Mitochondrial DNA variation of the bocachico Prochilodus magdalenae (Characiformes,Prochilodontidae) in the Magdalena River Basin,Colombia

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Deep phylogeographic break among white croaker Pennahia argentata (Sciaenidae, Perciformes) populations in North-western Pacific

Abstract:   The Quaternary cold periods in the North-western Pacific are thought to have greatly influenced the genetic structures of marine species. One hundred and thirty-two individuals of white croaker Pennahia argentata were sampled from 12 localities throughout its distribution range to estimate the demographic history and genetic structure based on mitochondrial DNA cytochrome b gene and control region sequences. Two distinct clades with net genetic divergence of 3% in the control region were detected, one in Chinese coastal waters and the other in Japanese coastal waters. These clades may have been isolated and diverged during Pleistocene low sea levels. Nucleotide diversity was much higher in the Chinese clade than in the Japanese clade. The demographic history of the two clades was examined using neutrality tests and mismatch analyses, and the results indicated Pleistocene population expansion in both clades. Molecular variance and pairwise F _ST analyses revealed significant differentiation between two Japanese populations and lack of genetic structure in the Chinese populations. The significant geographic structure in white croaker suggests a low level of dispersal in this species. The lack of phylogeographic structure in Chinese coastal waters may reflect a recent range expansion after the last glacial maximum and insufficient time to attain migration-drift equilibrium.     

基于线粒体控制区的江苏湖鲚群体遗传多样性和遗传结构分析#br#

为掌握江苏省重要湖泊湖鲚(Coilia nasus taihuensis)群体的遗传多样性和遗传结构,利用线粒体控制区(D-loop)全序列分析了6个湖泊(太湖、滆湖、高邮湖、白马湖、洪泽湖和骆马湖)湖鲚野生群体的遗传多样性水平和群体分化情况。结果表明,6个群体共214尾样本的D-loop序列中,共发现103个变异位点,92种单倍型。6个群体的单倍型多样性为0.726~0.951,核苷酸多样性为0.00552~0.01036,6个群体整体的单倍型和核苷酸多样性分别为0.857和0.00729,表明湖鲚群体的遗传多样性较高,且符合高单倍型多样性和低核苷酸多样性特点。分子方差分析(AMOVA)结果表明,群体间变异百分比为6.20%,群体内变异百分比为93.80%,说明遗传变异主要来自群体内部。群体总的遗传分化系数(F_st)为0.06199(P<0.01),两两群体间的F_st显示,滆湖群体与其他群体间存在极显著的遗传分化(P<0.001),而其他群体间无显著分化(P>0.05)。单倍型分子系统进化树和网络进化图显示,6个群体的单倍型形成了2个谱系,但谱系组成与群体地理分布无相关性。中性检验分析结果显示,湖鲚群体进化过程中经历过种群扩张,扩张时间大约发生在0.089~0.160百万年前。研究结果表明,湖鲚群体具有较高的遗传多样性,滆湖群体与其他群体具有极显著的遗传分化,且拥有多个独享单倍型,应将滆湖群体单独作为一个管理单位,其他5个群体作为一个整体进行管理和利用。     

Genetic population structure of the Pacific bluefin tuna Thunnus orientalis and the yellowfin tuna Thunnus albacares in the North Pacific Ocean

The genetic population structure of the Pacific bluefin tuna (PBF) Thunnus orientalis and the yellowfin tuna (YFT) T. albacares in the North Pacific Ocean was investigated. The polymorphism of microsatellite (SSR) loci and sequences of mitochondrial DNA control region (mtCR) were analyzed for 71 samples of PBF from Japan and Mexico and 45 samples of YFT from Japan and Panama. In the SSR analyses, both single-locus (?0.010 to 0.008 in PBF and ?0.023 to 0.020 in YFT) and global multilocus (0.003 in PBF and ?0.002 in YFT) F _ST values among the geographic populations were low and not significant in these species. In the mtCR analyses, neither the neighbor-joining tree nor the minimum spanning network showed genetic differentiation among the geographic populations in each species. The pairwise F _ST values among the geographic populations of them (?0.005 in PBF and ?0.020 to ?0.014 in YFT) were low and not significant. Our SSR and mtCR data suggested that genetic differentiations were not evident among the eastern and western populations in the North Pacific Ocean either in PBF or in YFT. Mismatch distributions, demographic parameters, and neutrality tests suggested that sudden population expansion of PBF and YFT in the North Pacific Ocean occurred 628,000–731,000 and 450,000–525,000 years ago, respectively.     

Genetic population structure of the bigeye tuna Thunnus obesus in the central Pacific Ocean based on mtDNA Cytb sequences

Bigeye tuna Thunnus obesus is considered an important fishery species around the world. There is no adequate genetic data available for the T. obesus population. Polymorphism of sequence variations in mitochondrial Cytb genes were assessed to explore the level of genetic variability and differentiation among eight populations of T. obesus sampled from the central Pacific Ocean. Overall, a total of 44 mtDNA haplotypes and 26 variable sites were detected in the 686 bp segment of mtDNA Cytb gene. Nucleotide diversity ranged from 0.17 to 0.27 % and the haplotype diversity ranged from 0.604 to 0.793. An analysis of molecular variance (AMOVA) test of bigeye tuna revealed that 99.38 % of the genetic variation occurred within populations. Both the maximum likelihood tree and the haplotype network indicated that two lineages of bigeye tuna coexisted in the central Pacific Ocean. Hierarchical AMOVA tests and pairwise analysis revealed no geographical isolation among haplotypes within the two lineages. High Nm values from this investigation indicated high rates of gene flow between the two sampling regions. Furthermore, tests of neutrality and mismatch distribution suggested that T. obesus might have experienced a population expansion, one that possibly occurred 110,000 years ago. Our study firstly unraveled the population genetic structure of the T. obesus in the central Pacific Ocean, and addressed the related fishery management issues including fishery stock identification, management, and conservation.     

Larval population structure of Engraulis encrasicolus in the Strait of Sicily as revealed by morphometric and genetic analysis

In order to investigate the larval population structure, specimens of Engraulis encrasicolus larvae from five different locations in the Strait of Sicily were analyzed by means of otolith readings, morphometric and genetic techniques. The distribution of age in day, identified by means of the otolith readings and associated with the oceanographic parameters, was useful to identify possible spawning areas and transport dynamics. The presence of more than one spawning area suggested the possibility that two or more sub‐populations may co‐exist in the study area. The morphometric characteristics were more adequate than genetic parameters to discriminate the different larval groups. The most relevant variables for the separation were the mouth length (ML) and the body diameter (BD). The population structure by means of genetic data reported the presence of two phylogroups co‐occurring among samples in each sampling locations specimens. The pattern of genetic divergence among anchovy larvae in the Strait of Sicily was congruent with previous studies conducted on adult populations present in other Mediterranean areas with different molecular markers. The habitat‐specific nature of the morphological variation and the lack of corresponding genetic variation among larvae from the different locations suggested that the observed differences in morphology could be linked to environmental parameters. The body form differences among different larvae samples could reflect the nutritional status of larvae. In fact, these differences were found among anchovy larvae collected in areas with different oxygen and fluorescence, which is an index of primary productivity and is linked to the availability of food for anchovy larvae.     

基于线粒体COⅠ基因序列的中国沿海缘边银鲈遗传多样性分析#br#

为了解中国沿海缘边银鲈(Gerres limbatus)的遗传背景,分析了9个地理群体140条样本线粒体细胞色素氧化酶Ⅰ(cytochrome oxidase subunitⅠ,COⅠ)基因5′端652 bp序列。结果发现14个变异位点,13个单倍型,其中有9个独有单倍型和4个共享单倍型,整体单倍型和核苷酸多样性都较低(H_d=0.276±0.050,π=0.0005±0.0001)。琼州海峡以东海域的遗传多样性(H_d=0.338~0.456,π=0.0006~0.0011)高于琼州海峡以西北部湾海区(H_d=0~0.295,π=0~0.0005)。单倍型网络图未出现明显谱系结构和地理结构。群体遗传分化系数F_st显示,硇洲群体与其他群体间出现不显著的中低度遗传分化(F_st=0.0773~0.1696,P>0.05),其他群体间分化不明显(F_st=-0.0415~0.0612,P>0.05),总体上群体间分化程度都不高。AMOVA分析显示,遗传变异绝大部分(95%以上)来源于群体内。中性检验结果显示,群体总体的Tajima’s D(-2.2549)和Fu’s F_s(-16.4725)结果均为显著性负值(P<0.01),核苷酸错配图呈现较为明显单峰,单倍型网络图呈典型星状结构,表明缘边银鲈历史上存在过种群扩张,扩张时期约为距今0.1304~0.0435百万年。由于总体单倍型多样性小于0.5,核苷酸多样性小于0.005,推测中国缘边银鲈种群曾经历过较为严重的瓶颈效应。宁德、硇洲群体的核苷酸多样性相对较高,应优先保护。北部湾各群体遗传多样性极低,需要采取措施避免遗传多样性下降。     

长江口及邻近海域4个不同地理群体凤鲚矢耳石形态差异

为探明相邻海域凤鲚（Coilia mystus）群体间的差异性,分别采集江苏吕四（吕四群体）、上海崇明（崇明群体）、浙江舟山（舟山群体）和浙江温州（温州群体）邻近海域的凤鲚共240尾。以凤鲚矢耳石为研究对象,利用耳石测量法和耳石框架法获得21个测量参数,通过公式转化为20个形态指标数据,并进行多元统计分析。非参数检验显示4个群体间14个形态指标具有显著性差异（P<0.05）;应用主成分分析构建了7个反映耳石形态特征的主成分,累计贡献率为81.79%,结果显示不同群体耳石的整体形态相似,各群体间的耳石形态差异主要体现在局部的框架形态指标;利用贡献率最大的9个形态指标构建了4个群体的判别方程,温州群体的判别准确率最高,为96.7%,其次是崇明群体（66.7%）、吕四群体（60.0%）和舟山群体（58.3%）;聚类分析表明崇明和舟山群体距离最近,其次为吕四群体,与温州群体距离最远。结果表明,崇明、舟山和吕四群体间矢耳石形态差异较小,而温州群体与这3个群体的差异最大,可单独确立为一个生态群体。可见,短距离洄游性凤鲚不同群体间耳石形态差异大小与群体地理阻隔程度相关。     

基于mtDNACytb基因序列的我国不同水系野生鲇种群遗传多样性与种群历史分析

为进一步了解鲇这一广布种的遗传多样性与种群遗传结构,阐明该经济鱼类的种群历史动态,本研究对我国长江(上游、中游)、珠江、福建、海南、辽河地区的野生鲇样本进行mtDNA Cytb基因序列测定与种群遗传多样性和遗传结构分析。结果显示,在所分析的216个序列样本中,共检测出78个单倍型,其中Hap_45在鲇不同群体中分布最为广泛;鲇总群体具有较高的单倍型多样性(Hd=0.948±0.009)和核酸多样性(Pi=0.017 99±0.000 55),暗示了其自然种群数量的相对稳定;单倍型系统发育与网络关系图分析显示,78种单倍型被分为4个分支,且不同单倍型分布相对集中,划分为4个谱系。中性检验与错配分析表明,不同水系野生鲇种群(4个谱系)在约晚更新世时期(0.04~0.05百万年)经历过近期种群扩张事件。     

华南6水系与澜沧江-湄公河攀鲈线粒体ND2基因的遗传多样性分析

测定了中国华南6水系及澜沧江(云南勐腊)-湄公河流域(柬埔寨洞里萨湖)的125尾攀鲈(Anabas testudineus)线粒体部分ND2基因1 010 bp序列,分析发现39个变异位点和12个单倍型,总遗传多样性较低(h=0.369,π=0.003 8),推测可能经历过严重的瓶颈效应;中国攀鲈群体遗传多样性更低(h=0.282,π=0.000 4),处于边缘区的中国攀鲈群体是造成低遗传多样性的主要原因。在单倍型网络图中柬埔寨和中国攀鲈各自聚类,具有明显地理结构和谱系结构,推测地质运动和气候变化导致基因交流受阻所致。核苷酸错配图和中性检验表明中国群体经历过种群扩张,时间约为(5.94~4.13)万年前。华南水系群体间基因交流通畅,不存在明显分化;但与云南澜沧江群体间分化大而显著(FST=0.775,P0.01),AMOVA分析显示变异主要来自组群间(77.41%),推测二者分化时间约为(4.0~2.8)万年前,云南群体受末次冰期的影响,基因交流受阻而出现分化。中国群体和柬埔寨群体可作为2个管理单位进行保护;就中国群体而言,韩江水系群体遗传多样性最高,建议优先保护;澜沧江与华南水系间群体分化显著且遗传多样性极低,建议对澜沧江水系群体进行保护,以避免种质资源灭绝。     

Population genetic structure and differential selection in mussel Mytilus chilensis

This study examines the genetic connectivity between natural banks of Chilean mussel, Mytilus chilensis, located in Reloncaví Fjord. This sector is the principal source of seed for commercial farming and has the second‐largest aquaculture production volume in the country. The objects of this work are as follows: (1) to estimate the degree of connectivity between patches (microscale) located in the intertidal/subtidal zones, evaluating the presence of selection processes; and (2) to identify connectivity patterns by gene flow between subpopulations (mesoscale) in order to determine whether they all correspond to a common population (meta‐population). We analysed individuals distributed in the intertidal and subtidal zones of five locations by sequencing the mitochondrial cytochrome oxidase I gene and eight nuclear DNA microsatellite loci. Comparison of the two tidal zones presented differences revealed by the COI gene. The locations presented low genetic differentiation; however, differences were found in both markers at the mouth of the fjord. The differences between the tidal zones may result from differentiated natural selection processes between the intertidal and subtidal environments, with those in the intertidal subjected to greater selective pressure. There is effective connectivity between the locations, facilitated by the capacity for dispersion of the larvae and certain oceanographic processes, which would also explain the differences observed in the location at the mouth of the fjord. Because these banks sustain mussel aquaculture activity throughout the country, it is important to take measures to ensure their proper maintenance, observing all the indicators including their genetic diversity and structure.     

泉水鱼长江流域3个地理群体的遗传结构分析

水电开发造成的栖息地片段化可能导致鱼类群体间出现生殖隔离,对流域内重要经济和特有鱼类的群体遗传结构产生不利影响。为探究长江流域梯级水电开发可能对泉水鱼(Pseudogyrincheilus procheilus)群体产生的遗传影响,利用线粒体控制区对泉水鱼长江流域的乌江、金沙江、大渡河3个地理群体的遗传结构进行了分析。结果表明,乌江群体的遗传多样性最高,平均核苷酸差异(k)和核苷酸多样性指数(Pi)分别为4.893和0.00668;金沙江群体遗传多样性最小,k和Pi值分别为0.561和0.00077,大渡河群体遗传多样性与乌江群体相近。泉水鱼3个地理群体之间有显著的遗传分化。乌江群体和大渡河群体间的基因流大于金沙江群体和其他2个群体间的基因流,金沙江群体和其他2个群体间有着较远的遗传距离。Fu's Fs检验结果显示,3个地理群体的Fs值均为负值,核苷酸不配对分布均呈现明显的单峰型,揭示了各个泉水鱼群体均经历了明显的群体扩张。研究结果反映出泉水鱼遗传多样性较为丰富,金沙江群体和其他群体间显著的遗传差异可能是由于历史扩张而非自然选择造成的,泉水鱼存在区域化适应的地理群体,可预见梯级水电开发对其遗传结构的影响将十分有限。     

基于线粒体控制区序列的光裸方格星虫群体遗传多样性分析

为了解光裸方格星虫的群体遗传结构和种质资源状况,对北部湾海域光裸方格星虫6个地理野生群体(广西北海、湛江、钦州、防城港、海南儋州,以及越南海防)共93个个体的线粒体DNA(mtDNA)控制区序列进行分析。共检测到107个变异位点,定义了85个单倍型,序列对AT有明显的偏倚性,群体总的单倍体多样性(Hd)和核苷酸多样性(Pi)分别为0.998和0.018 89。单倍型邻接聚类树分析6个群体无明显分支,各单倍型分布于单倍型网络中介图中亦没有明显的地理分支。各群体间的遗传分化系数Fst值为–0.018 13~0.028 05,遗传分化极不明显,AMOVA分析显示光裸方格星虫的遗传差异主要来自群体内(99.74%)。中性检验Tajima’s D和Fu’s Fs值均为负值,核苷酸不配对分布图呈明显的单峰形,提示光裸方格星虫群体在历史上曾出现群体扩张,推算出扩张时间为距今171万年前。目前光裸方格星虫仍具有较高的遗传多样性,6个地理群体间无明显遗传分化,存在频繁的基因交流,推测种群在早更新世曾出现群体扩张。     

三疣梭子蟹4个野生群体形态差异分析

通过对鸭绿江口、莱州湾、海州湾、舟山4个野生群体的三疣梭子蟹(Portunus trituberculatus)14项生物学外部形态性状的测量,采用多元分析方法对其进行比较分析。聚类分析结果表明,海州湾、舟山2个群体形态最为接近,鸭绿江口和莱州湾2个群体形态较为接近。对样本所属群体进行判别分析,4个群体雌蟹的综合判别率为87.0%,其中海州湾最低,为80.0%;莱州湾最高为92%。4个群体雄蟹的综合判别率为80.8%,其中海州湾最低,为72.0%;鸭绿江口最高,为96%。并建立4个群体各自的判别函数公式。通过对16项形态比例参数进行单因素方差分析,找到了4个群体间存在显著差异的形态比例参数。3种分析结果均认为,4个群体三疣梭子蟹在形态上已产生一定程度的差异,但所有的差异均未达到亚种水平,需要多项参数综合判别才能将4个群体的三疣梭子蟹区分开。     

Genetic population structure of <Emphasis Type="Italic">Nibea albiflora</Emphasis> in Yellow Sea and East China Sea

ABSTRACT:   The population genetic structure and level of gene flow of Nibea albiflora from the Yellow Sea and the East China Sea were examined with a 479-bp segment of a mtDNA control region. In total, 65 samples were collected from three locations and 37 haplotypes were obtained. Mean haplotype diversity and nucleotide diversity for the three populations ranged from 0.9130 ± 0.0308 (Zhoushan) to 0.9926 ± 0.0230 (Xiamen), and from 0.0073 ± 0.0043 (Qingdao) to 0.0099 ± 0.0057 (Xiamen). Analysis of molecular variance and pairwise F _ST revealed little genetic structure between the Yellow Sea and the East China Sea in N. albiflora . But based on the exact test of differentiation, the null hypothesis that N. albiflora within the Yellow Sea and the East China Sea constitutes a panmictic mtDNA gene pool was rejected. This might be caused by the broad spawning areas but not by the Yangtze River outflow. Mismatch distribution revealed that N. albiflora has undergone population expansion, possibly before the last 85 000–170 000 years. The existence of high gene flow between stocks in the studied area was supported by our results. Annual migrations, larval drift in the ocean currents, and recent range expansion could be the reasons for little genetic structure in the studied area.     

Spatial differentiation in the eastern Pacific yellowfin tuna revealed by microsatellite variation

ABSTRACT:   Five eastern Pacific yellowfin tuna samples (four northern: 10–25°N, 95–130°W, and one southern: 16–18°S, 95–97°W), collected from fishing vessels between 1994 and 2002 were analyzed for variation at seven microsatellite loci to evaluate their spatial genetic homogeneity. Single-locus homogeneity exact tests revealed significant genetic differentiation caused by three of seven loci. Pairwise sample comparisons of multilocus allele-frequency homogeneity tests and subpopulation division ( F _ST), revealed significant differentiation in comparisons between north equatorial samples and the south equatorial sample. amova analysis among collections grouped as northern and southern populations separated by the equator in the eastern Pacific confirmed the differentiation observed. These results may be considered as preliminary evidence of the presence of discrete populations in the eastern Pacific yellowfin tuna. The possibility that the spatial differentiation observed corresponds to temporal variation or non-random sampling cannot be discarded. The genetic differences encountered need to be corroborated by increasing sample sizes, including temporal replicates, and by the use of an alternative marker.     

Genetic diversity,population structure,and historical demography of a highly vagile and human-impacted seabird in the Pacific Ocean: The red-tailed tropicbird,Phaethon rubricauda

1. Many seabird breeding colonies have recovered from heavy anthropogenic disturbance after conservation actions. The widely distributed red-tailed tropicbird, Phaethon rubricauda, was used as a model species to assess potential anthropogenic impacts on the genetic diversity of breeding colonies in the Pacific Ocean.
2. Cytochrome c oxidase subunit I and control region sequences analyses were conducted across the range of the species in the Pacific Ocean. The study sites were at islands without human-related disturbance (non-impacted islands) and with human-related disturbance (impacted islands). We hypothesized that (i) breeding colonies of the red-tailed tropicbird on impacted islands have lower genetic diversity compared with colonies on non-impacted islands, and (ii) breeding colonies of the red-tailed tropicbird show significant fine and broad-scale genetic structure across the Pacific Ocean. Bayesian skyline analyses were conducted to infer past changes in population sizes.
3. Genetic diversity was similar between impacted and non-impacted islands. There was significant broad-scale genetic structure among colonies separated by over 6,000 km, but a lack of significant fine-scale genetic structure within Australasia and Hawai'i, although a significant level of differentiation was found within Chile with Φ_ST analyses. Skyline analyses showed that effective population sizes remained relatively constant through time, but experienced either a slight decrease or the end of an expansion event through the last 1,000 years. These changes may be related to the arrival of humans on Pacific islands.
4. Impacted islands may have received immigrants from other relatively close islands, buffering the loss of genetic diversity. However, it is also possible that colonies have retained ancestral variation or that a large effective population size coupled with a long generation time (13 years) has prevented the loss of genetic diversity in human-impacted islands. Future research using higher-resolution markers is needed to resolve the population genetic structure of the red-tailed tropicbird in an ecological time-scale.

     

增殖放流对日本囊对虾群体遗传多样性的影响评估

为评估增殖放流对日本囊对虾(Marsupenaeus japonicus)群体遗传多样性的影响,本研究分析了放流前捕捞渔获群体(FLQ)、放流后捕捞渔获群体(FLH)以及放流虾苗群体(FLXX)的遗传多样性水平。3个群体共测定了135尾日本囊对虾的线粒体D-loop序列,经比对分析确定测得的序列长度为938 bp,检测到237个变异位点,177个简约信息位点,定义了100种单倍型。经分析,核苷酸多样性指数由大到小依次为FLQ、FLH、FLXX,单倍型多样性指数大小为FLQ=FLHFLXX。AMOVA分析表明FLQ和FLH群体的遗传分化系数(F_(st))值为0.00629,其小于0.05,表明变异主要来自于群体内,且群体间无分化。FLH与FLXX的F_(st)值为0.08151(P0.01),其大于0.05,表明遗传变异大多发生在群体内,但群体间呈低度分化。Tajima’s D和Fu’s Fs中性检验结果均为负值,表明这3个群体偏离了中性模式,可能受到群体扩张和自然选择的作用。综上所述,增殖放流前后日本囊对虾群体均保持较高的遗传多样性水平,变异不存在显著性差异,且群体间无分化,说明增殖放流是目前维持日本囊对虾种质资源量较为有效的措施之一。     

日本沼虾4种群的形态差异分析

4种群日本沼虾（Macrobrachium nipponensis）分别取白洪泽湖、太湖、广西3地大然水域和浙江德清人工养殖池塘。经在相似条件下暂养7个月后，运用3种多元分析方法对四者的10项形态比例参数进行比较研究。聚类分析结果表明，养殖种群与洪泽湖种群的形态最接近，而与太湖种群、广四种群的趋异程度逐渐增加。主成分分析结果显示，养殖种群的成体规格小于吲期的3个野生种群，而3个野生种群中又以洪泽湖种群的规格最小。以判别分析建立了4种群的判别函数，判别准确率分别为：76．7％-86．7％（P1）和74．3％～96．0％（P2），综合判别率81．7％。3种多冗分析结果均认为，4种群R本淄虾在形态上已产生一定程度的差异，且集中表现在头胸甲部的性状上，但所有差异均未达到业种水平，须有多项参数综合判别才能辨别；养殖种群的小型化与选种不当密切相关。     

Population structure of the migratory fish Prochilodus lineatus (Characiformes) from rio Grande basin (Brazil), an area fragmented by dams

• 1. Prochilodus lineatus (Prochilodontidae, Characiformes) is a migratory species of great economic importance both in fisheries and aquaculture that is found throughout the Jacuí, Paraíba do Sul, Paraná, Paraguay and Uruguay river basins in South America. Earlier population studies of P. lineatus in the rio Grande basin (Paraná basin) indicated the existence of a single population; however, the range of this species has been fragmented by the construction of several dams. Such dams modified the environmental conditions and could have constrained the reproductive migration of P. lineatus, possibly leading to changes in the population genetic structure.
• 2. In order to evaluate how genetic diversity is allocated in the rio Grande basin, 141 specimens of P. lineatus from eight collection sites were analysed using polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) with 15 restriction enzymes.
• 3. Forty‐six haplotypes were detected, and 70% of them are restricted. The mean genetic variability indexes (h = 0.7721 and π = 1.6%) were similar to those found in natural populations with a large effective size. Fst and Exact Test values indicated a lack of structuring among the samples, and the model of isolation by distance was tested and rejected.
• 4. The haplotype network indicated that this population of P. lineatus has been maintained as a single variable stock with some differences in the genetic composition (haplotypes) between samples. Indications of population expansion were detected, and this finding was supported by neutrality tests and mismatch distribution analyses.
• 5. The present study focused on regions between dams to serve as a parameter for further evaluations of genetic variability and the putative impact of dams and repopulation programmes in natural populations of P. lineatus. Copyright © 2011 John Wiley & Sons, Ltd.