ocean probably represent the haplotype groups of relict ancestral populations. A comparison with a sympatric congener suggested that absolute physical barriers to gene flow may not be necessary for population divergence in eels.     

Genetic analysis of Black Tiger shrimp (Penaeus monodon) across its natural distribution range reveals more recent colonization of Fiji and other South Pacific islands

The Black Tiger shrimp (Penaeus monodon) has a natural distribution range from East Africa to the South Pacific Islands. Although previous studies of Indo-Pacific P. monodon have found populations from the Indian Ocean and Australasia to differ genetically, their relatedness to South Pacific shrimp remains unknown. To address this, polymorphisms at eight shared microsatellite loci and haplotypes in a 418-bp mtDNA-CR (control region) sequence were examined across 682 P. monodon from locations spread widely across its natural range, including the South Pacific islands of Fiji, Palau, and Papua New Guinea (PNG). Observed microsatellite heterozygosities of 0.82-0.91, allele richness of 6.85-9.69, and significant mtDNA-CR haplotype variation indicated high levels of genetic diversity among the South Pacific shrimp. Analysis of microsatellite genotypes using a Bayesian STRUCTURE method segregated Indo-Pacific P. monodon into eight distinct clades, with Palau and PNG shrimp clustering among others from Southeast Asia and eastern Australia, respectively, and Fiji shrimp clustering as a distinct group. Phylogenetic analyses of mtDNA-CR haplotypes delineated shrimp into three groupings, with shrimp from Fiji again being distinct by sharing no haplotypes with other populations. Depending on regional location, the genetic structures and substructures identified from the genotyping and mtDNA-CR haplotype phylogeny could be explained by Metapopulation and/or Member-Vagrant type evolutionary processes. Neutrality tests of mutation-drift equilibrium and estimation of the time since population expansion supported a hypothesis that South Pacific P. monodon were colonized from Southeast Asia and eastern Australia during the Pleistocene period over 60,000 years ago when land bridges were more expansive and linked these regions more closely.     

Trans‐Pacific and trans‐Arctic pathways of the intertidal macroalga Fucus distichus L. reveal multiple glacial refugia and colonizations from the North Pacific to the North Atlantic

Aim We examined the phylogeography of the cold‐temperate macroalgal species Fucus distichus L., a key foundation species in rocky intertidal shores and the only Fucus species to occur naturally in both the North Pacific and the North Atlantic. Location North Pacific and North Atlantic oceans (42° to 77° N). Methods We genotyped individuals from 23 populations for a mitochondrial DNA (mtDNA) intergenic spacer (IGS) (n = 608) and the cytochrome c oxidase subunit I (COI) region (n = 276), as well as for six nuclear microsatellite loci (n = 592). Phylogeographic structure and connectivity were assessed using population genetic and phylogenetic network analyses. Results IGS mtDNA haplotype diversity was highest in the North Pacific, and divergence between Pacific haplotypes was much older than that of the single cluster of Atlantic haplotypes. Two ancestral Pacific IGS/COI clusters led to a widespread Atlantic cluster. High mtDNA and microsatellite diversities were observed in Prince William Sound, Alaska, 11 years after severe disturbance by the 1989 Exxon Valdez oil spill. Main conclusions At least two colonizations occurred from the older North Pacific populations to the North Atlantic between the opening of the Bering Strait and the onset of the Last Glacial Maximum. One colonization event was from the Japanese Archipelago/eastern Aleutians, and a second was from the Alaskan mainland around the Gulf of Alaska. Japanese populations probably arose from a single recolonization event from the eastern Aleutian Islands before the North Pacific–North Atlantic colonization. In the North Atlantic, the Last Glacial Maximum forced the species into at least two known glacial refugia: the Nova Scotia/Newfoundland (Canada) region and Andøya (northern Norway). The presence of two private haplotypes in the central Atlantic suggests the possibility of colonization from other refugia that are now too warm to support F. distichus. With the continuing decline in Arctic ice cover as a result of global climate change, renewed contact between North Pacific and North Atlantic populations of Fucus species is expected.     

Population structure of the African savannah elephant inferred from mitochondrial control region sequences and nuclear microsatellite loci

Two hundred and thirty-six mitochondrial DNA nucleotide sequences were used in combination with polymorphism at four nuclear microsatellite loci to assess the amount and distribution of genetic variation within and between African savannah elephants. They were sampled from 11 localities in eastern, western and southern Africa. In the total sample, 43 haplotypes were identified and an overall nucleotide diversity of 2.0% was observed. High levels of polymorphism were also observed at the microsatellite loci both at the level of number of alleles and gene diversity. Nine to 14 alleles per locus across populations and 44 alleles in the total sample were found. The gene diversity ranged from 0.51 to 0.72 in the localities studied. An analysis of molecular variance showed significant genetic differentiation between populations within regions and also between regions. The extent of subdivision between populations at the mtDNA control region was approximately twice as high as shown by the microsatellite loci (mtDNA F(ST) = 0.59; microsatellite R(ST) = 0.31). We discuss our results in the light of Pleistocene refugia and attribute the observed pattern to population divergence in allopatry accompanied by a recent population admixture following a recent population expansion.     

A new look at geographic and phylogenetic relationships within the species group surrounding Octopus vulgaris (Mollusca, Cephalopoda): indications of very wide distribution from mitochondrial DNA sequences

The distribution of Octopus vulgaris has not yet been completely clarified. For a long time, a cosmopolitan distribution with unknown distribution limits had been assumed. This assumption has recently been questioned and it has been postulated that the distribution is restricted to the Mediterranean and the northeastern Atlantic. However, as our previous studies show, the existence of O. vulgaris can be confirmed for the Mediterranean and the whole eastern Atlantic, and evidence is provided for its occurrence in the western Atlantic. The aim of the present work is to extend our previous data matrix and to clarify whether O. vulgaris exists in the northwestern Pacific. Therefore, the sequence variation in ostensible O. vulgaris from 13 localities in the Mediterranean (France), the Atlantic Ocean [Lanzarote, Senegal, South Africa (Atlantic, Indian Ocean), Tristan da Cunha, north, middle and south Brazil], the Caribbean Sea (Venezuela) and the Pacific Ocean (Taiwan, Japan and Costa Rica) was examined using the mitochondrial genes coding for the 16S rRNA and cytochrome oxidase subunit III (COIII). Sequence divergence was relatively low between populations of O. vulgaris from the Mediterranean, the eastern and western Atlantic (except north Brazil), Venezuela, Taiwan and Japan compared with other species of the genus Octopus . Trees constructed by using maximum likelihood, neighbour joining and maximum parsimony algorithms (PAUP) show the above-mentioned populations from the Mediterranean, the western and eastern Atlantic, Venezuela and the northwestern Pacific (Japan and Taiwan) as a monophyletic cluster. Thus, even if the Octopus vulgaris -like octopus from north Brazil should turn out a cryptic species, the data of this work not only support our hypothesis of the distribution of O. vulgaris in the Mediterranean, the eastern and western Atlantic but also show that O. vulgaris is present in the northwestern Pacific, namely in the waters of Taiwan and Japan.     

Evidence for initial opening of the Pacific ocean in the Jurassic

An argument is presented for the east-west initial opening of the pacific Ocean during Early Jurassic times, on paleontological, biogeograhical, and geological grounds. A new reconstruction of the continents bordering the Pacific Ocean is proposed, based chiefly upon trans-Pacific, terrestrial biotic links that are not reflected in regions bordering the Atlantic. A new Arctic Ocean reconstruction is also proposed. Since the Atlantic and Indian Oceans were closed in the Early Jurassic as well, an expanding-earth model is adopted, instead of a Pangaen reconstruction on a present-sized earth. The model prposed here is also compatible with geological evidence for a narrow, epicontinental Tethys Sea. Sea-floor subduction along the perimeter of the Pacific appears to be actively taking place and in the past was much more extensive along the eastern border than on the western side. The tectonics of Antarctica, the Southwest Pacific, Indonesia, Japan, the Arctic region, western North America, Baja California, the Carribean, and the Gulf of Mexico are discussed in terms of the proposed model. The Pacific sea-floor spreading history is outlined and related to the initial opening of the North Atlantic 180 million years ago (Early Jurassic). The South Pacific and Indian Ocean are both considered to have opened some 155 million years ago (Late Jurassic). The original and present positions of the Jurassic equator are determined.     

Panbiogeographical analysis of distribution patterns in hagfishes (Craniata: Myxinidae)

Aim To analyse the worldwide distribution patterns of hagfishes using panbiogeographical track analysis, and to attempt to correlate these patterns with the tectonic history of the ocean basins. Location Atlantic and Pacific oceans. Method The distributions of 47 out of 70 species of hagfish (in the genera Eptatretus, Myxine, Nemamyxine, Neomyxine, and Paramyxine) were studied by the panbiogeographical method of track analysis. The analysis was performed using distributional data obtained from the collections included in the Ocean Biogeographic Information System (OBIS, http://www.iobis.org ) and FishBase ( http://www.fishbase.org ), with additional records from the literature. Individual tracks were obtained for each species by plotting localities and connecting them by minimum‐spanning trees. Generalized tracks were determined from the spatial overlap between individual tracks. Results Six generalized tracks were found: in the Gulf of Mexico, Caribbean Sea, South‐eastern Atlantic, Western Pacific, North‐eastern Pacific and South‐eastern Pacific. Main conclusions The distribution patterns of myxinids are marked by a high degree of endemism and vicariance, and are correlated with the tectonic features involved in many of the events that led to the development of oceanic basins. The main massing of the group is around the Pacific Basin. In the Atlantic Ocean, the distribution of Myxine glutinosa seems to correspond to a classic trans‐oceanic track and vicariance resulting from the opening of the Atlantic Ocean during the Cretaceous. In the Pacific Ocean, the distribution of the Eptatretus and Paramyxine species is clearly associated with the margins of the Pacific tectonic plate. The generalized tracks of hagfishes are shared by several other groups of marine organisms, including many from shallow tropical waters, implying a common history for this marine biota. Overall, vicariance is a major feature of hagfish distribution, suggesting vicariant differentiation of widespread ancestors as a result of sea‐floor spreading between continents in connection with ocean formation.     

Phylogeography of the pantropical sea urchin Tripneustes: contrasting patterns of population structure between oceans

To understand how allopatric speciation proceeds, we need information on barriers to gene flow, their antiquity, and their efficacy. For marine organisms with planktonic larvae, much of this information can only be obtained through the determination of divergence between populations. We evaluated the importance of ocean barriers by studying the mitochondrial DNA phylogeography of Tripneustes, a pantropical genus of shallow water sea urchin. A region of cytochrome oxidase I (COI) was sequenced in 187 individuals from locations around the globe. The COI phylogeny agreed with a previously published phylogeny of bindin that barriers important to the evolution of Tripneustes are: (1) the cold water upwelling close to the tip of South Africa, (2) the Isthmus of Panama, (3) the long stretch of deep water separating the eastern from the western Atlantic, and (4) the freshwater plume of the Orinoco and the Amazon rivers between the Caribbean and the coast of Brazil. These barriers have previously been shown to be important in at least a subset of the shallow water marine organisms in which phylogeography has been studied. In contrast, the Eastern Pacific Barrier, 5000 km of deep water between the central and the eastern Pacific that has caused the deepest splits in other genera of sea urchins, is remarkably unimportant as a cause of genetic subdivision in Tripneustes. There is also no discernible subdivision between the Pacific and Indian Ocean populations of this genus. The most common COI haplotype is found in the eastern, central, and western Pacific as well as the Indian Ocean. Morphology, COI, and bindin data agree that T. depressus from the eastern Pacific and T. gratilla from the western Pacific are, in fact, the same species. The distribution of haplotype differences in the Indo-Pacific exhibits characteristics expected from a sea urchin genus with ephemeral local populations, but with high fecundity, dispersal, and growth: there is little phylogenetic structure, and mismatch distributions conform to models of recent population expansion on a nearly global scale. Yet, comparisons between local populations produce large and significant F(ST) values, indicating nonrandom haplotype distribution. This apparent local differentiation is only weakly reflected in regional divergence, and there is no evidence of isolation by distance in correlations between F(ST) values and either geographical or current distance. Thus, Tripneustes in the Indo-Pacific (but not in the Atlantic) seems to be one large metapopulation spanning two oceans and containing chaotic, nonequilibrium local variation, produced by the haphazard arrival of larvae or by unpredictable local extinction.     

Genetic divergence between colonies of Flesh-footed Shearwater <Emphasis Type="Italic">Ardenna carneipes</Emphasis> exhibiting different foraging strategies

Increasing evidence suggests foraging segregation as a key mechanism promoting genetic divergence within seabird species. However, testing for a relationship between population genetic structure and foraging movements among seabird colonies can be challenging. Telemetry studies suggest that Flesh-footed Shearwater Ardenna carneipes that breed at Lord Howe Island or New Zealand, versus southwestern Australia or Saint-Paul Island in the Indian Ocean, migrate to different regions (North Pacific Ocean and northern Indian Ocean, respectively) during the non-breeding season, which may inhibit gene flow among colonies. In this study, we sequenced a 858-base pair mitochondrial region and seven nuclear DNA fragments (352–654 bp) for 148 individuals to test genetic differentiation among colonies of Flesh-footed Shearwaters. Strong genetic divergence was detected between Pacific colonies relative to those further West. Molecular analysis of fisheries’ bycatch individuals sampled in the Sea of Japan indicated that individuals from both western and eastern colonies were migrating through this area, and hence the apparent segregation of the non-breeding distribution based on telemetry is invalid and cannot contribute to the population genetic structure among colonies. The genetic divergence among colonies is better explained by philopatry and evidence of differences in foraging strategies during the breeding season, as supported by the observed genetic divergence between Lord Howe Island and New Zealand colonies. We suggest molecular analysis of fisheries’ bycatch individuals as a rigorous method to identify foraging segregation, and we recommend the eastern and western A. carneipes colonies be regarded as different Management Units.     

Global population structure of the spiny dogfish Squalus acanthias,a temperate shark with an antitropical distribution

The spiny dogfish (Squalus acanthias) is a temperate, coastal squaloid shark with an antitropical distribution in the Atlantic and Pacific oceans. The global population structure of this species is poorly understood, although individuals are known to undergo extensive migrations within coastal waters and across ocean basins. In this study, an analysis of the global population structure of the spiny dogfish was conducted using eight polymorphic nuclear microsatellite markers and a 566‐bp fragment of the mitochondrial ND2 gene region. A low level of genetic divergence was found among collections from the Atlantic and South Pacific basins, whereas a high level of genetic divergence was found among Pacific Ocean collections. Two genetically distinct groups were recovered by both marker classes: one exclusive to North Pacific collections, and one including collections from the South Pacific and Atlantic locations. The strong genetic break across the equatorial Pacific coincides with major regional differences in the life‐history characters of spiny dogfish, suggesting that spiny dogfish in areas on either side of the Pacific equator have been evolving independently for a considerable time. Phylogeographic analyses indicate that spiny dogfish populations had a Pacific origin, and that the North Atlantic was colonized as a result of a recent range expansion from the South American coast. Finally, the available data strongly argue for the taxonomic separation of the North Pacific spiny dogfish from S. acanthias and a re‐evaluation of the specific status of S. acanthias is warranted.     

Genetic Diversity and Population Structure of the Pelagic Thresher Shark (Alopias pelagicus) in the Pacific Ocean: Evidence for Two Evolutionarily Significant Units

There has been an increasing concern about shark overexploitation in the last decade, especially for open ocean shark species, where there is a paucity of data about their life histories and population dynamics. Little is known regarding the population structure of the pelagic thresher shark, Alopias pelagicus. Though an earlier study using mtDNA control region data, showed evidence for differences between eastern and western Pacific populations, the study was hampered by low sample size and sparse geographic coverage, particularly a lack of samples from the central Pacific. Here, we present the population structure of Alopias pelagicus analyzing 351 samples from six different locations across the Pacific Ocean. Using data from mitochondrial DNA COI sequences and seven microsatellite loci we found evidence of strong population differentiation between western and eastern Pacific populations and evidence for reciprocally monophyly for organelle haplotypes and significant divergence of allele frequencies at nuclear loci, suggesting the existence of two Evolutionarily Significant Units (ESU) in the Pacific Ocean. Interestingly, the population in Hawaii appears to be composed of both ESUs in what seems to be clear sympatry with reproductive isolation. These results may indicate the existence of a new cryptic species in the Pacific Ocean. The presence of these distinct ESUs highlights the need for revised management plans for this highly exploited shark throughout its range.