Estimates of Gene Flow in Drosophila Pseudoobscura Determined from Nucleotide Sequence Analysis of the Alcohol Dehydrogenase Region

The genetic structure of Drosophila pseudoobscura populations was inferred from a nucleotide sequence analysis of a 3.4-kb segment of the alcohol dehydrogenase (Adh) region. A total of 99 isochromosomal strains collected from 13 populations in North and South America were used to determine if any population departed from a neutral model and to estimate levels of gene flow between populations. This study also included the nucleotide sequences from two sibling species, D. persimilis and D. miranda. We estimated the neutral mutation parameter, 4N mu, in synonymous and noncoding sites for 17 subregions of Adh in each of nine populations with sample sizes greater than three. The nucleotide diversity data in the nine populations was tested for departures from an equilibrium neutral model with two statistical tests. The Tajima and the Hudson, Kreitman, Aguade tests showed that each population fails to reject a neutral model. Tests for genetic differentiation between populations fail to show any population substructure among the North American populations of D. pseudoobscura. The nucleotide diversity data is consistent with direct and indirect measures of gene flow that show extensive dispersal between populations of D. pseudoobscura.     

Genetic diversity of the endangered coastal violet <Emphasis Type="Italic">Viola grayi</Emphasis> Franchet et Savatier (Violaceae) and its genetic relationship to the species in subsection <Emphasis Type="Italic">Rostratae</Emphasis>

Viola grayi, a coastal violet, is found on sandy seashores in limited regions in Japan, but not on rocky sea cliffs or in inland areas. This stemmed violet is classified in the subsection Rostratae. Because of recent human activity on sandy seashores, this species is now recorded as endangered. The present status of this species was surveyed and its genetic diversity was analyzed using 17 newly developed simple sequence repeat markers. The results are compared with those for two commonly found inland violet species in the same subsection, V. grypoceras and V. kusanoana. The coastal violet populations showed markedly lower genetic diversity than those of the common species, V. grypoceras, whereas V. kusanoana showed intermediate genetic diversity. About a half of the total genetic variation of V. grayi is found among populations in analysis of molecular variance. In contrast, only less than 25% of the total variation is found among populations for the two common violets. These three species showed a remarkably high inbreeding coefficient, which indicates high inbreeding under natural mating conditions, although these species have both chasmogamous and cleistogamous flowers. In a population-based dendrogram, V. grayi was clustered in a single and concise group, whereas V. grypoceras and V. kusanoana were found in somewhat discrete positions. In the Bayesian analysis of genetic structure of the coastal violet, delta K was the highest at K = 7, and the seven clusters almost correspond to seven populations studied here. Implications of the conservation of this endangered coastal violet are presented.     

THE RELATIVE IMPORTANCE OF HISTORICAL EVENTS AND GENE FLOW ON THE POPULATION STRUCTURE OF A MEDITERRANEAN RAGWORT,SENECIO GALLICUS (ASTERACEAE)

Comparisons of cytoplasmic and nuclear diversity within and among natural plant populations have the potential to distinguish the relative influences of seed and pollen dispersal on contemporary gene flow, or alternatively, may permit inferences of the colonization history of a species via seed. We examined patterns of cpDNA and allozyme variation in Senecio gallicus, a diploid, annual plant that occurs in both coastal and ruderal inland areas of the Iberian Peninsula and southern France. The species appears to have a strong propensity for long-distance seed dispersal. Five cpDNA haplotypes were found by RFLP analysis among a sample of 111 individuals derived from 11 populations. Differences in haplotype frequencies across populations were most evident with respect to a dramatic increase in the frequency of a derived haplotype from coastal to inland localities. The level of cpDNA differentiation among populations within the inland group (θ₀ = 0.07) was significantly less than that seen within the coastal group (θ₀ = 0.41). In contrast, for allozymes, no significant difference in population structure was evident between collections from coastal and inland habitats. At the rangewide geographic scale, there was only a very weak association between inferred levels of gene flow and geographic distance for cpDNA, and no such association was found for allozymes. It appears that while seed movement in the species might be sufficiently great to disturb the pattern of isolation by distance for cpDNA, it cannot fully account for the nearly randomized spatial structure at polymorphic allozyme loci. It is suggested that isolation of populations in Atlantic-Mediterranean coastal refugia during previous glacial maxima, and the effects of subsequent colonization events in inland areas, have had an important effect on molding the present genetic structure of the species.     

Environmental and genetic determinants of reproduction in the house sparrow: a transplant experiment

A transplant experiment was carried out to examine whether genetic differentiation can explain geographical variation in the reproductive strategies of house sparrows Passer domesticus. Individuals from an inland and a coastal population in Central Norway were released on a small island, near the coastal area. No directional selection was found on any of the morphological characters from the release to the onset of breeding, but the proportion of the inland males that remained to start breeding on the island was smaller than that of the coastal males. The new environment influenced the time of egg laying which was, relative to the source populations, more delayed among the introduced inland females than among the coastal females. In 1992, chicks raised by inland females grew faster and were fed more frequently than chicks raised by coastal females. No difference was found between birds of inland and coastal origins in their breeding success and their relative number of surviving recruits. Transplanted parents from the inland fed their offspring more frequently than transplanted parents from the coastal area. This experiment shows that the plasticity of reproductive traits in combination with stochastic factors in the environment may lead to an establishment of introduced genes in small populations.     

Genetic variation within and among populations of Arabidopsis thaliana.

We investigated levels of nucleotide polymorphism within and among populations of the highly self-fertilizing Brassicaceous species, Arabidopsis thaliana. Four-cutter RFLP data were collected at one mitochondrial and three nuclear loci from 115 isolines representing 11 worldwide population collections, as well as from seven commonly used ecotypes. The collections include multiple populations from North America and Eurasia, as well as two pairs of collections from locally proximate sites, and thus allow a hierarchical geographic analysis of polymorphism. We found no variation at the mitochondrial locus Nad5 and very low levels of intrapopulation nucleotide diversity at Adh, Dhs1, and Gpa1. Interpopulation nucleotide diversity was also consistently low among the loci, averaging 0.0014. gst, a measure of population differentiation, was estimated to be 0.643. Interestingly, we found no association between geographical distance between populations and genetic distance. Most haplotypes have a worldwide distribution, suggesting a recent expansion of the species or long-distance gene flow. The low level of polymorphism found in this study is consistent with theoretical models of neutral mutations and background selection in highly self-fertilizing species.     

Genetic structure of coastal and inland populations of <Emphasis Type="Italic">Spergularia media</Emphasis> (L.) C. Presl (Caryophyllaceae) in Central Europe

In Central Europe, salt-influenced habitats are restricted mainly to the coastlines of the North Sea and the Baltic Sea. The few natural inland salt sites suffer from size reduction and loss in biodiversity, while anthropogenic salt sites around potash mining dumps experienced recent and massive de novo colonization by numerous halophytes. Our study aimed to elucidate the general patterns of gene flow among coastal and inland salt habitats. We used amplified fragment length polymorphisms to assess the genetic diversity and genetic structure of 18 European populations of the halophyte Spergularia media (Caryophyllaceae), sampled from inland and coastal salt sites of Germany, the Netherlands, Denmark, Austria, France and Italy. Estimates of genetic diversity on the population level were generally low, especially within inland salt habitats. Analyses of molecular variance showed comparatively strong differentiation among populations. Multivariate ordination (principal coordinate analysis) and a NeighborNet analysis revealed four distinct groups of populations that showed good correspondence to their geographic origins. A Bayesian analysis performed with the program Structure as well as high pairwise Φ _ST values supported the results of the phenetic analyses. The observed patterns of diversity and differentiation among inland populations of S. media are best explained by the isolated nature of suitable salt habitats, with concomitant reduction of gene flow to and among these sites. Our data support the hypothesis that the colonization of anthropogenic salt sites by S. media originated from natural inland habitats.     

Long‐term isolation of the coastal plant Calystegia soldanella (Convolvulaceae) in ancient freshwater Lake Biwa,Japan

Lake Biwa is an ancient freshwater lake that was formed approximately 4 Mya and harbours many coastal plants that commonly inhabit the seashore. We used chloroplast DNA haplotype analysis using two spacer sequences and simple sequence repeat (SSR) analysis using eight nuclear microsatellite markers to detect genomic signatures indicating long‐term isolation of inland populations of Calystegia soldanella in Lake Biwa from coastal populations. We used 348 samples from 63 populations for haplotype analysis and 478 samples from 27 populations for SSR analysis covering the inland and coastal distribution of the species. We detected seven haplotypes, and the distribution pattern of these haplotypes was geographically highly structured between Lake Biwa and the coast. Nuclear SSR analysis also supported genetic differentiation between Lake Biwa and coastal populations (analyses of molecular variance, 43%), and the grouping of Lake Biwa and coastal populations by a Neighbour‐joining tree. In addition, genetic diversity of the inland populations (mean H_E = 0.153) was significantly lower than that of coastal populations (mean H_E = 0.328). These results suggested that inland populations at Lake Biwa have been isolated from coastal populations for a very long time. The inland populations most likely experienced a bottleneck effect, resulting in sufficient in situ genetic divergence to clearly distinguish them from coastal populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 51–66.     

Geographical differentiation inferred from flavonoid content between coastal and freshwater populations of the coastal plant Lathyrus japonicus (Fabaceae)

Lake Biwa, one of the few ancient lakes in the world, harbors many coastal species that commonly inhabit seashores. The beach pea (Lathyrus japonicus) is a typical coastal species of this freshwater lake, and morphological and genetic differentiation between inland and coastal populations of this species have been reported. Inland and coastal habitats inflict distinct environmental stresses to plants, the latter imposing salt stress and high-light intensity, which leads to physiological differentiation. These abiotic stresses affect phenolic compounds, which play an important role in the response of plants to the toxic by-products of stress metabolism. We investigated physiological differentiation of phenolic compounds of the beach pea between inland and coastal habitats using high-performance liquid chromatography (HPLC) analysis. Flavonoid composition analyses revealed that patterns of flavonoid composition of inland populations at Lake Biwa were differentiated from those of coastal populations. All Lake Biwa individuals were fixed in the same flavonols glycosylated at 3- and 7-positions. In contrast, most coastal individuals contained flavonols glycosylated at 3-position alone, and these populations exhibited higher variation in flavonoid composition compared to among/within inland populations. Variation was likely lower in inland populations because of a bottleneck during landlocked periods, which is consistent with previous phylogeographic studies. A qualitative HPLC survey of flavonoid content revealed substantial variation among individuals regardless of locality. These results suggest that changes in the habitat environment may have led to beach pea acclimation via alteration of the quantity and quality of flavonoids.     

Contrasting patterns of nucleotide polymorphism at the alcohol dehydrogenase locus in the outcrossing Arabidopsis lyrata and the selfing Arabidopsis thaliana

Nucleotide variation at the alcohol dehydrogenase locus (Adh) was studied in the outcrossing Arabidopsis lyrata, a close relative of the selfing Arabidopsis thaliana. Overall, estimated nucleotide diversity in the North American ssp. lyrata and two European ssp. petraea populations was 0.0038, lower than the corresponding specieswide estimate for A. thaliana at the same set of nucleotide sites. The distribution of segregating sites across the gene differed between the two species. Estimated sequence diversity within an A. lyrata population with a large sample size (0.0023) was much higher than has previously been observed for A. thaliana. This North American population has an excess of sites at intermediate frequencies compared with neutral expectation (Tajima's D = 2.3, P < 0.005), suggestive of linked balancing selection or a recent population bottleneck. In contrast, an excess of rare polymorphisms has been found in A. thaliana. Polymorphism within A. lyrata and divergence from A. thaliana appear to be correlated across the Adh gene sequence. The geographic distribution of polymorphism was quite different from that of A. thaliana, for which earlier studies of several genes found low within-population nucleotide site polymorphism and no overall continental differentiation of variation despite large differences in site frequencies between local populations. Differences between the outcrossing A. lyrata and the selfing A. thaliana reflect the impact of differences in mating system and the influence of bottlenecks in A. thaliana during rapid colonization on DNA sequence polymorphism. The influence of additional variability-reducing mechanisms, such as background selection or hitchhiking, may not be discernible.     

Comparative studies of the population genetic structure of the Brachionus calyciflorus species complex from four inland lakes in Wuhu,China

To study how the population genetic structure in zooplankton respond to environmental conditions, using comparative limnology, the genetic diversity and genetic differentiation of the B. calyciflorus complex collected from four inland lakes in Wuhu City, China were investigated based on the 16S rRNA gene and nuDNA ITS sequences. The results displayed a high genetic diversity, and the nucleotide diversity of the 16S rRNA gene was higher than that of the ITS sequence. The phylogenetic analyses grouped the four populations into two cryptic species (Bc-JT and Bc-FL) with strong support. The two cryptic species were found in lakes with different trophic levels, demonstrating significant ecological specialization. The origins of clone TW12 were not consistent in the phylogenetic trees between two genetic markers, which might be attributed to the effects of male-mediated gene flow on the phylogenetic relationships of rotifers. The nucleotide diversity of the cryptic species Bc-JT was higher than that of Bc-FL, indicating that eutrophication might decrease the genetic diversity of cryptic species. The total phosphorus concentration in water bodies might be the most important factor affecting the genetic diversity of species.     

Genetic relationships of American alligator populations distributed across different ecological and geographic scales

Although much work has been conducted on coastal populations of the American alligator (Alligator mississippiensis), less is known about the population dynamics and genetic structure of populations of alligators confined to inland habitats. DNA microsatellite loci, derived from the American alligator, were used to investigate patterns of genetic variation within and between populations of alligators distributed at coastal and inland localities in Texas. These data were used to evaluate the genetic discreteness of different alligator stocks relative to their basic ecology at these sites. Observed mean heterozygosities across seven loci for both coastal and inland populations ranged from 0.50-0.61, with both inland and coastal populations revealing similar patterns of variation. Measures of F(st) revealed significant population differentiation among all populations; however, analyses of molecular variance (AMOVAs) failed to demonstrate any apparent geographic pattern relative to the population differentiation indicated by F(st) values. Each population contained unique alleles for at least one locus. Additionally, assignment tests based on the distribution of genotypes placed 76% of individuals to their source population. These genetic data suggest considerable subdivision among alligator populations, possibly influenced by demographic and life history differences as well as barriers to dispersal. These results have clear implications for management. Rather than managing alligators in Texas as a single panmictic population, translocation programs and harvest quotas should consider the ecological and genetic distinctiveness of local alligator populations.     

基于线粒体Cytb基因全序列的松江鲈群体遗传结构分析

对松江鲈(Trachidermus fasciatus Heckel)中国沿海7个群体和日本有明海群体的线粒体Cytb基因全序列进行了测定、分析。结果显示: 47个个体共检测到31个单倍型, 8个群体均呈现出较高的单倍型多样性(0.60-1.00)和较低的核苷酸多样性(0.0005-0.0041)的特点。AMOVA分析结果及单倍型邻接关系树和单倍型网络关系图均显示松江鲈分为中国和日本两个世系, 而中国世系的7个群体未呈现出明显的地理遗传结构。基于核苷酸Kimura双参数替代模型计算得出的中国和日本两个世系的净遗传距离, 再参照其他硬骨鱼类线粒体Cytb基因2%/Ma(百万年)的分歧速率, 推测松江鲈中日两个世系间分化时间约为41万年前。对中国世系进行群体历史动态分析, 中性检验结果均为负值且显著, 核苷酸不配对分布呈单峰型, 表明松江鲈中国世系曾发生过群体扩张, 其扩张时间大约为12万年前。       

沿海岛屿与内陆藓类植物遗传多样性和分化的比较研究——以真藓(Bryum argenteum Hedw.)为例

基于11个内陆居群和32个岛屿居群的252份标本,采用ISSR分子标记技术对真藓（Bryum argenteum Hedw.）的遗传多样性进行了研究。结果显示：岛屿与内陆居群间的遗传多样性差异显著,岛屿居群间的分化程度（G_st=0.453）大于内陆居群（G_st=0.387）,岛屿居群的遗传分化与地理来源间存在极显著相关性（r=0.478,n=175,P<0.001）。地理隔离效应是导致岛屿居群间遗传分化的重要因素。岛内居群间的遗传分化水平较低,仅有29.4%~29.7%的遗传多样性存在于居群间。聚类分析表明,43个居群可划分为10大类群,真藓遗传关系受地理因素和生境异质性的影响,水域隔离影响了真藓繁殖体在岛屿间的传播。     

Phylogeography of the Australian freshwater turtle Chelodina expansa reveals complex relationships among inland and coastal bioregions

We examined range‐wide mitochondrial phylogeographical structure in the riverine freshwater turtle Chelodina expansa to determine whether this species exhibits deep genetic divergence between coastal and inland hydrological provinces, as seen in co‐distributed freshwater taxa. We sequenced two mitochondrial loci, genealogical relationships were assessed using a network approach, and relationships among biogeographical regions were tested using analyses of molecular variance. Population history was evaluated using neutrality tests, indices of demographic expansion, and mismatch analyses. Twenty‐one haplotypes were recovered across two mitochondrial haplogroups separated by approximately 4% nucleotide divergence. The haplogroups have discrete geographical boundaries but only partially support a hypothesis of deep divergence between coastal and inland bioregions. The first haplogroup comprises populations from the inland Murray‐Darling Basin and from coastal catchments south of the Mary River in south‐east Queensland. The second haplogroup comprises populations from coastal catchments north of the Mary River. Cryptic phylogeographical barriers separating adjacent coastal populations are congruent with those demonstrated for other freshwater taxa and may result from the combined influences of the Conondale Range and alluvial deposits at the mouth of the Mary River. The findings of the present study demonstrate that freshwater taxa commonly display genetic differentiation within a biogeographical region where no boundaries have been recognized, highlighting the need to uncover cryptic microbiogeographical regions to aid conservation of freshwater biota. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 789–805.     

Landscape genetics and hierarchical genetic structure in Atlantic salmon: the interaction of gene flow and local adaptation

Disentangling evolutionary forces that may interact to determine the patterns of genetic differentiation within and among wild populations is a major challenge in evolutionary biology. The objective of this study was to assess the genetic structure and the potential influence of several ecological variables on the extent of genetic differentiation at multiple spatial scales in a widely distributed species, the Atlantic salmon, Salmo salar . A total of 2775 anadromous fish were sampled from 51 rivers along the North American Atlantic coast and were genotyped using 13 microsatellites. A Bayesian analysis clustered these populations into seven genetically and geographically distinct groups, characterized by different environmental and ecological factors, mainly temperature. These groups were also characterized by different extent of genetic differentiation among populations. Dispersal was relatively high and of the same magnitude within compared to among regional groups, which contrasted with the maintenance of a regional genetic structure. However, genetic differentiation was lower among populations exchanging similar rates of local as opposed to inter-regional migrants, over the same geographical scale. This raised the hypothesis that gene flow could be constrained by local adaptation at the regional scale. Both coastal distance and temperature regime were found to influence the observed genetic structure according to landscape genetic analyses. The influence of other factors such as latitude, river length and altitude, migration tactic, and stocking was not significant at any spatial scale. Overall, these results suggested that the interaction between gene flow and thermal regime adaptation mainly explained the hierarchical genetic structure observed among Atlantic salmon populations.     

Isolation and characterization of the genomic region from Drosophila kuntzei containing the Adh and Adhr genes

The nucleotide sequences of the Adh and Adhr genes of Drosophila kuntzei were derived from combined overlapping sequences of clones isolated from a genomic library and from cloned PCR and inverse-PCR fragments. Only a proximal promoter was detected upstream of the Adh gene, indicating that D. kuntzei Adh is regulated by a one-promoter system. Further upstream of the Adh structural gene, an adult enhancer region (AAE) was found that contains most of the regulatory sequences described for AAEs of other Drosophila species. Analysis of the ADH protein showed an amino acid change from valine to threonine in the active site at position 189 which is also found in D. funebris but is otherwise unique among DROSOPHILA: This difference alone may be responsible for the very low ADH activity found in this species and may cause a difference in substrate usage pattern. Codon bias in Adh and Adhr was comparable and found to be very low compared with other species. Phylogenetic analysis showed that D. kuntzei is closest related to D. funebris and D. immigrans. The time of divergence between D. kuntzei and D. funebris was estimated to be 14.2-20.2 Myr and that between D. kuntzei-D. funebris and D. immigrans to be 30.8-44.0 Myr. An analysis of the genetic variation in the Adh gene and upstream sequences of four European strains showed that this gene was highly variable. Overall nucleotide diversity (pi) was 0.0139, which is two times higher than that in D. melanogaster.     

Genetic and Ecotypic Differentiation in a Californian Plant Polyploid Complex (Grindelia,Asteraceae)

Studies of ecotypic differentiation in the California Floristic Province have contributed greatly to plant evolutionary biology since the pioneering work of Clausen, Keck, and Hiesey. The extent of gene flow and genetic differentiation across interfertile ecotypes that span major habitats in the California Floristic Province is understudied, however, and is important for understanding the prospects for local adaptation to evolve or persist in the face of potential gene flow across populations in different ecological settings. We used microsatellite data to examine local differentiation in one of these lineages, the Pacific Coast polyploid complex of the plant genus Grindelia (Asteraceae). We examined 439 individuals in 10 different populations. The plants grouped broadly into a coastal and an inland set of populations. The coastal group contained plants from salt marshes and coastal bluffs, as well as a population growing in a serpentine grassland close to the coast, while the inland group contained grassland plants. No evidence for hybridization was found at the single location where adjacent populations of the two groups were sampled. In addition to differentiation along ecotypic lines, there was also a strong signal of local differentiation, with the plants grouping strongly by population. The strength of local differentiation is consistent with the extensive morphological variation observed across populations and the history of taxonomic confusion in the group. The Pacific Clade of Grindelia and other young Californian plant groups warrant additional analysis of evolutionary divergence along the steep coast-to-inland climatic gradient, which has been associated with local adaptation and ecotype formation since the classic studies of Clausen, Keck, and Hiesey.     

沿海岛屿与内陆藓类植物遗传多样性和分化的比较研究——以真藓(Bryum argenteum Hedw.)为例

基于11个内陆居群和32个岛屿居群的252份标本,采用ISSR分子标记技术对真藓( Bryum argenteum Hedw.)的遗传多样性进行了研究。结果显示:岛屿与内陆居群间的遗传多样性差异显著,岛屿居群间的分化程度( G st = 0. 453)大于内陆居群( G st = 0. 387),岛屿居群的遗传分化与地理来源间存在极显著相关性( r = 0. 478, n = 175, P < 0. 001)。地理隔离效应是导致岛屿居群间遗传分化的重要因素。岛内居群间的遗传分化水平较低,仅有29. 4%~ 29. 7%的遗传多样性存在于居群间。聚类分析表明,43个居群可划分为10大类群,真藓遗传关系受地理因素和生境异质性的影响,水域隔离影响了真藓繁殖体在岛屿间的传播。     

陕西省林麝mtDNA D-loop区序列结构和种群遗传多样性

林麝(Moschus berezovskii)曾广泛分布于中国,由于盗猎和栖息地缩小,秦岭地区野生种群数量迅速下降,圈养繁殖种群已成立了几十年,但大多数圈养种群的遗传背景不清,种群规模增长非常缓慢。为了给这一物种的保护和管理提供有用的信息,调查了陕西省林麝1个圈养种群3个野生种群线粒体DNA(mt DNA)D-Loop 632 bp片段的遗传多样性和种群结构。在69个个体中其碱基组成为A+T的平均含量63.2%高于G+C含量36.8%,共检测到变异位点171个(约占总位点数的27.05%)。核苷酸多样性(Pi)为0.04424,平均核苷酸差异数(K)为19.908。69个个体分属32个单倍型,单倍型间的平均遗传距离(P)为0.070。32个单倍型构建的NJ系统树聚为3个分支,4个林麝群体中的单倍型是随机分布的。4个群体的平均遗传距离为0.043(标准误SE为0.005),凤县养殖场群体与留坝和陇县群体的亲缘关系较远。单倍型间的平均遗传距离为0.043,可见其遗传分化尚未达到种群分化的水平。结果表明,陕西省林麝群体mt DNA D-loop区序列存在着较丰富的变异和遗传多样性,凤县野生群体和凤县养殖场群体的核苷酸多样性和单倍型多样较高,养殖场种群没有出现近亲繁殖及遗传多样性下降的情况。凤县野生群体和凤县养殖场群体两者遗传分化较小,存在着较高的基因流水平。     

Mitochondrial DNA diversity in Atherina boyeri populations as determined by RFLP analysis of three mtDNA segments

The genetic differentiation and the phylogenetic relationships of eight Atherina boyeri Greek populations have been investigated at the mtDNA level. The populations studied are from two different lakes, a lagoon, the interface zone between the lagoon and the sea, and four marine sites. RFLP analysis of three mtDNA segments (12s rRNA, 16s rRNA and D-loop) amplified by PCR was used. Six, seven and eight restriction enzymes were found to have at least one recognition site at 12s rRNA, 16s rRNA and D-loop respectively. Twenty-one different haplotypes were detected among the populations studied. Several restriction patterns were revealed. These patterns can be used for the discrimination of the populations living in the sea ('marine' type populations) from the others inhabiting the lagoon and the lakes ('lagoon' type populations). The estimated net nucleotide sequence divergence between the populations examined ranged from 0 to 10.385%, while the Nst value of 0.92 indicates the existence of high interpopulation genetic differentiation. This high degree of differentiation detected between the 'lagoon' and 'marine' type populations makes the classification of these two types of populations as a single taxon questionable.