Genetic differentiation of Arctic charr <Emphasis Type="Italic">Salvelinus alpinus</Emphasis> complex from Transbaikalia revealed by microsatellite markers

Variation at eight microsatellite loci was studied in Arctic charr Salvelinus alpinus complex from five Transbaikalian mountain lakes. Samples from three lakes included two sympatric charr forms (dwarf and small) differing in trophic specialization, morphology and life cycle parameters. Sympatric forms were genetically closer to each other than to charr from other lakes which evidences their independent origin in each of these lakes as the result of sympatric speciation. In each lake, gene pools of sympatric forms were segregated to a different degree (estimates of F _ST varying from 0.030–0.184 and those of ρ _ST varying from 0.119–0.359). Hierarchical analysis of allelic frequencies variance (AMOVA) in Arctic charr from Lake Baikal, the Vitim, and the Olekma basins showed that variation among and within these basins accounted for 19.5% of the interpopulational variance each. In the AMOVA design, investigating differences among sympatric forms in three lakes these differences accounted for 7.1% of the total variance.     

High gene flow between populations of Macrotermes michaelseni (Isoptera, Termitidae)

Termite alates are thought to be poor active flyers, and this should lead to considerable genetic differentiation on small spatial scales. However, using four microsatellite loci for the termite Macrotermes michaelseni we found low values of genetic differentiation (F_ST) across a spatial scale of even more than 50 km. Genetic differentiation between populations increased with spatial distance up to 50 km. Furthermore, up to this distance, the scatter around the linear regression of genetic differentiation versus spatial distance increased with spatial distance. This suggests that across such spatial distances gene flow and genetic drift are of about equal importance, and near equilibrium. Using a regional F_ST as well as the distance between populations with non-significant F_ST-values (up to 25 km), gene flow is sufficiently high so that populations may be regarded as panmictic on spatial scales of 25 to 50 km. The apparent contradiction between dispersal distances observed in the field and estimates of gene flow from genetic markers may be due to the masses of swarming alates. Assuming a leptokurtic distribution of dispersal distances, atleast some alates are expected to travel considerable distances, most likely by passive drift. Received 25 January 2005; revised 11 April 2005; accepted 26 April 2005.     

Human disturbance reduces genetic diversity of an endangered tropical tree, <Emphasis Type="Italic">Prunus africana</Emphasis> (Rosaceae)

Human activities such as fragmentation and selective logging of forests can threaten population viability by modification of ecological and genetic processes. Using six microsatellite markers, we examined the effects of forest fragmentation and local disturbance on the genetic diversity and structure of adult trees (N = 110) and seedlings (N = 110) of Prunus africana in Kakamega Forest, western Kenya. Taking samples of adults and seedlings allowed for study of changes in genetic diversity and structure between generations. Thereby, adults reflect the pattern before and seedlings after intensive human impact. Overall, we found 105 different alleles in the six loci examined, 97 in adults and 88 in seedlings. Allelic richness and heterozygosity were significantly lower in seedlings than in adults. Inbreeding increased from adult tree to seedling populations. Genetic differentiation of adult trees was low (overall F _ST = 0.032), reflecting large population sizes and extensive gene flow in the past. Genetic differentiation of seedlings was slightly higher (overall F _ST = 0.044) with all of the 28 pairwise F _ST-values being significantly different from zero. These results suggest that human disturbance in Kakamega Forest has significantly reduced allelic richness and heterozygosity, increased inbreeding and slightly reduced gene flow in P. africana in the past 80–100 years.     

Generation of a neutral FST baseline for testing local adaptation on gill raker number within and between European whitefish ecotypes in the Baltic Sea basin

Divergent selection at ecologically important traits is thought to be a major factor driving phenotypic differentiation between populations. To elucidate the role of different evolutionary processes shaping the variation in gill raker number of European whitefish (Coregonus lavaretus sensu lato) in the Baltic Sea basin, we assessed the relationships between genetic and phenotypic variation among and within three whitefish ecotypes (sea spawners, river spawners and lake spawners). To generate expected neutral distribution of F_ST and to evaluate whether highly variable microsatellite loci resulted in deflated F_ST estimates compared to less variable markers, we performed population genetic simulations under finite island and hierarchical island models. The genetic divergence observed among (F_CT = 0.010) and within (F_ST = 0.014–0.041) ecotypes was rather low. The divergence in gill raker number, however, was substantially higher between sea and river spawners compared to observed microsatellite data and simulated neutral baseline (P_CT > F_CT). This suggests that the differences in gill raker number between sea and river spawners are likely driven by divergent natural selection. We also found strong support for divergent selection on gill raker number among different populations of sea spawners (P_ST > F_ST), most likely caused by highly variable habitat use and diverse diet. The putative role of divergent selection within lake spawners initially inferred from empirical microsatellite data was not supported by simulated F_ST distributions. This work provides a first formal test of divergent selection on gill raker number in Baltic whitefish, and demonstrates the usefulness of population genetic simulations to generate informative neutral baselines for P_ST–F_ST analyses helping to disentangle the effects of stochastic evolutionary processes from natural selection.     

Genetic structure and signature of population decrease in the critically endangered freshwater cyprinid <Emphasis Type="Italic">Chondrostoma lusitanicum</Emphasis>

The endemic and critically endangered cyprinid Chondrostoma lusitanicum has a very restricted distribution range. In order to estimate genetic diversity, characterize population structure and infer the demographic history, we examined six microsatellite loci and cytochrome b (mtDNA) sequences from samples taken throughout C. lusitanicum’s geographical range. Estimates of genetic diversity were low in all samples (average He < 0.35). The microsatellite data pointed to a major difference between northern (Samarra and Tejo drainages) and southern (Sado and Sines drainages) samples. This separation was not so clear with mtDNA, since one sample from the Tejo drainage grouped with the southern samples. This could be related with ancestral polymorphism or with admixture events between northern and southern sites during the late Pleistocene. Nevertheless, both markers indicate high levels of population differentiation in the north (for microsatellites F _ST >  0.23; and for mtDNA Φ_ST > 0.74) and lower levels in the south (F _ST < 0.05; Φ_ST < 0.40). With microsatellites we detected strong signals of a recent population decrease in effective size, by more than one order of magnitude, starting in the last centuries. This is consistent with field observations reporting a severe anthropogenic-driven population decline in the last decades. On the contrary mtDNA suggested a much older expansion. Overall, these results suggest that the distribution of genetic diversity in C. lusitanicum is the result of both ancient events related with drainage system formation, and recent human activities. The potential effect of population substructure generating genetic patterns similar to a population decrease is discussed, as well as the implications of these results for the conservation of C. lusitanicum. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic divergence in nuclear genomes between populations of <Emphasis Type="Italic">Fagus crenata</Emphasis> along the Japan Sea and Pacific sides of Japan

Genetic diversity and structure in Fagus crenata were studied by analyzing 14 nuclear microsatellite loci in 23 populations distributed throughout the species’ range. Although population differentiation was very low (F _ST = 0.027; R _ST = 0.041), both neighbor-joining tree and Bayesian clustering analyses provided clear evidence of genetic divergence between populations along the Japan Sea (Japan Sea lineage) and Pacific (Pacific lineage) sides of Japan, indicating that physical barriers to migration and gene flow, notably the mountain ranges separating the populations along the Japan Sea and Pacific sides, have promoted genetic divergence between these populations. The two lineages of the nuclear genome are generally consistent with those of the chloroplast genome detected in a previous study, with several discrepancies between the two genomes. Within-population genetic diversity was generally very high (average H _E = 0.839), but decreased in a clinal fashion from southwest to northeast, largely among populations of the Japan Sea lineage. This geographical gradient may have resulted from the late-glacial and postglacial recolonization to the northeast, which led to a loss of within-population genetic diversity due to cumulative founder effects.     

Application of Microsatellite Markers to Population Genetics Studies of Japanese Flounder Paralichthys olivaceus

We examined population genetic structure by means of microsatellite analysis among 7 Japanese flounder (Paralichthys olivaceus) populations collected from coastal sea areas around Japan. As was expected, all of the 11 microsatellite loci examined were variable in all populations (number of alleles per locus, 15.2–18.2; average of expected heterozygosity, 0.74–0.78). Eleven population pairs in 21 possible pairwise comparisons showed significant genetic heterogeneity associated with allele frequency distributions or fixation index (F _ST ). Modified Cavalli-Sforza chord distance (D _A ) and Nei's standard genetic distance (D _ST ) ranged from 0.051 to 0.090, and from 0.000 to 0.025, respectively. There was evidence that the populations assessed in this study were not drawn from a single panmictic population; however, it appears that Japanese flounder populations around Japan are not well-structured, as an estimate of the fixation index value among the 7 localities was very low (F _ST = 0.0025). Received April 27, 2001; accepted June 27, 2001.     

Fine-scale population genetic structure in Alaskan Pacific halibut (<Emphasis Type="Italic">Hippoglossus stenolepis</Emphasis>)

Pacific halibut collected in the Aleutian Islands, Bering Sea and Gulf of Alaska were used to test the hypothesis of genetic panmixia for this species in Alaskan marine waters. Nine microsatellite loci and sequence data from the mitochondrial (mtDNA) control region were analyzed. Eighteen unique mtDNA haplotypes were found with no evidence of geographic population structure. Using nine microsatellite loci, significant heterogeneity was detected between Aleutian Island Pacific halibut and fish from the other two regions (F _ST range = 0.007–0.008). Significant F _ST values represent the first genetic evidence of divergent groups of halibut in the central and western Aleutian Archipelago. No significant genetic differences were found between Pacific halibut in the Gulf of Alaska and the Bering Sea leading to questions about factors contributing to separation of Aleutian halibut. Previous studies have reported Aleutian oceanographic conditions at deep inter-island passes leading to ecological discontinuity and unique community structure east and west of Aleutian passes. Aleutian Pacific halibut genetic structure may result from oceanographic transport mechanisms acting as partial barriers to gene flow with fish from other Alaskan waters.     

Genetic differentiation among coastal and offshore common bottlenose dolphins,Tursiops truncatus,in the eastern North Pacific Ocean

Common bottlenose dolphins (Tursiops truncatus) are found worldwide in temperate and tropical regions, often occurring as distinct coastal and offshore ecotypes. Along the west coast of the United States, two stocks are recognized for management based on morphological and photo‐identification studies: a California coastal stock, estimated at 450–500 individuals, and a California/Oregon/Washington offshore stock of about 1,000 animals. This study is the first to analyze genetic differentiation between these stocks. We examined both the hypervariable portion of the mitochondrial DNA (mtDNA) control region and fifteen microsatellite markers for coastal (n = 64) and offshore (n = 69) dolphins. Significant genetic differentiation was found between the two stocks for mtDNA (Φ_ST = 0.30, P < 0.001; F_ST = 0.14, P < 0.001) and microsatellite loci (F_ST = 0.19, P < 0.001). Coastal dolphins had less genetic diversity than offshore dolphins. Further substructuring within the offshore stock was not detected. The level of genetic differentiation between the coastal and offshore dolphins is consistent with long‐term separation and reinforces recognizing them as separate stocks. These findings are particularly important for management of the smaller, less genetically diverse, coastal stock that is vulnerable to a variety of anthropogenic threats.     

Selection on life‐history traits and genetic population divergence in rotifers

A combination of founder effects and local adaptation – the Monopolization hypothesis – has been proposed to reconcile the strong population differentiation of zooplankton dwelling in ponds and lakes and their high dispersal abilities. The role genetic drift plays in genetic differentiation of zooplankton is well documented, but the impact of natural selection has received less attention. Here, we compare differentiation in neutral genetic markers (F_ST) and in quantitative traits (Q_ST) in six natural populations of the rotifer Brachionus plicatilis to assess the importance of natural selection in explaining genetic differentiation of life‐history traits. Five life‐history traits were measured in four temperature × salinity combinations in common‐garden experiments. Population differentiation for neutral genetic markers – 11 microsatellite loci – was very high (F_ST = 0.482). Differentiation in life‐history traits was higher in traits related to sexual reproduction than in those related to asexual reproduction. Q_ST values for diapausing egg production (a trait related to sexual reproduction) were higher than their corresponding F_ST in some pairs of populations. Our results indicate the importance of divergent natural selection in these populations and suggest local adaptation to the unpredictability of B. plicatilis habitats.     

QST < FST As a signature of canalization

A key aim of evolutionary biology – inferring the action of natural selection on wild species – can be achieved by comparing neutral genetic differentiation between populations (F_ST) with quantitative genetic variation (Q_ST). Each of the three possible outcomes of comparisons of Q_ST and F_ST (Q_ST > F_ST, Q_ST = F_ST, Q_ST < F_ST) is associated with an inference (diversifying selection, genetic drift, uniform selection, respectively). However, published empirical and theoretical studies have focused on the Q_ST > F_ST outcome. We believe that this reflects the absence of a straightforward biological interpretation of the Q_ST < F_ST pattern. We here report recent evidence of this neglected evolutionary pattern, provide guidelines to its interpretation as either a canalization phenomenon or a consequence of uniform selection and discuss the significant importance this issue will have for the area of evolutionary biology.     

Population- and sociogenetic structure of the leaf-cutter ant <Emphasis Type="Italic">Atta colombica</Emphasis> (Formicidae,Myrmicinae)

Relatedness and genetic variability in colonies of social insects are strongly influenced by the number of queens present and the number of matings per queen, but also by the genetic variability in the population. Thus, multiple paternity will enhance within-colony genetic variability more strongly when the males a queen mates with are unrelated. To study the kin-structure within colonies of the leaf-cutter ant Atta colombica and the population structure of this species around Barro Colorado Island, Panama, we developed five polymorphic microsatellite loci with a range of three to 17 alleles in At. colombica, all of which cross-amplify in other higher attines as well. The average effective mating frequency calculated from four-locus microsatellite genotypes was 1.89 ± 0.12 (harmonic mean ± SE) and thus slightly lower than the average observed mating frequency of 2.50 ± 0.11 (arithmetic mean ± SE) over the 55 colonies studied, confirming former studies that utilized fewer loci. The discrepancy between observed mating frequency and effective mating frequency is most probably due to paternity skew within colonies. The study population proved to be genetically diverse and in Hardy-Weinberg equilibrium, suggesting random mating within the study area. No population substructure was observed, neither considering nuclear (global F _ST = 0.011 ± 0.003 SE) nor mitochondrial markers (mean Φ_ST = 0.008). Consequently, gene flow is obviously promoted by both sexes across the range investigated here. Thus, multiple mating and long-distance dispersal appear to be two interconnected behavioural mechanisms to create and maintain genetic diversity in At. colombica. The advantages of this system are partly offset by paternity skew and the non-zero relatedness among colony fathers found in the study population. Received 18 March 2008; revised 14 July 2008; accepted 18 July 2008.     

Microgeographic structure of Anopheles gambiae in western Kenya based on mtDNA and microsatellite loci

The population genetic structure of the Anopheles gambiae in western Kenya was studied using length variation at five microsatellite loci and sequence variation in a 648-nt mtDNA fragment. Mosquitoes were collected from houses in villages spanning up to 50 km distance, The following questions were answered, (i) Are mosquitoes in a house more related genetically to each other than mosquitoes between houses? (ii) What degree of genetic differentiation occurs on these geographical scales? (iii) How consistent are the results obtained with both types of genetic markers? At the house level, no differentiation was detected by F_ST and R_ST, and the band sharing index test revealed no significant associations of alleles across loci. Likewise, indices of kinship based on mtDNA haplotypes in houses were even lower than in the pooled sample. Therefore, the hypothesis that mosquitoes in a house are more related genetically was rejected. At increasing geographical scales, microsatellite allele distributions were similar among all population samples and no subdivision of the gene pool was detected by F_ST or R_ST. Likewise, estimates of haplotype divergence of mtDNA between populations were not higher than the within population estimates, and mtDNA-based F_ST values were not significantly different from zero. That sequence variation in mtDNA provided matching results with microsatellite loci (while high genetic variation was observed in all loci), suggested that this pattern represents the whole genome. The minimum area associated with a deme of A. gambiae in western Kenya is therefore larger than 50 km in diameter.     

Rolling stones and stable homes: social structure,habitat diversity and population genetics of the Hawaiian spinner dolphin (Stenella longirostris)

Spinner dolphins (Stenella longirostris) exhibit different social behaviours at two regions in the Hawaiian Archipelago: off the high volcanic islands in the SE archipelago they form dynamic groups with ever‐changing membership, but in the low carbonate atolls in the NW archipelago they form long‐term stable groups. To determine whether these environmental and social differences influence population genetic structure, we surveyed spinner dolphins throughout the Hawaiian Archipelago with mtDNA control region sequences and 10 microsatellite loci (n = 505). F‐statistics, Bayesian cluster analyses, and assignment tests revealed population genetic separations between most islands, with less genetic structuring among the NW atolls than among the SE high islands. The populations with the most stable social structure (Midway and Kure Atolls) have the highest gene flow between populations (mtDNA Φ_ST < 0.001, P = 0.357; microsatellite F_ST = ?0.001; P = 0.597), and a population with dynamic groups and fluid social structure (the Kona Coast of the island of Hawai’i) has the lowest gene flow (mtDNA 0.042 < Φ_ST < 0.236, P < 0.05; microsatellite 0.016 < F_ST < 0.040, P < 0.001). We suggest that gene flow, dispersal, and social structure are influenced by the availability of habitat and resources at each island. Genetic comparisons to a South Pacific location (n = 16) indicate that Hawaiian populations are genetically depauperate and isolated from other Pacific locations (mtDNA 0.216 < F_ST < 0.643, P < 0.001; microsatellite 0.058 < F_ST < 0.090, P < 0.001); this isolation may also influence social and genetic structure within Hawai’i. Our results illustrate that genetic and social structure are flexible traits that can vary between even closely‐related populations.     

High degree of genetic differentiation in marine three‐spined sticklebacks (Gasterosteus aculeatus)

Populations of widespread marine organisms are typically characterized by a low degree of genetic differentiation in neutral genetic markers, but much less is known about differentiation in genes whose functional roles are associated with specific selection regimes. To uncover possible adaptive population divergence and heterogeneous genomic differentiation in marine three‐spined sticklebacks (Gasterosteus aculeatus), we used a candidate gene‐based genome‐scan approach to analyse variability in 138 microsatellite loci located within/close to (<6 kb) functionally important genes in samples collected from ten geographic locations. The degree of genetic differentiation in markers classified as neutral or under balancing selection—as determined with several outlier detection methods—was low (F_ST = 0.033 or 0.011, respectively), whereas average F_ST for directionally selected markers was significantly higher (F_ST = 0.097). Clustering analyses provided support for genomic and geographic heterogeneity in selection: six genetic clusters were identified based on allele frequency differences in the directionally selected loci, whereas four were identified with the neutral loci. Allelic variation in several loci exhibited significant associations with environmental variables, supporting the conjecture that temperature and salinity, but not optic conditions, are important drivers of adaptive divergence among populations. In general, these results suggest that in spite of the high degree of physical connectivity and gene flow as inferred from neutral marker genes, marine stickleback populations are strongly genetically structured in loci associated with functionally relevant genes.     

Population genetic structure and conservation of marbled murrelets (<Emphasis Type="Italic">Brachyramphus marmoratus</Emphasis>)

Marbled murrelets (Brachyramphus marmoratus) are coastal seabirds that nest from California to the Aleutian Islands. They are declining and considered threatened in several regions. We compared variation in the mitochondrial control region, four nuclear introns and three microsatellite loci among194 murrelets from throughout their range except Washington and Oregon. Significant population genetic structure was found: nine private control region haplotypes and three private intron alleles occurred at high frequency in the Aleutians and California; global estimates of F _ST or Φ_ST and most pairwise estimates involving the Aleutians and/or California were significant; and marked isolation-by-distance was found. Given the available samples, murrelets appear to comprise five genetic management units: (1) western Aleutian Islands, (2) central Aleutian Islands, (3) mainland Alaska and British Columbia, (4) northern California, and (5) central California.     

Unexpected cryptic species diversity in the widespread coral Seriatopora hystrix masks spatial‐genetic patterns of connectivity

Mounting evidence of cryptic species in a wide range of taxa highlights the need for careful analyses of population genetic data sets to unravel within‐species diversity from potential interspecies relationships. Here, we use microsatellite loci and hierarchical clustering analysis to investigate cryptic diversity in sympatric and allopatric (separated by 450 km) populations of the widespread coral Seriatopora hystrix on the Great Barrier Reef. Structure analyses delimited unique genetic clusters that were confirmed by phylogenetic and extensive population‐level analyses. Each of four sympatric yet distinct genetic clusters detected within S. hystrix demonstrated greater genetic cohesion across regional scales than between genetic clusters within regions (<10 km). Moreover, the magnitude of genetic differentiation between different clusters (>0.620 G”_ST) was similar to the difference between S. hystrix clusters and the congener S. caliendrum (mean G”_ST 0.720). Multiple lines of evidence, including differences in habitat specificity, mitochondrial identity, Symbiodinium associations and morphology, corroborate the nuclear genetic evidence that these distinct clusters constitute different species. Hierarchical clustering analysis combined with more traditional population genetic methods provides a powerful approach for delimiting species and should be regularly applied to ensure that ecological and evolutionary patterns interpreted for single species are not confounded by the presence of cryptic species.     

Fine‐scale spatial and temporal population genetics of Aedes japonicus,a new US mosquito,reveal multiple introductions

The newly introduced mosquito Aedes japonicus has expanded from its original range in Northeastern Asia to 29 US states (including Hawaii) plus Canada and northern Europe. Our objectives were to test an earlier hypothesis of multiple introductions of this species to the Northeastern US and evaluate putative temporal changes in genetic makeup. Using a panel of seven microsatellite loci, we confirmed the existence of two abundant genetic forms in specimens originally collected in 1999–2000 (F_ST value based on microsatellite data = 0.26) that matches the disjunctive distribution of mitochondrial haplotypes. To examine the distribution of the two genetic ‘types’ across Pennsylvania we created a fine‐scale genetic map of Ae. japonicus using 439 specimens collected from 54 Pennsylvania counties in 2002–2003. We also made direct comparisons between collections in 1999–2000 and new collections made in 2004–2005 obtained from the same areas in the northeastern US. We observed that the strong association between mtDNA haplotype and microsatellite signature seen in 1999–2000 had weakened significantly by 2002 across Pennsylvania, a trend continued to some extent in 2004–2005 in PA, NJ, and NY, indicating that once easily distinguishable separate introductions are merging. The two expanding genetic forms create a complex correlation between spatial and genetic distances. The existence of multiple introductions would be obscured without sampling early and across time with highly polymorphic molecular markers. Our results provide a high‐resolution analysis of the spatial and temporal dynamics of a newly introduced disease vector and argue that successive introductions may be a common pattern for invasive mosquitoes.     

Long‐distance geneflow and habitat specificity of the rock‐dwelling coppertail skink,Ctenotus taeniolatus

Rock boulders or ‘bush‐rocks’ provide essential habitat for many organisms and there has been interest in rehabilitating areas denuded of rock with artificial substitutes. We examine whether the density and size of bush rock influences the density of the coppertail skink (Ctenotus taeniolatus). The success of habitat rehabilitation is contingent on dispersal of rock‐dwelling organisms into areas that have been remediated. To gauge the likelihood of this we characterize geneflow of coppertail skinks among discrete patches of rocky habitat associated with ridge tops. We genotyped 154 individuals from seven localities at six microsatellite DNA loci and from a subset of these individuals we obtained sequence data from the mitochondrial ND4 region. Our field survey established that lizard density was positively associated with the availability of suitably sized bush‐rock (P < 0.001), highlighting the importance of maintaining this habitat element, or replacing it where it has been lost. Despite the presence of habitat features that might be presumed as barriers to dispersal for coppertail skinks, such as intervening gullies and dense vegetation, our genetic data demonstrated high levels of geneflow among rocky ridge tops. Levels of partitioning estimated by global F_ST were significant but low for both microsatellite (F_ST = 0.020) and mitochondrial data (F_ST = 0.113). Spatial autocorrelation of genotypic similarity supports our conclusion of regular longer‐distance geneflow, and we infer lower levels of dispersal in juveniles than in adults. This study suggests that dispersal of coppertail skinks can be sufficient to naturally colonize areas of restored habitat.     

Risso’s dolphins (<Emphasis Type="Italic">Grampus griseus</Emphasis>) in UK waters are differentiated from a population in the Mediterranean Sea and genetically less diverse

The Risso’s dolphin (Grampus griseus) has a worldwide distribution, but little is known about their population genetic structure. Local coastal populations are never known to be abundant, and are sometimes under anthropogenic impact. Therefore the question of regional differentiation by genetic drift and overall diversity levels is of conservation interest. Here we present preliminary data that clearly indicate genetic differentiation and lower genetic diversity of a population sampled in UK waters (primarily from the Western Isles, Scotland) compared to a Mediterranean sample. Significant differentiation was found in comparison with a sample from the Mediterranean for both microsatellite DNA markers (F _ST = 0.0296) and mtDNA sequence data (F _ST = 0.260; ϕ _ST = 0.542). Allelic diversity was lower in the UK for nearly all loci.