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Spatial Scales of Pollen and Seed-Mediated Gene Flow in Tropical Rain Forest Trees

University of Michigan Department of Ecology and Evolutionary Biology and Herbarium 830 North University Avenue Ann Arbor MI 48109 USA
Tropical Plant Biology 04/2008; 1(1):20-33. DOI: 10.1007/s12042-007-9006-6

ABSTRACT Gene flow via seed and pollen is a primary determinant of genetic and species diversity in plant communities at different
spatial scales. This paper reviews studies of gene flow and population genetic structure in tropical rain forest trees and
places them in ecological and biogeographic context. Although much pollination is among nearest neighbors, an increasing number
of genetic studies report pollination ranging from 0.5–14km for canopy tree species, resulting in extensive breeding areas
in disturbed and undisturbed rain forest. Direct genetic measures of seed dispersal are still rare; however, studies of fine
scale spatial genetic structure (SGS) indicate that the bulk of effective seed dispersal occurs at local scales, and we found
no difference in SGS (Sp statistic) between temperate (N = 24 species) and tropical forest trees (N = 15). Our analysis did find significantly higher genetic differentiation in tropical trees (F
ST = 0.177; N = 42) than in temperate forest trees (F
ST = 0.116; N = 82). This may be due to the fact that tropical trees experience low but significant rates of self-fertilization and bi-parental
inbreeding, whereas half of the temperate tree species in our survey are wind pollinated and are more strictly allogamous.
Genetic drift may also be more pronounced in tropical trees due to the low population densities of most species.

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