title: Persistence of long-distance, insect-mediated pollen movement for a tropical canopy tree species in remnant forest patches in an urban landscape.
abstract: 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.
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: A M E
authors.initials: AM
authors.lastname: Noreen
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: M A
authors.initials: MA
authors.lastname: Niissalo
authors.affiliation: National Institute of Education Singapore, Singapore.
authors.forename: S K Y
authors.initials: SK
authors.lastname: Lum
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: E L
authors.initials: EL
authors.lastname: Webb
mesh_terms: D000818:Animals; D003247:Conservation of Natural Resources; D007887:Fabaceae / Q000235:genetics*; D065928:Forests; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D007313:Insecta; D018895:Microsatellite Repeats; D011058:Pollen / Q000235:genetics; D054817:Pollination; D012846:Singapore; D014197:Trees / Q000235:genetics; D014507:Urbanization