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

Abstract

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.

Effect of balancing selection on spatial genetic structure within populations: theoretical investigations on the self-incompatibility locus and empirical studies in Arabidopsis halleri

“…For a given value of the standard deviation of overall gene dispersal, patterns of SGS at either the S-locus or the unlinked neutral loci were similar when varying the relative dispersal distances of pollen and seeds. This simulation result has been obtained previously for a neutral locus by Heuertz et al (2003), and is a consequence of the general theoretical result by Rousset (2000), that the slope of the kinship-distance curves is only weakly influenced by the shape of gene dispersal distributions. Our study results indicate that this prediction holds for loci subject to frequency-dependent selection.…”

“…At the end of each run, we analyzed the SGS on 1600 individuals located in a 40 Â 40 grid centered on the initial grid, a procedure often used to minimize edge effects (Heuertz et al, 2003). For each locus we computed the matrix of pairwise kinship coefficients among all pairs of individuals (F r ), using J Nason's estimator (Loiselle et al, 1995).…”

“…The absolute value of statistic b is a measure of the extent of SGS. It is inversely proportional to the overall axial standard deviation of dispersal distances and is only weakly influenced by the shape of pollen and seed dispersal distributions (Hardy and Vekemans, 1999;Rousset, 2000;Heuertz et al, 2003). To visualize SGS, we produced spatial autocorrelograms by plotting mean kinship coefficients, F r (d) (computed among pairs of individuals classified according to 40 nonoverlapping intervals of interindividual distance d) on the y axis and distance d expressed in number of steps along the grid on the x axis.…”

Lack of genetic structure and evidence for long-distance dispersal in ash (Fraxinus excelsior) populations under threat from an emergent fungal pathogen: implications for restorative planting

“…Our spatial autocorrelation analyses found little evidence for the breeding "subunits" previously suggested to exist within ash woodlands (Heuertz et al 2001;Morand et al 2002). The mean value of Sp calculated for the 36 populations studied (0.006) was lower than the mean value reported for trees (0.010) by Vekemans and Hardy (2004) and the mean value from six microsatellite-based studies in tropical trees (0.017; Hardy et al 2006), although higher than that calculated for a Romanian population of F. excelsior (0.002; Heuertz et al 2003). This may be due at least in part to the differing densities of ash trees in the various woodlands analysed in the present study.…”

Sex-specific pattern of spatial genetic structure in dioecious and clonal tree species, Populus alba L.

“…Dioecious plant species analyzed by the authors had on average 6-fold higher SGS than monoecious species. According to theoretical considerations and empirical studies, seed dispersal range has a predominant impact on building SGS in natural populations (Vekemans and Hardy 2004;Heuertz et al 2003;Chybicki and Burczyk 2013). In dioecious species, the number of seed sources is half in compared to monoecious species.…”