Phylogeography of the pipefish, <Emphasis Type="Italic">Urocampus carinirostris</Emphasis>, suggests secondary intergradation of ancient lineages

We assayed the pattern of mitochondrial DNA evolution in the live bearing, seagrass specialist pipefish, Urocampus carinirostris, in eastern Australia. These life history attributes were predicted to result in strong phylogeographic structure in U. carinirostris. Phylogenetic analysis of cytochrome b sequences detected two monophyletic mtDNA clades that differed by 8.69% sequence divergence - a large level of intraspecific divergence for a marine fish. The geographical distribution of clades was non-random and resembled clinal secondary intergradation over a 130-km stretch of coastline. Contrary to phylogeographic predictions, this large phylogeographic break does not occur across a traditionally recognised biogeographic boundary. Analyses of historical demography suggested that individuals belonging to the most widespread clade underwent a population expansion from a small refuge population during the Pleistocene.     

Global phylogeography of the fissiparous sea-star genus <Emphasis Type="Italic">Coscinasterias</Emphasis>

The fissiparous starfish genus Coscinasterias (Verrill) is represented in shallow waters around many of the world's continents. This wide distribution could be explained by dispersal, vicariance, or translocation associated with shipping, and represents an excellent system for marine biogeographic research. We conducted a global phylogeographic analysis of 42 Coscinasterias mtDNA cytochrome oxidase 1 sequences (15 haplotypes) from 18 sites, including representatives of all four recognised species. Phylogenetic analysis yielded a robust phylogeny, with strong support for the monophyly of the genus (90% bootstrap support) and of each separate species (99-100%). Haplotypes exhibited strong phylogeographic structure, with robust mtDNA clades often associated with distinct land masses. A general lack of genetic differentiation within sites may reflect fissiparity. However, shared haplotypes over larger distances (e.g. across Japan), and the presence of related haplotypes on adjacent land masses (e.g. Tasmania, New Zealand; 1.6-1.8%) suggest that long-distance dispersal is an important biogeographical process for Coscinasterias. The 4.0-4.4% divergence between Japanese and South African sister groups may relate to transequatorial dispersal around the onset of the Pleistocene. Divergent Atlantic and Mediterranean populations of C. tenuispina (maximum 1.5%) may deserve subspecific recognition, and high divergences within Australian C. muricata (maximum 8.0%) suggest a species complex.     

Population genetic structure of North American <Emphasis Type="Italic">Ophiactis</Emphasis> spp. brittle stars possessing hemoglobin

With the discovery of previously unreported populations of hemoglobin-possessing Ophiactis from the Texas coast in the Gulf of Mexico, an investigation into its population structure, including populations of O. simplex from the Pacific coast of California and O. rubropoda from the Atlantic coast of Florida, was undertaken using DNA sequence data from the mitochondrial COI gene. The reconstructed haplotype network suggests that California populations contain the ancestral source of mtDNA variation, and there is no evidence of recent introductions into Texas. Population genetic analyses reveal the California, Florida, and Texas Ophiactis populations to each be significantly differentiated from one another. Sequence divergence among the three areas is shallower than would be predicted given biogeographic history. Texas and Florida populations are equally genetically diverged from California populations as they are to one another, despite the greater potential for gene flow between these areas. The genetic distinctiveness of the Texas populations and the concordance of this pattern with phylogeographic patterns in other brittle star systems indicate an isolated and independent evolutionary history and we hypothesize that the three geographic regions included in this study each serve as hypotheses of population-level lineages that remain to be tested with independent sources of data.     

Inter-oceanic genetic differentiation among albacore (<Emphasis Type="Italic">Thunnus alalunga</Emphasis>) populations

Albacore (Thunnus alalunga) is a highly migratory pelagic species distributed in all tropical and temperate oceans. Recent analyses using both mitochondrial DNA (mtDNA) and nuclear DNA markers have demonstrated genetic subdivision within and between Atlantic and Pacific populations. However, although numerous biological differences have been reported for Atlantic and Mediterranean albacore, the genetic differentiation for these basins has not been demonstrated. We characterized 373 base pairs of nucleotide sequence from the mitochondrial DNA control region of 134 individuals collected in the Pacific (n=30), the northeast (NE) Atlantic (n=54) and the Mediterranean (n=50). Analysis of molecular variance (AMOVA) revealed a small, but highly significant, proportion of genetic variation separating these three regions (_st =0.041; P=0.009), a pattern also supported by pairwise comparisons. These results demonstrate for the first time the genetic distinctiveness of the Mediterranean albacore from the NE Atlantic population giving support to the current management practices based on separate units. This outcome is concordant with reported migratory movements related to reproductive behavior between the NE Atlantic and the Mediterranean Sea. Additionally, the phylogenetic analyses of DNA sequences revealed the presence of a shallow genetic discontinuity with no geographic association. These two phylogroups are more likely the result of the demographic history of this species (i.e. long demographic stable history) as opposed to historical vicariance as has been proposed for other highly migratory fishes.Communicated by P.W. Sammarco, Chauvin     

Phylogeography of two species of <Emphasis Type="Italic">Lysidice</Emphasis> (Polychaeta,Eunicidae) associated to the seagrass <Emphasis Type="Italic">Posidonia oceanica</Emphasis> in the Mediterranean Sea

The aim of this work was to define the phylogeographic patterns of the two species of polychaete Eunicidae, Lysidice ninetta Audouin and Milne Edwards and Lysidice collaris Grube, both associated as sheath borers to the Mediterranean seagrass Posidonia oceanica, and with reference to their different origin and their actual geographic distribution. L. ninetta is distributed in the Atlantic and in the Mediterranean Sea while L. collaris is a tropical species, whose introduction into the Mediterranean Sea through the Suez Canal (lessepsian migrant) has been hypothesized in recent years. The two species have been often confused in the past, although they appear morphologically distinct. They share the same microhabitat (Posidonia sheaths) and they co-exist along a broad bathymetric range (1–30 m). Several populations for both taxa were sampled all along the coast of the Mediterranean basin. A variable no coding region of nuclear DNA (rDNA, ITS1) and a portion of a more conservative coding region of mitochondrial DNA (sub-unit one of citochrome oxidase, COI) were used as molecular markers. Both markers confirmed the separation between the two species. Low intraspecific polymorphism was present in L. collaris, together with absence of phylogeographic structure. In L. ninetta, instead, the presence of intraspecific cryptic lineages, sympatric in some sites, was recorded. Clustering of single populations in the two main clades was not always consistent between markers. The mitochondrial COI region showed more resolution at the given spatial scale. Our results suggest that Lysidice collaris could be recently introduced into the Mediterranean Sea from one or more separate events. On the other hand, for L. ninetta one could presume a re-colonization of the Mediterranean basin from the Atlantics, after the Messinian crisis (dry-out of the Mediterranean Sea, 5.5 my) with the subsequent separation of intraspecific lineages. The phylogeographic patterns of both Lysidice spp. are disjoined with respect to that of the host plant, P. oceanica. The obtained results suggest that environmental constraints and evolutionary history of these polychaetes and their host plant act in different ways to determine their actual genetic spatial structure.     

Mitochondrial DNA variation and population structure in the spiny lobster Panulirus argus

Adult spiny lobsters (Panulirus argus) were collected from nine locations throughout the tropical and subtropical northwest Atlantic Ocean and examined for mitochondrial DNA (mtDNA) variation. 187 different mtDNA haplotypes were observed among the 259 lobsters sampled. Haplotype diversity was calulated to be 0.986 and mean nucleotide sequence-diversity was estimated to be 1.44%; both of these values are among the highest reported values for a marine species. Analysis of molecular variance (AMOVA) and phenetic clustering both failed to reveal any evidence of genetic structure within and among populations of P. argus. The present data are consistent with high levels of gene flow among populations of P. argus resulting from an extended planktonic larval stage and strong prevailing ocean currents.     

Marine biogeographic disjunction in central New Zealand

We present a phylogeographic analysis of an abundant New Zealand endemic sea-star, Patiriella regularis, to help pinpoint the location of an important biogeographic disjunction in central New Zealand. The analysis incorporates 284 mtDNA control region sequences (approximately 800 bp) of P. regularis from 22 coastal locations around New Zealand. We detected 132 haplotypes, with a mean divergence of 0.96%. AMOVA analysis of New Zealand samples is consistent with a north-south biogeographic disjunction across central New Zealand (among-group genetic variance=6.10%; P=0.0005). Cook Strait, the shallow marine strait separating the main islands, is not correlated with the disjunction: samples from northern South Island are genetically indistinguishable from North Island samples (variance=1.69%; P=0.073). These results are consistent with the hypothesis that upwelling zones south of Cook Strait constitute a significant barrier to larval dispersal.Communicated by M.S. Johnson, Crawley     

Where is the western limit of the tropical Indian Ocean seaweed flora? An analysis of intertidal seaweed biogeography on the east coast of South Africa

New, large-scale collections have been made of marine benthic macroalgae (seaweeds) on the east coast of South Africa, and the distributions of shallow-water species were analyzed in detail by multivariate, clustering and -diversity methods. The two northernmost sites are distinct, with a predominance of tropical species, and it is concluded that the changeover from a tropical Indian Ocean flora to a temperate South African flora occurs most rapidly in the vicinity of St. Lucia, 135 km south of the Mozambique border. It is imperative that all future biogeographical studies on the South African inshore marine biota include detailed collections north of St. Lucia. The remaining 440 km of the South African east coast (southern and central Kwazulu-Natal Province) is populated by a mixture of tropical and temperate elements, with only 2% endemism in this data set. This, thus, represents a true overlap region, with relatively equal numbers of species with affinities in the temperate Agulhas and tropical Indo–West Pacific floras, rather than a distinctive sub-tropical marine province, as the South African east coast is considered to be by most previous authors. The distinction between this overlap region and the south coast (Agulhas) region proper is not as clearly distinct. The change from a temperate to a tropical flora shows a relative increase in green algae from 15% to 25% of the species present. Criteria for the delineation of marine biogeographical regions are critically discussed, and it is concluded that the monitoring of distributions of all species, including rare species, is necessary. This is particularly relevant with regard to using these data to assess effects of potential changes in seawater temperature, including those which may be caused by global warming. Criteria for the delimitation of biogeographic entities such as "marine provinces" need to be clearly spelt out in all investigations.Communicated by O. Kinne, Oldendorf/Luhe     

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.     

Is the Great Barracuda (<Emphasis Type="Italic">Sphyraena barracuda</Emphasis>) a reef fish or a pelagic fish? The phylogeographic perspective

Current taxonomy indicates a single global species of the Great Barracuda (Sphyraena barracuda) despite differences in color and behavior between Atlantic and Pacific forms. To investigate these differences and qualify the dispersal characteristics of this unique coastal–pelagic teleost (bony fish), we conducted a global phylogeographic survey of 246 specimens from thirteen sampling locations using a 629-base pair fragment of mtDNA cytochrome b. Data indicate high overall gene flow in the Indo-Pacific over large distances (>16,500 km) bridging several biogeographic barriers. The West Atlantic population contains an mtDNA lineage that is divergent from the Indo-Pacific (d = 1.9%), while the East Atlantic (N = 23) has two mutations (d = 0.6%) apart from the Indo-Pacific. While we cannot rule out distinct evolutionary partitions among ocean basins based on behavior, coloration, and near-monophyly between Atlantic and Indo-Pacific subpopulations, more investigation is required before taxonomic status is revised. Overall, the pattern of high global dispersal and connectivity in S. barracuda more closely resembles those reported for large oceanic predators than reef-associated teleosts.     

Song dialects do not restrict gene flow in an urban population of the orange-tufted sunbird, <Emphasis Type="Italic">Nectarinia osea</Emphasis>

Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. In this study, we test the hypothesis that song dialect, a culturally transmitted trait, is related to the population genetic structure of the orange-tufted sunbird, Nectarinia osea. To address this, we compared mitochondrial DNA (mtDNA) sequence variation together with allele frequencies at five microsatellite loci from an urban population of sunbirds exhibiting two distinct song dialects on a microgeographic scale. Our findings reveal no association between dialect membership and genetic composition. All genetic measures, from both mitochondrial and nuclear DNA, indicate high levels of gene flow between both dialect populations. The low F _ST values obtained from mtDNA and microsatellite analysis imply that the variation among dialects does not account for more than 2%, at best, of the overall genetic variation found in the entire population. These measures fall well within the range of similar measures obtained in other studies of species exhibiting vocal dialects, most of which fail to detect any dialect-based genetic differentiation. The persistence of dialects in the orange-tufted sunbird may thus best be explained by dispersal of individuals across dialect boundaries and possibly from surrounding areas, followed by postdispersal vocal matching. Because genetic structuring appears weaker than cultural structure in this species, we discuss the behavioral mechanisms underlying dialect maintenance in the presence of apparent gene flow.     

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

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

Genetic structure of Atlantic and Gulf of Mexico populations of sea bass,menhaden, and sturgeon: Influence of zoogeographic factors and life-history patterns

To assess the influence of zoogeographic factors and life-history parameters (effective population size, generation length, and dispersal) on the evolutionary genetic structure of marine fishes in the southeastern USA, phylogeographic patterns of mitochondrial DNA (mtDNA) were compared between disjunct Atlantic and Gulf of Mexico populations in three coastal marine fishes whose juveniles require an estuarine or freshwater habitat for development. Black sea bass (Centropristis striata), menhaden (Brevoortia tyrannus andB. patronus) and sturgeon (Acipenser oxyrhynchus) samples were collected between 1986 and 1988. All species showed significant haplotype frequency differences between the Atlantic and Gulf, but the magnitude and distribution of mtDNA variation differed greatly among these taxa: sea bass showed little within-region mtDNA polymorphism and a clear phylogenetic distinction between the Atlantic and Gulf; menhaden showed extensive within-region polymorphism and a paraphyletic relationship between Atlantic and Gulf populations; and sturgeon exhibited very low mtDNA diversity both within regions and overall. Evolutionary effective sizes of the female populations (N _f (e)) estimated from the mtDNA data ranged fromN _f (e) = 50 (Gulf of Mexico sturgeon) toN _f (e) = 800 000 (Atlantic menhaden), and showed a strong rank-order agreement with the current-day census sizes of these species. The relationship betweenN _f (e) and the estimated times of divergence (t) among mtDNA lineages (from conventional clock calibrations) predicts the observed phylogenetic distinction between Atlantic and Gulf sea bass, as well as the paraphyletic pattern in menhaden, provided the populations have been separated by the same long-standing zoogeographic barriers thought to have influenced other coastal taxa in the southeastern USA. However, vicariant scenarios alone cannot explain other phylogenetic aspects of the menhaden (and sturgeon) mtDNA data and, for these species, recent gene flow between the Atlantic and Gulf coasts is strongly implicated. These data are relevant to management and conservation issues for these species.Please address all requests for reprints to Dr. J. C. Avise     

Experimental evidence for the effects of the thalassinidean sandprawn <Emphasis Type="Italic">Callianassa kraussi</Emphasis> on macrobenthic communities

Bioturbation by thalassinidean sandprawns is known to structure soft-bottom communities, and field observations have suggested that the sandprawn Callianassa kraussi is a significant force influencing macrofaunal communities. To investigate causal relationships, a field experiment was undertaken in Durban Bay, South Africa, in which experimental cages were used to exclude or include C. kraussi and the abundance of macrofauna in these treatments documented. Cage effects were assessed by comparing macrofauna in inclusion cages with that of unmanipulated areas containing high densities of C. kraussi equivalent to those in inclusion cages. Measurements were made in 3 months, in March, June and September 2005. Total abundance and species richness of macrofauna were significantly greater in exclusion cages than in inclusion treatments during all sampling seasons, while diversity differed between these treatments in June and September only. Ordinations indicated that macrofaunal assemblages in exclusion cages differed statistically from inclusion and control treatments in all three sampling seasons. In general, the surface-grazing gastropod Nassarius kraussianus and suspension and deposit-feeding species such as the polychaetes Prionospio sexoculata and Desdemona ornata, cumaceans, and the bivalves Dosinia hepatica and Eumarcia paupercula were significantly more abundant in prawn-exclusion plots, implying that they are negatively affected by bioturbation by C. kraussi, whereas burrowing infauna were not affected.     

Population structure of loggerhead turtle (Carettacaretta) nesting colonies in the Atlantic and Mediterranean as inferred from mitochondrial DNA control region sequences

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     

Population Structure and Cryptic Evolutionary Units in the Alligator Snapping Turtle

The alligator snapping turtle (  Macroclemys temminckii ) is a long-lived, slow-growing chelydrid turtle found in Gulf of Mexico drainages from Florida to Texas (U.S.A.). Populations are thought to be depleted throughout the range due in part to an increased harvest in the 1960s through 1980s. To identify population and evolutionary units, 420 base pairs were sequenced within the mitochondrial DNA control region of 158 specimens from 12 drainages. Results indicate substantial phylogeographic structuring and strong population-level separations among river drainages. Eight of 11 haplotypes were observed to be river-specific, providing diagnostic markers for most drainages. Three partitions are resolved in the mtDNA genealogy, corresponding to the eastern, central, and western portion of the species' range. These separations coincide with recognized biogeographic provinces. The population structure by river system indicates that many drainages are distinct management units, with the Suwannee River lineage possibly deserving special attention, based on the criterion of genetic distinctiveness. The partitioning of M. temminckii into river-specific populations illustrates the management framework and conservation challenges that apply to a broad array of riverine species. Drainage-specific molecular markers may be used to identify the geographic origin of turtle products in the marketplace.     

Phylogeography of the Indo-Pacific parrotfish Scarus psittacus: isolation generates distinctive peripheral populations in two oceans

Phylogenetic, phylogeographic, population genetic and coalescence analyses were combined to examine the recent evolutionary history of the widespread Indo-Pacific parrotfish, Scarus psittacus, over a geographic range spanning three marine biogeographic realms. We sequenced 164 individuals from 12 locations spanning 17,000 km, from 55oE to 143oW, using 322 base pairs of mitochondrial control region (D-loop). S. psittacus displayed high haplotype (h = 0.83–0.98), but low nucleotide (<1%) diversity. Most (>83%) genetic variation was within populations. AMOVA revealed significant partitioning and identified five geographic groups. These included one central population and four populations peripheral to the centre. The central population occupied reefs from Western Australia to Tahiti and represented the central Indo-Pacific biogeographic realm. Cocos Keeling was distinct from central and western Indo-Pacific biogeographic realms occupying a position intermediate to these. Peripheral populations (Hawaii, Marquesas) represented the eastern Indo-Pacific biogeographic realm, while Seychelles represented the western Indo-Pacific biogeographic realm. All but the central population expanded (<163 kya). Whilst all populations experienced major sea level and SST changes associated with Pleistocene glaciation cycles, the genetic structure of the central population was relatively homogenous unlike the remaining genetically distinctive populations.     

Evidence of stock separation in southern hemisphere organge roughy (Hoplostethus atlanticus,Trachichthyidae) from restriction-enzyme analysis of mitochondrial DNA

Restriction enzyme analysis of mitochondrial DNA (mtDNA) was used to test for genetic homogeneity of orange roughy (Hoplostethus atlanticus) in the southern hemisphere. Two hundred and eighty-six orange roughy specimens were collected from seven general localities: the Great Australian Bight; South Australia (off southeastern Kangaroo Island); the west coast of Tasmania; the east coast of Tasmania; New South Wales; New Zealand and South Africa. Mitochondrial DNA was extracted from developing ovary tissue and analysed with 10 six-base enzymes and 3 four-base enzymes. Both forms of analysis revealed a low level of genetic diversity in this species. The six-base enzyme study found no evidence of reproductively isolated populations of orange roughy in southeastern Australian waters. However, an analysis of 107 fish with 3 four-base enzymes identified at least partial genetic separation of the New South Wales (NSW) sample of orange roughy from South Australian (off southeastern Kangaroo Island) and Tasmanian samples. This finding supports biological evidence for the presence of a distinct subpopulation of orange roughy in NSW waters. The four-base study also provided evidence of the presence of genetically distinct samples of orange roughy occurring in the same localities off southeastern Kangaroo Island from consecutive years. Additional sampling and the use of a greater number of four-base enzymes may be needed to determine if any genetic structuring exists among orange roughy south of New South Wales.     

Population structure and genetic diversity in green turtles nesting at Tortuguero,Costa Rica,based on mitochondrial DNA control region sequences

The green turtle (Chelonia mydas) nesting population at Tortuguero, Costa Rica, is the largest nesting aggregation in the Atlantic, by at least an order of magnitude. Previous mitochondrial DNA (mtDNA) surveys based on limited sampling (n = 41) indicated low genetic diversity and low gene flow with other Caribbean nesting colonies. Furthermore, a survey of nuclear DNA diversity invoked the possibility of substructure within the Tortuguero rookery. To evaluate these characteristics, mtDNA control region sequences were determined for green turtles nesting at Tortuguero in 2001 (n = 157) and 2002 (n = 235). The increased sample revealed three additional haplotypes; five haplotypes are now known for Tortuguero female green turtles. Analyses of molecular variance indicated that there was no significant spatial population structure along the 30-km nesting beach. In addition, no temporal population structure was detected either between the two nesting seasons or within the nesting season. As a result of the larger sample size and additional haplotypes, estimates of genetic separation among Caribbean nesting colonies have changed and the concordance of phylogenetic and phylogeographic patterns reported in the past for green turtles in the Greater Caribbean has weakened. The five haplotypes from Tortuguero represent 36% of the haplotypes identified in green turtle nesting aggregations in the Greater Caribbean and 17% of the haplotypes known to occur in nesting or foraging aggregations in the Greater Caribbean. Haplotype diversity (0.16) and nucleotide diversity (0.0034) for the Tortuguero population are substantially lower than those for the combined rookeries in the Greater Caribbean (0.44 and 0.0078, respectively). Although comprehensive evaluation of regional genetic diversity requires nuclear DNA data, our study indicates that conserving genetic diversity in Caribbean green turtles will require careful management of the smaller rookeries in addition to the Tortuguero rookery.     

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

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