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 Abies firma 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.

为探究种群内交配模式变异（mating pattern variability）的产生机制，同步考察两大核心依赖因子——树木体量（tree size）与配子扩散距离（dispersal distance）——对雌雄同株树木（monoecious trees）下一代繁殖贡献的两个性组分（sexual components of reproductive contributions），即父本贡献（paternal contributions）与母本贡献（maternal contributions）——的差异化影响，具备重要学术意义。本研究以日本冷杉（Abies firma）的自然种群为研究对象，借助直接双亲分析（direct biparentage analysis）获取的成年植株对种子库（seed pools）的独立父本与母本贡献数据、与繁殖投入（reproductive effort）潜在相关的树木体量数据，以及用于评估扩散距离的植株位置数据，对上述依赖关系展开了系统性分析。在三次结实大年（mast years）的调查周期内，种群内承担父本贡献的成年植株，其体量等级普遍高于承担母本贡献的成年植株。基于三年整合分析结果，成年植株的父本贡献显著受树木体量调控，这与“较大植株对雄性繁殖功能的相对资源分配高于雌性繁殖功能”的学术推测相一致。父本贡献不受扩散距离影响，这表明即便在种群内部，风媒针叶树种（wind-pollinated conifer species）的父本配子也可通过外部扩散完成授粉过程。与之相对，母本贡献同时显著受树木体量与扩散距离的双重调控。上述研究结果表明，两大依赖因子对父本与母本贡献的差异化作用，可推动种群内交配模式的多样性，进而维持下一代种群的整体遗传变异（genetic variability）水平。