Genetic population structure of sardine (<Emphasis Type="Italic">Sardina pilchardus</Emphasis>) off Morocco detected with intron polymorphism (EPIC-PCR)

The upwelling systems along the coast of Morocco support some of the largest populations of sardine (Sardina pilchardus) in the world. Although these populations provide a base for a substantial fishing industry, virtually nothing is known about the genetic stock structure of this fish. Samples (n = 346), collected from seven sites along the Atlantic coast and in the Alboran Sea, were examined for exon-primed intron-crossing PCR (EPIC-PCR) polymorphism. Two markers, CaM-4 and Ops-1, had 6 and 9 alleles, respectively, after the pooling of gel fragments into 5 bp length classes, Correspondence analysis and the distribution of F _st among samples indicated that Moroccan populations were divided into two groups with F _st = 0.034 (P < 0.05) across the Gibraltar Strait. Populations along the Atlantic coast of Morocco comprise one genetic unit, except for a weak genetic boundary south of Cape Ghir and the peculiar behavior of the Safi sample would indicate a genetic drift. Complex ocean hydrodynamics around Gibraltar Strait and across Cape Ghir, likely, contributes to these genetic isolations. These results point out the usefulness of population genetic studies in stock management for sardine populations that may be particularly vulnerable to overexploitation especially during upwelling intensity shifts.     

Population genetics of the nurse shark (Ginglymostoma cirratum) in the western Atlantic

The nurse shark, Ginglymostoma cirratum, inhabits shallow, tropical, and subtropical waters in the Atlantic and the eastern Pacific. Unlike many other species of sharks, nurse sharks are remarkably sedentary. We assayed the mitochondrial control region and eight microsatellite loci from individuals collected primarily in the western Atlantic to estimate the degree of population subdivision. Two individuals from the eastern Atlantic and one from the Pacific coast of Panama also were genotyped. Overall, the mtDNA haplotype (h = 48 ± 5%) and nucleotide (π = 0.08 ± 0.06%) diversities were low. The microsatellite data mirror the mitochondrial results with the average number of alleles ([`(N)]<sub>A</sub> \bar{N}_{A}  = 9) and observed heterozygosity ([`(H)]_O \bar{H}_{O}  = 0.58) both low. The low levels of diversity seen in both the mtDNA and the microsatellite may be due to historical sea level fluctuations and concomitant loss of shallow water habitat. Eight of the 10 pair-wise western Atlantic F _ST estimates for mtDNA indicated significant genetic subdivision. Pair-wise F _ST values for the microsatellite loci indicated a similar pattern as the mtDNA. The western Atlantic population of nurse sharks is genetically subdivided with the strongest separation seen between the offshore islands and mainland Brazil, likely due to deep water acting as a barrier to dispersal. The eastern and western Atlantic populations were closely related. The eastern Pacific individual is quite different from Atlantic individuals and may be a cryptic, sister species.     

Microsatellite analysis of albacore tuna (<Emphasis Type="Italic">Thunnus alalunga</Emphasis>): population genetic structure in the North-East Atlantic Ocean and Mediterranean Sea

Stock heterogeneity was investigated in albacore tuna (Thunnus alalunga, Bonnaterre 1788), a commercially important species in the North Atlantic Ocean and Mediterranean Sea. Twelve polymorphic microsatellite loci were examined in 581 albacore tuna from nine locations, four in the north-east Atlantic Ocean (NEA), three in the Mediterranean Sea (MED) and two in the south-western Pacific Ocean (SWP). Maximum numbers of alleles per locus ranged from 9 to 38 (sample mean, 5.2–22.6 per locus; overall mean, 14.2 ± 0.47 SE), and observed heterozygosities per locus ranged from 0.44 to 1.00 (overall mean: 0.79 ± 0.19 SE). Significant deficits of heterozygotes were observed in 20% of tests. Multilocus F _ST values were observed ranging from 0.00 to Θ = 0.036 and Θ′ = 0.253, with a mean of Θ = 0.013 and Θ′ = 0.079. Pairwise F _ST values showed that the SWP, NEA and MED stocks were significantly distinct from one another, thus corroborating findings in previous studies based on mitochondrial DNA, nuclear DNA (other than microsatellites) and allozyme analyses. Heterogeneity was observed for the first time between samples within the Mediterranean Sea. GENELAND indicated the potential presence of three populations across the NEA and two separate populations in the Mediterranean Sea. Observed genetic structure may be related to migration patterns and timing of movements of subpopulations to the feeding grounds in either summer or autumn. We suggest that a more intensive survey be conducted throughout the entire fishing season to ratify or refute the currently accepted genetic homogeneity within the NEA albacore stock.     

Population structure of short-beaked common dolphins (<Emphasis Type="Italic">Delphinus delphis</Emphasis>) in the North Atlantic Ocean as revealed by mitochondrial and nuclear genetic markers

The understanding of population structure and gene flow of marine pelagic species is paramount to monitoring, management and conservation studies. Such studies are often hampered by the potentially high dispersal behavior of the species, the lack of obvious geographical barriers in the marine environment and the scarce sample availability. Short-beaked common dolphins (Delphinus delphis) are widespread in coastal and open-ocean habitats of the North Atlantic Ocean, nevertheless population structure and migratory patterns are poorly understood. Furthermore, concern has been raised about the status of the species because large numbers of dolphins have been taken incidentally in several fisheries throughout the North Atlantic in the past decades. In the present study, a large number of individual samples were obtained from seasonal and spatial aggregations of common dolphins from western (wNA) and eastern North Atlantic (eNA) regions, mostly using opportunistic sampling (i.e. from incidental entanglement in fishing gear or beach-cast carcasses). Genetic variability was investigated using nuclear (14 microsatellite loci) and mitochondrial (360 bp of the control region) genetic markers. Levels of genetic diversity were relatively high in all sampled areas and no evidence of recent reduction of effective population size (i.e. bottleneck) was detected at the nuclear loci. Significant population structure was detected between the two main regions (wNA and eNA) where it appeared to be more pronounced at mitochondrial (F _ST = 0.018, P < 0.001) than nuclear markers (F _ST = 0.005, P < 0.05), indicating the presence of at least two genetically distinct populations of common dolphins in the North Atlantic Ocean. In contrast, no significant genetic structure was detected between temporal aggregations of dolphins from within the same region, suggesting possible seasonal movement patterns at a regional scale. The observed levels of genetic differentiation between classes of markers are discussed here as a possible consequence of migratory patterns or recent population subdivision. An erratum to this article can be found at     

Allozyme variation in European populations of the oyster Ostrea edulis

Variations at 22 enzyme coding loci were surveyed in 11 populations of the oyster Ostrea edulis L., which were sampled between 1988 and 1990 along the Atlantic and Mediterranean coasts of Europe. Atlantic oyster beds suffered a steady decline during the last century, and restocking of beds with oysters of foreign origin has probably resulted in a high degree of interbreeding of natural oyster stocks from all Atlantic Europe. Our study confirms the low levels of genetic variability previously reported for the oyster populations from the Atlantic coasts, and extends it to the Mediterranean coasts. The locus arginine-kinase (ARK ^*) exhibited a high degree of interpopulation differentiation (F _ST=0.289), resulting from extensive variation in gene frequencies along a geographical cline. However, the overall genetic differentiation between populations was slight, and similar to that reported for other local populations of bivalves (mean genetic distance between populations is 0.010, mean F _ST=0.062). A general pattern of increasing differentiation along the coastline in an Atlantic-mediterranean direction emerged; but genetic differentiation among the Atlantic populations was not significantly lower than that observed among the Mediterranean populations. This and other results suggest that the effects of extensive transplantation of oysters among various areas in Europe are detectable only in some particular localities. The geographical distribution of low-frequency alleles suggests a restriction to gene flow outwards from the Mediterranean Sea, across the Straits of Gibraltar.     

Microsatellite DNA markers and morphometrics reveal a complex population structure in a merobenthic octopus species (<Emphasis Type="Italic">Octopus maorum</Emphasis>) in south-east Australia and New Zealand

Five polymorphic microsatellite loci were developed and then used to assess the population genetic structure of a commercially harvested merobenthic octopus species (Octopus maorum) in south-east Australian and New Zealand (NZ) waters. Beak and stylet morphometrics were also used to assess population differentiation in conjunction with the genetic data. Genetic variation across all loci and all sampled populations was very high (mean number alleles = 15, mean expected heterozygosity = 0.85). Microsatellites revealed significant genetic structuring (overall F _ST = 0.024, p < 0.001), which did not fit an isolation-by-distance model of population differentiation. Divergence was observed between Australian and NZ populations, between South Australia and north-east Tasmania, and between two relatively proximate Tasmanian sites. South Australian and southern Tasmanian populations were genetically homogeneous, indicating a level of connectivity on a scale of 1,500 km. Morphometric data also indicated significant differences between Australian and NZ populations. The patterns of population structuring identified can be explained largely in relation to regional oceanographic features.     

Regional differentiation and post-glacial expansion of the Atlantic silverside, <Emphasis Type="Italic">Menidia menidia,</Emphasis> an annual fish with high dispersal potential

The coastal marine environment of the Northwest Atlantic contains strong environmental gradients that create distinct marine biogeographic provinces by limiting dispersal, recruitment, and survival. This region has also been subjected to numerous Pleistocene glacial cycles, resulting in repeated extirpations and recolonizations in northern populations of marine organisms. In this study, we examined patterns of genetic structure and historical demography in the Atlantic silverside, Menidia menidia, an annual marine fish with high dispersal potential but with well-documented patterns of clinal phenotypic adaptation along the environmental gradients of the Northwest Atlantic. Contrary to previous studies indicating genetic homogeneity that should preclude regional adaptation, results demonstrate subtle but significant (F _ST = 0.07; P < 0.0001) genetic structure among three phylogeographic regions that partially correspond with biogeographic provinces, suggesting regional limits to gene flow. Tests for non-equilibrium population dynamics and latitudinal patterns in genetic diversity indicate northward population expansion from a single southern refugium following the last glacial maximum, suggesting that phylogeographic and phenotypic patterns have relatively recent origins. The recovery of phylogeographic structure and the partial correspondence of these regions to recognized biogeographic provinces suggest that the environmental gradients that shape biogeographic patterns in the Northwest Atlantic may also limit gene flow in M. menidia, creating phylogeographic structure and contributing to the creation of latitudinal phenotypic clines in this species.     

Temporal genetic variation in populations of the limpet Cellana grata from Hong Kong shores

Variations in the relative contributions of gene flow and spatial and temporal variation in recruitment are considered the major determinants of population genetic structure in marine organisms. Such variation can be assessed through repeated measures of the genetic structure of a species over time. To test the relative importance of these two phenomena, temporal variation in genetic composition was measured in the limpet Cellana grata, among four annual cohorts over 10 years at four rocky shores in Hong Kong. A total of 408 limpets, comprising individuals from 1998, 1999, 2006 and 2007 cohorts were screened for genetic variation using five microsatellite loci. Minor but significant genetic differentiation was detected among samples from the 1998/1999 collection (F _ST = 0.0023), but there was no significant differentiation among the 2006/2007 collection (F _ST = 0.0008). Partitioning of genetic variation among shores was also significant in 1998/1999 but not in the 2006/2007 collection, although there was no correlation between genetic and geographic distances. There was no significant difference between collections made in 1998/1999 and 2006/2007. This lack of clear structure implies a high level of gene flow, but differentiation with time may be the result of stochastic recruitment variation among shores. Estimates of effective population size were not high (599, 95% C.L. 352–11397), suggesting the potential susceptibility of the populations to genetic drift, although a significant bottleneck effect was not detected. These findings indicate that genetic structuring between populations of C. grata in space and time may result from spatio-temporal variation in recruitment, but the potential development of biologically significant differentiation is suppressed by a lack of consistency in recruitment variability and high connectivity among shores.     

Cryptic species and population structuring of the Atlantic and Pacific seabob shrimp species, Xiphopenaeus kroyeri and Xiphopenaeus riveti

Seabob shrimps of the genus Xiphopenaeus are important fishery resources along the Atlantic and Pacific coasts of Central and South America. The genus was considered to comprise two species: the Atlantic Xiphopenaeus kroyeri (Heller, Sitzungsber Math Naturwiss cl kaiserliche Akad Wiss Wien 45:389–426, 1862), and the Pacific Xiphopenaeus riveti (Bouvier, Bull Mus Hist Nat Paris 13:113–116, 1907). In a recent review, Xiphopenaeus was regarded as a monotypic genus, on the basis that no clear morphological differences could be found between Pacific and Atlantic specimens (Pérez Farfante and Kensley, Mem Mus Nat Hist Nat Paris 175:1–79, 1997). In the present work, nuclear (allozymes), and mitochondrial (Cytochrome Oxidase I) genes were used to demonstrate the validity of X. riveti and reveal the presence of two cryptic species of Xiphopenaeus within X. kroyeri in the Atlantic Ocean. The high levels of molecular divergence among these species contrast with their high morphological resemblance. Interspecific sequence divergences (Kimura 2-parameter distance) varied from 0.106 to 0.151, whereas intraspecific distances ranged from 0 to 0.008 in Xiphopenaeus sp. 1, from 0 to 0.003 in Xiphopenaeus sp. 2, and from 0.002 to 0.005 in X. riveti. In addition, five diagnostic allozyme loci were found between sympatric samples of Xiphopenaeus sp. 1 and 2 along the Brazilian coast. The results suggest that Xiphopenaeus sp. 2 from the Atlantic is more closely related to the Pacific X. riveti than to the Atlantic Xiphopenaeus sp. 1. Furthermore, a high level of genetic structuring (Xiphopenaeus sp. 1: F _ST =0.026; P<0.05; Xiphopenaeus sp. 2: F _ST =0.055; P<0.01) was found in the Brazilian Xiphopenaeus populations, indicating the presence of different genetic stocks in both Atlantic species. These findings have important commercial implications as they show that the fisheries of the two Atlantic species must be managed separately, and that each one is comprised of different populations.Communicated by O. Kinne, Oldendorf/Luhe     

Low levels of global genetic differentiation and population expansion in the deep-sea teleost <Emphasis Type="Italic">Hoplostethus atlanticus</Emphasis> revealed by mitochondrial DNA sequences

The orange roughy Hoplostethus atlanticus is a well-known commercial species with a global distribution. There is no consensus about levels of connectivity among populations despite a range of techniques having been applied. We used cytochrome c oxidase subunit I (COI) and cytochrome b sequences to study genetic connectivity at a global scale. Pairwise Φ_ST analyses revealed a lack of significant differentiation among samples from New Zealand, Australia, Namibia, and Chile. However, low but significant differentiation (Φ_ST = 0.02–0.13, P < 0.05) was found between two Northeast Atlantic sites and all the other sites with COI. AMOVA and the haplotype genealogy confirmed these results. The prevalent lack of genetic differentiation is probably due to active adult dispersal under the stepping-stone model. Demographic analyses suggested the occurrence of two expansion events during the Pleistocene period.     

Genetic structure of Patagonian toothfish (Dissostichus eleginoides) populations on the Patagonian Shelf and Atlantic and western Indian Ocean Sectors of the Southern Ocean

The genetic structure of Patagonian toothfish populations in the Atlantic and western Indian Ocean Sectors of the Southern Ocean (SO) were analysed using partial sequences of the mitochondrial 12S rRNA gene and seven microsatellite loci. Both haplotype frequency data (F _ST>0.906, P<0.01) and microsatellite genotype frequency data (F _ST=0.0141–0.0338, P<0.05) indicated that populations of toothfish from around the Falkland Islands were genetically distinct from those at South Georgia (eastern Atlantic Sector SO), around Bouvet Island (western Atlantic Sector SO) and the Ob Seamount (western Indian Ocean Sector of the SO). Genetic differentiation between these populations is thought to result from hydrographic isolation, as the sites are separated by two, full-depth, ocean-fronts and topographic isolation, as samples are separated by deep water. The South Georgia, Bouvet and Ob Seamount samples were characterised by an identical haplotype. However, microsatellite genotype frequencies showed genetic differentiation between South Georgia samples and those obtained from around Bouvet Island and nearby seamounts (F _ST=0.0037, P<0.05). These areas are separated by large geographic distance and water in excess of 3,000 m deep, below the distributional range of toothfish (<2,200 m). No significant genetic differentiation was detected between samples around Bouvet Island and the Ob Seamount although comparisons may have been influenced by low sample size. These localities are linked by topographic features, including both ridges and seamounts, that may act as oceanic “stepping stones” for migration between these populations. As for other species of deep-sea fish, Patagonian toothfish populations are genetically structured at the regional and sub-regional scales.     

Population genetic structure and genetic diversity of three critically endangered <Emphasis Type="Italic">Pristis</Emphasis> sawfishes in Australian waters

Northern Australia is considered to be one of the last strongholds for three critically endangered sawfishes, Pristis zijsron, Pristis clavata, and Pristis microdon, making these populations of global significance. Population structure and levels of genetic diversity were assessed for each species across northern Australia using a portion of the mitochondrial control region. Statistically significant genetic structure was detected in all three species, although it was higher in P. microdon (F _ST = 0.811; N = 149) than in either P. clavata (F _ST = 0.419; N = 73) or P. zijsron (F _ST = 0.202; N = 49), possibly due to a much higher and/or localized level of female philopatry in P. microdon. The overall levels of haplotype diversity in P. zijsron (h = 0.555), P. clavata (h = 0.489), and P. microdon (h = 0.650) were moderate, although it appears to be reduced in the assemblages of P. zijsron and P. clavata in the Gulf of Carpentaria (h = 0.342 and h = 0.083, respectively). Since female migration (replenishment) between regions is unlikely, conservation plans should strive to maintain current levels of diversity and abundances in the regional assemblages of each species.     

Population differentiation in megrim (<Emphasis Type="Italic">Lepidorhombus whiffiagonis</Emphasis>) and four spotted megrim (<Emphasis Type="Italic">Lepidorhombus boscii</Emphasis>) across Atlantic and Mediterranean waters and implications for wild stock management

Megrim, Lepidorhombus whiffiagonis, and four spot megrim, Lepidorhombus boscii, are two marine fish species of high commercial interest. Despite their quite heavy exploitation little is known on the genetic structure of their populations. The present work aimed at characterizing the first seven microsatellites markers available for the two megrim species. These new markers were in a second step employed to describe the population structure of the two species among their almost entire habitat range (Atlantic and Mediterranean samples). Our study confirmed the existence of a strong genetic difference between Atlantic and Mediterranean megrim species already described in the literature for L. whiffiagonis on the basis of variations at ribosomal genes. Additionally our analysis gave the first evidences of a strong genetic differentiation among Atlantic populations in both megrim species (within Atlantic global F_ST in L. whiffiagonis and L. boscii were respectively 0.158 and 0.145). When describing megrim population structure, the comparison between allele-frequency-based tests (F_ST comparisons) and genotype-based inferences (Bayesian approach) gave evidences of a hierarchical structure of the populations. In conclusion, our work enlighten the existence of two different stocks within the Atlantic Ocean and one in the Mediterranean Sea that will clearly need to be managed separately. As the present results do not fully support the current megrim stock boundaries they will surely help to rethink megrim management policies in the future.     

Sibling species in interstitial flatworms: a case study using<Emphasis Type="Italic"> Monocelis lineata</Emphasis> (Proseriata: Monocelididae)

The genetic relationships between morphologically indistinguishable marine and brackish-water populations of Monocelis lineata (O.F. Müller, 1774) (Proseriata: Monocelididae) were analysed by means of allozyme electrophoresis. Fifteen samples of M. lineata (13 from the Mediterranean and two from the Atlantic) from coastal marine and brackish-water habitats were examined for variation at 18 loci. Eleven loci were polymorphic in at least one population of M. lineata. Low levels of within-population genetic variability were found, with average observed and expected heterozygosity values ranging from H_o=0.015±0.015 to 0.113±0.044, and from H_e=0.028±0.028 to 0.138±0.054, respectively. The occurrence of a number of private alleles indicated a marked genetic divergence among populations of M. lineata, with Rogers genetic distances ranging from D_R=0.003 to 0.676 and a highly significant F_ST value (0.918±0.012, P<0.001). UPGMA (unweighted pair-group method using arithmetic average) cluster analysis and multidimensional scaling showed a clear genetic divergence between marine and brackish-water populations. Moreover, Atlantic and Mediterranean populations were sharply separated. Our results suggest that M. lineata is a complex of sibling species.Communicated by R. Cattaneo-Vietti, Genova     

Molecular genetic variation in tarpon (<Emphasis Type="Italic">Megalops atlanticus</Emphasis> Valenciennes) in the northern Atlantic Ocean

The tarpon (Megalops atlanticus) is a highly valued game fish and occasional food fish in the eastern and western Atlantic Ocean. Tarpon have a high capacity for dispersal, but some regional biological differences have been reported. In this study we used two molecular genetic techniques—protein electrophoresis of nuclear DNA loci, and restriction fragment length polymorphism analysis of the mitochondrial DNA (mtDNA)—to assess this species population genetic structure in the eastern (coastal waters off Gabon and Sierra Leone, Africa) and western (coastal waters off Florida, Caribbean Sea) Atlantic Ocean north of the equator. Genetic differentiation was observed between tarpon from Africa and tarpon from the western Atlantic Ocean. A unique allele and haplotype, significant differences in allozyme allele and mtDNA haplotype frequencies between the African and western Atlantic samples, and significant F_ST analyses suggest that levels of gene flow between tarpon from these two regions is low. Among the western Atlantic Ocean collections, genetic diversity values and allele and haplotype frequencies were similar. AMOVA analyses also showed a degree of genetic relatedness among most of the western Atlantic Ocean collections: however, some significant population structuring was detected in the allozyme data. A regional jackknifed F_ST analysis indicated the distinction of the Costa Rica population from the other western Atlantic populations and, in pairwise analyses, F_ST values tended to be higher (i.e., genetic relatedness was lower) when the Costa Rican sample was paired with any of the other western Atlantic samples. These data suggest that Costa Rican tarpon could be partially isolated from other western Atlantic tarpon populations. Ultimately, international cooperation will be essential in the management of this species in both the eastern and western Atlantic Ocean.Communicated by P.W. Sammarco, Chauvin     

Geographic structure in Alaskan Pacific ocean perch (<Emphasis Type="Italic">Sebastes alutus</Emphasis>) indicates limited lifetime dispersal

Prevailing oceanographic processes, pelagic larvae, adult mobility, and large populations of many marine species often leads to the assumption of wide-ranging populations. Applying this assumption to more localized populations can lead to inappropriate conservation measures. The Pacific ocean perch (Sebastes alutus, POP) is economically and ecologically valuable, but little is known about its population structure and life history in Alaskan waters. Fourteen microsatellite loci were used to characterize geographic structure and connectivity of POP collections (1999–2005) sampled along the continental shelf break from Dixon Entrance to the Bering Sea. Despite opportunities for dispersal, there was significant, geographically related genetic structure (F _ST = 0.0123, P < 10⁻⁵). Adults appear to belong to neighborhoods at geographic scales less than 400 km, and possibly as small as 70 km, which indicates limited dispersal throughout their lives. The population structure observed has a finer geographic scale than current management, which suggests that measures for POP fisheries conservation should be revisited.     

Colonization of the northwest Atlantic by the blue mussel, <Emphasis Type="Italic">Mytilus trossulus</Emphasis> postdates the last glacial maximum

Blue mussels in the genus Mytilus first arrived in the Atlantic Ocean from the Pacific during the Pliocene, following the opening of the Bering Strait. Repeated periods of glaciation throughout the Pleistocene led to re-isolation of the two ocean basins and the allopatric divergence of Mytilus edulis in the Atlantic and M. trossulus in the Pacific. Mytilus trossulus has subsequently colonized the northwest Atlantic (NW Atlantic) so that the two species are presently sympatric and hybridize throughout much of the Canadian Maritimes and the Gulf of Maine. To estimate when M. trossulus arrived in the NW Atlantic, we have examined sequence variation within a portion of the female mtDNA lineage large untranslated region (F-LUR) for 156 mussels sampled from three Pacific and eleven Atlantic populations of M. trossulus. Although we found no evidence of reciprocal monophyly for Pacific and NW Atlantic M. trossulus, limited gene flow between ocean basins has led to the divergence of unique sequence clades within each ocean basin. In contrast, relative genetic homogeneity indicates high levels of gene flow within each basin. Coalescence-based analysis of the F-LUR sequences suggests that M. trossulus recolonized the NW Atlantic from the northeast Pacific subsequent to a demographic expansion in the Pacific that occurred ~96,000 years before present (ybp). Estimates of timing of divergence for Pacific and NW Atlantic populations and the time since expansion among NW Atlantic sequence clades indicate that M. trossulus arrived in the NW Atlantic more recently, between 20,000 and 46,000 ybp. Given that these estimates overlap with the dates of peak ice in the NW Atlantic during the last glacial maximum (LGM, ~18,000–21,000 ybp), we suggest that colonization of the NW Atlantic by M. trossulus occurred during, but more likely just subsequent to, the LGM and was followed by rapid temporal and spatial expansion in the region.     

Local and regional genetic connectivity in a Caribbean coral reef fish

Coupled bio-physical models of larval dispersal predict that the Costa Rica–Panama (CR–PAN) reefs should constitute a demographically isolated region in the western Caribbean. We tested the hypothesis that CR–PAN coral reef fish populations would be isolated from Mesoamerican Barrier Reef System (MBRS) populations. To test that, we assessed population genetic structure in bicolor damselfish (Stegastes partitus) from both regions. Adult fish were genotyped from five reefs in CR–PAN and from four reefs along the MBRS at 12 microsatellite loci. Between-region F _ST (F _ST = 0.0030, P < 0.005) and exact test (x ² = 74.34, df = 18, P < 0.0001) results indicated that there is weak but significant genetic differentiation between regions, suggesting some restriction in connectivity along the Central American coastline, as predicted by bio-oceanographic models. Additionally, there is among-site genetic structure in the CR–PAN region, relative to the MBRS and between regions, suggesting higher self-recruitment within CR–PAN. This finding may be explained by differences in habitat characteristics.     

Endemism and dispersal: comparative phylogeography of three surgeonfishes across the Hawaiian Archipelago

To evaluate the hypothesis that a general correlation exists between species range size and dispersal ability, we surveyed mitochondrial cytochrome b sequence variation in three surgeonfish species with vastly different ranges: Ctenochaetus strigosus, Hawaiian endemic, N = 531; Zebrasoma flavescens, North Pacific, N = 560; Acanthurus nigrofuscus, Indo-Pacific, N = 305. Collections were made throughout the 2,500 km expanse of the Hawaiian Archipelago and adjacent Johnston Atoll. Analyses of molecular variance demonstrate that all three species are capable of maintaining population connectivity on a scale of thousands of km (all species global Φ_ST = NS). However, rank order comparison of pairwise Φ_ST results and Exact test P-values revealed modest but significantly different patterns of gene flow among the three species surveyed, with the degree of genetic structure increasing as range size decreases (P = 0.001). These results are consistent with mtDNA surveys of four additional Hawaiian reef fauna in which a wide-spread Indo-Pacific species exhibited genetic homogeneity across the archipelago, while three endemics had significant population subdivision over the same range. Taken together, these seven cases invoke the hypothesis that Hawaii’s endemic reef fishes evolved from species with reduced dispersal ability that, after initial colonization, could not maintain contact with parent populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.