Global phylogeography of pantropical plants with sea-drifted seeds: Hibiscus and Rhizophora’s case

Date: 28th April 2010
Time: 4pm
Venue: Seminar room 2 (S2-0410)

Speaker: Dr Koji Takayama, Post-Doctoral Research Fellow, Plant Systematics and Taxonomy Lab, Chiba University, Japan
Host: Dr Edward Webb

Title: Global phylogeography of pantropical plants with sea-drifted seeds: Hibiscus and Rhizophora‘s case


“Pantropical plants with sea-drifted seeds” is widely distributed plant in the littoral areas of the tropics worldwide, and their seeds can drift in sea-water. The species integration throughout the amazing distribution range has been explained by their enormous capacities of seed dispersal, however, there are no empirical data to indicate if dispersal by sea-drifted seeds is sufficient to maintain the genetic unity of these species throughout such a wide distribution range. To address the importance of sea-drifted seed dispersal for the speciation and integration of the pantropical plants, I and a few collaborators collected several thousands of samples from c. 30 countries. I performed phylogeographic analyses and population genetics to investigate genetic structures in Hibiscus tiliaceus and its allied species (Malvaceae), and genus Rhizophora (Rhizophoraceae).
A phylogenetic tree of cpDNA sequences in Hibiscus tiliaceus suggested the possibility that recurrent speciation from H. tiliaceus has given rise to all of its four allied species (Takayama et al. 2006). These results implied that widely distributed plant could be the source of speciation for limited distributed ones. Both the distribution of cpDNA haplotype and population analysis using microsatellite markers suggested that substantial gene flow via long distance seed dispersal has occurred among populations within the Pacific and Indian Ocean regions (Takayama et al. 2008). Gene flow by long-distance seed dispersal is actually responsible for species integration of H. tiliaceus in the wide distribution range. On the other hand, clear genetic structures of cpDNA haplotypes were observed between populations over American continent in Hibiscus pernambucensis. The presence of the cpDNA haplotype largely shared in Atlantic region by H. tiliaceus and H. pernambucensis indicated the occurrence of cpDNA introgression between these two species across the Atlantic Ocean. Clear genetic diversifications between populations over American continent were also found in Rhizophora mangle and R. racemosa. The common patterns of genetic differentiation indicated that the American continent could be a clear geographic barrier that prevents gene flow by sea-dispersal for pantropical plants with sea-drifted seeds. Other recent results obtained from nuclear gene analyses will also be introduced in the seminar.

About the Speaker:
Koji Takayama received his Ph.D. from University of Tokyo, Japan where he performed investigation into phylogeopraphy of pantropical plants with sea-drifted seeds, Hibiscus tiliaceus and its allied. The plants have extremely wide distributed that may be achieved by dispersal of their sea-drifted seeds. During this period he carried out field survey covering five continents and molecular works using cpDNA and microsatellite loci, and he revealed global genetic structure of this plants. After this period, he has been a post-doctoral research fellow in Chiba University, Japan and progress phylogeographic study of wide distributed plants, especially in mangrove.

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