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 gene flow of forest-dependent tree species in urban landscapes. 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. We genotyped the vast majority of adults (N=179) and a large number of recruits (N=2103) with 8 highly polymorphic microsatellite markers. Spatial genetic structure of the recruit and adult cohorts was significant, showing routine gene dispersal distances of ~100–400 m. Parentage analysis showed that 97% of recruits were within 100 m of their mother tree, and a high frequency of relatively short-distance pollen dispersal (median ~143–187 m). Despite routine seed and pollen dispersal distances of within a few hundred meters, interpatch gene flow occurred between all patches and was dominated by pollen movement: parentage analysis showed 76 pollen versus 2 seed interpatch dispersal events, and the seedling neighborhood model estimated ~1–6% seed immigration and ~21–46% pollen immigration rates, depending on patch. In addition, the smallest patch (containing five adult K. malaccensis trees) was entirely surrounded by >2.5 km of ‘impervious’ substrate, yet had the highest proportional pollen and seed immigration estimates of any patch. Hence, contrary to our hypothesis, insect-mediated gene flow persisted across an urban landscape, 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提速，城市森林斑块已然成为生物多样性的核心储存库。然而，当前学界对城市化景观中依赖森林生境的树木物种的基因流几乎尚无系统性认知。本研究以新加坡城市化景观中的3处残存森林斑块为研究对象，针对虫媒风播的热带树种马来甘巴豆（Koompassia malaccensis）开展基因流相关研究。研究团队利用8个高多态性微卫星标记（microsatellite marker），对绝大多数成年个体（N=179）与大量幼龄个体（N=2103）完成了基因分型。幼树与成年种群的空间遗传结构均呈显著模式，表明该物种的常规基因扩散距离约为100~400米。亲本分析结果显示，97%的幼树与其母树的空间距离不足100米，且花粉扩散以短距离为主，中位数介于143~187米之间。尽管种子与花粉的常规扩散距离均在数百米以内，但所有斑块之间均发生了斑块间基因流，且该过程以花粉传播为主：亲本分析共鉴定出76次跨斑块花粉扩散事件与2次跨斑块种子扩散事件；基于幼苗邻域模型（seedling neighborhood model）估算，不同斑块的种子迁入率约为1%~6%，花粉迁入率约为21%~46%，具体数值因斑块而异。此外，面积最小的斑块（仅包含5株成年马来甘巴豆个体）完全被超过2.5公里的不透水地表基质环绕，但其花粉与种子的迁入比例均为所有斑块中最高。因此，本研究结果与原假说相悖：昆虫介导的基因流在城市化景观中依然持续存在；此外，部分研究结果也与农林混合景观中虫媒冠层树木的关键研究发现高度吻合。