Genetic diversity of Gracilaria Changii and Gracilaria Edulis (Gracilariaceae,Rhodophyta) in Malaysian waters / Yow Yoon Yen

• Main Author: Yow, Yoon Yen
• Format: Thesis
• Published: 2014
• Subjects: Q Science (General); QH Natural history
• Online Access: http://studentsrepo.um.edu.my/4855/1/SHC070044_Yow_Yoon_Yen.pdf; http://studentsrepo.um.edu.my/4855/

Gracilaria is the second largest genus of red algae that is widely distributed from the sub-boreal to tropical waters, and some are endemic to the Southeast Asian countries. G. changii (Xia et Abbott) Abbott, Zhang et Xia and G. edulis (Gmelin) Silva are potential species for commercialization in Malaysia as they have high yields of good quality agar with high gel strength for production of agarose and food grade agar. There is no cultivation of Gracilaria changii and Gracilaria edulis in Malaysia and regular sampling at various coastal areas in Peninsular Malaysia has indicated that the wild populations of these species are decreasing. Little is known about intraspecific genetic diversity and phylogeographic distribution of these economically important species despite its potential commercialization. The understanding of genetic diversity in both species will provide valuable information for conservation, plant breeding management and strain selection for cultivation. To assess suitable markers for inferring intraspecific genetic variation of the G. changii, the cox2-3 spacer and the cox1 gene were used on 40 specimens of G. changii from Peninsular Malaysia. Seven distinct mitochondrial haplotypes were identified with the cox1 gene and three mitochondrial haplotypes with the cox2-3 spacer. Intraspecific nucleotide differences ranged from 0-6 bp over 923 bp for the cox1 and 0-4 bp over 363 bp for the cox2-3 spacer, respectively. The results showed that the mitochondrial marker of the cox1 gene is a suitable intraspecific marker as it is more variable compared with the cox2-3 spacer. The cox1 gene was selected as the marker for the subsequent study which involved larger sampling areas and sampling size on the genetic diversity study of G. changii and G. edulis. This study presents the first attempt in assessing the intraspecific genetic diversity of G. changii and G. edulis from Malaysia, selected regions in Southeast Asian countries (Indonesia, Thailand, and Vietnam) and Japan using the mitochondrial marker of the cox1 gene. Eight mitochondrial haplotypes (C1-C8) were revealed from 278 specimens of G. changii with nucleotide differences ranging from 0-6 bp (0-0.7%) over 923 bp. 15 mitochondrial haplotypes (E1-E15) were identified from 140 specimens of G. edulis varying from 0-20 bp (0-2.4%) over 846 bp. Results showed that haplotype C1 and haplotype E1 were the basal haplotypes of G. changii and G. edulis, respectively. Populations at Morib (Selangor) or Teluk Pelanduk (Negeri Sembilan) were suggested as probable ancestral populations of G. changii; Teluk Pelanduk (Negeri Sembilan), Batu Tengah (Malacca) or Kukup (Johore) as the ancestral populations of G. edulis. The specimens of G. edulis revealed a higher value of haplotype diversity, Hd (0.5291) and nucleotide diversity, Pi (0.00318) in comparison to G. changii (Hd = 0.3755; Pi = 0.00055). The lower haplotype diversity in G. changii relative to G. edulis in Malaysia shows either a more recent introduction or a higher rate of gene flow of G. changii relative to G. edulis. These species do not share similar histories. Their genetic variation and phylogeographic distributions may have been affected differently by the Malaysian continental drift, and recent colonization events through artificial introductions or natural distributions. The present study showed that the cox1 gene is a highly divergent genetic marker. This marker is applicable to resolve intraspecific genetic variation and phylogeographic structure for these ecologically and economically important species.