Data from: Pollen dispersal patterns and population persistence in a small isolated population of Fagus crenata

The potential of long-distance pollen dispersal and the effects of small population size and population isolation on persistence of Fagus crenata populations were investigated in a small, severely isolated population (the Gofuku-ji population) and two other populations located within 7 km of this population (including 87 adult trees in total). Parentage analysis using 13 microsatellite loci showed that 94 of 100 seedlings derived from seeds collected from the Gofuku-ji population had parent pairs within this population, six had one parent within the population, and four of the six seedlings had alleles that were not detected in any of the three populations, indicating that some pollen is dispersed over distances exceeding 7 km. The estimated expected heterozygosity and effective population size were lower in the Gofuku-ji population than in previously examined large continuous populations. Therefore, levels of genetic diversity within the population may have been reduced by strong genetic drift and limitations of pollen- and seed-mediated gene flow associated with the small size and severe isolation. The contemporary mating pattern estimated at the seedling stage was biased toward outbreeding, which may be explained by possible processes: the level of inbreeding in the adult trees is increased; then, inbreeding frequently occurs but is rarely successful, while outbreeding successfully produces offspring. Additionally, high levels of significant linkage disequilibrium and higher numbers of alleles than expected under mutation–drift equilibrium from analyses of the populations’ evolutionary history suggest that the Gofuku-ji population may have experienced admixture before its severe isolation. Therefore, the persistence of the Gofuku-ji population is being adversely affected by the decrease in population size and severe isolation. Further studies of gene flow via pollen in other populations with various degrees of isolation could enhance our understanding of the effects of population isolation and long-distance pollen dispersal in F. crenata and similar species.

本研究以一处严重隔离的小型种群（五合寺种群，Gofuku-ji population）以及该种群周边7公里范围内的另外两个种群（共计87株成年树）为研究对象，旨在探究长距离花粉扩散的潜力，以及小型种群规模与种群隔离对钝齿水青冈（Fagus crenata）种群存续的影响。基于13个微卫星位点（microsatellite loci）的亲权分析（parentage analysis）结果显示：从五合寺种群采集的种子萌发获得的100株幼苗中，94株的亲本对均来自该种群内部，6株仅1个亲本来自该种群；其中6株幼苗里有4株携带了在三个研究种群中均未检出的等位基因，这表明存在部分花粉扩散距离超过7公里的情况。五合寺种群的期望杂合度（expected heterozygosity）与有效种群大小（effective population size）均低于此前已研究的大型连续种群。由此推测，种群规模狭小与严重隔离所引发的强烈遗传漂变（genetic drift），以及花粉和种子介导的基因流（gene flow）受限，可能导致该种群的遗传多样性水平下降。基于幼苗阶段估算的当代交配模式偏向远交（outbreeding），这一现象可通过以下过程解释：成年个体的近交（inbreeding）水平升高，使得近交虽频繁发生但极少成功，而远交则可顺利产生后代。此外，对种群进化历史的分析显示，其存在高水平的显著连锁不平衡（linkage disequilibrium），且等位基因数量多于突变-漂变平衡（mutation–drift equilibrium）下的预期值，这表明五合寺种群在严重隔离前可能曾经历过遗传混合（admixture）事件。综上，种群规模缩减与严重隔离正对五合寺种群的存续产生负面影响。未来可针对不同隔离程度的其他种群开展花粉介导的基因流相关研究，以加深我们对钝齿水青冈及类似物种中种群隔离与长距离花粉扩散效应的理解。