Abstract
Southeast Asia has been known as one of the biodiversity hotspots in the world. Repeated glacial cycles during Pleistocene were believed to cause isolation of marine taxa in refugia, resulting in diversification among lineages. Recently, ocean current was also found to be another factor affecting gene flow by restricting larval dispersal in animals. Macroalgae are unique in having mode of reproduction that differs from that of animals. Our study on the phylogeographical pattern of the brown macroalga Sargassum polycystum using nuclear Internal Transcribed Spacer 2 (ITS2), plastidal RuBisCO spacer (Rub spacer) and mitochondrial cytochrome oxidase subunit-III (Cox3) as molecular markers revealed genetic homogeneity across 27 sites in Southeast Asia and western Pacific, in sharp contrast to that revealed from most animal studies. Our data suggested that S. polycystum persisted in single refugium during Pleistocene in a panmixia pattern. Expansion occurred more recently after the Last Glacial Maximum and recolonization of the newly flooded Sunda Shelf could have involved asexual propagation of the species. High dispersal ability through floating fronds carrying developing germlings may also contribute to the low genetic diversity of the species.
Highlights
Southeast Asia is well known to be a hotspot for biodiversity
Genetic diversity A total of 261, 191 and 185 sequences were obtained from 27 sampling sites and Genbank for Internal Transcribed Spacer 2 (ITS2) (294 bp), Rub spacer (163 bp) and Cox3 (379 bp) respectively (Table S1 in File S1)
Interspecific and intraspecific phylogenetic relationship HKY+G model determined by jMODELTEST was used to analyze the taxonomic status of haplotypes from combined sequences of ITS2, Rub spacer and Cox3
Summary
Southeast Asia is well known to be a hotspot for biodiversity. This high biodiversity is believed to have been contributed by its complex geological history. Isolated basins such as the South China Sea, Sulu Sea, Celebes Sea and Flores Sea served as refugia for marine taxa. Their isolation led to the diversification of lineages among populations [2,3,4]. The high genetic diversity in marine taxa in Southeast Asia is caused by past isolations, and by restricted larval dispersal by recent oceanic conditions
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