Trophic relations of the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Front,Scotia Sea

Samples of the squid Martialia hyadesi were collected aboard two Japanese squid-jigging vessels carrying out commercial fishing trials at the Antarctic Polar Frontal Zone, north Scotia Sea, in February 1989. The dissected stomachs of 61 specimens were classified according to fullness and the contents were examined visually. Identifiable food items included fish sagittal otoliths, crustacean eyes, the lappets on euphausiid first antennule segments and cephalopod sucker rings. The most frequent items in the squid's diet were the myctophid fishes Krefftichthys anderssoni and Electrona carlsbergi, the euphausiid Euphausia superba and a hyperiid amphipod, probably Themisto gaudichaudi. A small proportion of the sample had been feeding cannibalistically. Total lengths of the fish prey were estimated from sagittal otolith size using published relationships. All fish were relatively small; 7 to 35% of squid mantle-length. However, it is possible that some heads of larger fish are discarded by the squid and so are not represented by otoliths in the stomach contents. Over the size range of squid in the sample there was no relationship between size of fish prey and size of squid. Similarly, when the squid sample was divided into groups according to prey categories: crustaceans, crustaceans+fish, fish, cephalopod, there was no evidence that dietary preference was related to squid size. The prevalence of copepod-feeding myctophids in the diet of this squid, which is itself a major prey item of some higher predators in the Scotia Sea, suggests that a previously unrecognised food chain: copepod-myctophid-M. hyadesi-higher predator, may be an important component of the Antarctic oceanic ecosystem.     

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.     

Genetic variation in the neritic squid Loligo forbesi (Myopsida: Loliginidae) in the northeast Atlantic Ocean

Horizontal starch gel electrophoresis was employed to investigate levels of genetic differentiation between 13 samples of the neritic squid species Loligo forbesi Steenstrup obtained from throughout the majority of its known geographical range. Six enzyme loci identified in a preliminary study as being polymorphic were screened for variation between samples. No significant differences in allele distribution were detected between any of the samples obtained from the Faroe Bank in the north to Lisbon in the south, suggesting that squid throughout this range in the vicinity of the continental shelf are able to maintain panmixia, and effectively belong to a single population sharing a common gene pool. No clinal variation in allele distribution was detected throughout this range, a result which complements the findings of a detailed morphological companion study of the same individuals. Comparison of this homogenous European continental shelf population with squid from the Azores revealed highly significant (P<0.01) differences in allele distribution at five of the six polymorphic enzyme loci studied. A genetic identity value (I) equivalent to 0.93 over 33 loci was obtained. Analysis of F-statistics suggested migration rates between sites to be as low as one individual per five generations, a rate deemed insufficient under most models to prevent divergence by random genetic drift. The large distance and oceanic depths separating the Azores from continental Europe seem to present an effective barrier to gene flow to L. forbesi, a squid belonging to a family considered to be confined in distribution to relatively shallow, near coastal waters. The two populations of squid in the Azores and along the European continental shelf currently both ascribed to L. forbesi should therefore probably best be regarded as relative subspecies.     

Contrasting population structures in two sympatric fishes in the Baltic Sea basin

Detailed multispecies studies on the patterns of genetic variability and differentiation in marine environments are still rare. Using mitochondrial and nuclear genetic markers, we compared genetic variability and population structuring of threespine (Gasterosteus aculeatus) and ninespine (Pungitius pungitius) sticklebacks from the same eleven marine and six freshwater locations within the Baltic Sea basin. Analyses of both marker types revealed a significantly lower degree of genetic structuring in both marine and freshwater populations of threespine than those ninespine sticklebacks. Isolation-by-distance (IBD) was detected across the marine populations in both species, suggesting spatially limited gene flow. However, the levels of genetic diversity and differentiation across the localities were uncorrelated between the two species in both marine and freshwater environments. Accordingly, estimates of effective population sizes were larger and migration rates were higher for three- than for ninespine sticklebacks. Hence, ninespine stickleback populations from the Baltic Sea basin appear to be subject to stronger genetic drift than sympatric threespine sticklebacks, and the proximate reason for this difference is likely to be found from autecological differences between the two species. In accordance with the earlier studies, genetic variability was higher and the degree of genetic differentiation was lower in marine than in freshwater populations in both species.     

Inter-simple sequence repeat markers reveal strong genetic differentiation among populations of the endangered mollusc Patella ferruginea (Gastropoda: Patellidae) from two Sardinian marine protected areas

The giant Mediterranean limpet Patella ferruginea Gmelin, 1791 is an endangered marine gastropod, whose range has progressively shrinked to few, restricted areas, due to intense human exploitation. We have studied the genetic structure of the species, in order to (1) gather information about the levels of genetic variability within and between natural populations of P. ferruginea collected in two Sardinian marine protected areas (MPAs) (Penisola del Sinis—Isola di Mal di Ventre and Isola dell’ Asinara), and (2) make an attempt to find relationships between ecological and biological attributes of the species and the genetic differentiation of the populations studied. The genetic study was carried out by means of the analysis of ten inter-simple sequence repeat (ISSR) primers on a total of 40 individuals collected at four localities. Genetic analysis evidenced (1) medium to high levels of within-population genetic variability, (2) a pattern of genetic structuring that varied with spatial scales, and (3) a strong genetic differentiation between the two MPAs. Although preliminary, these results suggest that gene flow may be present only at very small geographic scale, raising concerns on the future of the conservation of the species.     

Calanoid copepod,cladoceran, and rotifer eggs in sea-bottom sediments of northern Californian coastal waters: Identification,occurrence and hatching

In Ireland, mussels on exposed rocky shores constitute an interbreeding mixture of two forms of mussels,Mytilus edulis L. and the Mediterranean musselM. galloprovincialis Lmk. This paper presents an in-depth analysis, carried out between October 1984 and December 1986, of genetic variability at two partially diagnostic loci,Odh andEst-D, in two exposed-shore populations ofMytilus spp. in the west of Ireland. Significant differences at theOdh locus were observed in the genetic composition of adult mussels from different tidal levels. These differences were repeatable whether one was analysing replicate samples at a single point in time, samples collected at different points in time, i.e., in different years, or samples collected from different shores. Mussels recruiting to artificial substrates set out for a period of one month at different tidal levels at one of these sites were also observed to be genetically different; mussels higher up the shore exhibited higher frequencies of those alleles characteristically at high frequency inM. galloprovincialis for both theOdh andEst-D loci. Hence, the genetic differences observed in adult mussels are much more exaggerated in juveniles and are already apparent within the first month of benthic life. Possible reasons for the observed microgeographic differentiation are discussed. It is concluded that the observed genetic differences between mussels at different tidal levels arise either in the pelagic/attachment stage or very shortly after settlement.     

High levels of gene flow in the surf bivalve Donax deltoides (Bivalvia: Donacidae) on the east coast of Australia

We surveyed patterns of allelic variation within twelve samples of the pipi Donax deltoides Lamarck from beaches separated by up to 1200 km but connected to varying degrees by the East Australian Current. We used these data to test the prediction that the irregular patterns of water movement would cause genetic differentiation in pipis, so that there would be more genetic variation within and among the more southern regions than the northern regions. We found that six loci were at least moderately variable within all samples, and there were no clear geographic patterns in allelic frequencies. In general, genotype frequencies within samples were consistent with predictions for an outcrossed, sexually reproducing species, and we detected no evidence of population subdivision. Within samples, with the exception of the peptidase loci, single-locus genotype frequencies were in close agreement with expectations for Hardy–Weinberg equilibrium. We observed no significant linkage disequilibrium for any pairwise comparison of loci in any sample. Our hierarchical analysis of genetic variation revealed little variation among all samples (F st = 0.009). Loci showed consistently low levels of subdivision (F st from 0.003 to 0.018). We found almost no variation among the four geographic regions sampled (F rt = 0.001). All variation was therefore attributable to variation among samples within regions (F sr = 0.010). These data imply that larvae are moving between regions and that levels of present or recent gene flow are high, and support the conclusions of other studies which have inferred widespread gene flow for animals dispersing via planktonic, outcrossed larvae in parts of this region. This implies that the East Australian Current is sufficient to produce strong larval connections despite its intermittent nature. If existing levels of population subdivision reflect current levels of gene flow, then these data imply that D. deltoides represents a single fishery on the east coast of Australia. Received: 16 September 1996 / Accepted: 25 September 1996     

Genetic variation in seven goby species (Perciformes: Gobiidae) assessed by electrophoresis and taxonomic inference

Data on the electrophoretic patterns of 20 enzyme loci were used to investigate relationships among seven Mediterranean goby species. The study evidenced different levels of genetic variability among the species. On the whole, the degrees of genetic differentiation were consistent with the current taxonomic recognition of species and genera. Phenetic and phylogenetic analyses agreed in clustering the samples in three groups, i.e. the Gobius (including Zosterisessor ophiocephalus), the Lesueurigobius species and Pomatoschiarua minutus. The taxa analysed probably evolved following the complex geological and climatic events that have been affecting the Mediterranean basin ever since the Miocene. Received: 20 June 1998 / Accepted: 5 February 1999     

The relationship between population genetic structure and pelagic larval duration in coral reef fishes on the Great Barrier Reef

Pelagic larval duration (PLD) is a commonly used proxy for dispersal potential in coral reef fishes. Here we examine the relationship between PLD, genetic structure and genetic variability in geographically widespread and ecological generalist species from one coral reef fish family (Pomacentridae) that differs in mean larval duration by more than a month. The genetic structure was estimated in eight species using a mitochondrial molecular marker (D-loop) and in a sub-set of five species using nuclear molecular markers (ISSRs). Estimates of genetic differentiation were similar among species with pelagic larvae, but differed between molecular markers. The mtDNA indicated no structure in all species except one, while the ISSR indicated some structure between the sampling locations in all species. We detected a relationship between PLD and genetic structure using both markers. These relationships, however, were caused by a single species, Acanthochromis polyacanthus, which differs from all the other species examined here in lacking a larval phase. With this species excluded, there was no relationship between PLD and genetic structure using either marker despite a range of PLDs of more than 20 days. Genetic diversities were generally high in all species and did not differ significantly among species and locations. Nucleotide diversity and total heterozygosity were negatively related to maximum PLD but again these relationships were caused by A. polyacanthus and disappeared when this species was excluded. These genetic patterns are consistent with moderate gene flow among well-connected locations and indicate that at this phylogenetic level (i.e., within family) the duration of the pelagic larval phase is unrelated to the patterns of genetic differentiation.     

Population genetic structure of the milkfish,<Emphasis Type="Italic"> Chanos chanos</Emphasis>, based on PCR-RFLP analysis of the mitochondrial control region

The milkfish, Chanos chanos (Forsskål, 1775) is a pelagic, monotypic gonorhynchiform widely distributed in the tropical Indo-Pacific. This study evaluates temporal variability of milkfish samples from the Philippine archipelago, and spatial variability at two geographic scales based on restriction fragment length polymorphism (RFLP) analysis of a portion of the mitochondrial control region. High levels of genetic diversity characterize the milkfish control region (mean h=0.908, =1.59%), with 74 haplotypes detected among the 367 fish analyzed. For temporal analysis of Philippine samples, milkfish were collected over 2 years from three sites (inter-annual variation), and sampled twice within a year during different seasons at four sites (intra-annual variation). No significant temporal variability was detected between or within years. Significant spatial differentiation among the Philippine samples was observed (F_ST=0.006, P<0.05), with two northeastern samples, Claveria and Dingalan, found to be genetically distinct. However, an hierarchical analysis of molecular variance (AMOVA), where samples were grouped into four geographic regions, revealed very low levels of genetic partitioning, with less than 1% of the total variation attributed to between-region differences, and lack of genetic structure. Nonetheless, the existence of putative northeastern Philippine populations is not discounted. Strong genetic structure across broad geographical scales was revealed by AMOVA, with 11% of the molecular variance based on haplotype frequencies allocated between three distinct groups: Indian Ocean, west Pacific (Philippines) and north central Pacific (Hawaii) The broad-scale genetic structure points to limited gene flow among disjunct Indo-Pacific populations.Communicated by T. Ikeda, Hakodate     

Genetic structure of dictyoceratid sponge populations on the western Coral Sea reefs

Allozyme variation at six polymorphic loci was examined in foliose dictyoceratid sponges from isolated reefs in the western Coral Sea. Four major genetic groups corresponding to the species Phyllospongia lamellosa, P. alcicornis, Carterospongia flabellifera and Collospongia auris were examined. A further two rare morphotypes from individual reefs formed genetic outliers to the P. lamellosa group, and may represent further taxa related to P. lamellosa. Gene frequencies in individual reef populations were largely in Hardy-Weinberg equilibrium, suggesting that random mating occurred in local populations of all four common species. Genetic variability was high and observed heterozygosities within populations ranged from 0.13 to 0.40. All four taxa showed significant genetic differentiation among populations (F _ST=0.05 to 0.36). Genetic distances (Nei's D) among populations within species ranged from 0 to 0.723 and increased with increasing geographical separation. There was evidence that genetic differentiation between populations to the north and to the south of the southern limit of the South Equatorial Current (SEC) divergence was greater than expected on the basis of their geographical separation. The SEC divergence may form a partial barrier to gene flow among populations of these ecologically important sponges on the submerged Queensland Plateau. Levels of migration among populations of three of the species was less than those required to prevent divergence of the populations through genetic drift (Nm<1). Restricted migration among populations may provide a mechanism to explain the occurrence of highly divergent populations of dictyoceratid sponges whose specific identity is not clear, and may allow them additionally to develop partial reproduction isolation from other populations.     

Cephalopod prey of the grey-headed albatrossDiomedea chrysostoma

Cephalopod remains were collected, at regular intervals throughout the fledging period, from the stomach contents of chicks of the grey-headed albatrossDiomedea chrysostoma at Bird Island, South Georgia, in 1984 and 1986 and from regurgitations of adults at the nest in 1986. The 1984 sample was taken during a season characterised by abnormal local oceanographic conditions in which the breeding success was very low; in 1986 conditions were normal and breeding success was high. Cephalopod beaks (289 from adults; 5 651 from chicks) were identified, and allometric equations were used to estimate the biomass represented. Five cephalopod species belonging to five families (Gonatidae, Onychoteuthidae, Psychroteuthidae, Ommastrephidae and Cranchiidae) contributed 98% by number and 97% of the biomass fed to chicks. The most important species was the ommastrephidMartialia hyadesi, contributing 68.9 to 77.4% by number and 72.5 to 79.3% of the total biomass fed to chicks. The relative proportions of cephalopod species in the chicks' diet were similar between 1984 and 1986, but the total number and biomass was significantly less in 1984. There is evidence of growth ofM. hyadesi between January and June.     

Genetic structure,lack of sex-biased dispersal and behavioral flexibility in the pair-living fat-tailed dwarf lemur, <Emphasis Type="Italic">Cheirogaleus medius</Emphasis>

Mating system and dispersal patterns influence the spatio-genetic structure within and between populations. Among mammals, monogamy is rare, and its socio-genetic consequences have not been studied in detail before. The goal of our study was to investigate population history, demographic structure, and dispersal patterns in a population of pair-living fat-tailed dwarf lemurs, Cheirogaleus medius, a small, nocturnal primate from western Madagascar, and to infer their underlying behavioral mechanisms. Tissue samples for DNA extraction were obtained from a total of 140 individuals that were captured in two subpopulations about 3 km apart. Analyses of mtDNA variability at the population level revealed very low levels of genetic variability combined with high haplotype diversity, which is indicative of a recent population bottleneck. We found no evidence for spatial clustering of same-sexed individuals with identical haplotypes within each of two subpopulations but significant clustering between them. Thus, a high level of local subpopulation differentiation was observed (F _ST = 0.230). The sexes showed equal variances in the number of individuals representing each haplotype, as well as equal levels of aggregation of identical haplotypes. Hence, both sexes disperse from their natal area, one pattern expected in a pair-living mammal. There is a possibility of behavioral and social flexibility in this species, however, because we documented pronounced differences in density and sex ratio between the two subpopulations, suggesting that single study sites or populations may not be representative of a given local population or even species.     

Genetic protein variation in red mullet (Mullus barbatus) and striped red mullet (M. surmuletus) populations from the Mediterranean Sea

Starch-gel electrophoresis of allozymes was used to differentiate the two red mullet species (Mullus barbatus L. and M. surmuletus L.) in the Mediterranean Sea and, further, to investigate the genetic stock structure of M. barbatus in the eastern Mediterranean area. Twenty putative enzyme-coding loci were examined in eight M. barbatus samples caught in the Aegean and Ionian Seas (Greece) and in the Gulf of Lion (France), and two M. surmuletus samples caught in the Aegean and Gulf of Lion. A high degree of genetic polymorphism was found in both species. Species-specific electrophoretic patterns were found in PGI* and PGM*. Estimates of variance of allele frequencies among samples (F _ST) and ² analyses both revealed significant differences (P < 0.05) among the M. barbatus samples. Most of the genetic variation was among samples regardless of region. The mean value of Nei's genetic distance between the two species was 0.329. Genetic distance among M. barbatus samples was low (maximum Nei's D = 0.012), with the sample from Platania differing most from other M. barbatus samples. This is probably be due to founder effects existing at this area. These results suggest that allozyme analysis may provide important information on the genetic structure of the red mullet to ensure sustainable management of this species. Received: 7 May 1997 / Accepted: 13 October 1997     

Genetic heterogeneity among New Zealand species of hydrothermal vent mussels (Mytilidae: Bathymodiolus)

Molecular systematic studies provide evidence for three new species of Bathymodiolus-like hydrothermal vent mussels (Bivalvia: Mytilidae) from relatively shallow waters (depth less than 750 m) associated with the Kermadec Arc off northern New Zealand. Mitochondrial COI sequences from the three putative new species differed substantially from those of other known bathymodiolin species from the Pacific and Indian Oceans. Population genetic analysis of one of these species (Bathymodiolus new species NZ-1) revealed heterogeneity in allozyme gene frequencies between samples collected from two seamounts about 50 km apart. Factors that might contribute to genetic differentiation between neighbouring seamounts are discussed.Communicated by M.S. Johnson, Crawley     

Evolutionary genetics of marine Mysis spp. (Crustacea: Mysidacea)

Inter-and intraspecific allozyme differentiation in the mysid crustacean genus Mysis in the North Atlantic region was studied in order to evaluate earlier concepts of evolutionary and systematic relationships and to assess patterns of subdivision within widespread taxa. The results support a relatively ancient divergence of the marine and non-marine species of the genus, and are generally in line with the current subgeneric tridivision into Mysis s.str., Michteimysis and Auricomysis. However, the North American littoral species M. gaspensis should be returned to subgenus Mysis s.str. from its present position in Michteimysis with M. mixta. The closest observed affinities within Mysis s.str. were between M. gaspensis and the freshwater M. relicta group, and between M. oculata and M. litoralis. Intraspecific differentiation among North European coastal populations of M. oculata and M. litoralis was moderately strong (F _ST0.1), suggesting population bottlenecks and limited dispersal in the post-glacial time. On the other hand, ransoceanic differences were not essentially greater, indicating the systematic homogeneity and long-term dispersal capacity in the marine species. This contrasts with the strong genetic and systematic fragmentation earlier found within the circumboreal M. relicta species group.     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Phylogeographic patterns of the mysid Mesopodopsis slabberi (Crustacea, Mysida) in Western Europe: evidence for high molecular diversity and cryptic speciation

The phylogeographic patterns among populations of Mesopodopsis slabberi (Crustacea, Mysida), an ecological important mysid species of marine and estuarine habitats, were analysed by means of DNA sequencing of a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) and the 16S ribosomal RNA genes. Samples of M. slabberi collected from five Atlantic and two Western Mediterranean populations were investigated. Very high levels of within-population molecular diversity were observed in all samples (mean h=0.807 and π=0.0083), with exception of the Mediterranean Ebro population which contained only one haplotype. Differentiation among populations was high, and a clear phylogeographic break was observed between the Atlantic and Mediterranean populations. Moreover, a strong differentiation was detected between both populations in the Western Mediterranean Sea (Alicante and Ebro delta), while two divergent lineages occurred in sympatry within the Atlantic Mondego estuary. The high congruence between both the COI and 16S rRNA sequence data, the reciprocal monophyly of the different mitochondrial clades and the levels of nucleotide divergence between them suggest the presence of a complex of cryptic species within M. slabberi. Estimations of divergence time between the different mitochondrial lineages indicate that a split occurred during the late Miocene/early Pliocene. Such a divergence could be concordant with vicariant events during sea-level drops within the Mediterranean region at that time. However, within the Mediterranean Sea, the potential of divergence through ecological diversification cannot be ruled out.     

Oceanographic and biological landscapes used by the Southern Giant Petrel during the breeding season at the Patagonian Shelf

The study of how and why marine animals distribute themselves at sea has important conservation and management implications of the species and their habitats. We characterize the oceanographic and biological landscapes of the marine areas used by breeding Southern Giant Petrels (Macronectes giganteus) at Patagonian colonies and explore inter-sexual and inter-colony differences. The at-sea movements of 16 adults (7 males and 9 females) were studied by means of satellite telemetry techniques during 1999, 2000, 2002, and 2004 breeding seasons. Southern Giant Petrels utilized an oceanographic scenario characterized by high productivity, warm sea surface temperature, and shallow waters. The biological landscape was characterized by a high availability of squid and carrion nearby colonies. Females spent more time in the shelf break and exploited deeper waters than males. In contrast, males spent more time in coastal areas and they showed a higher spatial overlap with areas of high squid density than females. Such a prosperous foraging scenario for both sexes may play a key role in the growth of the breeding population of Southern Giant Petrel Patagonian colonies.     

Worms without borders: genetic diversity patterns in four Brazilian <Emphasis Type="Italic">Ototyphlonemertes</Emphasis> species (Nemertea,Hoplonemertea)

Understanding the evolutionary processes from recent demographic history is especially difficult for interstitial organisms due to their poorly known natural history. In this study, the genetic variation and population history of the four Ototyphlonemertes (Diesing in Sitz ber Math Nat Kl Akad Wiss Wien 46:413–416, 1863) species were evaluated from samples collected along the Brazilian coast (between 27°31′S and 13°00′W) in 2006. The mitochondrial region cytochrome c oxidase subunit 3 (COX3) is analyzed to assess the genetic variation of these dioecious species. Although these species have a sympatric distribution along the coast, our data suggest that their levels of differentiation and their demographic histories differ sharply. There is strong evidence of gene flow among demes in O. erneba and O. evelinae, and their level of structuring is much lower than for the other two species. Indeed, the COX3 fragment reveals cryptic lineages in O. lactea and O. parmula. The results seem to contradict the high genetic structuring and low intrapopulational variability expected with the ecological constriction and habitat discontinuity faced by these organisms, meaning that there might be gene flow among populations or their dispersal capability has been underestimated.