Geographic Structure of a True Pantropical Plant with Sea-drifted Seeds, Ipomoea pes-caprae (Convolvulaceae), Revealed by Nuclear Markers

摘要

"Pantropical plants with sea-drifted seeds" exhibit extremely wide distribution in the tropics and subtropics of the world, and the wide distribution range were attributed to long distance seed dispersal by ocean currents. We performed phylogeographicanalyses on Ipomoea pes-caprae (Convolvulaceae) that is one of the 'true-pantropical' species, using two low copy nuclear genes, HSP-90 and Waxy. Using 272 samples collected from 34 populations throughout the global distribution range, seven and five haplotypes were recognized in HSP-90 and Waxy respectively, and the geographic distributions of haplotypes showed clear geographic structure. Several haplotypes were distributed in AEP (Atlantic - East Pacific) or IWP (Indo - West Pacific) regions almost specifically, while some haplotypes were very widespread across AEP or IWP regions. The presence of the same haplotypes over populations isolated by the ocean suggests that long distance dispersal by ocean currents is responsible for gene flow within thewide distribution range. Both the East Pacific and African Continent acted as geographic barriers that have prevented seed dispersal. Presence of more haplotypes in Africa or Indian Oceanic regions may suggest that the origin of the species was in theseregions and that the species expanded its distribution toward the New World.