A review on the genetic structure of ecologically and economically important mangrove species in the Indo-West Pacific

Abstract Higher levels of genetic diversity were reported among the central populations of many mangrove species (Avicennia, Rhizophora, Bruguiera, Ceriops, Xylocaprus and Sonneratia) in the Indo-West Pacific (IWP) than those in the range limits. Interestingly, the highest proportions of variation were coming from individuals, and in some cases, among populations based on hierarchical analysis of molecular variance (AMOVA). Molecular data suggest that Malay Peninsula was considered as the undisputed geographic barrier causing genetic differentiation among populations in the IWP region. This strong genetic structuring produced divergence among mangrove populations of Indian Ocean and South China Sea. A cryptic barrier was also observed by distinct genetic clusters between South China Sea and Southwestern Pacific using high resolution markers such as chloroplast DNA (cpDNA) intergenic spacers and nuclear loci. It was surmised that the rise of the Sunda Shelf after sea level drop in the past glaciation periods resulted in limited gene flow, and to a greater extent, isolation by genetic drift among populations between the two sub-regions. Populations at the distribution margin having high genetic diversity were likely attained by the introgression of varieties due to sea level oscillations. The recent geo-climatic changes that raised awareness to species extinction, will likely affect vulnerable mangroves either to genetic bottlenecks or worse extinction. Previous literature claimed that overexploitation of mangroves will also push them to extinction. Therefore, this review on the current genetic diversity studies can provide insights for conservation strategies in the light of combined human and physical forces that impact these mangrove species.