Moving past barriers — Sea-drifted seeds shape regional distribution of genetic diversity of a coastal legume in the Indo-West Pacific

Canavalia rosea, a perennial vine of the legume (Fabaceae) family, is commonly found in the tropical and subtropical coasts of the world. The long-distance dispersal ability of its sea-drifted seeds has aided the species to attain a pantropical distribution. While there has been some progress on its global phylogeography, the influence of evolutionary mechanisms on the genetic composition of C. rosea at a regional scale is still unknown. In this study, we used 13 nuclear microsatellite markers and 376 samples of C. rosea from 29 sampling sites to estimate the genetic diversity and assessed the influence of gene flow and demographic features on the population structure of the species in the Indo-West Pacific (IWP) region. We found high genetic diversity and moderate genetic differentiation of C. rosea in this region. Both spatial and non-spatial clustering algorithms revealed a subtle genetic structure created by the oceanic circulation pattern of the South China Sea (SCS), thereby differentiating the sampling sites of northern SCS from the rest and even creating a genetic break within the north of SCS. However, the Bayesian analysis of migration rate and direction revealed that propagules of C. rosea could move around the cryptic barriers of ocean currents and the land barrier of the Malay Peninsula, thereby weakening the genetic differentiation between these population clusters. Although a significant relationship between geographic distance and genetic differentiation was found, our findings suggested that a continuous distribution model of gene flow could have influenced the population structure of C. rosea in this region. •Canavalia rosea is a pantropical plant with sea-drifted seeds.•We assessed phylogeography of this coastal legume at regional scale.•We found high genetic diversity in the Indo-West Pacific.•Oceanic currents acted as barrier to gene flow and created subtle genetic structure.•Species’ dispersal ability across the barriers weaken genetic differentiation.