Tiantong National Observation Station of Forest Ecosystems, Department of Environmental Sciences, East China Normal University, Shanghai 200062, China.
Mol Ecol. 2011 Nov;20(21):4421-32. doi: 10.1111/j.1365-294X.2011.05293.x. Epub 2011 Oct 10.
Fragmentation reduces population sizes, increases isolation between habitats and can result in restricted dispersal of pollen and seeds. Given that diploid seed dispersal contributes more to shaping fine-scale spatial genetic structure (SGS) than haploid pollen flow, we tested whether fine-scale SGS can be sensitive to fragmentation even if extensive pollen dispersal is maintained. Castanopsis sclerophylla (Lindley & Paxton) Schottky (Fagaceae), a wind-pollinated and gravity seed-dispersed tree, was studied in an area of southeast China where its populations have been fragmented to varying extents by human activity. Using different age classes of trees in areas subject to varying extents of fragmentation, we found no significant difference in genetic diversity between prefragmentation vs. postfragmentation C. sclerophylla subpopulations. Genetic differentiation among postfragmentation subpopulations was also only slightly lower than among prefragmentation subpopulations. In the most fragmented habitat, selfing rates were significantly higher than zero in prefragmentation, but not postfragmentation, cohorts. These results suggest that fragmentation had not decreased gene flow among these populations and that pollen flow remains extensive. However, significantly greater fine-scale SGS was found in postfragmentation subpopulations in the most fragmented habitat, but not in less fragmented habitats. This alteration in SGS reflected more restricted seed dispersal, induced by changes in the physical environments and the prevention of secondary seed dispersal by rodents. An increase in SGS can therefore result from more restricted seed dispersal, even in the face of extensive pollen flow, making it a sensitive indicator of the negative consequences of population fragmentation.
片段化会减少种群规模，增加栖息地之间的隔离程度，并可能导致花粉和种子的扩散受到限制。鉴于二倍体种子扩散比单倍体花粉流对塑造细尺度空间遗传结构（SGS）的贡献更大，我们测试了即使维持广泛的花粉扩散，细尺度 SGS 是否仍然容易受到片段化的影响。Castanopsis sclerophylla（Lindley & Paxton）Schottky（壳斗科）是一种风授粉和重力散播种子的树木，在中国东南部的一个地区进行了研究，该地区的种群由于人类活动而受到不同程度的片段化。我们在受到不同程度片段化影响的地区使用不同年龄的树木，发现与前片段化相比，后片段化的 C. sclerophylla 亚种群之间的遗传多样性没有显著差异。后片段化亚种群之间的遗传分化也略低于前片段化亚种群。在最片段化的栖息地中，自交率在前片段化的队列中显著高于零，但在后片段化的队列中则不然。这些结果表明，片段化并没有降低这些种群之间的基因流，花粉流仍然很广泛。然而，在最片段化的栖息地中，后片段化亚种群的细尺度 SGS 显著高于前片段化亚种群，而在较不片段化的栖息地中则不然。这种 SGS 的变化反映了种子扩散的限制，这是由物理环境的变化和啮齿动物对二次种子扩散的阻止引起的。因此，即使存在广泛的花粉流，由于种子扩散受到限制，SGS 的增加也可能导致，使其成为种群片段化负面后果的敏感指标。
