Population Genetic Diversity Of The Habitat-forming Red Alga Gracilaria Vermiculophylla Along The China Coasts

The red alga Gracilaria vermiculophylla taxonomically belongs to Gracilaria, Gracilariaceae, Gracilariales, Florideophyceae, Rhodophyta. As a habitat-forming species, it has been demonstrated to play an essential role in shaping coastal marine communities and maintaining intertidal ecosystems along the China coasts. Few studies however have been conducted about population genetic structure and distribution patterns of genetic variation. In this master thesis, we compiled partial mitochondrial DNA cytochrome c oxidase subunit I gene(cox1) and amplified fragment length polymorphism(AFLP) marker to perform DNA-based barcoding identification and population genetic surveys. The main results are summarized as follows:First of all, 426 samples from 18 geographic populaions were collected and applied to amplify mitochondrial cox1 sequnences. We obtained 641 bp of mt DNA cox1 sequences which identified 21 polymorphic sites and yielded 15 haplotypes. Phylogenetic inferences, haplotype networking and principal coordinate analysis consistently indicated that G. vermiculophylla populations along the China coasts have diverged into two groups: the North group comprises specimens from the Yellow-Bohai Sea and the Shengsi Island, and the South group comprises specimens from the five locations south of Xiamen, Fujian province. Molecular variance and Nei’s genetic distances revealed low genetic differentiation between populations in each group while the group-level of genetic divergence is comparable to the degree of subspecies differentiation in the genus Gracilaria.Furthermore, 421 individuals from 17 geographic populaions were surveyed for AFLP analysis. Totally, 987 bands with size ranging from 60 to 500 bp were detected across all samples using 5 selective primer combinations in capillary electrophoresis. Of these bands 434 are polymorphic and account for 43.97%. We calculated genetic diversity parameters and Nei’s genetic distance, constructed Neighbor-joining phylogenetic tree and conducted PCA and Strcuture analysis. These analyses revealed that G. vermiculophylla has diverged into South and North groups which are concordant with the results detected by cox1 marker. The South group may represent the variant Gracilaria vermiculophylla var. zhengii. Within the North group, AFLP also decteced genetic differentiation between sub-group North 1 which comprised YY, EY, SY and YH individuals and sub-group North 2 which comprises specimens from LR, SD, DC, JM, CD, HN, HS and ZZ. Individuals in the two northern sub-groups exchanged, infiltrated and intergrated in the area around the Maidao Island, Qingdao city. We also detected great genetic differentiation(FST = 0.225) between Shandong peninsula and Liaodong peninsula which may be due to frequent genetic exchange(Nm = 1.486).