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.

Genetic rescue by distant trees mitigates qualitative pollen limitation imposed by fine‐scale spatial genetic structure

“…However, we must note that differences between distant donor and distant donor control treatments were not statically significant. Taken together, our results are consistent with those of recent studies (Breed et al, ; Castilla et al, ; Noreen, Niissalo, Lum, & Webb, ; O'Connell, Castilla, Lee, & Jha, ) stressing a critical role of highly‐mobile pollinators for the maintenance of the genetic connectivity and the reproductive processes of highly or obligate outcrossing tree species. Given that P. bourgaeana is pollinated by a diverse array of functional groups (Diptera, Hymenoptera, Coleoptera and Lepidoptera), further studies using paternity analysis may enlighten whether long‐distance pollen dispersal is exclusively performed by specific functional groups of pollinators.…”

Endangered but genetically stable—Erythrophleum fordii within Feng Shui woodlands in suburbanized villages

“…fordii is primarily by pollen dispersal. As both mp and dp are directly related to the sizes and degrees of isolation of areas, they should vary among species and populations within species with similar pollination insects (Braga & Collevatti, ; Manoel et al, ; Monthe, Hardy, Doucet, Loo, & Duminil, ; Noreen et al, ; Sebbenn et al, ; Tambarussi, Boshier, Vencovsky, Freitas, & Sebbenn, ). For example, for a Neotropical tree Copaifera langsdorffii in a highly isolated and fragmented forest fragment (4.8 ha), Manoel et al () found its mp and dp values were 0.08 and 66 m, respectively; while for a tropical tree Entandrophragma cylindricum in a relatively large and continuous forest, Monthe et al () found its mp and dp values were 0.32–0.40 and 506–540 m, respectively.…”

“…Therefore, we consider the pollen flow in the population of TB village moderate. Because pollination insects, such as bees, could carry pollen to very long distances (Braga & Collevatti, ; Dick, Etchelecu, & Austerlitz, ; Manoel et al, ; Noreen et al, ; Sebbenn et al, ; Tambarussi et al, ), it is possible to find larger mp and dp in larger and more continuous populations of E . fordii than those in our study, based on pollen‐mediated gene dispersal capacities of E .…”

“…Theoretically, human disturbances change pollen mutualisms in Feng Shui woodlands and, subsequently, alter a population's genetic variation. However, empirical evidence does not always support this in other disturbed habitats (Giombini, Bravo, Sica, & Tosto, ; Noreen, Niissalo, Lum, & Webb, ; Rosas, Quesada, Lobo, & Sork, ). Therefore, the genetic consequences for a small population or due habitat disturbance are both species and location specific (Owusu, Schlarbaum, Carlson, & Cailing, ; Schwarcz et al, ).…”

Genetic analysis suggests extensive gene flow within and between catchments in a common and ecologically significant dryland river shrub species; Duma florulenta (Polygonaceae)

“…In addition, observations of floral visitors in the field (flies beetles and tiger moths in particular) suggest that the species may be largely insect-pollinated. While there is record of long-distance insect-mediated dispersal of pollen in the order of hundreds of kilometers (Ahmed, Compton, Butlin, & Gilmartin, 2009), long-distance dispersal of pollen by insects usually ranges from hundreds of meters to a few kilometers (Jha & Dick, 2010;Millar, Coates, & Byrne, 2014;Noreen, Niisalo, Lum, & Webb, 2016;White, Boshier, & Powell, 2002).…”