Molecular phylogenetic geography of pan tropic sea dispersed plants : Gene flow and species differentiation through geographic barrier.

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Pan tropic sea dispersed plants are widely distributed on the sea coast of the world tropics. Their population genetics were analyzed on many samples gathered from all over the tropics and subtropics to know their differentiation process into species and rates of gene flows between populations to keep the species.A phylogenetic tree constructed using the nucleotide sequences of a c.7,500 bp portion of chloroplast DNA suggested the possibility that recurrent speciation from H.tiliaceus has given rise to all of its allied species. Three major sequence haplotypes of H.tiliaceus had wide and overlapping distributions throughout the Pacific, Atlantic and Indian Ocean regions. Statistical analysis using F_<ST> and AMOVA did not show significant genetic differentiation among the H.tiliaceus populations in the three oceanic regions. These results suggested substantial gene flow occurred between populations in the different oceanic regions due to sea-drifted seeds. A strong genetic difference b … More etween the Pacific and Atlantic populations of H.pernambucensis was observed, which indicates that gene flow in this species between the two regions has been prevented. The wide and dominant distribution of a haplotype shared by H.pernambucensis and H.tiliaceus in the Atlantic region suggests significant introgression between the two species in this region.Ipomoea pes-caprae is divided into two geographical subspecies, subsp.brasiliensis distributed in the world tropics and subsp. pes-caprae of the Indian Ocean. Although both subspecies have sea-dispersed seeds, their distribution ranges are overlapped in the Indian Ocean. By the analysis using AFLP marker the genetic differentiation between these subspecies was clearly observed. Moreover gene flows among distant populations were observed. Geographic distance was slightly correlated with genetic distance.The genus Canavalia consists of about 50 species mostly distributed in the world tropics and subtropics. Among them several species as C.rosea have wide distribution range over the tropics and subtropics. Phylogenetic tree constructed by ITS sequences of nrDNA using extensive samples suggested that the Hawaiian endemic subgen.Maunaloa was derived from C.rosea that migrated to Hawaii by sea-drift dispersal, and loss of sea-drift ability occurred in the speciation process. Less