Population genetic structure in the mangrove genus Rhizophora from Indo-West Pacific region

Abstract

Rhizophora is one of the most widely distributed mangrove genera in the world’s tropical and warm subtropical coasts, occurring in both Indo-West Pacific (IWP) and Atlantic-East Pacific (AEP) regions. The geographical distribution and genetic structure of Rhizophora populations could be strongly affected by historical geomorphic changes in the coastal regions and gene flow by dispersal of floating propagules following oceanic currents. Unlike the counterpart of Rhizophora species in the AEP region (mainly R. mangle and R. racemosa), little is known about population genetic structure of Rhizophora taxa in the IWP region (R. apiculata, R. stylosa, and R. mucronata) on a large geographical scale. Here, we use eight microsatellite markers to investigate population genetic structure of Rhizophora covering major geographical areas of the IWP region, including more than 800 individuals from 55 populations that are representative of all three taxa. Our preliminary investigation of R. stylosa and R. mucronata reveals low to moderate genetic diversity, with the expected heterozygosity ranging from 0.212 to 0.611 within populations in R. mucronata, and from 0.119 to 0.658 in R. stylosa. High FST values (> 0.15) between most of pairwise populations in both taxa suggest considerable genetic differentiation and limited gene flow within each species. Significant FIS values are also found in most populations, suggesting the presence of selfing or biparental inbreeding in local populations despite wind pollination. Although propagules of Rhizophora species are reported to be capable of long distance dispersal, our result suggests strong population genetic structure and limited gene flow among broad geographical regions in the studied species. Both the founder effect and population fragmentation could have contributed to this pattern of genetic variation and population structure in mangroves.