Data from: Persistence of long-distance, insect-mediated pollen movement for a tropical canopy tree species in remnant forest patches in an urban landscape

As deforestation and urbanization continue at rapid rates in tropical regions, urban forest patches are essential repositories of biodiversity. However, almost nothing is known about the effects of urbanization on gene flow of forest-dependent tree species. Buildings, roads and other “impervious” substrates considerably constrict the movement of small animals, and for many plant species the restricted movement of seed or pollen dispersers could have far-reaching genetic consequences. In this study, we investigated gene flow in the insect-pollinated, wind-dispersed tropical tree Koompassia malaccensis in and among three remnant forest patches in the urbanized landscape of Singapore. Most mature trees in the study had reproduced; parentage analysis assigned 93% of adults to at least one seedling, which likely contributed to the high allelic richness in the recruit cohort. Spatial genetic structure (SGS) of the recruit and adult cohorts was significant. Supporting this result, parentage analysis showed that 97% of recruits were within 100 m of their mother tree, and there was a high frequency of relatively short distance pollen dispersal (median 143–187 m) — a distance similar to the nearest-neighbour distances (median 105–127 m). Despite these similarities among patches, smaller patches with fewer adults displayed higher self-fertilization. The smallest patch was entirely surrounded by >2.5 km of “impervious” habitat; the SGS in this patch was significantly different from the recruits of the other patches and the adult cohort, with high levels of selfing (30.9%), low within-patch outcrossed parent pairs (n = 7), and the highest pollen and seed extra-patch immigration estimates of the three patches (seed: 2.0–6.7%; pollen 13.8–48.3%). Hence, contrary to our hypothesis, insect-mediated gene flow persists across >2.5 km of urban “impervious” substrate, and several of our results also parallel key findings from insect-pollinated canopy trees sampled in mixed agricultural-forest landscapes.

随着热带地区森林砍伐与城市化进程持续加速，城市森林斑块已然成为生物多样性的关键储存库。然而，学界对城市化如何影响依赖森林的树种的基因流（gene flow）仍知之甚少。建筑物、道路及其他“不透水”地表会显著限制小型动物的活动；对于多数植物类群而言，种子或花粉传播者的活动受限可能会引发深远的遗传后果。本研究以新加坡城市化景观中三处残存森林斑块内及斑块间的虫媒传粉、风散播热带树种马来甘巴豆（Koompassia malaccensis）为研究对象，探究其基因流特征。研究区内多数成熟树木均完成了繁殖；亲子分析（parentage analysis）结果显示，93%的成年个体至少可被匹配为一株幼苗的亲本，这或许是幼苗种群拥有较高等位基因丰富度的重要原因。幼苗种群与成年种群均表现出显著的空间遗传结构（SGS），该结果得到了亲子分析的佐证：97%的幼苗与其母树的距离不超过100米，且花粉传播多为短距离（中位数为143~187米）——该距离与种群内最近邻距离（中位数105~127米）相近。尽管各斑块间存在上述共性，但成年个体更少的小型斑块表现出更高的自交（self-fertilization）率。其中最小的斑块完全被超过2.5公里的“不透水”生境环绕，其空间遗传结构与其余两处斑块的幼苗种群及成年种群均存在显著差异：该斑块内自交率高达30.9%，斑块内异交亲本对数量极少（n=7），且是三处斑块中花粉与种子跨斑块迁入估计量最高的区域（种子迁入率：2.0%~6.7%；花粉迁入率：13.8%~48.3%）。综上，与我们的研究假设相悖，昆虫介导的基因流可跨越超过2.5公里的城市“不透水”生境维持；本研究的多项关键结果，也与农林混合景观中虫媒传粉冠层树木的相关研究发现高度一致。