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1.
The ocean quahog, Arctica islandica (Linnaeus, 1767), is a commercially important bivalve found on continental shelves throughout much of the North Atlantic.
To assess genetic subdivision in this species, we sequenced 385 nucleotides of the mitochondrial cytochrome b (cyt b) gene from 83 specimens collected from 12 localities between September 1998 and July 1999 (based on preliminary data, the
Internal Transcribed Spacers, ITS, of the nuclear ribosomal repeat were not useful). The cyt b data delimited 11 haplotypes with 0.26 to 8.1% nucleotide difference (coded by 36 variable nucleotide positions) among them.
Only three haplotypes were detected in 39 specimens collected along the USA coastline, compared to five haplotypes from nine
Icelandic individuals. The western Atlantic populations ranging from Penobscot Bay (Maine, USA) to southern Virginia showed
relatively low diversity and appeared genetically similar in that region. Based on the presence of shared haplotypes, AMOVA
analyses, and phylogenetic reconstructions, Icelandic populations appear to be more genetically similar to western Atlantic
populations than eastern Atlantic populations. Specimens from the Faroe Islands (n=4) show mixed affinities. These data are consistent with the hypothesis that a warm Holocene climatic optimum (ca. 7,500
years BP), and not glacial refugia, shaped the present-day genetic structure in A. islandica.
Received: 18 January 2000 / Accepted: 26 June 2000 相似文献
2.
In spite of historical and current interest in Ciona intestinalis and its congeners, little is known about evolutionary relationships among the members of the genus Ciona. Here 744-bp sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene are used to examine phylogenetic relationships among three described species (C. intestinalis, C. roulei, C. savignyi) sampled from multiple coastal sites in the Northeast Pacific (CA, USA), Northwest Atlantic (from New Hampshire to Connecticut,
USA), Northeast Atlantic (Sweden and The Netherlands), and Mediterranean (Banyuls-sur-Mer, France). The samples were collected
in June–October 2005. The COI sequences of Northeast Pacific/Mediterranean (Type A) and Northwest Atlantic (Type B) C. intestinalis differ by ∼12% and C. roulei is nested within Type B C. intestinalis. Ciona savignyi differs from all other haplotypes by 13–16%. A previously undescribed but morphologically distinct Ciona sp. found at the Banyuls-sur-Mer site was >10% divergent from all other haplotypes. Although these data arise from a single
gene study, they indicate that further elucidation of species relationships within the genus and of the species’ distributions
will be needed if continuing invasions and potential reproductive isolation are to be investigated. 相似文献
3.
Direct-developing intertidal Lasaea spp. occur in the North Atlantic as both continental margin and oceanic island populations. We conducted a molecular phylogenetic
analysis of representative populations in order to test colonization hypotheses for North Atlantic oceanic islands. Thirty
individuals each were collected in 1995 and 1996 from two continental putative source populations (Florida, Iberia) and two
oceanic island populations (Bermuda, Azores). They were sequenced for a 462 nucleotide portion of the mitochondrial large
ribosomal subunit (16S) gene. No amphi-Atlantic genotypes were detected: Bermudan lineages co-clustered exclusively with Floridian
congeners, and Azorean samples formed an exclusive clade with Iberian haplotypes. Our data indicate that geographical proximity
to continental source populations is a better predictor of phylogenetic relationships in North Atlantic Lasaea spp. than present-day oceanic surface circulation patterns. The phylogenetic trees generated are not consistent with colonization
of oceanic islands by indirect-developing ancestral lineages or by truly trans-oceanic rafting events. However, they are consistent
with predicted topologies resulting from limited (≤ 2000 km), long-distance colonization by rafting (against present-day circulation
patterns in the case of the Azores) and from anthropogenic introductions.
Received: 17 December 1998 / Accepted: 7 June 1999 相似文献
4.
E. A. Perry G. B. Stenson S. E. Bartlett W. S. Davidson S. M. Carr 《Marine Biology》2000,137(1):53-58
Harp seals (Pagophilus groenlandicus Erxleben, 1777) comprise three populations based upon whelping areas in the Greenland Sea, White Sea, and Northwest Atlantic.
The last comprises two subpopulations, one whelping in the Gulf of St. Lawrence (“Gulf ”) and one on the pack ice of the southern
Labrador/northern Newfoundland coastal shelf (“Front”). A total of 40 female seals from the four whelping areas were collected
during the 1990 and 1992 whelping seasons. DNA sequence variation was examined in a 307 bp region of the mitochondrial cytochrome
b gene. Eleven variable nucleotide positions defined 13 genotypes: a significant fraction of the genotypic variance (F
ST=0.12, or 0.09 as measured by Weir's coancestry coefficient θ) is attributable to differentiation between Northwest and Northeast
Atlantic populations. There was no significant differentiation between the two whelping areas in the Northwest Atlantic, or
between the Greenland Sea and White Sea. These findings suggest significant reproductive isolation exists between trans-Atlantic
breeding populations.
Received: 18 January 1999 / Accepted: 22 February 2000 相似文献
5.
S. E. Encalada K. A. Bjorndal A. B. Bolten J. C. Zurita B. Schroeder E. Possardt C. J. Sears B. W. Bowen 《Marine Biology》1998,130(4):567-575
Mitochondrial (mt) DNA control region sequences were analyzed for 249 Atlantic and Mediterranean loggerhead turtles (Carettacaretta Linnaeus, 1758) to elucidate nesting population structure and phylogeographic patterns. Ten haplotypes were resolved among
individuals sampled between 1987 and 1993, from ten major loggerhead nesting areas in the region. Two distinct phylogenetic
lineages were distinguished, separated by an average of 5.1% sequence divergence. Haplotype frequency comparisons between
pairs of populations showed significant differentiation between most regional nesting aggregates and revealed six demographically
independent groups, corresponding to nesting beaches from: (1) North Carolina, South Carolina, Georgia and northeast Florida,
USA; (2) southern Florida, USA; (3) northwest Florida, USA; (4) Quintana Roo, Mexico; (5) Bahia, Brazil; and (6) Peloponnesus
Island, Greece. The distribution of mtDNA haplotypes is consistent with a natal homing scenario, in which nesting colonies
separated by a few hundred kilometers represent isolated reproductive aggregates. However, a strong exception to this pattern
was observed in the first group defined by mtDNA data (North Carolina to northeast Florida), which included samples from four
nesting locations spread across thousands of kilometers of coastline. These locations were characterized by a single haplotype
in 104 out of 105 samples, providing inadequate resolution of population divisions. In view of the subdivisions observed elsewhere,
we attribute the lack of differentiation between North Carolina and northeast Florida to recent colonization of these warm
temperate coastlines (after the Wisconsin glaciation) not to ongoing gene flow among spatially distinct nesting locations.
The relationships among observed haplotypes suggest a biogeographic scenario defined by climate, natal homing, and rare dispersal
events. The redefined relationships among nesting aggregations in the western Atlantic region (southeastern USA and adjacent
Mexico) prompt a reconsideration of management strategies for nesting populations and corresponding habitats in this region.
Received: 28 October 1996 / Accepted: 24 October 1997 相似文献
6.
Megan E. Mach Elizabeth J. Sbrocco Lyndie A. Hice Tara A. Duffy David O. Conover Paul H. Barber 《Marine Biology》2011,158(3):515-530
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. 相似文献
7.
Brent William Murray John Y. Wang Shih-Chu Yang John D. Stevens Aaron Fisk Jörundur Svavarsson 《Marine Biology》2008,153(6):1015-1022
Sleeper sharks are a poorly studied group of deep-sea sharks. The subgenus, Somniosus, contains three morphologically similar species: S. microcephalus found in the Arctic and North Atlantic; S. pacificus in the North Pacific; and S. antarcticus in the Southern Ocean. These sharks have been reported mainly in temperate to polar waters and occasionally in subtropical
locations. They have not been recorded in tropical waters. This study investigates the relationships among the accepted species
of Somniosus through analysis of mitochondrial cytochrome b sequence variation. Seventy-five samples were examined from four sampling locations in the North Pacific, Southern Ocean
and North Atlantic. Twenty-one haplotypes were found. A minimum spanning parsimony network separated these haplotypes into
two divergent clades, an S. microcephalus and an S. pacificus/antarcticus clade, strongly supporting the distinction of S. microcephalus as a separate species from the Pacific sleeper shark species. Analysis of genetic structure within the S. pacificus/antarcticus clade (analysis of molecular variance, allele frequency comparisons, and a nested clade analysis) showed limited or no differences
amongst three populations. Further examination of genetic variation at more variable mtDNA and nuclear markers is needed to
examine the species status of S. pacificus and S. antarcticus. 相似文献
8.
Escolar (Lepidocybium flavobrunneum) is a large, mesopelagic fish that inhabits tropical and temperate seas throughout the world, and is a common bycatch in
pelagic longline fisheries that target tuna and swordfish. Few studies have explored the biology and natural history of escolar,
and little is known regarding its population structure. To evaluate the genetic basis of population structure of escolar throughout
their range, we surveyed genetic variation over an 806 base pair fragment of the mitochondrial control region. In total, 225
individuals from six geographically distant locations throughout the Atlantic (Gulf of Mexico, Brazil, South Africa) and Pacific
(Ecuador, Hawaii, Australia) were analyzed. A neighbor-joining tree of haplotypes based on maximum likelihood distances revealed
two highly divergent clades (δ = 4.85%) that were predominantly restricted to the Atlantic and Indo-Pacific ocean basins.
All Atlantic clade individuals occurred in the Atlantic Ocean and all but four Pacific clade individuals were found in the
Pacific Ocean. The four Atlantic escolar with Pacific clade haplotypes were found in the South Africa collection. The nuclear
ITS-1 gene region of these four individuals was subsequently analyzed and compared to the ITS-1 gene region of four individuals
from the South Africa collection with Atlantic clade haplotypes as well as four representative individuals each from the Atlantic
and Pacific collections. The four South Africa escolar with Pacific mitochondrial control region haplotypes all had ITS-1
gene region sequences that clustered with the Pacific escolar, suggesting that they were recent migrants from the Indo-Pacific.
Due to the high divergence and geographic separation of the Atlantic and Pacific clades, as well as reported morphological
differences between Atlantic and Indo-Pacific specimens, consideration of the Atlantic and Indo-Pacific populations as separate
species or subspecies may be warranted, though further study is necessary. 相似文献
9.
J. M. Quattro D. S. Stoner W. B. Driggers C. A. Anderson K. A. Priede E. C. Hoppmann N. H. Campbell K. M. Duncan J. M. Grady 《Marine Biology》2006,148(5):1143-1155
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. 相似文献
10.
Within its distribution range in the northeastern Atlantic, the stalked barnacle Pollicipes pollicipes shows a well-defined pattern of genetic variation, comprising (a) a subtropical/temperate northern assemblage, made up of
populations distributed between 47°N and 28°N along the French, Iberian, North African and Canary Islands coastlines, and
(b) a single isolated and highly divergent tropical population in the Cape Verde Islands (16°N), at the southernmost limit
of the species’ distribution. However, within the northern assemblage several populations show a level of genetic differentiation
that allows rejection of the hypothesis of genetic homogeneity. The congruence observed between genetic and hydrographic patterns
suggests a crucial role of hydrodynamics, and of the dispersal of the planktonic larvae, in the determination of population
structure. Along the southern European Atlantic coast, the Iberian Poleward Current and mesoscale hydrographic structures
are, respectively, facilitating gene flow at the regional level and genetic differentiation at the local level. On the Atlantic
coast of North Africa, the homogenizing equatorward flow of the Canary Current does not extend as far as the Cape Verde Islands.
A demographic expansion is dated to the late Pleistocene, preceding the Eemian interglacial, and is oldest in the case of
the long-standing Cape Verde population, sustained by a stable tropical habitat. The divergence between the Cape Verde population
and the remaining populations is thus ancient, and suggests that oceanic current patterns may constitute a generalized physical
barrier to the dispersal of marine organisms between Cape Verde and the rest of Macaronesia. 相似文献
11.
H. R. Schwaninger 《Marine Biology》1999,135(3):411-423
Morphologically plastic, cryptic, or geographically widespread species pose similar challenges to the evolutionary biologist:
their taxonomic status is often unclear yet must be known to study almost any aspect of their biology, ecology, evolution,
or biogeography. The marine bryozoan Membranipora membranacea (L.) is morphologically plastic and geographically widespread in temperate oceans of the Northern and Southern Hemispheres,
and its taxonomy is unclear. This study examined genetic relationships among allopatric populations and sympatric morphs of
this species, or species complex. Colonies were collected from 1992 to 1995. Allozymes were used to elucidate the relationships
among four widely separated populations, two in the North Atlantic and two in the North Pacific Ocean. Allozymes and mtDNA
sequencing were used to clarify the genetic relationships among three sympatric morphs that might correspond to the species
M. villosa Hincks and M. membranacea in the northeastern Pacific (Washington State). Populations in the North Atlantic and North Pacific had no fixed allelic
differences at the loci tested but were separated by an average Nei's genetic distance of 0.581, suggesting their near-sibling
species status. Populations from Friday Harbor (Washington) and Catalina Island (California) were not significantly differentiated,
which was attributed to high gene flow. Populations on either side of the North Atlantic were genetically indistinguishable,
which is most likely due to the recent establishment of the West Atlantic populations from European founders. At Friday Harbor,
sympatric morphs varying in their spination and spine inducibility were genetically indistinguishable, supporting the hypothesis
that M. villosa is an induced phenotype of M. membranacea and not a distinct species in the northeastern Pacific. Since such phenotypic plasticity is common in cheilostome bryozoans,
the morphospecies concept must be used with caution.
Received: 31 August 1998 / Accepted: 10 August 1999 相似文献
12.
The distribution and genetic structure of many marine invertebrates in the North Atlantic have been influenced by the Pleistocene glaciation, which caused local extinctions followed by recolonization in warmer periods. Mitochondrial DNA markers are typically used to reconstruct species histories. Here, two mitochondrial markers [16S rDNA and cytochrome c oxidase I (COI)] were used to study the evolution of the widely distributed hydrozoan Obelia geniculata (Linnaeus, 1758) from the North Atlantic and the Pacific and, more specifically, in the context of North Atlantic phylogeography. Samples were collected from six geographic localities between 1998 and 2002. Hydroids from the North Atlantic, North Pacific (Japan), and South Pacific (New Zealand) are reciprocally monophyletic and may represent cryptic species. Using portions of the 16S rDNA and COI genes and the date of the last trans-Arctic interchange (3.1–4.1 million years ago), the first calibrated rate of nucleotide substitutions in hydrozoans is presented. Whereas extremely low substitution rates have been reported in other cnidarians, mainly based on anthozoans, substitution rates in O. geniculata are comparable to other invertebrates. Despite a life history that ostensibly permits substantial dispersal, there is apparently considerable genetic differentiation in O. geniculata. Divergence estimates and the presence of unique haplotypes provide evidence for glacial refugia in Iceland and New Brunswick, Canada. A population in Massachusetts, USA, appears to represent a relatively recent colonization event.Communicated by J.P. Grassle, New Brunswick 相似文献
13.
The number and wide variety of southeastern United States marine taxa with significant differentiation between Gulf of Mexico and Atlantic Ocean populations suggests that these taxa may have experienced major vicariance events, whereby populations were subdivided by geological or ecological barriers. The present study compared variation in morphology, allozymes, and mtDNA in Gulf of Mexico and western Atlantic populations of the longwrist hermit crab Pagurus longicarpus Say collected during 1997 and 1998. Combined Atlantic populations had significantly fewer denticles on the second segment of the third maxilliped than did Gulf of Mexico populations, and the mean ratio of dactyl length to propodus length was significantly greater in the Atlantic crabs than in the Gulf of Mexico crabs. Allozyme allele frequencies at three loci showed genetic differentiation between a Gulf of Mexico population and two Atlantic populations. Analysis of mtDNA sequence data revealed a clear reciprocal monophyly between Gulf and Atlantic populations, with an estimated divergence age of ~0.6 million years ago. This estimated age of divergence is significantly more recent than an age previously estimated for its congener Pagurus pollicaris (~4 million years ago), suggesting that species with a similar genetic break between Gulf and Atlantic populations may not necessarily share an identical history. Surprisingly, there is evidence of geographic subdivision within Atlantic populations of P. longicarpus along the east coast of North America. This differentiation is especially strong between Nova Scotia and southern populations, suggesting that the Nova Scotia population may represent survivors from a northern refugium during the last glacial maximum. 相似文献
14.
The tellinid bivalve Macoma balthica (L.) has an extensive geographic range that reaches from temperate to arctic coastal waters in the North Atlantic and North Pacific oceans. Recent studies have indicated that eastern and western North Atlantic populations are morphologically and genetically different from one another, and that they may have diverged as sibling species. To determine the genetic relationship between M. balthica from the Pacific and Atlantic coasts of North America, populations from each coast were examined at 11 enzyme loci using standard starch gel electrophoresis. Allele frequency data indicate that M. balthica populations from San Francisco Bay, California appear more closely related to western North Atlantic populations than to populations from Oregon. We suggest that San Francisco Bay populations were introduced relatively recently from western North Atlantic populations. The Oregon populations are probably a natural extension of northern populations that occur along Northern Asia and in the eastern North Atlantic. 相似文献
15.
Molecular systematic analyses of marine taxa are crucial for recording ocean biodiversity, so too are elucidation of the history
of population divergence and the dynamics of speciation. In this paper we present the joined phylogeography of the calanoid
copepod Calanus helgolandicus (Claus 1863) from the North East (NE) Atlantic and the Adriatic Sea and the closely related C. euxinus (Hulsemann 1991) from the Black Sea based on sequences of a mitochondrial Cytochrome Oxidase subunit I (COI) fragment. Coalescent-based
Bayesian methods and minimum spanning networks are used to reconstruct the history of population divergence. Our results reveal
that copepod populations from all three basins share a great number of haplotypes and demonstrate a close genetic affinity
of C. euxinus with C. helgolandicus. The data do not support significant genetic structuring among samples within seas. Coalescent analyses suggest divergences
between NE Atlantic, Mediterranean, and Black Sea populations dating back to the middle Pleistocene, with the NE Atlantic–Mediterranean
divergence being the earliest and the Mediterranean–Black Sea divergence the most recent. These middle Pleistocene dates are
much older than the estimated dates of colonisation of the Mediterranean and Black Seas based on paleoclimatic scenarios.
Our results do not rule out that the assumed colonisations took place but they indicate that the populations colonising the
Mediterranean and the Black Sea were already, and have since remained, diverged. The chaetognath Sagitta setosa, which has a comparable distribution pattern and feeds upon the copepods, provides a unique opportunity to compare phylogeographic
patterns and distinguish among alternative hypotheses. The dates produced in this paper are in agreement with those estimated
elsewhere for S. setosa. We propose that a great deal of the genetic make-up of marine planktonic populations comprises divergences that date back
to long before the last glacial maximum. We consider questions on the taxonomic status of C. euxinus to remain open. However, its high genetic affinity to the C. helgolandicus calls for further investigation. 相似文献
16.
Patterns of mtDNA diversity in North Atlantic populations of the mussel Mytilus edulis 总被引:3,自引:3,他引:0
Patterns of (female) mitochondrial DNA diversity were investigated in the blue mussel Mytilus edulis. Mytilus edulis is a ubiquitous member of contemporary North Atlantic hard-substrate communities and well represented in studies of this
region. Mytilus edulis was surveyed in North America and Europe, as well as mid-Atlantic sites in Greenland, Iceland, and the Faroe Islands. Mitochondrial
DNA sequences revealed considerable population structure but no monophyly of haplotypes between any major regions. Coalescent
analyses suggest that migration across the Atlantic Ocean has prominently been from North American source populations and
that Greenland was colonized recently and exclusively from North America. In North America, there was support for two regional
groups along the North American coastline. Surprisingly, we also found evidence of recombination between some Mytilus edulis and Mytilus galloprovincialis female mtDNA sequences, particularly in northern Europe.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
An erratum to this article can be found at 相似文献
17.
The origin of the deep-sea benthic fauna is poorly understood and represents an enormous gap in our understanding of basic
evolutionary phenomena. One obstacle to studying evolutionary patterns in the deep sea has been the technical difficulty of
measuring genetic variation in species that are typically minute, rare, and must be recovered from extreme depths. We used
molecular genetic techniques to quantify variation in the 16S rRNA mitochondrial gene within and among populations of the
common protobranch bivalve Deminucula atacellana (Schenck, 1939). We analyzed 89 individuals from nine samples collected in the 1960s along a depth gradient from 1100 to
3800 m in the western North Atlantic. Genetic variability within populations is much lower than between populations, and peak
haplotype numbers occur near the center of its depth distribution. Continental slope (<2500 m) and rise (>2500 m) populations
were genetically distinct despite the lack of any obvious topographic or oceanographic features that would impede gene flow.
These findings indicate that the deep-sea macrofauna can have strong population structure over small (134 km) spatial scales,
similar to that observed in shallow-water and terrestrial organisms. This surprisingly high biodiversity at the genetic level
affords the potential for adaptation and evolutionary diversification, the ultimate historical causes of high species diversity
in the deep-sea benthos.
Received: 24 July 1997 / Accepted: 26 January 1998 相似文献
18.
D. W. Foltz S. D. Fatland M. Eléaume K. Markello K. L. Howell K. Neill C. L. Mah 《Marine Biology》2013,160(5):1285-1296
Genetic structure and connectivity of populations of the globally distributed and eurybathic sea star Hippasteria phrygiana (Parelius 1768) were studied in 165 individuals sampled from three oceanic regions: the North Pacific Ocean, the South Pacific Ocean (considered to include the adjacent regions of the Southern Ocean and the southern Indian Ocean) and the North Atlantic Ocean. A nuclear gene region (ATP synthase subunit α intron #5, ATPSα) and a mitochondrial gene region (cytochrome oxidase subunit I, COI) were amplified and sequenced. Significant heterogeneity was detected in an AMOVA analysis among the three sampled oceanic regions for COI, but not for ATPSα. Neither gene showed significant genetic heterogeneity within the North Atlantic, as assessed by ΦST values. Significant heterogeneity was detected for COI (but not ATPSα) in the North Pacific, but the converse was true in the South Pacific. Coalescent simulations suggested that the three regions have been diverging with little or no gene flow for the past 50–75,000 years, a time frame that corresponds to the onset of the last glacial period of the Pleistocene. A possible genetic signature of recent population expansion (or non-neutrality) was detected for each gene in the North Pacific, but not in the other two oceanic regions. 相似文献
19.
Restriction-site variation in mitochondrial (mt) DNA was assayed among 1675 red drum (Sciaenops ocellatus Linnaeus) sampled from 20 localities along the southeastern coast of the USA (western Atlantic) and the Gulf of Mexico (Gulf).
Up to four consecutive year-classes (cohorts) were sampled at most localities. Nucleotide-sequence divergence among 170 mtDNA
haplotypes identified ranged (in percentage) from 0.184 to 1.913, with a mean (±SD) of 0.887 ± 0.300. Comparisons of mtDNA
haplotype frequencies across year-classes within localities were non-significant, indicating temporal stability of breeding
components within localities. Significant heterogeneity in mtDNA haplotype frequencies was found across all localities, between
(pooled) samples from the western Atlantic and the Gulf, and among geographically spaced, regional groupings in the Gulf.
Genetic divergence between subpopulations of red drum in the western Atlantic and Gulf follows a pattern exhibited in other
marine fishes, and probably stems from physical (historical environmental heterogeneity, absence of suitable habitat, and
current patterns) and, perhaps, behavioral factors. Genetic differences among red drum in the Gulf appear to be due largely
to an isolation-by-distance effect that is attributable to behavioral factors. The latter may include female philopatry to
natal bays or estuaries, limited offshore (coastwise) movement of females relative to their natal bay or estuary, or both.
Genetic divergence among red drum in the Gulf occurs despite high gene flow (estimated as the number of genetic effective
migrants in an island mode). Conservation and management of red drum should be based on the premise that strategies for a
given bay or estuary will impact geographically proximal bays or estuaries more than distal ones. Trajectories of correlograms
in spatial autocorrelation analysis suggest a geographic neighborhood size, relative to genetic migration of red drum from
a bay or estuary, of roughly 500 to 600 km.
Received: 22 July 1998 / Accepted: 19 November 1998 相似文献
20.
Vermilion snapper (Rhomboplites aurorubens) were collected from four sites off the Atlantic coast of the USA and one site in the Gulf of Mexico to evaluate effective
population size and genetic stock structure. Previous studies had suggested geographic variation in the ratio of males to
females, so this population characteristic was explored in conjunction with the genetic analysis. Sex ratio varied greatly
among the five sample sites; males comprised 57% of samples in the Gulf of Mexico, while within the South Atlantic Bight they
comprised between 36% (Morehead City, North Carolina) and 53% (Carolina Beach, North Carolina) of samples. No clear geographic
trends in the sex ratio emerged; instead, it was found to vary with fish length, the percentage of males decreasing with increasing
size. Allelic variation assessed at seven dinucleotide microsatellite loci was large; gene diversities ranged from 0.43 to
0.95 and allelic counts from 7 to 39. Estimates of the effective population size ranged from 24 500 (based on the infinite-alleles
model) to 150 500 (based on the stepwise-mutation model). There was evidence for excess homozygosity within samples: estimates
of F
IS
(the correlation of alleles within individuals) ranged from 0.01 to 0.03 among the seven loci, and three estimates were significantly
greater than zero. Differentiation among localities was very weak, as estimates of F
ST
(the correlation of alleles within populations) were on the order of 0.001 to 0.002 and genetic distance estimates between
localities were not related to geographic distances. This suggested that vermilion snapper in the South Atlantic Bight (Cape
Hatteras, North Carolina to Cape Canaveral, Florida) and Gulf of Mexico are likely to consist of one genetic stock. Despite
the overall homogeneity, there were indications of a temporally dynamic local structure that would bear further examination.
Received: 6 July 1998 / Accepted: 9 February 1999 相似文献