Abstract
Ocean currents are an important driver of evolution for sea‐dispersed plants, enabling them to maintain reciprocal gene flow via sea‐dispersed diaspores and obtain wide distribution ranges. Although geographic barriers are known to be the primary factors shaping present genetic structure of sea‐dispersed plants, cryptic barriers which form clear genetic structure within oceanic regions are poorly understood. To test the presence of a cryptic barrier, we conducted a phylogeographic study together with past demographic inference for a widespread sea‐dispersed plant, Vigna marina, using 308 individuals collected from the entire Indo‐West Pacific (IWP) region. Chloroplast DNA variation showed strong genetic structure that separated populations into three groups: North Pacific (NP), South Pacific (SP) and Indian Ocean (IN) (F′CT among groups = 0.954–1.000). According to the Approximate Bayesian computation inference, splitting time between NP and SP was approximately 20,200 years (95%HPD, 4,530–95,400) before present. Moreover, a signal of recent population expansion was detected in the NP group. This study clearly showed the presence of a cryptic barrier in the West Pacific region of the distributional range of V. marina. The locations of the cryptic barrier observed in V. marina corresponded to the genetic breaks found in other plants, suggesting the presence of a common cryptic barrier for sea‐dispersed plants. Demographic inference suggested that genetic structure related to this cryptic barrier has been present since the last glacial maximum and may reflect patterns of past population expansion from refugia.
Highlights
Oceans are important corridors for estuarine and coastal plant species as they enable the exchange of individuals and help to maintain ge‐ netic uniformity with remote populations across distributional ranges
The aim of this study was to reveal the presence and process of formation of a cryptic barrier in Vigna marina in two ways: (a) to eval‐ uate the genetic diversity and population genetic structure through‐ out the species distributional range using chloroplast DNA and show if clear genetic structure caused by a cryptic barrier exists within the west Pacific region, and (b) to infer the past demographic history of V. marina in this region using the approximate Bayesian computation (ABC) approach to assess the processes of formation of the cryptic barrier that shaped the genetic structure
The principal component analysis (PCA) showed that the observed data were located around the center of the cluster of points of the simulated data based on the posterior distributions (Supporting Information Figure S2), suggesting that scenario 2 was a good fit for the observed data
Summary
Oceans are important corridors for estuarine and coastal plant species as they enable the exchange of individuals and help to maintain ge‐ netic uniformity with remote populations across distributional ranges. The past demo‐ graphic history of sea‐dispersed plants has not yet been well ex‐ amined, recent advances in population genetics with approximate Bayesian computation (ABC) enable a deeper understanding of the past demographic dynamics of species, in terms of evolutionary parameters such as effective population size, time scale of diver‐ gence and population size change (Bertorelle, Benazzo, & Mona, 2010) By taking this approach we can deepen our understanding of the processes forming cryptic barriers. Some adaptations for oceanic dispersal are recognized in this spe‐ cies, such as remarkable salt tolerance (Tomooka, Kaga, Isemura, & Vaughan, 2011), seed buoyancy and viability in sea water (Nakanishi, 1988) This species has a wider distributional range than any other tree species of mangroves (e.g. B_gymnorhiza and R. stylosa) in the IWP region. The aim of this study was to reveal the presence and process of formation of a cryptic barrier in Vigna marina in two ways: (a) to eval‐ uate the genetic diversity and population genetic structure through‐ out the species distributional range using chloroplast DNA (cpDNA) and show if clear genetic structure caused by a cryptic barrier exists within the west Pacific region, and (b) to infer the past demographic history of V. marina in this region using the ABC approach to assess the processes of formation of the cryptic barrier that shaped the genetic structure
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