title: Comparative Analysis of the Pattern of Population Genetic Diversity in Three Indo-West PacificRhizophoraMangrove Species.
abstract: Rhizophoraspecies are the most widely distributed mangrove trees in the Indo-West Pacific (IWP) region. Comparative studies of these species with shared life history traits can help identify evolutionary factors that have played most important roles in determining genetic diversity within and between populations in ocean-current dispersed mangrove tree species. We sampled 935 individuals from 54 natural populations for genotyping with 13 microsatellite markers to investigate the level of genetic variation, population structure, and gene flow on a broad geographic scale inRhizophora apiculata, Rhizophora mucronata, andRhizophora stylosaacross the IWP region. In contrast to the pattern expected of long-lived woody plants with predominant wind-pollination, water-dispersed seeds and wide geographic range, genetic variation within populations was generally low in all the three species, especially in those peripheral populations from geographic range limits. Although the large water-buoyant propagules ofRhizophorahave capacity for long distance dispersal, such events might be rare in reality, as reflected by the low level of gene flow and high genetic differentiation between most of population pairs within each species. Phylogeographic separation of Australian and Pacific island populations from SE Asian lineages previously revealed with DNA sequence data was still detectable inR. apiculatabased on genetic distances, but this pattern of disjunction was not always evident inR. mucronataandR. stylosa, suggesting that fast-evolving molecular markers could be more suitable for detecting contemporary genetic structure but not deep evolutionary divergence caused by historical vicariance. Given that mangrove species generally have small effective population sizes, we conclude that genetic drift coupled with limited gene flow have played a dominant role in producing the current pattern of population genetic diversity in the IWPRhizophoraspecies, overshadowing the effects of their life history traits. Recent population fragmentation and disturbances arising from human activities could further endanger genetic diversity in mangrove trees.
authors.affiliation: School of Biological Sciences, The University of Hong Kong Hong Kong, China.
authors.forename: Yu-Bin
authors.initials: YB
authors.lastname: Yan
authors.affiliation: The Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University Townsville, QLD, Australia.
authors.forename: Norm C
authors.initials: NC
authors.lastname: Duke
authors.affiliation: School of Biological Sciences, The University of Hong Kong Hong Kong, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Sun
keywords: Rhizophora; gene flow; genetic diversity; genetic drift; inbreeding coefficient; mangroves; microsatellites; population structure