Local genetic structure in a clonal dioecious angiosperm

We used seven microsatellite loci to characterize genetic structure and clonal architecture at three different spatial scales (from meters to centimetres) of a Cymodocea nodosa population. C. nodosa exhibits both sexual reproduction and vegetative propagation by rhizome elongation. Seeds remain buried in the sediment nearby the mother plant in a dormant stage until germination. Seed dispersal potential is therefore expected to be extremely restricted. High clonal diversity (up to 67% of distinct genotypes) and a highly intermingled configuration of genets at different spatial scales were found. No significant differences in genetic structure were found among the three spatial scales, indicating that genetic diversity is evenly distributed along the meadow. Autocorrelation analyses of kinship estimates confirmed the absence of spatial clumping of genets at small spatial scale and the expectations of a very restricted seed dispersal (observed dispersal range 1-21 m) in this species.     

Within-population genetic structure and clonal diversity of a threatened endemic metallophyte, Viola calaminaria (Violaceae)

We studied the within-population genetic structure and the clonality extent of Viola calaminaria, a rare endemic species of calamine soils, by means of RAPD markers in two populations (one recent and one ancient) with expected harsh and heterogeneous heavy-metal stress. At a very local scale (0.2-3 m), clonal propagation was detected in both populations, but the levels of clonal diversity were high (number of genets/number of ramets sampled = 0.9 [recent] and 0.76 [ancient]) and the maximal observed extension of the clones was 0.4 m. This indicated that clonality is not, for the species, an important mode of propagation and that clonal growth cannot be interpreted as a strategy for propagating or perpetuating adapted genotypes under harsh ecological constraints. Spatial autocorrelations revealed a significant (P < 0.001) negative value of correlogram slope in the two populations even when a single individual per clone was considered (i.e., analysis at the genet level). We conclude that spatial genetic structure at a very local scale reflects limited gene flow due to restricted seed dispersal rather than variation in clonal pattern in response to environmental heterogeneity. At a larger scale (2-30 m), spatial autocorrelations revealed a positive (P < 0.001) correlation at < 3 m and a random pattern at larger distances for the two populations. This suggested a patchy distribution of the genetically linked individuals associated with a disrupted pattern at a longer distance probably due to gene flow by pollen dispersal and a seed bank effect. The implications for the conservation of V. calaminaria are discussed.     

Absence of isolation by distance patterns at the regional scale in the fungal plant pathogen Leptosphaeria maculans

Outcomes of host-pathogen coevolution are influenced by migration rates of the interacting species. Reduced gene flow with increasing spatial distance between populations leads to spatial genetic structure, as predicted by the isolation by distance (IBD) model. In wind-dispersed plant-pathogenic fungi, a significant spatial genetic structure is theoretically expected if local spore dispersal is more frequent than long-distance dispersal, but this remains to be documented by empirical data. For 29 populations of the oilseed rape fungus Leptosphaeria maculans sampled from two French regions, genetic structure was determined using eight minisatellite markers. Gene diversity (H = 0.62-0.70) and haplotypic richness (R = 0.96-1) were high in all populations. No linkage disequilibrium was detected between loci, suggesting the prevalence of panmictic sexual reproduction. Analysis of molecular variance showed that > 97% of genetic diversity was observed within populations. Genetic differentiation was low among populations (F(st) < 0.05). Although direct methods previously revealed short-distance dispersal for L. maculans, our findings of no correlation between genetic and geographic distances among populations illustrate that the IBD model does not account for dispersal of the fungus at the spatial scale we examined. These results indicate high gene flow among French populations of L. maculans, suggesting high dispersal rates and/or large effective population sizes, two characteristics giving the pathogen high evolutionary potential against the deployment of resistant oilseed rape cultivars.     

Clonal and fine-scale genetic structure in populations of a restricted Korean endemic, Hosta jonesii (Liliaceae) and the implications for conservation

BACKGROUND AND AIMS: In plant populations the magnitude of spatial genetic structure of apparent individuals (including clonal ramets) can be different from that of sexual individuals (genets). Thus, distinguishing the effects of clonal versus sexual individuals in population genetic analyses could provide important insights for evolutionary biology and conservation. To investigate the effects of clonal spread on the fine-scale spatial genetic structure within plant populations, Hosta jonesii (Liliaceae), an endemic species to Korea, was chosen as a study species. METHODS: Using allozymes as genetic markers, spatial autocorrelation analysis of ramets and of genets was conducted to quantify the spatial scale of clonal spread and genotype distribution in two populations of H. jonesii. KEY RESULTS: Join-count statistics revealed that most clones are significantly aggregated at < 3-m interplant distance. Spatial autocorrelation analysis of all individuals resulted in significantly higher Moran's I values at 0-3-m interplant distance than analyses of population samples in which clones were excluded. However, significant fine-scale genetic structure was still observed when clones were excluded. CONCLUSIONS: These results suggest that clones enhance the magnitude of spatial autocorrelation due to localized clonal spread. The significant fine-scale genetic structure detected in samples excluding clones is consistent with the biological and ecological traits exhibited by H. jonesii including bee pollination and limited seed dispersal. For conservation purposes, genetic diversity would be maximized in local populations of H. jonesii by collecting or preserving individuals that are spaced at least 5 m apart.     

Clonality strongly affects the spatial genetic structure of the nurse species Aechmea nudicaulis (L.) Griseb. (Bromeliaceae)

Aechmea nudicaulis is a clonal bromeliad common to the Brazilian Atlantic forest complex and is found abundantly in the sandy coastal plain vegetation (restinga) on the north coast of Rio de Janeiro state, Brazil. This restinga site is structured in vegetation islands, and the species plays a key role as a nurse plant, much favoured by its clonality. We studied the clonal structure and consequences of clonality on the population spatial genetic structure (SGS) of this species using six nuclear microsatellites. Spatial autocorrelation analysis was performed to study the effects of sexual and clonal reproduction on the dispersal of A. nudicaulis. Analyses were performed at the genet (i.e. excluding clonal repeats) and ramet levels. Genotypic richness was moderate (R = 0.32), mostly as a result of the dominance of a few clones. The spatial distribution of genets was moderately intermingled, the mean clone size was 4.9 clonal fragments per genet and the maximum clonal spread was 25 m. Expected heterozygosities were high and comparable with those found in other clonal plants. SGS analyses at the genet level revealed significantly restricted gene dispersal (Sp = 0.074), a strong SGS compared with other herbaceous species. The clonal subrange extended across 23 m where clonality had a significant effect on SGS. The restricted dispersal and SGS pattern in A. nudicaulis, coupled with high levels of genetic diversity, indicated a recruitment at windows of opportunity (RWO) strategy. Moreover, the spatial distribution of genetic variation and the habitat occupation pattern in A. nudicaulis were dependent not only on the intrinsic biological traits of the species (such as spacer size and mating system), but also on biotic interactions with neighbouring species that determined suitable habitats for germination and the establishment of new genets. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 329–342.     

Species diversity and population density affect genetic structure and gene dispersal in a subtropical understory shrub

Aims The dispersal of pollen and seeds is spatially restricted and may vary among plant populations because of varying biotic interactions, population histories or abiotic conditions. Because gene dispersal is spatially restricted, it will eventually result in the development of spatial genetic structure (SGS), which in turn can allow insights into gene dispersal processes. Here, we assessed the effect of habitat characteristics like population density and community structure on small-scale SGS and estimate historical gene dispersal at different spatial scales.Methods In a set of 12 populations of the subtropical understory shrub Ardisia crenata, we assessed genetic variation at 7 microsatellite loci within and among populations. We investigated small-scale genetic structure with spatial genetic autocorrelation statistics and heterogeneity tests and estimated gene dispersal distances based on population differentiation and on within-population SGS. SGS was related to habitat characteristics by multiple regression.Important findings The populations showed high genetic diversity (H e = 0.64) within populations and rather strong genetic differentiation (F ′ ST = 0.208) among populations, following an isolation-by-distance pattern, which suggests that populations are in gene flow–drift equilibrium. Significant SGS was present within populations (mean Sp = 0.027). Population density and species diversity had a joint effect on SGS with low population density and high species diversity leading to stronger small-scale SGS. Estimates of historical gene dispersal from between-population differentiation and from within-population SGS resulted in similar values between 4.8 and 22.9 m. The results indicate that local-ranged pollen dispersal and inefficient long-distance seed dispersal, both affected by population density and species diversity, contributed to the genetic population structure of the species. We suggest that SGS in shrubs is more similar to that of herbs than to trees and that in communities with high species diversity gene flow is more restricted than at low species diversity. This may represent a process that retards the development of a positive species diversity–genetic diversity relationship.     

Spatial genetic structure in populations of the terrestrial orchid Cephalanthera longibracteata (Orchidaceae)

Orchid seeds are unusual for being the smallest among flowering plants. These dust-like seeds are wind-borne and, thus, would seem to have the potential for long-distance dispersal (a common perception); this perception has led to a prediction of near-random spatial genetic structure within orchid populations. Mathematical models (e.g., simple ballistic model) for wind-dispersed seeds and wind-tunnel experiments, in contrast, indicate that most seeds of orchids should fall close to the maternal plant (<6 m), supporting a prediction of significant fine-scale genetic structure within populations. In reality we do not know much about seed dispersion in orchids. To determine which of these two predictions is more appropriate, Wright's F statistics and spatial autocorrelation analysis were used to examine the genetic structure within two adult populations of the terrestrial orchid Cephalanthera longibracteata (Orchidaceae) in southern Korea. In results comparable to those of other self-compatible, mixed-mating plant species, C. longibracteata populations exhibited low levels of genetic diversity (mean H(e) = 0.036) and a significant excess of homozygosity (mean F(IS) = 0.330), consistent with substantial inbreeding via selfing and/or mating among close relatives in a spatially structured population. Spatial autocorrelation analysis revealed significant positive genetic correlations among plants located <10 m, with relatedness at <3 m comparable to that expected for half sibs and first cousins. This genetic structure supports the prediction that the majority of seed dispersal occurs over distances of less than 10 m and is responsible for generating substantial overlap in seed shadows within C. longibracteata populations.     

Nitric oxide (NO): a key player in the senescence of Medicago truncatula root nodules

The ectomycorrhizal fungus Tricholoma populinum is host-specific with Populus species. T. populinum has wind-dispersed progagules and may be capable of long-distance dispersal. In this study, we tested the hypothesis of a panmictic population between Scandinavia and North America. DNA sequences from five nuclear loci were used to assess phylogeographic structure and nucleotide divergence between continents. Tricholoma populinum was composed of Scandinavian and North American lineages with complete absence of shared haplotypes and only one shared nucleotide mutation. Divergence of these lineages was estimated at approx. 1.7-1.0 million yr ago (Ma), which occurred after the estimated divergence of host species Populus tremula and Populus balsamifera/Populus trichocarpa at 5 Ma. Phylogeographic structure was not observed within Scandinavian or North American lineages of T. populinum. Intercontinental divergence appears to have resulted from either allopatric isolation; a recent, rare long-distance dispersal founding event followed by genetic drift; or the response in an obligate mycorrhizal fungus with a narrow host range to contractions and expansion of host distribution during glacial and interglacial episodes within continents. Understanding present genetic variation in populations is important for predicting how obligate symbiotic fungi will adapt to present and future changing climatic conditions.     

Clonal and spatial genetic structure in natural populations of Luohanguo (Siraitia grosvenorii), an economic species endemic to South China,as revealed by RAPD markers

Clonal growth is generally expected to have significant effects on the spatial genetic structure within populations. In this study, random amplified polymorphic DNA (RAPD) markers were used to reveal clonal and spatial genetic structure of four natural populations of Luohanguo (Siraitia grosvenorii), an economic vine species endemic to South China. A total of 351 ramets were assigned to 76 distinct multi-locus genotypes (i.e. genets), with the G/N varying from 0.121 to 0.350. No widespread genet was found across different populations. The clonal diversity (D) and evenness (E) ranged from 0.333 to 0.828 and from 0 to 0.741, respectively. While most genets consisted of fewer than five ramets, we observed some dominant genets that had much more (up to 69) ramets and spread over large areas. Spatial autocorrelation analyses revealed a spatial genetic structure (i.e. significant positive autocorrelation within 20 m and negative autocorrelation beyond 40 m) in one population, but not in other three populations with smaller population size. This study highlights the importance of clonal growth in shaping the spatial genetic structure in Luohanguo, which may have complex effects on the dynamics and evolution of its declining populations.     

Spatial distribution of ectomycorrhizal Basidiomycete Russula subsect. Foetentinae populations in a primary dipterocarp rainforest

The spatial distribution of basidiocarps of the ectomycorrhizal Basidiomycete Russula subsect. Foetentinae was assessed in a primary forest in the Western Ghats (India) dominated by the ectomycorrhizal tree species Vateria indica and Dipterocarpus indicus. Over a 7,700-m² sampling area, both trees and basidiocarps of Russula subsect. Foetentinae were mapped during the first month of the 2002 rainy season. First-order spatial analysis revealed that the distribution of the 45 collected carpophores was highly aggregated, with 60% of all basidiocarps located at a distance lower than 1 m from the nearest one. The genetic structure of the Russula subsect. Foetentinae population was studied by inter-simple sequence repeat polymorphism analysis using three primers. Eighteen of the 45 genotypes were represented by single basidiocarps. Twenty-seven basidiocarps were identified as belonging to 11 genets or separated ramets. Five genets were small, with diameters ranging from 0.5 to 5 m. The six others were large, with a diameter ranging from 31 m to a maximum measured distance of 70 m. In spite of the lack of data concerning the reproductive biology of this species, the presence of large genets suggests that mature stands may shelter well-spread underground mycelium, crucial for durable interaction with plant partner.     

Analysis of genetic structure of a Suillus grevillei population in a Larix kaempferi stand by polymorphism of inter-simple sequence repeat (ISSR)

Clones of ectomycorrhizal fungi can colonize new areas through production of vegetative mycelium or spore dispersal, but the relative importance of these processes in nature is not known. In this study, sporocarps of an ectomycorrhizal fungus, Suillus grevillei , were mapped and sampled from a Larix kaempferi stand at the foot of Mt Fuji. DNA was extracted directly from each sporocarp, and DNA polymorphism was analysed by polymerase chain reaction (PCR) amplification of inter-simple sequence repeat (ISSR) regions primed by (GTG)₅, (GCC)₅ and (GACA)₄. Different sensitivities to detect polymorphism were found among the three primers, with (GACA)₄ showing the highest sensitivity. Forty seven sporocarps were analysed by the three ISSR primers and divided into 34 genets based on combination of PCR fingerprints. In the population 28 genets were represented by individual sporocarps. In most cases, sporocarps grown in aggregation (within a circle of 50 cm diameter) showed some different ISSR band patterns. These results suggest that genets of S. grevillei at the test site are relatively small. The genetic similarities between the 34 genets were also calculated and similarity groups were determined by the criterion that all similarity F values of genets within a group were not <80%. In general, the genets within a similarity group located close to each other. The results of multiple different but highly related genets in a small area suggest that the population of S. grevillei in this stand is not spread and maintained by clonal mycelium extension but is reproduced by spore dispersal.     

Local genetic population structure in an endangered plant species, Silene tatarica (Caryophyllaceae)

Genetic substructuring in plant populations may evolve as a consequence of sampling events that occur when the population is founded or regenerated, or if gene dispersal by pollen and seeds is restricted within a population. Silene tatarica is an endangered, perennial plant species growing along periodically disturbed riverbanks in northern Finland. We investigated the mechanism behind the microspatial genetic structure of S. tatarica in four subpopulations using amplified fragment length polymorphism markers. Spatial autocorrelation revealed clear spatial genetic structure in each subpopulation, even though the pattern diminished in older subpopulations. Parentage analysis in an isolated island subpopulation indicated a very low level of selfing and avoidance of breeding between close relatives. The mean estimated pollen dispersal distance (24.10 m; SD = 10.5) was significantly longer and the mean seed dispersal distance (9.07 m; SD = 9.23) was considerably shorter than the mean distance between the individuals (19.20 m; SD = 13.80). The estimated indirect and direct estimates of neighbourhood sizes in this subpopulation were very similar, 32.1 and 37.6, respectively. Our results suggested that the local spatial genetic structure in S. tatarica was attributed merely to the isolation-by-distance process rather than founder effect, and despite free pollen movement across population, restricted seed dispersal maintains local genetic structure in this species.     

Within-population spatial genetic structure, neighbourhood size and clonal subrange in the seagrass Cymodocea nodosa

Abstract The extent of clonality within populations strongly influences their spatial genetic structure (SGS), yet this is hardly ever thoroughly analysed. We employed spatial autocorrelation analysis to study effects of sexual and clonal reproduction on dispersal of the dioecious seagrass Cymodocea nodosa. Analyses were performed both at genet level (i.e. excluding clonal repeats) and at ramet level. Clonal structure was characterized by the clonal subrange, a spatial measure of the linear limits where clonality still affects SGS. We show that the clonal subrange is equivalent to the distance where the probability of clonal identity approaches zero. This combined approach was applied to two meadows with different levels of disturbance, Cadiz (stable) and Alfacs (disturbed). Genotypic richness, the proportion of the sample representing distinct genotypes, was moderate (0.38 Cadiz, 0.46 Alfacs) mostly due to dominance of a few clones. Expected heterozygosities were comparable to those found in other clonal plants. SGS analyses at the genet level revealed extremely restricted gene dispersal in Cadiz (Sp = 0.052, a statistic reflecting the decrease of pairwise kinship with distance), the strongest SGS found for seagrass species, comparable only to values for selfing herbaceous land plants. At Cadiz the clonal subrange extended across shorter distances (20-25 m) than in Alfacs (30-35 m). Comparisons of sexual and vegetative components of gene dispersal suggest that, as a dispersal vector within meadows, clonal spread is at least as important as sexual reproduction. The restricted dispersal and SGS pattern in both meadows indicates that the species follows a repeated seedling recruitment strategy.     

High genetic diversity in a population of the ectomycorrhizal basidiomycete laccaria amethystina in a 150-year-old beech forest

The genetic structure of a population of the ectomycorrhizal basidiomycete Laccaria amethystina (Bolt. ex Hooker) Murr. was assessed in a closed 150-year-old beech (Fagus sylvatica L.) forest in the Vosges Mountains in northeastern France. During the autumn of 1994 and 1997, sporophores were collected from three 100-m2 sampling plots located along a 120-m transect crossing the beech stand. The genetic variation of 676 sporophores was initially estimated using heteroduplex analysis of the ribosomal DNA intergenic spacer (IGS1). Ten unique IGS1 heteroduplex/homoduplex patterns were identified, although three types represented most of the sporophores analysed. Each group of IGS1 type was then analysed using random amplified microsatellite analysis (RAMS). RAMS resolved 388 different genotypes amongst the 634 sporophores analysed from the three plots during the autumn of 1994 and 1997. Density as high as 130 genets per 100 m2 was observed during the autumn of 1994. The largest clone covered approximately 1 m2, but most genets covered a few cm2 and produced only one to three sporophores. Only eight genotypes identified in 1994 were found in 1997. Although L. amethystina has the capacity for vegetative persistence, the present study indicates that its populations maintain a genetic structure more consistent with a high frequency of sexual reproduction. This suggests that beech trees could be recolonized by new genotypes each year. Alternatively, this spatial distribution may also arise from erratic fruiting of underground persistent genets. These features (i.e. numerous genets of small size), typical of ruderal species, contrast with studies carried out on other ectomycorrhizal basidiomycetes occurring in mature closed forests.     

Hierarchical analysis of population genetic structure in the monogynous ant Cataglyphis cursor using microsatellite and mitochondrial DNA markers

Despite having winged queens, female dispersal in the monogynous ant Cataglyphis cursor is likely to be restricted because colonies reproduce by fission. We investigated the pattern of population genetic structure of this species using eight microsatellite markers and a mitochondrial DNA (mtDNA) sequence, in order to examine the extent of female and nuclear gene flow in two types of habitat. Sampling was carried out at a large spatial scale (16 sites from 2.5 to 120 km apart) as well as at a fine spatial scale (two 4.5-km transects, one in each habitat type). The strong spatial clustering of mtDNA observed at the fine spatial scale strongly supported a restricted effective female dispersal. In agreement, patterns of the mtDNA haplotypes observed at large and fine spatial scales suggested that new sites are colonized by nearby sites. Isolation by distance and significant nuclear genetic structure have been detected at all the spatial scales investigated. The level of local genetic differentiation for mitochondrial marker was 15 times higher than for the nuclear markers, suggesting differences in dispersal pattern between the two sexes. However, male gene flow was not sufficient to prevent significant nuclear genetic differentiation even at short distances (500 m). Isolation-by-distance patterns differed between the two habitat types, with a linear decrease of genetic similarities with distance observed only in the more continuous of the two habitats. Finally, despite these low dispersal capacities and the potential use of parthenogenesis to produce new queens, no signs of reduction of nuclear genetic diversity was detected in C. cursor populations.     

Restricted mating dispersal and strong breeding group structure in a mid-sized marsupial mammal (Petrogale penicillata)

Ecological genetic studies have demonstrated that spatial patterns of mating dispersal, the dispersal of gametes through mating behaviour, can facilitate inbreeding avoidance and strongly influence the structure of populations, particularly in highly philopatric species. Elements of breeding group dynamics, such as strong structuring and sex-biased dispersal among groups, can also minimize inbreeding and positively influence levels of genetic diversity within populations. Rock-wallabies are highly philopatric mid-sized mammals whose strong dependence on rocky terrain has resulted in series of discreet, small colonies in the landscape. Populations show no signs of inbreeding and maintain high levels of genetic diversity despite strong patterns of limited gene flow within and among colonies. We used this species to investigate the importance of mating dispersal and breeding group structure to inbreeding avoidance within a 'small' population. We examined the spatial patterns of mating dispersal, the extent of kinship within breeding groups, and the degree of relatedness among brush-tailed rock-wallaby breeding pairs within a colony in southeast Queensland. Parentage data revealed remarkably restricted mating dispersal and strong breeding group structuring for a mid-sized mammal. Breeding groups showed significant levels of female kinship with evidence of male dispersal among groups. We found no evidence for inbreeding avoidance through mate choice; however, anecdotal data suggest the importance of life history traits to inbreeding avoidance between first-degree relatives. We suggest that the restricted pattern of mating dispersal and strong breeding group structuring facilitates inbreeding avoidance within colonies. These results provide insight into the population structure and maintenance of genetic diversity within colonies of the threatened brush-tailed rock-wallaby.     

Genetic spatial autocorrelation can readily detect sex-biased dispersal

Sex-biased dispersal is expected to generate differences in the fine-scale genetic structure of males and females. Therefore, spatial analyses of multilocus genotypes may offer a powerful approach for detecting sex-biased dispersal in natural populations. However, the effects of sex-biased dispersal on fine-scale genetic structure have not been explored. We used simulations and multilocus spatial autocorrelation analysis to investigate how sex-biased dispersal influences fine-scale genetic structure. We evaluated three statistical tests for detecting sex-biased dispersal: bootstrap confidence intervals about autocorrelation r values and recently developed heterogeneity tests at the distance class and whole correlogram levels. Even modest sex bias in dispersal resulted in significantly different fine-scale spatial autocorrelation patterns between the sexes. This was particularly evident when dispersal was strongly restricted in the less-dispersing sex (mean distance <200 m), when differences between the sexes were readily detected over short distances. All tests had high power to detect sex-biased dispersal with large sample sizes (n ≥ 250). However, there was variation in type I error rates among the tests, for which we offer specific recommendations. We found congruence between simulation predictions and empirical data from the agile antechinus, a species that exhibits male-biased dispersal, confirming the power of individual-based genetic analysis to provide insights into asymmetries in male and female dispersal. Our key recommendations for using multilocus spatial autocorrelation analyses to test for sex-biased dispersal are: (i) maximize sample size, not locus number; (ii) concentrate sampling within the scale of positive structure; (iii) evaluate several distance class sizes; (iv) use appropriate methods when combining data from multiple populations; (v) compare the appropriate groups of individuals.     

Genetic spatial clustering: significant implications for conservation of wild soybean (Glycine soja: Fabaceae)

Knowledge of spatial patterns of genetic variation within populations of wild relative species has significant implications with respect to sampling strategies for ex situ and in situ conservation. To study spatial genetic structure of wild soybean (Glycine soja Sieb. et Zucc.) at the fine scale, three natural populations in northern China were analyzed using inter-simple sequence repeat (ISSR) fingerprints for estimating kinship coefficients. A regression analysis of kinship coefficients against spatial distances revealed that individuals occurring close together tended to be more genetically related. The Sp statistic further indicated a comparable spatial pattern among the three wild soybean populations with similar Sp values (mean = 0.0734, varied from 0.0645 to 0.0943) detected across the three populations. Genetic patches were on average ca. 20 m in size, and the effective neighborhood sizes varied between 10 and 15 m. The spatial genetic structure evident in the wild soybean populations may be attributed to the restricted seed dispersal and predominant inbreeding mating system of this species. The detection of family structure in the populations of wild soybean has a significant implication for the effective conservation of the important genetic resources.     

Estimating seed vs. pollen dispersal from spatial genetic structure in the common ash

Spatial genetic structure was analysed with five highly polymorphic microsatellite loci in a Romanian population of common ash (Fraxinus excelsior L.), a wind-pollinated and wind-dispersed tree species occurring in mixed deciduous forests over almost all of Europe. Contributions of seed and pollen dispersal to total gene flow were investigated by analysing the pattern of decrease in kinship coefficients among pairs of individuals with geographical distance and comparing it with simulation results. Plots of kinship against the logarithm of distance were decomposed into a slope and a shape component. Simulations showed that the slope is informative about the global level of gene flow, in agreement with theoretical expectations, whereas the shape component was correlated with the relative importance of seed vs. pollen dispersal. Hence, our results indicate that insights into the relative contributions of seed and pollen dispersal to overall gene flow can be gained from details of the pattern of spatial genetic structure at biparentally inherited loci. In common ash, the slope provided an estimate of total gene dispersal in terms of Wright's neighbourhood size of Nb = 519 individuals. No precise estimate of seed vs. pollen flow could be obtained from the shape because of the stochasticity inherent to the data, but the parameter combinations that best fitted the data indicated restricted seed flow, sigmas pound 14 m, and moderate pollen flow, 70 m pound sigmap pound 140 m.     

Deep phylogeographic break among Octopus variabilis populations in China: Evidence from mitochondrial and nuclear DNA analyses

The genetic structure of marine populations is greatly influenced by the dispersal ability of the organisms, and it is intuitive that a limited dispersal capability would result in greater genetic differentiation. Octopus variabilis is a typical cephalopod species that shows limited dispersal potential, and previous genetic surveys by a mitochondrial DNA analyses revealed high levels of genetic differentiation among its populations, suggesting the existence of cryptic or subspecies. To test this hypothesis, amplified fragment length polymorphisms (AFLPs) and the cytochrome oxidase II (COII) gene sequence were used to re-evaluate the spatial genetic structure of five populations of O. variabilis along the coast of China. Four distinct groups were identified within these five populations: the Dalian + Qingdao, Zhoushan, Wenzhou, and Dongshan groups. A deep genetic break among the Dongshan, Wenzhou, and other two groups were specifically recognized by both genetic markers. A considerable number of distinct alleles for AFLP and a deep divergence of 13.9–19.4% in the COII gene sequences were found among them, suggesting the occurrence of potential cryptic or subspecies of O. variabilis. A genetic structure of isolation by distance was identified in O. variabilis by a Mantel test, with the geographic distance explaining 62% of the variation in genetic differentiation. This result suggests that gene flow is geographically restricted for this species and that limited dispersal may be the main reason for the genetic differentiation among O. variabilis populations. The present results indicate that special care should be taken in future fishery exploitation and conservation efforts for this species and that conservation management should include populations representing all lineages.