The authors have declared that no competing interests exist.
Conceived and designed the experiments: PA SWC. Performed the experiments: SWC. Analyzed the data: SWC CCC PA AC. Contributed reagents/materials/analysis tools: SWC PA CCC AC GG CT. Wrote the manuscript: SWC PA CCC. Served as contact person / collaborator in Indonesia so no specific permission for collecting in Indonesia was required: GG.
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
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. The repeated glacial cycles during Pleistocene caused fluctuation of sea level. This resulted in the formation of exposed land (e.g. Sunda Shelf) in relatively shallow sea that connected adjacent islands to form land bridges [
Most of the marine phylogeographical studies in Southeast Asia, however, were on animals. Seaweeds, which exhibit a largely different dispersal mode than the animals, may provide new insights in understanding the phylogeographical processes in this region. Oceanic circulation has a profound effect on much of the population structure of marine animals as genetic connectively is highly associated with their pelagic larval duration. Unlike animals, seaweeds produce immobile germlings after fertilization and dispersal distance is expected to be much shorter. This may lead to higher genetic differentiation among seaweed populations. In North Atlantic, extensive phylogeographical studies have been carried out using multilocus molecular markers on brown algae [
There are currently more than 300 species of
Field studies did not involve any endangered or protected species. This study also involved collaborative works between institutions so no special permits were needed for sampling. Samples were collected from 22 sampling sites either by snorkeling or sampling during low tide (
Pie chart size is proportional to sample size. Abbreviations for sample sites are given in Table S1 in File S1. Dominant currents are shown in solid lines [
Primers for the three markers and PCR profiles were listed in [
To ensure all the samples were
To investigate the phylogenetic relationship within
Population structure of
A Mantel test [
Demographic history was only conducted for Cox3 data as there was no molecular clock available for ITS2 and Rub spacer. Mismatch distribution was used to detect any recent population expansion which is indicated with a unimodel distribution [
The mutation rate of Cox3 of
A total of 261, 191 and 185 sequences were obtained from 27 sampling sites and Genbank for ITS2 (294 bp), Rub spacer (163 bp) and Cox3 (379 bp) respectively (Table S1 in
HKY+G model determined by jMODELTEST was used to analyze the taxonomic status of haplotypes from combined sequences of ITS2, Rub spacer and Cox3. Phylogenetic trees inferred from Bayesian Inference and Maximum Likelihood methods with other species in the subgenus
Tajima’s D and Fu’s Fs gave significant negative value for ITS2 and insignificant negative value for Rub spacer and Cox3 (Table S1 in
1: South China Sea and Gulf of Thailand; 2: West Coast of Malay Peninsula; 3: West Java; 4: Celebes Sea and Flores Sea; 5: Guam; 6: Pacific Islands. Directionality of gene flows between selected subregions based on Cox3 is shown with Ne, the mean number of effective migrants per generation. All values are within the range of 440 to 665. Other details of gene flow among subregions based on all three markers are listed in Tables S6-S8 in File S1 respectively.
Mismatch distribution of all markers fit the sudden expansion model (
Bar chart and line graph indicate the observed and expected frequency respectively.
The overall genetic diversity of
Among the three molecular markers used, Rub spacer showed lowest genetic variability that is comparable to that in other studies on
Overall, the population structure of
Different from the marine animals studied,
Asexual propagation alone would not be sufficient to explain the lack of genetic structure in
Nonetheless, despite an overall homogeneous pattern of
Star-shaped haplotype network (
The absence of significant population structure in
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Voucher numbers of sequences from Genbank are presented after species name. Representative sequences from each haplotype of
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We thank Phang Siew Moi (Malaysia), Floredel Dangan, Edna Ganzon-Fortes, Lea Jimenez, Danilo Largo, Filemon Romero (Philippines), Jaruwan Mayakun, Achana Prathep (Thailand), Dang Diem Hong, Dam Duc Tien (Vietnam), for their hospitality during our collecting trips or for help with the collection of samples. Yeung Chung Wing assisted in collection especially in sites in Indonesia. We also thank