title: Long-distance dispersal by sea-drifted seeds has maintained the global distribution of Ipomoea pes-caprae subsp. brasiliensis (Convolvulaceae).
abstract: Ipomoea pes-caprae (Convolvulaceae), a pantropical plant with sea-drifted seeds, is found globally in the littoral areas of tropical and subtropical regions. Unusual long-distance seed dispersal has been believed to be responsible for its extraordinarily wide distribution; however, the actual level of inter-population migration has never been studied. To clarify the level of migration among populations of I. pes-caprae across its range, we investigated nucleotide sequence variations by using seven low-copy nuclear markers and 272 samples collected from 34 populations that cover the range of the species. We applied coalescent-based approaches using Bayesian and maximum likelihood methods to assess migration rates, direction of migration, and genetic diversity among five regional populations. Our results showed a high number of migrants among the regional populations of I. pes-caprae subsp. brasiliensis, which suggests that migration among distant populations was maintained by long-distance seed dispersal across its global range. These results also provide strong evidence for recent trans-oceanic seed dispersal by ocean currents in all three oceanic regions. We also found migration crossing the American continents. Although this is an apparent land barrier for sea-dispersal, migration between populations of the East Pacific and West Atlantic regions was high, perhaps because of trans-isthmus migration via pollen dispersal. Therefore, the migration and gene flow among populations across the vast range of I. pes-caprae is maintained not only by seed dispersal by sea-drifted seeds, but also by pollen flow over the American continents. On the other hand, populations of subsp. pes-caprae that are restricted to only the northern part of the Indian Ocean region were highly differentiated from subsp. brasiliensis. Cryptic barriers that prevented migration by sea dispersal between the ranges of the two subspecies and/or historical differentiation that caused local adaptation to different environmental factors in each region could explain the genetic differentiation between the subspecies.
authors.affiliation: Department of Biology, Graduate School of Science, Chiba University, 1-33 Yayoi, Inage, Chiba, Japan.
authors.forename: Matin
authors.initials: M
authors.lastname: Miryeganeh
authors.affiliation: The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takayama
authors.affiliation: Faculty of Education, University of the Ryukyus, 1 Senbaru, Nakagami-gun Okinawa, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Tateishi
authors.affiliation: Department of Biology, Graduate School of Science, Chiba University, 1-33 Yayoi, Inage, Chiba, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kajita
mesh_terms: D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D056426:Genetic Loci; D005819:Genetic Markers; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes / Q000235:genetics; D038622:Internationality; D027741:Ipomoea / Q000502:physiology*; D008969:Molecular Sequence Data; D009711:Nucleotides / Q000235:genetics; D009792:Oceans and Seas; D011110:Polymorphism, Genetic; D058614:Seed Dispersal / Q000502:physiology*
chemical_list: D005819:Genetic Markers; D009711:Nucleotides
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