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.
Highlights
Seed dispersal is the only way for most land plants to colonize new sites and expand their distribution ranges, because populations of plants are mostly spatially isolated from each other by hundreds of meters or more
Because the regional populations studied here, except for those separated by the American continents, are separated by barriers more than 1,000 km wide (Africa and the East Pacific Ocean) that have shaped the genetic structure of many seadispersal species [5], long-distance dispersal by sea-drifted seeds is the only way to maintain migration among very distant populations of the subsp. brasiliensis connected by the ocean
Different effects of barriers shape the genetic structure of subsp. brasiliensis As was briefly discussed earlier, our study suggests that other land and oceanic barriers known to shape the genetic structure of widespread sea-dispersal plants have different effects on the genetic structure of subsp. brasiliensis
Summary
Seed dispersal is the only way for most land plants to colonize new sites and expand their distribution ranges, because populations of plants are mostly spatially isolated from each other by hundreds of meters or more. Most mangroves have seeds or propagules that can drift on seawater and be transported by ocean currents. They have wide distribution ranges, they are still limited at the broadest scales. Various mangrove species from different families distribute only either in the IndoWest Pacific (IWP) or Atlantic East-Pacific (AEP) regions [4] These two biogeographic regions are common for many mangrove species and other sea-dispersed plants, indicating that the East Pacific Ocean and African continent have worked as important barriers for seed dispersal for most species of widespread seadispersed plants [4], [5]. There are a few groups of seadispersed plants that have overcome those barriers and have a global distribution range
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
