Data from: Limited pollen dispersal, small genetic neighborhoods, and biparental inbreeding in Vallisneria americana Michx. (Hydrocharitaceae)

Premise of the study: Pollen dispersal is a key process that influences ecological and evolutionary dynamics of plant populations by facilitating sexual reproduction and gene flow. Habitat loss and fragmentation have the potential to reduce pollen dispersal within and among habitat patches. We assessed aquatic pollen dispersal and mating system characteristics in Vallisneria americana -- a water-pollinated plant with a distribution that has been reduced from historic levels. Methods: We examined pollen neighborhood size, biparental inbreeding, and pollen dispersal, based on seed paternity using the indirect paternity method KinDist, from samples of 18 - 39 mothers and 14 - 20 progeny per mother from 3 sites across 2 years. Key Results: On average, fruits contained seeds sired by 7 fathers. We found significant biparental inbreeding and limited pollen dispersal distances (0.8 - 4.34 m). However, in a number of cases correlated paternity did not decline with distance and dispersal could not be reliably estimated. Conclusions: Frequent pollen dispersal is not expected among patches, and even within patches gene flow via pollen will be limited. Limited pollen dispersal establishes genetic neighborhoods which, unless overcome by seed and propagule dispersal, will lead to genetic differentiation even in a continuous population. Unless loss and fragmentation drive populations to extreme sex bias, local pollen dispersal is likely to be unaffected by habitat loss and fragmentation per se because the spatial scale of patch isolation already exceeds pollen dispersal distances. Therefore, managing specifically for pollen connectivity is only relevant over very short distances.

研究背景：花粉传播是通过促进有性生殖与基因流，进而调控植物种群生态与进化动态的核心过程。生境丧失与生境破碎化可能会削弱生境斑块内部及斑块间的花粉传播能力。本研究针对分布范围较历史水平有所缩减的水媒植物美洲苦草（Vallisneria americana），对其水生生境中的花粉传播与交配系统特征进行了评估。
研究方法：本研究依托2个年度内3个采样位点的样本数据，采用间接父本分析方法KinDist，通过子代种子的父本鉴定，对18至39株母本以及每株母本对应的14至20株子代样本展开分析，以此考察花粉邻域大小、双亲近交程度及花粉传播特征。
核心研究结果：平均而言，单个果实内的种子由7个不同父本授粉获得。本研究检测到显著的双亲近交现象，且花粉传播距离受限（0.8~4.34米）。然而，部分样本的相关父本并未随距离增加而下降，导致花粉传播距离无法被可靠估算。
研究结论：斑块间几乎不存在频繁的花粉传播，即便在同一斑块内部，依靠花粉介导的基因流也较为有限。受限的花粉传播会形成遗传邻域，若无法通过种子与繁殖体传播打破这一格局，即便在连续分布的种群中也会引发遗传分化。除非生境丧失与破碎化导致种群出现极端的性偏倚，否则生境破碎化本身不会对局域花粉传播造成显著影响——这是因为斑块隔离的空间尺度已经超出了花粉传播的有效距离。因此，专门针对花粉连通性的管理措施仅在极短距离范围内具备实际应用价值。