MORPHOLOGICAL AND GENETIC VARIATION IN THE POPULATIONS OF SARGASSUM HEMIPHYLLUM (PHAEOPHYCEAE) IN THE NORTHWESTERN PACIFIC¹

Abstract

Difficulty in species identification of Sargassum (Sargassaceae, Fucales) is partly attributed to the high polymorphism among its individuals and populations. This study aimed at assessing morphological and genetic variations in two varieties, var. hemiphyllum J. Agardh and var. chinense J. Agardh, of Sargassum hemiphyllum (Turner) C. Agardh, a widely distributed species in the northwestern Pacific. We investigated 26 measurable, five numerical, and 33 categorical morphological parameters associated with different branching levels of specimens from each of six localities within its distribution range using cluster analysis (CA) and principal coordinate analysis (PCoA). Leaf size of the primary and secondary branching levels and the vesicle size of the secondary branches of the specimens examined were determined to be the most important morphological parameters that were significantly different among populations. Change in leaf and vesicle length of individuals among the six populations followed a latitudinal gradient, with smaller leaves and vesicles associated with northern populations and larger ones in the southern populations. The possible influence of the gradual change in sea surface temperatures (SSTs) along this gradient in the northwestern Pacific on leaf and vesicle morphologies of this species was suggested. PCR-RFLP analysis of the RUBISCO spacer in the chloroplast genome revealed two distinct and highly homogenous clades, a China clade and a Japan-Korea clade, which corresponded to var. chinense and var. hemiphyllum, respectively. The formation of refugia along the "Paleo-coast" in the East China Sea during glacial periods is suggested to have led to the vicariance of ancestral populations of S. hemiphyllum and thus to have promoted genetic differentiation. The massive freshwater outflow of the Yellow and Yangtze rivers may continue to act as a barrier, prolonging the allopatric distribution of the two varieties.

190 Years of Sargassum Taxonomy, Facing the Advent of DNA Phylogenies

“…Agardh, 1820;Montagne, 1845). Nowadays, the world has been more extensively explored and phycologists study the morphological and molecular variability of populations based on tens of specimens collected at various geographical levels (Tatarenkov et al, 2007;Zhao et al, 2007;Cheang et al, 2008), sequence genomes (Oudot-Le Secq et al, 2002Secq et al, , 2006, and attempt to identify species with genetic barcodes (Saunders, 2005;Robba et al, 2006;Chase et al, 2007).…”

Phylogeography of the marine macroalga Sargassum hemiphyllum (Phaeophyceae, Heterokontophyta) in northwestern Pacific

“…ITS2 was thus used in the present study in order to reveal the possible hybridization between S. hemiphyllum and its variety. The haplotype sequences, instead of PCR‐RFLP, of Rubisco spacer ( Rbc spacer) were utilized to reveal the population structure of specimens from additional localities, compared to those in Cheang et al. (2008).…”

Thallus variation of Sargassum polycystum from Central Java, Indonesia

“…The thallus of the main branch has a bigger diameter and darker color than the following branches. The thalli of Menganti Sargassum mostly are having the sole branch, primary branch, only one individual out of 30 individuals has a secondary branch (Cheang et al 2008).…”

“…Toward the life of seaweeds, distribution of nutrition leads to variation in thalli and so its alginate content. The seaweeds dispersal is related with its genetic character and environment (Cheang et al 2008). The Sargassum seaweeds are abundantly grown along the beach with coral reefs substrate, with enough sunshine, shallowness of 4 m with the strong current, the salinity of 28-35 ‰, pH 6-8, and temperature of 25-32 0 C (Ibrahim et al 2014;Raymundo et al 2007).…”

“…Thallus variation temporary different in individuals, between individuals, the environment, and between local variations. These variations exist due to genetic polymorphism and environment (Cheang et al 2008). Polymorphism thallus forms occur in the population in the habitat and the same time.…”