Estimates Of Gene Flow Research Articles

Montane refugia predict population genetic structure in theLarge‐blotchedEnsatina salamander

Understanding the biotic consequences of Pleistocene range shifts and fragmentation remains a fundamental goal in historical biogeography and evolutionary biology. Here, we combine species distribution models (SDM) from the present and two late Quaternary time periods with multilocus genetic data (mitochondrial DNA and microsatellites) to evaluate the effect of climate-induced habitat shifts on population genetic structure in the Large-blotched Ensatina (Ensatina eschscholtzii klauberi), a plethodontid salamander endemic to middle and high-elevation conifer forest in the Transverse and Peninsular Ranges of southern California and northern Baja California. A composite SDM representing the range through time predicts two disjunct refugia, one in southern California encompassing the core of the species range and the other in the Sierra San Pedro Mártir of northern Baja California at the southern limit of the species range. Based on our spatial model, we would expect a pattern of high connectivity among populations within the northern refugium and, conversely, a pattern of isolation due to long-term persistence of the Sierra San Pedro Mártir population. Our genetic results are consistent with these predictions based on the hypothetical refugia in that (i) historical measures of population connectivity among stable areas are correlated with gene flow estimates; and (ii) there is strong geographical structure between separate refugia. These results provide evidence for the role of recent climatic change in shaping patterns of population persistence and connectivity within the Transverse and Peninsular Ranges, an evolutionary hotspot.

Molecular evidence supports hypervariability in Phytophthora colocasiae associated with leaf blight of taro

The oomycete Phytophthora colocasiae that causes taro leaf blight is the most devastating disease of taro and is widely distributed worldwide. Molecular and phenotypic techniques were employed for assessing and exploiting the genetic variability among four populations of P. colocasiae obtained from a fine spatial scale (multiple leaf blight lesions on single taro leaf). Phenotypic characters such as virulence, morphology and mating type showed no variation. ITS characterization revealed detectable polymorphism among isolates of P. colocasiae. The mean number of haplotypes (H), haplotype diversity (HD), nucleotide diversity (π), and nucleotide substitution rate (θ) among analyzed sequences were 6.75, 1.00, 0.069, and 0.088 respectively. High levels of inter and intra specific variation were detected by random amplified polymorphic DNA (RAPD) assays. Moderate genetic diversity (H = 0.2651) was observed among populations of P. colocasiae. Analysis of molecular variance (AMOVA) confirmed that most of the genetic variability was confined to within a population (63.54 %). The coefficient of genetic differentiation among populations (G ST ) was 0.2007 and estimates of gene flow (Nm) among populations was 1.991 migrants per generation. Cluster analysis using UPGMA revealed that individuals from the same population failed to cluster in one distinct group. The results of the study reveal considerable genetic diversity among and within populations of P. colocasiae obtained from fine spatial scale. The possible mechanisms and implications of this genetic variation are discussed.

After continents divide: comparative phylogeography of reef fishes from theRedSea andIndianOcean

AbstractAimTheRedSea is a biodiversity hotspot characterized by a unique marine fauna and high endemism. This sea began formingc. 24 million years ago with the separation of theAfrican andArabian plates, and has been characterized by periods of desiccation, hypersalinity and intermittent connection to theIndianOcean. We aim to evaluate the impact of these events on the genetic architecture of theRedSea reef fish fauna.LocationRedSea andWesternIndianOcean.MethodsWe surveyed seven reef fish species from theRedSea and adjacentIndianOcean using mitochondrialDNAcytochromecoxidase subunit I and cytochromebsequences. To assess genetic variation and evolutionary connectivity within and between these regions, we estimated haplotype diversity (h) and nucleotide diversity (π), reconstructed phylogenetic relationships among haplotypes, and estimated gene flow and time of population separation usingBayesian coalescent‐based methodology.ResultsOur analyses revealed a range of scenarios from shallow population structure to diagnostic differences that indicate evolutionary partitions and possible cryptic species. Conventional molecular clocks and coalescence analyses indicated time‐frames for divergence between these bodies of water ranging from 830,000 years to contemporary exchange or recent range expansion. Colonization routes were bidirectional, with some species moving from theIndianOcean to theRedSea compared with expansion out of theRedSea for other species.Main conclusionsWe conclude that: (1) at least someRedSea reef fauna survived multiple salinity crises; (2) endemism is higher in theRedSea than previously reported; and (3) theRedSea is an evolutionary incubator, occasionally contributing species to the adjacentIndianOcean. The latter two conclusions – elevated endemism and species export – indicate a need for enhanced conservation priorities for theRedSea.

Genetic differentiation among sexually compatible relatives of Brassica napus L.

Analysis of gene flow between Brassica napus L. and its sexually compatible relatives that could be found in the wild in Slovenia was performed by microsatellite analysis using fifteen selected primer pairs. Genotypes included in the study were obtained from the field survey of sexually compatible relatives of B. napus in natural habitats around Slovenia and from reference collections. Two different wild species of all the presented sexually compatible relatives of B. napus were found in Slovenia, B. rapa and Sinapis arvensis. The reference genotypes included varieties and wild forms from internal collections as marketable seeds or from gene banks. Reference genotypes were represented by the following species and subspecies: B. napus ssp. napobrassica, B. napus ssp. napus, B. nigra, B. oleracea, B. rapa ssp. oleifera, Diplotaxis muralis; D. tenuifolia, Raphanus raphanistrum, R. sativus, R. sativus var. oleiformis, Rapistrum rugosum, S. alba and S. arvensis. Estimation of gene flow described by average number of migrants was 0.72 followed by 0.20 migrants. Due to the observed gene migrations, genetic drift and selection, Hardy-Weinberg equilibrium was not met. The mean number of alleles over all loci was 16.9, the average polymorphic information content was 0.43. We found four highly divergent and polymorphic loci (Na12-C08, Na10-A08, Ni3-G04b and BRMS-050) at statistically significant level (p<0.05) of gene flow detected. Over all gene diversity intra-individual among populations (0.55) was lower than inter-individual among population (0.77). The results of genetic linkages based standard genetic distance and unweighted pair group method with arithmetic mean clustering method, generally divided the genotypes in three divergent groups. Similar results were obtained by principal coordinate analysis where three main groups were constructed according to three factors. A real number of genetic clusters demonstrated a clear separation between populations, where only one was comprised from genotypes from other origins. The 30.7 % out-crossing rate of B. rapa and S. arvensis populations from filed survey represents the potential for spontaneous inter-and intra-specific gene flow under Slovenian production area.

Genetic diversity of Pinus roxburghii sarg. collected from different Himalayan regions of India assessed by random amplified polymorphic DNA analysis

Present study was aimed at molecular genetic fingerprint profile of 15 genotypes of three populations of Pinus roxburghii Sarg. from Himalayan regions of India using random amplified polymorphic DNA (RAPD) based markers. Needles of Pinus roxburghii Sarg. were collected from Dharamshala, Himachal Pradesh (HP), Nainital, Uttarakhand (UK) and Darjeeling, West Bengal (WB) regions of India. The samples were subjected to DNA extraction and RAPD analysis using oligonucleotide purification cartridge (OPC) primers. Out of 15 primers tested, nine primers gave scorable bands. Altogether 48 bands were obtained, out of which 43 were found to be polymorphic. Number of amplified fragments with RAPD primers ranged from four to eight with the size of amplicon ranging from 500 to 7,000bp. Investigation of natural diversity at intraspecies level was performed with 15 genotypes. Forty-eight amplification products were scored by RAPD and showed 89.58% polymorphism with a mean intrapopulation genetic diversity (Hpop) of 0.2754. A significant inter- and intrapopulation diversity was observed, with the percentage of polymorphic loci (Pp) ranging from 50.09 to 70.83%, Shannon's information index (I) from 0.3262 to 0.4689 and Nei's gene diversity (h) from 0.2032 to 0.3335 with mean Nei's gene diversity 0.377 and the overall estimate of gene flow being (Nm) 1.3555. Unweighted pair-group method with arithmetic average (UPGMA) analysis based Dendrogram showed single cluster. The variation amongst the samples of the three ecological regions can be attributed to varied climatic conditions and may help in conservation/future cultivation of these species.

Contrasting Historical and Recent Gene Flow among African Buffalo Herds in the Caprivi Strip of Namibia

Population genetic structure is often used to infer population connectivity, but genetic structure may largely reflect historical rather than recent processes. We contrasted genetic structure with recent gene-flow estimates among 6 herds of African buffalo (Syncerus caffer) in the Caprivi Strip, Namibia, using 134 individuals genotyped at 10 microsatellite loci. We tested whether historical and recent gene flows were influenced by distance, potential barriers (rivers), or landscape resistance (distance from water). We also tested at what scales individuals were more related than expected by chance. Genetic structure across the Caprivi Strip was weak, indicating that historically, gene flow was strong and was not affected by distance, barriers, or landscape resistance. Our analysis of simulated data suggested that genetic structure would be unlikely to reflect human disturbances in the last 10-20 generations (75-150 years) because of slow predicted rates of genetic drift, but recent gene-flow estimates would be affected. Recent gene-flow estimates were not consistently affected by rivers or distance to water but showed that isolation by distance appears to be developing. Average relatedness estimates among individuals exceeded random expectations only within herds. We conclude that historically, African buffalo moved freely throughout the Caprivi Strip, whereas recent gene flow has been more restricted. Our findings support efforts to maintain the connectivity of buffalo herds across this region and demonstrate the utility of contrasting genetic inferences from different time scales.

Time matters: Some interesting properties of the population differentiation measures GST and D overlooked in the equilibrium perspective

AbstractGenetic differentiation of populations has been traditionally quantified by Wright's F‐statistics, typically assuming mutation–migration–drift equilibrium. However, the equilibrium perspective can be unrealistic as many natural populations are likely not yet in equilibrium. Therefore, understanding the behaviors, robustness, and power of the differentiation indexes under non‐equilibrium conditions has important implications. Here, we report an extensive examination of the properties of two major indexes GST and D under non‐equilibrium conditions by theoretical deduction under the infinite allele model (IAM) and simulation under the stepwise mutation model (SMM). Several properties of GST and D valid under both SMM and IAM, which have not been recognized under the equilibrium perspective, were unveiled. First, if gene flow is very weak (e.g., m < 10−4), GST, like D, also takes a fairly long time to reach equilibrium if mutation rate is not very large. When GST (D) is in equilibrium depends on when HS and HT are both in equilibrium. Under IAM and complete isolation, this is determined by the product of µ and t: GST will not approach equilibrium as long as µt ≪ 1. Under SMM, 10−4 appears to be the rough threshold migration rate; when m < 10−4, GST approaches equilibrium much slower and later than HS, whereas the opposite is true when m > 10−4. Second, contrary to the popular belief, µ ≪ m is neither an obligatory request for GST to be an effective differentiation measure nor a sufficient condition for using GST to estimate gene flow level (Nm), if GST is not yet approaching equilibrium. Third, under SMM (but not IAM) and complete isolation, when population size is large (e.g., ≥1000), mutation rate shows a great impact on GST but only a mild influence on D; hence D can be much less sensitive to mutation rate heterogeneity than GST in certain situations. Fourth, whatever the level of gene flow, drift plays a dominant role on GST, whereas gene flow appears to have a stronger influence on D when subpopulations exchange individuals (even only infrequently). Moreover, GST appears to have a larger power to detect recent population genetic events than D. Finally, it is the migration rate (m), not the absolute number of migrants (Nm), that determines the speed at which GST or D approaches equilibrium. These results suggest that GST and D bear unique revealing powers under non‐equilibrium conditions.

Spatial genetic structure and asymmetrical gene flow within the Pacific walrus

AbstractPacific walruses (Odobenus rosmarus divergens) occupying shelf waters of Pacific Arctic seas migrate during spring and summer from 3 breeding areas in the Bering Sea to form sexually segregated nonbreeding aggregations. We assessed genetic relationships among 2 putative breeding populations and 6 nonbreeding aggregations. Analyses of mitochondrial DNA (mtDNA) control region sequence data suggest that males are distinct among breeding populations (ΦST = 0.051), and between the eastern Chukchi and other nonbreeding aggregations (ΦST = 0.336–0.449). Nonbreeding female aggregations were genetically distinct across marker types (microsatellite FST = 0.019; mtDNA ΦST = 0.313), as was eastern Chukchi and all other nonbreeding aggregations (microsatellite FST = 0.019–0.035; mtDNA ΦST = 0.386–0.389). Gene flow estimates are asymmetrical from St. Lawrence Island into the southeastern Bering breeding population for both sexes. Partitioning of haplotype frequencies among breeding populations suggests that individuals exhibit some degree of philopatry, although weak. High levels of genetic differentiation among eastern Chukchi and all other nonbreeding aggregations, but considerably lower genetic differentiation between breeding populations, suggest that at least 1 genetically distinct breeding population remained unsampled. Limited genetic structure at microsatellite loci between assayed breeding areas can emerge from several processes, including male-mediated gene flow, or population admixture following a decrease in census size (i.e., due to commercial harvest during 1880–1950s) and subsequent recovery. Nevertheless, high levels of genetic diversity in the Pacific walrus, which withstood prolonged decreases in census numbers with little impact on neutral genetic diversity, may reflect resiliency in the face of past environmental challenges.

Divergent pattern of nuclear genetic diversity across the range of the Afromontane Prunus africana mirrors variable climate of African highlands

Afromontane forest ecosystems share a high similarity of plant and animal biodiversity, although they occur mainly on isolated mountain massifs throughout the continent. This resemblance has long provoked questions on former wider distribution of Afromontane forests. In this study Prunus africana (one of the character trees of Afromontane forests) is used as a model for understanding the biogeography of this vegetation zone. Thirty natural populations from nine African countries covering a large part of Afromontane regions were analysed using six nuclear microsatellites. Standard population genetic analysis as well as Bayesian and maximum likelihood models were used to infer genetic diversity, population differentiation, barriers to gene flow, and recent and all migration among populations. Prunus africana exhibits strong divergence among five main Afromontane regions: West Africa, East Africa west of the Eastern Rift Valley (ERV), East Africa east of the ERV, southern Africa and Madagascar. The strongest divergence was evident between Madagascar and continental Africa. Populations from West Africa showed high similarity with East African populations west of the ERV, whereas populations east of the ERV are closely related to populations of southern Africa, respectively. The observed patterns indicate divergent population history across the continent most likely associated to Pleistocene changes in climatic conditions. The high genetic similarity between populations of West Africa with population of East Africa west of the ERV is in agreement with faunistic and floristic patterns and provides further evidence for a historical migration route. Contrasting estimates of recent and historical gene flow indicate a shift of the main barrier to gene flow from the Lake Victoria basin to the ERV, highlighting the dynamic environmental and evolutionary history of the region.

Development of microsatellite markers for the endangered medicinal plant Launaea arborescens (Asteraceae)

Microsatellite loci were developed in Launaea arborescens, an endangered and medicinal Asteraceae species in North Africa, for further investigation of its conservation genetics. • We isolated and characterized 10 polymorphic and nine monomorphic microsatellite loci from L. arborescens using the protocol of Fast Isolation by AFLP of Sequences COntaining repeats (FIASCO). For the 10 polymorphic loci, the number of alleles detected per locus varied from two to six, and the observed and expected heterozygosities ranged from 0.000 to 0.833 and 0.059 to 0.713, respectively. • The polymorphic markers provide a useful tool for conservation genetics studies of L. arborescens, including analysis of mating system, estimating gene flow, and identifying discrete genetic units within the species.

Diversity and genetic structure in natural populations of Hancornia speciosa var. speciosa Gomes in northeastern Brazil

Hancornia speciosa Gomes is a fruit tree native from Brazil that belongs to Apocinaceae family, and is popularly known as Mangabeira. Its fruits are widely consumed raw or processed as fruit jam, juices and ice creams, which have made it a target of intense exploitation. The extractive activities and intense human activity on the environment of natural occurrence of H. speciosa has caused genetic erosion in the species and little is known about the ecology or genetic structure of natural populations. The objective of this research was the evaluation of the genetic diversity and genetic structure of H. speciosa var. speciosa. The genetic variability was assessed using 11 allozyme loci with a sample of 164 individuals distributed in six natural populations located in the States of Pernambuco and Alagoas, Northeastern Brazil. The results showed a high level of genetic diversity within the species (<img border=0 id="_x0000_i1026" src="/img/revistas/rbf/v34n4/a23img01.jpg" align=absmiddle>e= 0.36) seeing that the most of the genetic variability of H. speciosa var. speciosa is within its natural populations with low difference among populations ( <img border=0 id="_x0000_i1027" src="/img/revistas/rbf/v34n4/a23img02.jpg" align=absmiddle > or = 0.081). The inbreeding values within (<img border=0 id="_x0000_i1028" src="/img/revistas/rbf/v34n4/a23img03.jpg" align=absmiddle> = -0.555) and among populations (<img border=0 id="_x0000_i1029" src="/img/revistas/rbf/v34n4/a23img04.jpg" align=absmiddle> =-0.428) were low showing lacking of endogamy and a surplus of heterozygotes. The estimated gene flow ( <img border=0 id="_x0000_i1030" src="/img/revistas/rbf/v34n4/a23img05.jpg" align=absmiddle>m ) was high, ranging from 2.20 to 13.18, indicating to be enough to prevent the effects of genetic drift and genetic differentiation among populations. The multivariate analyses indicated that there is a relationship between genetic and geographical distances, which was confirmed by a spatial pattern analysis using Mantel test (r = 0.3598; p = 0.0920) with 1000 random permutations. The high genetic diversity index in these populations indicates potential for in situ genetic conservation.

Genetic variation of the Turnip mosaic virus population of Vietnam: A case study of founder, regional and local influences

Turnip mosaic virus (TuMV) is one of the most important viruses infecting a wide range of plant species, primarily from the family Brassicaceae. Thirty TuMV isolates were collected from Brassica and Raphanus plants in Vietnam during 2006–2008. Host reaction studies showed that many of the isolates belonged to Brassica/Raphanus (BR) host-infecting type. Sequence-based phylogenetic and population genetic analyses were made of the complete polyprotein gene sequences, and of four non-recombinogenic regions of those sequences (i.e. genes of the helper-component proteinase protein, protein 3, nuclear inclusion b protein and coat protein). These were used to assess the subpopulation differentiation and divergence between Vietnamese TuMV populations and those of nearby Asian countries. Nine inter- and intralineage recombination type patterns were identified in the genomes of the Vietnamese isolates, of which seven were novel. All the Vietnamese non-recombinant isolates fell into the world-B group of TuMV and clustered with Chinese isolates. The estimates of genetic differentiation and gene flow reveal that the TuMV populations of Vietnam, China and Japan are genetically linked but have clear local founder effects. This, the first population genetic study of a TuMV population in Southeast Asia, indicates the importance of such studies for providing the scientific basis of control strategies.

Comparative phylogeography in Fijian coral reef fishes: a multi-taxa approach towards marine reserve design.

Delineating barriers to connectivity is important in marine reserve design as they describe the strength and number of connections among a reserve's constituent parts, and ultimately help characterize the resilience of the system to perturbations at each node. Here we demonstrate the utility of multi-taxa phylogeography in the design of a system of marine protected areas within Fiji. Gathering mtDNA control region data from five species of coral reef fish in five genera and two families, we find a range of population structure patterns, from those experiencing little (Chrysiptera talboti, Halichoeres hortulanus, and Pomacentrus maafu), to moderate (Amphiprion barberi, Φst = 0.14 and Amblyglyphidodon orbicularis Φst = 0.05) barriers to dispersal. Furthermore estimates of gene flow over ecological time scales suggest species-specific, asymmetric migration among the regions within Fiji. The diversity among species-specific results underscores the limitations of generalizing from single-taxon studies, including the inability to differentiate between a species-specific result and a replication of concordant phylogeographic patterns, and suggests that greater taxonomic coverage results in greater resolution of community dynamics within Fiji. Our results indicate that the Fijian reefs should not be managed as a single unit, and that closely related species can express dramatically different levels of population connectivity.

Defining evolutionary boundaries across parapatric ecomorphs of Black Salamanders (Aneides flavipunctatus) with conservation implications

The accurate delimitation of evolutionary population units represents an important component in phylogeographic and conservation genetic studies. Here, we used a combined population assignment and historical demographic approach to study a complex of ecomorphologically distinctive populations of Black Salamanders (Aneides flavipunctatus) that are parapatrically distributed and meet at a three-way contact zone in north-western California. We used mitochondrial tree-based and multilocus clustering methods to evaluate a priori two- (Northern and Southern) and three (Northern, Coast and Inland) population hypotheses derived from previous studies. Mitochondrial results were consistent with the two- and three-population hypotheses, while the nDNA clustering results supported only the two-population hypothesis. Historical demographic analyses and mtDNA gene divergence estimates revealed that the Northern and Southern populations split during the Pliocene (2-5 Ma). Subdivision of the Southern population into Coast and Inland populations was estimated to be late Pleistocene (0.24 Ma), although our mtDNA results suggested a Pliocene divergence. Effective gene flow estimates (2N(e)m) suggest that either the two- or three-population hypotheses remain valid. However, our results unexpectedly revealed that the Northern population might instead represent two parapatric populations that separated nearly 4 Ma. These results are surprising because the Pliocene divergence between these ecomorphologically conservative forms is similar or older than for the ecomorphologically divergent Coast and Inland sister populations. We conclude that Black Salamanders in north-western California belong to at least three or four populations or species, and these all meet criteria for being Evolutionary Significant Units or 'ESUs' and therefore warrant conservation consideration.

Pollen and seed flow patterns of Carapa guianensis Aublet. (Meliaceae) in two types of Amazonian forest

Various factors affect spatial genetic structure in plant populations, including adult density and primary and secondary seed dispersal mechanisms. We evaluated pollen and seed dispersal distances and spatial genetic structure of Carapa guianensis Aublet. (Meliaceae) in occasionally inundated and terra firme forest environments that differed in tree densities and secondary seed dispersal agents. We used parentage analysis to obtain contemporary gene flow estimates and assessed the spatial genetic structure of adults and juveniles. Despite the higher density of adults (diameter at breast height ≥ 25 cm) and spatial aggregation in occasionally inundated forest, the average pollen dispersal distance was similar in both types of forest (195 ± 106 m in terra firme and 175 ± 87 m in occasionally inundated plots). Higher seed flow rates (36.7% of juveniles were from outside the plot) and distances (155 ± 84 m) were found in terra firme compared to the occasionally inundated plot (25.4% and 114 ± 69 m). There was a weak spatial genetic structure in juveniles and in terra firme adults. These results indicate that inundation may not have had a significant role in seed dispersal in the occasionally inundated plot, probably because of the higher levels of seedling mortality.

Coalescent and biophysical models of stepping‐stone gene flow in neritid snails

Marine species in the Indo-Pacific have ranges that can span thousands of kilometres, yet studies increasingly suggest that mean larval dispersal distances are less than historically assumed. Gene flow across these ranges must therefore rely to some extent on larval dispersal among intermediate 'stepping-stone' populations in combination with long-distance dispersal far beyond the mean of the dispersal kernel. We evaluate the strength of stepping-stone dynamics by employing a spatially explicit biophysical model of larval dispersal in the tropical Pacific to construct hypotheses for dispersal pathways. We evaluate these hypotheses with coalescent models of gene flow among high-island archipelagos in four neritid gastropod species. Two of the species live in the marine intertidal, while the other two are amphidromous, living in fresh water but retaining pelagic dispersal. Dispersal pathways predicted by the biophysical model were strongly favoured in 16 of 18 tests against alternate hypotheses. In regions where connectivity among high-island archipelagos was predicted as direct, there was no difference in gene flow between marine and amphidromous species. In regions where connectivity was predicted through stepping-stone atolls only accessible to marine species, gene flow estimates between high-island archipelagos were significantly higher in marine species. Moreover, one of the marine species showed a significant pattern of isolation by distance consistent with stepping-stone dynamics. While our results support stepping-stone dynamics in Indo-Pacific species, we also see evidence for nonequilibrium processes such as range expansions or rare long-distance dispersal events. This study couples population genetic and biophysical models to help to shed light on larval dispersal pathways.

Is dispersal guided by the environment? A comparison of interspecific gene flow estimates among differentiated regions of a newt hybrid zone

How frequently genes pass through a hybrid zone may be influenced by the environment. Accordingly, in long hybrid zones that span more than one environmental setting, different patterns may emerge. The varied conditions allow testing of hypotheses on dispersal as a function of the environment. We reconstruct the amount and direction of gene flow across a heterogeneous hybrid zone of two species of marbled newts (Triturus marmoratus and Triturus pygmaeus), in four widely separated areas of the Iberian Peninsula from one mitochondrial and three nuclear genes. The main variables associated with the position of the contact zone are precipitation, rivers, altitude and relief. In some sections of the contact zone, however, its position is not correlated with any environmental factor and is instead determined by the shortest geographical distance between fixed positions at either side (mountains in the East and river in the West). In areas where the position of the zone is stable, gene flow was bidirectional. External data show that T.pygmaeus has superseded T.marmoratus over a large area and here gene flow was unidirectional. The prediction that a major river would reduce gene flow was not confirmed.

Marker Based Estimation of Gene Flow in Tropical Rice Fields and Its Ecological Consequences

Pollen mediated gene flow is the most widely debated biosafety issue in case of genetically modified crop plants and is a primary determining factor for permitting their field release, particularly major food crops like rice. The alleged consequences of gene escape into wild/weedy relatives that coexist together with cultivated forms in rice fields in several countries is perceived to be a major concern. In an effort to estimate the gene flow in rice in a tropical environment, rice varieties stacked with three bacterial blight (BB) resistance alleles and a cytoplasmic male sterile (CMS) line were used as donors and receiver of pollen respectively and the pollen flow was tracked with molecular markers that are closely linked to BB resistance genes. The study could detect gene flow up to 20 m distance with environmental factors like temperature and humidity influencing it. The gene flow observed at longer distances than the 10 m distance suggested earlier advocate caution and suggests that all the relevant biosafety issues need to be addressed prior to release of GM rice in tropical countries where sympatric association of wild relatives with cultivated rice with frequent crop-weedy gene flow both ways is quite common.

Intracoastal shipping drives patterns of regional population expansion by an invasive marine invertebrate

Understanding the factors contributing to expansion of nonnative populations is a critical step toward accurate risk assessment and effective management of biological invasions. Nevertheless, few studies have attempted explicitly to test hypotheses regarding factors driving invasive spread by seeking correlations between patterns of vector movement and patterns of genetic connectivity. Herein, we describe such an attempt for the invasive tunicate Styela clava in the northeastern Pacific. We utilized microsatellite data to estimate gene flow between samples collected throughout the known range of S. clava in the region, and assessed correlation of these estimates with patterns of intracoastal commercial vessel traffic. Our results suggest that recent shipping patterns have contributed to the contemporary distribution of genetic variation. However, the analysis also indicates that other factors—including a complex invasion history and the influence of other vectors—have partially obscured genetic patterns associated with intracoastal population expansion.

A decade of amphibian population genetic studies: synthesis and recommendations

Amphibians are declining globally, and a comprehensive understanding of the spatial distribution of genetic diversity will inform conservation efforts. However, studies that estimate amphibian population genetic structure and gene flow have not yet been synthesized. Our search of literature from 2001 to 2010 yielded 552 amphibian population and landscape genetic studies, of which 139 explicitly estimated gene flow or genetic structure. We examined these works for general trends and conducted a meta-analysis of reported FST values. The majority of studies took place in temperate forests in North America and Europe, with no studies of caecilians and few studies of direct-developing species. Among landscape genetic studies, rivers, roads, and mountain ridges were the predominant barriers identified. Conservation status was the only factor that showed a significant relationship with FST, with the least concern IUCN status differing significantly from the near threatened (NT) status as well as from any combination of IUCN statuses that included NT. Recent technological advances will help researchers fill taxonomic and geographic research gaps, thereby facilitating management plans that address a greater diversity of amphibian species.