Phylogenetic Study of Sargassum polycystum (Sargassaceae, Ochrophyta) in Eastern Samar, Philippines Based on the Nuclear rDNA Sequences

Abstract

Sargassum polycystum is an economically important seaweed endemic to Southeast Asian waters. Genetic diversity studies conducted for this alga have been based on samples from various areas in the Indo-Pacific region. Here, we examined the phylogenetic patterns of S. polycystum in Eastern Samar, Philippines using the nuclear ribosomal DNA (rDNA) region – including ITS1, 5.8S gene, and ITS2. The phylogenetic and haplotype analyses using these loci indicate that the Eastern Samar samples contain 13 haplotypes. Using the ITS2 region sequences alone (to include other Indo-Pacific samples), we found that the number of Eastern Samar haplotypes was reduced to six, with one common haplotype found in Singapore and Indonesia. Our findings indicate that the genetic diversity of Eastern Samar S. polycystum is substantially higher than previously suggested. Consistent with the previous hypothesis, the populations of S. polycystum in Southeast Asian waters indicate a range expansion. The study could extend our understanding of the genetic diversities of S. polycystum in the Philippines and elsewhere.