Effects of tree size-dependency and dispersal distance-dependency on paternal and maternal reproductive contributions of adult trees to the dispersed seeds in a natural <i>Abies firma</i> population

To consider the mechanisms by which mating pattern variability is generated in populations, it is important to examine simultaneously how the two major dependency factors (tree size and dispersal distance of gametes) differently affect the two sexual components of reproductive contributions (paternal and maternal contributions) in the next generation of monoecious trees. These dependencies were examined in a natural population of Abies firma using data on the separate paternal and maternal contributions of adult trees to the seed pools obtained from direct biparentage analysis, tree size data which is potentially related to reproductive effort, as well as tree location data to assess dispersal distances. Over the course of three reproductive events (mast years), paternally contributing adult trees within the population were generally distributed in larger size classes than were maternally contributing adult trees. Based on analysis integrating over three years, paternal contribution of adult trees was significantly dependent on tree size, which is concordant with the suggestion that larger trees exhibit higher relative allocation to the male reproductive function than to the female reproductive function. Paternal contribution was not dependent on dispersal distance, indicating the external dispersal of paternal gametes in wind-pollinated conifer species even within the population. In contrast, maternal contribution was both significantly tree size- and dispersal distance-dependent. These findings suggest that the divergent effect of the two dependency factors on paternal and maternal contributions promotes diversity in mating patterns within the population, which in turn maintains the overall genetic variability of the next generation.