雌雄异株的红豆杉中种子和花粉基因的扩散，面临着强烈的种群破碎化。
Seed and pollen gene dispersal in Taxus baccata, a dioecious conifer in the face of strong population fragmentation.
机构信息
Department of Genetics, Institute of Experimental Biology, Kazimierz Wielki University, Bydgoszcz, Poland.
出版信息
Ann Bot. 2018 Aug 27;122(3):409-421. doi: 10.1093/aob/mcy081.
BACKGROUND AND AIMS
Dispersal is crucial due to its direct impact on dynamics of a species' distribution as well as having a role in shaping adaptive potential through gene flow. In plants forming scarce and small populations, knowledge about the dispersal process is required to assess the potential for colonizing new habitats and connectivity of present and future populations. This study aimed to assess dispersal potential in Taxus baccata, a dioecious gymnosperm tree with a wide but highly fragmented distribution.
METHODS
Seed and pollen dispersal kernels were estimated directly in the framework of the spatially explicit mating model, where genealogies of naturally established seedlings were reconstructed with the help of microsatellite markers. In this way, six differently shaped dispersal functions were compared.
KEY RESULTS
Seed dispersal followed a leptokurtic distribution, with the Exponential-Power, the Power-law and Weibull being almost equally best-fitting models. The pollen dispersal kernel appeared to be more fat-tailed than the seed dispersal kernel, and the Lognormal and the Exponential-Power function showed the best fit. The rate of seed immigration from the background sources was not significantly different from the rate of pollen immigration (13.1 % vs. 19.7 %) and immigration rates were in agreement with or below maximum predictions based on the estimated dispersal kernels. Based on the multimodel approach, 95 % of seeds travel <109 m, while 95 % of pollen travels <704 m from the source.
CONCLUSIONS
The results showed that, at a local spatial scale, yew seeds travel shorter distances than pollen, facilitating a rapid development of a kinship structure. At the landscape level, however, although yew exhibits some potential to colonize new habitats through seed dispersal, genetic connectivity between different yew remnants is strongly limited. Taking into account strong population fragmentation, the study suggests that gene dispersal may be a limiting factor of the adaptability of the species.
背景与目的
扩散对于物种分布的动态具有直接影响，并且通过基因流在塑造适应潜力方面发挥作用。在形成稀少和小种群的植物中，需要了解扩散过程，以评估其在新栖息地的殖民潜力以及现有和未来种群的连通性。本研究旨在评估 Taxus baccata 的扩散潜力，这是一种雌雄异株的裸子植物，分布广泛但高度碎片化。
方法
在空间显式交配模型的框架内直接估计种子和花粉的扩散核，其中使用微卫星标记重建自然建立的幼苗的系谱。通过这种方式，比较了六种不同形状的扩散函数。
主要结果
种子扩散遵循尖峰分布，指数幂律、幂律和威布尔分布几乎同样拟合得最好。花粉扩散核比种子扩散核更胖尾，对数正态和指数幂律函数拟合得最好。来自背景源的种子移民率与花粉移民率没有显著差异（13.1%比 19.7%），移民率与基于估计的扩散核的最大预测值一致或低于最大预测值。基于多模型方法，95%的种子传播距离<109 米，而 95%的花粉传播距离<704 米。
结论
结果表明，在局部空间尺度上，紫杉种子的传播距离比花粉短，有利于亲缘关系结构的快速发展。然而，在景观尺度上，尽管紫杉通过种子扩散具有一定的潜力来殖民新栖息地，但不同紫杉残体之间的遗传连通性受到强烈限制。考虑到种群的严重碎片化，研究表明基因扩散可能是物种适应性的限制因素。
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