Aim Biogeographic barriers restrict the movement of individuals, resulting in population divergence, genetic differentiation, endemism and speciation. Yet, some barriers demonstrate unequal effect across species depending on species dispersal, which manifests in varying genetic structure. We test the hypotheses that the genetic structure of four coastal mangrove species would reflect differences in dispersal potential across the Malay Peninsula, a major biogeographic barrier in the Indo-West Pacific region. Location Twelve sites from the east and west coasts of the Malay Peninsula. Taxon Mangrove trees Avicennia alba, Sonneratia alba, Bruguiera gymnorhiza, and Rhizhophora mucronata. Methods For each species, we characterized genetic structure and gene flow using seven to 12 species-specific nuclear microsatellite markers. We tested for east-west genetic differentiation across the peninsula, a stepping-stone migration pattern, and assessed the proportion of recent dispersal and direction of historical migration along the Malacca Strait. Results Significant east-west genetic differentiation across the peninsula was observed in A. alba, S. alba and B. gymnorhiza, and the effect was most pronounced for the two species with lower dispersal potential (A. alba, S. alba). In contrast, the two species with higher dispersal potential (B. gymnorhiza and R. mucronata) exhibited much higher proportion of recent inter-population migration along the Malacca Strait. The signature of historical colonization from refugia in the Andaman Sea (north-to-south migration along the Malacca Strait) predominated for A. alba and S. alba. Historical south-north migration predominated for R. mucronata and B. gymnorhiza. Main conclusions This study is the first to implicate dispersal potential as a causal factor of varying mangrove species genetic structure across a biogeographic barrier. The Malay Peninsula functions as a filter to gene flow rather than a barrier. The genetic structure in mangrove species with a higher dispersal potential is more congruent with contemporary gene flow while that of species with a lower dispersal potential reflects historical processes.Our findings hint at the role of dispersal potential as a predictor of gene flow in mangroves.

We sampled all species at the same twelve sites along the east and west coasts of the Malay Peninsula (n = 22-49 individuals per species per locality). A leaf sample was collected from each individual, dried and stored using silica gel. Genomic DNA was extracted from leaf samples collected from each individual plant using a modified CTAB method (Doyle & Doyle, 1987). Species-specific nuclear microsatellite loci were then employed to genotype the samples in each species. Eight, eight, seven and 12 loci were employed for A. alba, S. alba, B. gymnorhiza and R. mucronata, respectively (see manuscript). All loci were genotyped using primers labelled with one of the four fluorescent dyes, 6-FAM, VIC, NED and PET. Amplified products were run on an ABI 3031xl automated sequencer (Applied Biosystems) with the GeneScan-600 LIZ size standard (Applied Biosystems) and analyzed using GeneMapper ® 4.1 software (Applied Biosystems). 

We uploaded individual file for each species in GENEPOP format, named by the abbreviation of the species name (e.g. AA = Avicennia alba). Missing data was denoted by "0".