Chloroplast Phylogeography of a Widely Distributed Mangrove Species, Excoecaria Agallocha, in the Indo-West Pacific Region

Excoecaria agallocha is one of the predominant mangrove species in the Indo-West Pacific (IWP) region with an extensive range of distribution. To infer the current geographical patterns of genetic variation and provide new insights on the historical population dynamics of mangrove species in the IWP region, we sampled E. agallocha across its distribution range and investigated the phylogeography of this species using four chloroplast DNA (cpDNA) fragments. Our results showed that E. agallocha possessed a high degree of species-level genetic diversity, while the average genetic diversity within populations was much lower. The presence of population genetic structure was supported by the estimates of genetic differentiation and the analysis of molecular variance (AMOVA). Of the ten haplotypes identified, no haplotypes were shared between the East Indian Ocean (EIO), the West Pacific Ocean (WPO), and the North Australian (NA) regions. Genealogy analysis, haplotype distribution patterns, and the principal coordinate analysis (PCoA) consistently suggested the existence of three haplotype groups distributed in distinct geographical locations. The genealogical breaks observed and further analysis of geographic/genetic barriers indicated that both land barriers and oceanic currents may have played important roles in the divergence and demography of E. agallocha.