Population connectivity through seed and pollen dispersal determines the genetic diversity, adaptive potential, and demography of plant metapopulations. In wind-pollinated trees, population connectivity is typically maintained by long-distance pollen flow, counteracting the genetic differentiation generated by drift and restricted seed dispersal. Although strong population fragmentation is theoretically expected to disrupt connectivity in forest trees, empirical evidence remains scarce and inconclusive. We investigated contemporary connectivity within a network of small remnant populations of a declining conifer (Taxus baccata L.), which have been hypothesized to be largely isolated from each other. We tested this hypothesis using molecular data for adult trees and naturally recruited seedlings from all known remnants across a fragmented landscape spanning a length of 20 ​km, and a specifically designed statistical approach to quantify contemporary pollen and seed migration rates between populations. We additionally assessed dispersal potential using a spatially explicit parentage analysis to estimate seed and pollen dispersal kernels within one of the remnants. Estimated pairwise migration rates between populations were barely detectable for seeds, while they were larger (up to 1.1%) and significant for pollen. Both seed and pollen migration rates decreased with geographic distance between populations, more steeply in the case of pollen migration. According to parentage-based dispersal kernels, 51.8% of seeds and 11.4% of pollen travel less than 25 ​m, whereas 0.2% of seeds and 36.1% of pollen travel more than 250 ​m from a source tree. In addition, 1.2% of pollen can travel more than 2.5 ​km. We showed that strong present-day population fragmentation, with separation distances over a few kilometers between small fragments, can substantially limit the connectivity of a wind-pollinated declining tree, leading to low pollen-mediated contemporary gene flow and null or virtually null demographic connectivity via seed dispersal.

中文翻译：

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风授粉下降针叶树 Taxus baccata L 的元种群内的连通性中断。


通过种子和花粉传播的种群连通性决定了植物元种群的遗传多样性、适应潜力和人口统计学。在风授粉树木中，种群连通性通常由长距离花粉流维持，抵消了漂移和限制种子传播产生的遗传分化。尽管理论上预计强烈的种群碎片化会破坏森林树木的连通性，但实证证据仍然稀缺且不确定。我们研究了衰落的针叶树 （Taxus baccata L.） 的小残余种群网络内的当代连通性，这些种群被假设在很大程度上彼此隔离。我们使用成年树木的分子数据来检验这一假设，并在 20 公里长的碎片化景观中从所有已知残余物中自然招募幼苗，并使用专门设计的统计方法来量化种群之间的当代花粉和种子迁移率。我们还使用空间明确的亲缘关系分析评估了传播潜力，以估计其中一个残余物内的种子和花粉传播核。估计的种群之间的成对迁移率对于种子几乎无法检测到，而它们更大（高达 1.1%）并且对花粉很重要。种子和花粉迁移率都随着种群之间的地理距离而降低，在花粉迁移的情况下更为陡峭。根据基于亲缘关系的传播粒，51.8% 的种子和 11.4% 的花粉从源树移动不到 25 m，而 0.2% 的种子和 36.1% 的花粉从源树移动超过 250 m。此外，1.2% 的花粉可以传播超过 2.5 公里。 我们表明，当今强烈的种群碎片化，小碎片之间的分离距离超过几公里，可以大大限制风授粉的衰落树木的连通性，导致低花粉介导的当代基因流和通过种子传播的零或几乎为零的人口连接。