Data from: Low plant density enhances gene dispersal in the Amazonian understory herb Heliconia acuminata

In theory, conservation genetics predicts that forest fragmentation will reduce gene dispersal, but in practice, genetic and ecological processes are also dependent on other population characteristics. We used Bayesian genetic analyses to characterize parentage and propagule dispersal in Heliconia acuminata L. C. Richard (Heliconiaceae), a common Amazonian understory plant that is pollinated and dispersed by birds. We studied these processes in two continuous forest sites and three 1-ha fragments in Brazil's Biological Dynamics of Forest Fragments Project. These sites showed variation in the density of H. acuminata. Ten microsatellite markers were used to genotype flowering adults and seedling recruits and to quantify realized pollen and seed dispersal distances, immigration of propagules from outside populations, and reproductive dominance among parents. We tested whether gene dispersal is more dependent on fragmentation or density of reproductive plants. Low plant densities were associated with elevated immigration rates and greater propagule dispersal distances. Reproductive dominance among inside-plot parents was higher for low density than for high density populations. Elevated local flower and fruit availability is probably leading to spatially more proximal bird foraging and propagule dispersal in areas with high density of reproductive plants. Nevertheless, genetic diversity, inbreeding coefficients and fine-scale spatial genetic structure were similar across populations, despite differences in gene dispersal. This result may indicate that the opposing processes of longer dispersal events in low-density populations versus higher diversity of contributing parents in high-density populations balance the resulting genetic outcomes and prevent genetic erosion in small populations and fragments.

理论上，保护遗传学（conservation genetics）预测森林片段化会降低基因扩散，但实际中遗传与生态过程同时受其他种群特征调控。本研究采用贝叶斯遗传分析方法，对亚马逊林下常见、由鸟类传粉并传播繁殖体的尖嘴赫蕉（Heliconia acuminata L. C. Richard，赫蕉科Heliconiaceae）的亲子关系与繁殖体扩散特征进行了表征。研究选取巴西森林片段化生物动力学项目（Biological Dynamics of Forest Fragments Project）内的2块连续森林样地与3块1公顷的森林片段开展实验，这些样地的尖嘴赫蕉种群密度存在差异。本研究使用10个微卫星标记（microsatellite markers）对开花成株与幼苗定植个体进行基因分型，以此量化实际花粉与种子扩散距离、种群外繁殖体的迁入率，以及亲本间的生殖优势。本研究检验了基因扩散更依赖于森林片段化程度，还是生殖植株的种群密度。结果显示，较低的植株密度与更高的繁殖体迁入率和更大的繁殖体扩散距离相关；相较于高密度种群，低密度种群的样地内亲本间生殖优势更高。生殖植株高密度区域内充足的花与果实资源，可能促使鸟类觅食活动在空间上更为集中，进而导致繁殖体扩散距离更近。尽管基因扩散模式存在差异，但各样地的遗传多样性、近交系数（inbreeding coefficients）以及精细空间遗传结构（fine-scale spatial genetic structure）均无显著差异。该结果表明，低密度种群中更长的扩散事件与高密度种群中更多样的贡献亲本所带来的相反过程相互制衡，最终维持了种群的遗传结局，避免了小种群与森林片段中出现遗传侵蚀（genetic erosion）。