Enzyme activities and allozyme polymorphism in two genetic types (or sibling species) of the genus Marenzelleria (Polychaeta: Spionidae) in Europe

Two populations of Marenzelleria spp. from the North Sea and the Baltic Sea that had already been characterized by allozyme electrophoresis and found genetically different in 1994 were again examined in 1997. The genetic identity (I = 1.0) examined in 1994 and 1997 shows that the structures of the populations of genetic Type I in the North Sea (Ringkobing Fjord) and genetic Type II in the Baltic Sea (Darss–Zingst Bodden chain) are stable. Three diagnostic gene loci that were determined additionally (citrate synthase, one locus; alanine aminotransferase, two loci) support the hypothesis of the existence of two sibling species of the genus Marenzelleria in Europe. In addition, the activities of ten electrophoretically separated enzyme systems were measured in the worms immediately after removal from their habitat and after they had been kept in the laboratory for 2 months. Under both conditions four enzymes showed significant differences between genetic types. The higher activity of the alanine aminotransferase of the North Sea worms (Type I) is discussed in the context of the different preferred salinities of the two Marenzelleria sibling species. Received: 21 January 1999 / Accepted: 13 July 1999     

Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands

An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined, giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H _e  = 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F _is (0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F _st value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front, relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time. Received: 24 July 1997 / Accepted: 31 October 1997     

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     

Mitochondrial DNA analysis of the genetic relationships among populations of scad mackerel (Decapterus macarellus, D. macrosoma, and D. russelli) in South-East Asia

The genetic relationships among South-East Asian populations of the scad mackerels Decapterus macarellus, D. macrosoma and D. russelli (Pisces: Carangidae) were investigated. In 1995 and 1996, 216 fish were sampled in seven localities spanning the seas of Indonesia and were examined for restriction-site polymorphisms using ten restriction enzymes for the mitochondrial (mt) DNA control region, amplified by the polymerase chain-reaction. The inferred phylogeny of haplotypes led to the recognition of three distinct mitochondrial lineages or phylads consistent with the distinctions of current taxonomy. All 15 mtDNA haplotypes found in D. macarellus and all 9 haplotypes found in D. macrosoma were arranged as star-like clusters, suggesting recent evolutionary history. In contrast, the phylad formed by 6 haplotypes in D. russelli from the Sulawesi Sea exhibited diffuse topology, suggesting that ancestral lineages of this species have been retained to the present. Average nucleotide-divergence estimates between haplotypes of different phylads were between 0.042 and 0.135, suggesting ancient separation, in consistency with published allozyme data. High levels of haplotype diversity, but no geographical heterogeneity, was detected within D. macarellus from the Molucca Sea and the Banda Sea. Populations of D. macrosoma exhibited both significant differences between adjacent regions (Sunda Strait and Java Sea), and broadscale genetic homogeneity from the South China Sea to the Sulawesi Sea via the Java Sea and Makassar Strait. The geographic isolation of the D. macrosoma population sampled in the Sunda Strait suggests that this region constitute a sharp transition zone between the Indian Ocean and the Sunda Shelf. Near-monomorphism of haplotypes and low nucleotide diversity (d _X) were observed in the samples of D. macrosoma from the continental shelf (haplotype-diversity estimates, h, = 0.00 to 0.25 ± 0.08 and d _X = 0.000 to 0.002). This was in contrast to the comparatively high haplotype and nucleotide diversities observed in other pelagic fish species including D. macarellus (h = 0.82 ± 0.05, d _X = 0.012 to 0.015) and D. russelli (h = 0.63 ± 0.12, d _X = 0.016), and in the oceanic D. macrosoma population sampled in the Sunda Strait (h = 0.67 ± 0.31, d _X = 0.005). We hypothesise that this may be the consequence of recent and perhaps repeated bottleneck events that have affected the D. macrosoma population sampled on the continental shelf. Received: 29 September 1997 / Accepted: 3 September 1999     

Icy heritage: ecological evolution of the postglacial Baltic Sea reflected in the allozymes of a living fossil,the priapulid Halicryptus spinulosus

Genetic variation of 16 allozyme loci in 397 Halicryptus spinulosus (Priapulida) revealed overall polymorphism of P=0.438 and Hardy-Weinberg expectations for heterozygosity of H _e=0.060 for Baltic Sea stocks, H _e=0.143 for the White Sea and H _e=0.121 for Iceland. Maximal unbiased standard distances of D=0.0693 separated Baltic and White Sea populations. Nordic and Baltic populations could be distinguished by allozymes, but Baltic subsamples proved cohesive. Gene flow amounted to effective exchange values per generation of N _m=2.94 over 650 km of continuous habitat, N _m=10.65 over 175 km, and N _m=13.85 over 20 km. Gene flow started to decrease with geographic distance beyond a dispersal threshold of 20 km, but hierarchical G _ST-statistics indicated light isolation by distance beyond a minimum of 8 km. Gene flow is high for a benthic worm assumed to lack dispersal by pelagic larva, a paradox which cannot be resolved now. Baltic populations are characterized by lower heterozygosity than Nordic stocks. In the Baltic Basin, temporally continuous brackish-water conditions have only existed for the past 7000 years. The two possible colonization routes of H. spinulosus to the geologically young Baltic Sea imply genetic drift, whether by founder effect (sweepstake colonization from Iceland) or by refugial bottlenecking during the Ancylus phase of the Baltic Basin after a direct connection to the White Sea had been sequestered. Continued genetic drift is emphasized by lower heterozygosity in the ecologically unstable Belt Sea compared to the central Baltic. Allozymes falsify the reduced-mutability hypothesis to explain bradytelic evolution of Priapulida. Regional genetic homogeneity, ample polymorphism, and preference for anoxic black mud qualify H. spinulosus populations as indicators of microevolutionary responses to water circulation regimes or pollution in the Baltic Sea.     

Genetic structure of a scleractinian coral, Mycedium elephantotus, in Taiwan

The genetic structure of Mycedium elephantotus (Pallas, 1766) populations from three regions around Taiwan was examined using allozyme electrophoresis. Eight loci were scored from seven enzyme systems. Seven loci were polymorphic under the 95% criterion. The high ratio of observed to expected genotypic diversities at the collection sites (G _O:G _E=0.8 to 1.0) indicate that M. elephantotus propagates predominantly by sexual reproduction. Allele frequencies of M. elephantotus differed significantly among regions (D=0.024 to 0.256, F _ST=0.032 to 0.218, p < 0.001), while populations among collection sites within each region were homogeneous (D=0.000 to 0.015, F _ST=0.010 to 0.022, p > 0.05). Genetic differentiation between populations from southern Taiwan and the Penghu Islands is greater than that between southern and northern Taiwan populations, although the former two regions are much closer geographically. The UPGMA dendrogram based on Nei's unbiased genetic distance showed a clear subdivision of populations into two groupings, northern Taiwan/Penghu Islands and southern Taiwan. A higher level of gene flow was found between M. elephantotus populations in northern Taiwan and the Penghu Islands (N _m=7.56) than that between populations in southern Taiwan and other regions (N _m=0.90 to 1.72). The pattern of genetic subdivision among regions is consistent with the pattern of ocean currents, indicating that genetic differentiation is likely driven by surface circulation vicariance. Received: 2 December 1997 / Accepted: 15 September 1998     

Genetic structure of the flounders Platichthys flesus and P. stellatus at different geographic scales

The genetic structure of the flounders Platichthys flesus L. and P. stellatus Pallas was investigated on different spatial scales through analysis of allozyme variation at 7 to 24 polymorphic loci in samples collected from different regions (Baltic Sea, North Sea, Brittany, Portugal, western Mediterranean, Adriatic Sea, Aegean Sea and Japan) in 1984 to 1987. No geographic variation was evident within a region. Some pattern of differentiation by distance was inferred within the Atlantic, while the Mediterranean comprised three geographically isolated populations and was itself geographically isolated from the Atlantic (fixed allele differences at up to three loci were found among P. flesus populations from the Atlantic, the western Mediterranean, the Adriatic Sea, the Aegean Sea and also P. stellatus from the coast of Japan). Sea temperature during the reproductive period probably acts as a barrier to gene flow between populations. Genetic distances among European flounder populations (P. flesus) were higher than, or of the same magnitude as, the genetic distance between Pacific (P. stellatus) and European flounder populations, suggesting that P. flesus is paraphyletic and/or there is no phylogenetic basis to recognising P. stellatus as a different species. The divergence between P. flesus and P. stellatus was thus inferred to be more recent than the divergence between the present P. flesus populations from the NE Atlantic and eastern Mediterranean. The eastern Mediterranean populations are thought to originate from the colonisation of the Mediterranean by a proto-P. flesus/P. stellatus ancestor, whereas the present western Mediterranean population has undergone a more recent colonisation event by P. flesus. Patterns of mitochondrial DNA variation, established on a smaller array of P. flesus samples, were in accordance with the geographic patterns inferred from the allozyme survey. In addition, they supported the hypothesis of a two-step colonisation of the western Mediterranean. These results contribute to our understanding of the biogeography of the Mediterranean marine fauna, especially the group of boreal remnants to which P. flesus belongs. Received: 7 February 1997 / Accepted: 26 March 1997     

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

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

Restricted gene flow and evolutionary divergence between geographically separated populations of the Antarctic octopus Pareledone turqueti

Samples of the Antarctic octopus Pareledone turqueti were taken from three locations on the Scotia Ridge in the Southern Ocean. The genetic homogeneity of these populations was investigated using isozyme electrophoresis. Whilst panmixia appeared to be maintained around South Georgia (F _ST = 0) gene flow between this island and Shag Rocks, an island only 150 km away but separated by great depths, was extremely limited (F _ST = 0.74). These results are examined with respect to the discontinuous distribution of P. turqueti throughout Antarctica. An estimate of effective population size was also calculated (N _e = 3600). Received: 7 March 1997 / Accepted: 27 March 1997     

Evidence of limited gene flow in three species of coral reef fishes in the lagoon of New Caledonia

Allozyme variation was used to investigate the genetic structure of the coral reef fishes Stegastes nigricans, Epinephelus merra and Acanthurus triostegus around New Caledonia. Each species was sampled from each of three sites in the ≃1000 km circumference of the lagoon of New Caledonia. Allelic variation was recorded for each species at 14, 13 and 17 loci, respectively, and heterozygosity diversity (H s) was 0.082, 0.065 and 0.116, respectively. Analysis of genetic differentiation between sites produced inconsistent results between species, with spatial heterogeneity in two species (S. nigricans, F st  = 0.038; A. triostegus, F st = 0.049) and homogeneity in one species (E. merra, F st = 0.000). Hydrological and climatic data from the lagoon suggest that the eastern and western sides of the lagoon are isolated, since they lie in water masses of different origin. This may explain the genetic differentiation and restricted gene flow found at a local scale for S. nigricans and A. triostegus. Homogeneity in populations of E. merra is discussed in relation to its low genetic diversity and its reproductive behaviour. Received: 23 April 1997 / Accepted: 25 September 1997     

Is Syllis gracilis (Polychaeta: Syllidae) a species complex? An allozyme perspective

The genetic relationships between morphologically indistinguishable marine and brackish populations of Syllis gracilis Grube, 1840 (Polychaeta: Syllidae) were studied by means of allozyme electrophoresis. Samples of S. gracilis from marine coastal and brackish-water habitats were examined for variation at 13 presumptive loci. In addition, a sample of the closely related species S. prolifera (Krohn, 1852) was analysed. Five loci were multiallelic in at least one population of S. gracilis and eight loci in S. prolifera. Low to moderate levels of within-population genetic variability were found, with average expected heterozygosity values ranging from H = 0.068 (±0.043 SE) to 0.187 (±0.069 SE) in the populations of S. gracilis; higher values were found in S. prolifera (H = 0.325 ± 0.076). The presence of various private alleles indicated a marked genetic divergence among populations of S. gracilis, with Nei's genetic distances ranging from D = 0.000 to 0.833 and a highly significant F _ST value. Furthermore, evidence for strong genetic heterogeneity between two sympatric marine populations was found. UPGMA cluster analysis and multidimensional scaling pointed out a clear genetic divergence between brackish and marine populations. At least two genetically divergent entities occurred in marine and brackish habitats. This could be due to local adaptation of individuals coming from marine populations to brackish habitats, but more presumably to the occurrence of a species complex within S. gracilis. Received: 6 June 1999 / Accepted: 7 February 2000     

Microsatellite analysis of plaice (Pleuronectes platessa L.) in the NE Atlantic: weak genetic structuring in a milieu of high gene flow

Many species of marine fish are typified by large population sizes, strong migratory behavior, high fecundity, and pelagic eggs and larvae that are passively transported by ocean currents, all features that tend to increase gene flow, and hence reduce genetic partitioning, among localized populations. The plaice, Pleuronectes platessa, is a commercially important demersal species that exhibits all of these characteristics. We analyzed genetic variation at eight microsatellite loci in samples of spawning adults (N = 348) from the coasts of Ireland, Iceland, and, for the first time, from the Baltic Sea. Significant differentiation was observed between Iceland and Irish and Baltic Sea samples. However, there were no genetic differences between Irish and Baltic Sea samples, which contrast with the significant differentiation reported between Baltic Sea and North Sea/Atlantic populations of other flatfish species. To increase the data set, we carried out a cross-calibration exercise, allowing us to perform a joint analysis of data with an earlier study on adult and juvenile plaice (N = 480) collected over a broad geographic range, using six microsatellite loci in common to the two studies. Significant differentiation was observed between fish collected at the northern (Iceland, Faeroes, Norway) and southern (Bay of Biscay) parts of the species range. In contrast, the results showed little evidence of genetic structuring over much of the continental shelf of Europe. We believe that bathymetric and hydrographic barriers are the major factors shaping genetic structure, while lack of structure over much of the European continental shelf may be explained by a combination of past historical events, population structure, and dynamics of the 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     

Are there two species of the polychaete genus Marenzelleria in Europe?

North Sea and Baltic Sea populations of the introduced polychaete Marenzelleria viridis (Verrill, 1873) reproduce at different times (spring and autumn, respectively). Enzyme separation by starch gel electrophoresis revealed major differences between specimens from the Baltic Sea and those from the North Sea (collected in 1992 and 1993) but a high degree of homogeneity among populations from the same sea. Three enzyme loci, glucose-6-phosphate isomerase (GPI-A, GPI-B) and malate dehydrogenase (MDH), were fixed to 100% by different alleles in the North and Baltic Sea populations, respectively. Different alleles are dominant for mitochondrial aspartate aminotransferase (mAAT) with allele frequencies of ca. 0.97 in all sampled populations from the North Sea and Baltic Sea, respectively, but heterozygotes were found in all populations. These genetic differences could be due to environmentally induced selection or genetically different origins of the populations, suggesting that populations of the genus Marenzelleria in the North and Baltic Seas may be two different species.     

Genetic relationships between marine and marginal-marine populations of Cerithium species from the Mediterranean Sea

Results of isozyme electrophoresis were used to explore the genetic relationships between several Mediterranean morphs of Cerithium (Gastropoda: Prosobranchia), for which taxonomy is currently uncertain because of high intraspecific variability and low interspecific differentiation. The large species, classically known as C. vulgatum Bruguière, 1789 was identified at four sites (two in the French Mediterranean and two in southern Spain). Two different larval types were found in the French sites, but poecilogony could not be demonstrated. Individuals collected from harbours were not genetically distinct from open-sea populations of classic C. vulgatum. However, a population in the Embiez lagoon (French Mediterranean) which morphologically resembles C. vulgatum did display distinct genetic traits, supporting its status as a separate species. Of the small Cerithium species usually known as C. rupestre, two sympatric species (C.“rupestre” Risso, 1826 and C. lividulum Risso, 1826) were distinguished. Genotype frequencies within the analysed populations revealed much heterozygote deficiency. F _ST values (fixation index measuring the effects of population subdivision) suggest a higher genetic differentiation for C. lividulum populations than for C. vulgatum populations. We assume that a high larval dispersal capability (via planktotrophy) allows a high gene flow between populations of C. vulgatum. Received: 24 November 1998 / Accepted: 24 September 1999     

Genetic variability and level of differentiation in North Sea and Baltic Sea populations of the green alga<Emphasis Type="Italic"> Cladophora rupestris</Emphasis>

Cladophora rupestris is a perennial filamentous macroalga belonging to the Chlorophyta. It is widely distributed on both sides of the northern Atlantic Ocean and penetrates into the brackish Baltic Sea down to ca. 4 psu salinity. In this paper we present evidence for genetic differentiation of a Baltic form of this marine alga. We assessed genetic structure within and among 11 populations ranging along a salinity gradient from the Norwegian coast to the northern Baltic Sea proper. Samples of 328 individuals were studied using starch-gel protein electrophoresis to evaluate genetic variability and interpopulation differentiation based on allozymes. Of 11 loci examined, only one was polymorphic. For this locus, encoding superoxide dismutase (SOD-3), a total of seven alleles were distinguished. We found two genetically differentiated groups of populations of C. rupestris, one Baltic Sea group and one North Sea group, with a distinct border in the southern Kattegat near the entrance to the Baltic Sea. The genetic differentiation for SOD-3, expressed as pairwise F_ST values between the populations, was generally higher within the Baltic Sea group (0.10-0.43) than within the North Sea group (0.05-0.10); in the latter group also fewer pairs of populations differed significantly. Pairs of populations from different groups had the highest F_ST values (0.20-0.60). Hierarchical analysis of variance showed that 29.6% of the total variation in the SOD-3 locus was explained by variation between the two groups, while only 4.2% was explained by variation among the populations within the groups. The remaining variation (66.2%) was found within the populations.     

Genetic differentiation in two sibling species of the brackish-water polychaete Hediste japonica complex (Nereididae)

Genetic divergence among ten populations of small- and large-egg forms of the brackish-water polychaete Hediste japonica complex was investigated on 14 isozyme loci by electrophoretic analysis. The two forms were distinguishable by complete allele substitutions at five loci, resulting in high genetic differentiation (Nei's D: 0.533 to 0.662). No genetic evidence of hybridization between the two forms was detected in sympatric populations in three rivers. These results indicate that the two forms are reproductively isolated, clearly showing that the two forms are distinct species. The genetic differentiation among populations was higher in the large-egg form (D: 0.005 to 0.111, G _ST: 0.435) than that in the small-egg form (D: 0.000 to 0.001, G _ST: 0.020). This genetic difference between the two forms seems to be attributable to a difference in their life histories. The average expected heterozygosity was low in populations of both the large-egg form (0.005 to 0.068) and the small-egg form (0.014 to 0.038) in comparison with other marine invertebrates. Received: 11 April 1997 / Accepted: 8 September 1997     

Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Mitochondrial DNA analysis of harbour porpoises (Phocoena phocoena) in the Baltic Sea, the Kattegat–Skagerrak Seas and off the west coast of Norway

Incidental mortality of harbour porpoises, Phocoena phocoena, from captures in fishing gear has been documented consistently as severe in some European waters. Since fishing effort varies greatly among regions, management units must be defined for more effective conservation of this species. In this study, analysis of mitochondrial DNA (mtDNA) restriction fragments was performed to investigate the population structure of harbour porpoises in the Baltic Sea, the joint Kattegat–Skagerrak Seas and off the west coast of Norway. Mitochondrial DNA of 65 harbour porpoises collected from three regions was analysed with nine restriction enzymes. Analysis of the heterogeneity in the frequency distribution of haplotypes among provisional subpopulations revealed significant differences, which supports the recognition of three different subpopulations and thus three separate management units. Furthermore, indices of haplotypic diversity (range: 0.211 to 0.628) and nucleotide diversity (range: 0.070 to 0.168) of these provisional subpopulations were much lower than for western North Atlantic subpopulations, which is consistent with the view that harbour porpoises in European waters, particularly in the Baltic Sea, are depleted. Received: 21 August 1996 / Accepted: 19 September 1996     

Allozyme variation in global populations of striped mullet, Mugil cephalus (Pisces: Mugilidae)

The striped mullet, Mugil cephalus Linnaeus, 1758, is one of the few species of marine shore fish with a worldwide circumtropical distribution. Because of this distribution and the dependency of M. cephalus on coastal waters during various phases of its life cycle, as well as nearshore living habits, questions have been raised regarding levels of genetic divergence and gene flow among transoceanic populations. To cast more light on this, allozyme variation at 27 presumptive gene loci was investigated in ten globally diverse populations. The observed heterozygosity ranged from 0.018 (Hawaii) to 0.081 (Florida), averaging 0.050. The proportion of polymorphic loci showed a similar trend. Several populations were characterised by fixed allelic differences. Estimated gene diversities were very high, the allele frequency variation among populations was found to be 68%; genetic distances reached 0.242, with an average of 0.117. Estimated rates of gene flow were high among Mediterranean populations (Nm = 7.26), and between Mediterranean and East Atlantic populations (Nm= 2.86), but extremely low between non-contiguous populations within the Indian, Pacific and Atlantic Oceans, where Nm ranged from 0.03 to 0.05. Received: 7 April 1997 / Accepted: 4 February 1998