Relative contribution of contemporary pollen and seed dispersal to the effective parental size of seedling population of California valley oak (Quercus lobata, Nee)

For plant populations, gene movement through pollen and seed dispersal governs the size of local genetic neighbourhoods and shapes the opportunities for natural selection and genetic drift. A critical question is how together these two processes influence the evolutionary dynamics of local populations. To assess the respective contributions of pollen and seed flow, we propose a novel indirect assessment of the separate male and female gametic contributions to total effective parental size (N(e)), based on parental correlations estimated via kinship coefficients, that can be applied to data sets that include unambiguous genotypes for male and female gametic contributions. Using the endemic Californian valley oak (Quercus lobata) as our study species, we apply this method to a set of microsatellite genotypes for two distinct ecological sets of naturally recruiting seedlings with acorns attached. We found that the effective numbers of contributing male parents (N(ep)) exceed effective numbers of female parents (N(em)) for seedlings established beneath adult trees (N(ep) = 8.1 and N(em) = 1.1), as well as for seedlings established away from adult trees (N(ep) = 15.4 and N(em) = 2.7), illustrating that seed dispersal enhances pollen dispersal and increases the effective number of seed sources in open seedling patches. The resulting effective parental size of seedling populations translates into smaller effective numbers of parents for undispersed vs. dispersed seedlings (N(e) = 3.6 and N(e) = 6.7, respectively). This study introduces a novel statistic method and provides important new evidence that, on a short-term temporal scale, seed dispersal shapes the local neighbourhood size of new recruits.