Shigehiro Yamamoto

Effects of seed- and pollen-mediated gene dispersal on genetic structure among Quercus salicina saplings.

We evaluated the effects of seed- and pollen-mediated gene dispersal on genetic structure among Quercus salicina saplings. Parentage analysis using 10 microsatellite markers indicated that the 111 adult trees located within a 11.56 ha plot in the Tatera Forest Reserve, Japan, included only one parent of 44.2% and both parents of 40.7% of the 226 saplings located in a 1-ha core plot at its center. Coancestry (Fij) estimates indicated that there was strong genetic structure among the saplings. The numbers of pairs of full- and half-siblings were high among neighboring saplings, suggesting that there was strong maternal half-sibling family structure among the saplings around their seed parents, probably generated by the spatially limited seed dispersal and the small extent of overlapping seed shadows owing to the low density of adults. The frequencies also suggest that the maternal half-sibling families are interspersed with full-siblings, produced by correlated mating, probably because pollination frequency depends on the distance between parents. The frequencies of pairs of half-siblings decreased as the distance between saplings increased, but did not fall to zero even at distances up to the 90–95 m class, suggesting that paternal half-siblings originating from correlated paternity were widely distributed owing to extensive pollen flow. We separately examined the genetic structure for maternal and paternal alleles in the saplings. Unsurprisingly, very strong genetic structure was detected for maternal alleles. However, weak (but significant) genetic structure was also detected for paternal alleles. Therefore, pollen dispersal may affect the extent of genetic structure as well as seed dispersal.

Interannual genetic heterogeneity of pollen pools accepted by Quercus salicina individuals

Since flowering often varies among years in wind‐pollinated woody species, the genetic composition of pollen pools accepted by seed parents can differ between years. The interannual heterogeneity of pollen flow may be important for maintaining genetic diversity within populations because it can increase genetic variation within populations and the effective sizes of the populations. In this study we examined heterogeneity, using paternity analysis and analysis of molecular variance, in the genetic composition of pollen pools among different reproductive years for six Quercus salicina seed parents in an 11.56‐ha plot in a temperate old‐growth evergreen broadleaved forest. The genotypes at seven microsatellite loci were determined for 111 adult trees and 777 offspring of the six seed parents in 2–5 reproductive years. Genetic differentiation of pollen pools among different reproductive years for each seed parent was significant over all seed parents and for each of four seed parents that were analysed for more than 2 years, but not for either of the other two seed parents (analysed for 2 years). For both the pollen pools originating from inside the plot and those originating from outside it, genetic differentiation among different reproductive years for each seed parent was significant over all seed parents. However, among‐year genetic differentiation in the pollen pools originating from within the plot was detected for all four of the seed parents that were analysed for more than 2 years, but for only one of the four in the pools originating from outside the plot. Genetic diversity (estimated as allelic richness and gene diversity) was higher for pollen pools over all reproductive years than for pollen pools in single years. These results indicate that the year‐to‐year genetic variation of pollen pools increases genetic diversity in offspring and is strongly affected by the variation in pollen parents within the plot because of their high pollination contributions. The high year‐to‐year variation in pollen parents within the plot and overall supports the hypothesis that the offspring produced across years represent a larger genetic neighbourhood.

Effects of canopy gaps on the genetic structure of Camellia japonica saplings in a Japanese old-growth evergreen forest

The genetic structure of Camellia japonica saplings was investigated in relation to canopy conditions in an old-growth evergreen forest in Tsushima, Japan. To elucidate effects of canopy gaps on genetic structure, a 1 ha study site was divided into 20 × 20 m quadrats, which were classified into a gap quadrats (GAP), closed canopy quadrats (CLS) and mixed quadrats. Five GAP quadrats and six CLS quadrats were analyzed separately. Isolation-by-distance was tested by examining the correlation between genetic distance and geographic distance. A significant positive correlation was detected for GAP quadrats, whilst that for CLS quadrats was significantly smaller and not significantly different from zero. On the other hand, an analysis using Morans I spatial autocorrelation coefficients indicates that the genetic structure is weaker in GAP quadrats than in CLS quadrats in short distance classes. The values were significantly positive for both types of quadrat. These results, along with our field observations on flowering, suggest that canopy gaps affect the genetic structure of C. japonica saplings in two distinct ways. First, canopy gaps may promote flowering and mating in an isolation-by-distance manner within canopy gaps. Second, canopy gaps may promote seed production and resulting overlap in seed shadows may weaken fine-scale genetic structures.