Studies On Genetic Structure Of Sargassum Thunbergii And S. Muticum Populations And Germling Development Of S. Thunbergii

Genetic variations and structures of four populations of Sargassum thunbergii (Mert.) O. Kuntze and four populations of S. muticum (Yendo) Fensholt from Shandong peninsula of China were studied with random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers. It will be helpful in estimating the transmission of genes and the influential factors, predicting the changes of long-term survival and the continued evolution of the detected populations and species, and better understanding of the population dynamics and preservation of marine biodiversity. Besides, early development of S. thungergii germlings were carried out under controlled laboratory conditions, which will provide the basic information on reproductive biology and seedlings nursery of S. thunbergii.To the genetic variations of four populations of S. thunbergii, a total of 28 RAPD primers and 19 ISSR primers were amplified, showing 174 loci and 125 loci respectively. Calculation of genetic diversity with different indicators (P%, percentage of polymorphic loci; H, the expected heterozygosity; I, Shannon's information index) revealed low or moderate level of genetic variations within each population, and high genetic differentiations were determined with pairwise Nei's unbiased genetic distance (D) and fixation index (FST) among the populations. Analysis of molecular variance (AMOVA) was used to apportion the variations among and within the S. thunbergii populations. It indicated that most variations were ascribed to among populations, being 57.57% by RAPD and 59.52% by ISSR respectively. Furthermore, the Mantel test suggested that the genetic differentiations among the 4 populations were related to the geographical distances (r> 0.5), namely, conformed to the IBD (isolation by distance) model, as expected from UPGMA (unweighted pair group method with arithmetic averages) cluster analysis.While to four populations of S. muticum, the selected 24 RAPD primers and 19 ISSR primers were amplified, yielding 164 loci and 122 loci respectively. Estimates of genetic diversity with three different indicators (P%, H, I) revealed low or moderate level of genetic variations within each population, and high level of genetic differentiations were determined with pairwise D and FST among the populations. The Mantel test showed that two types of matrices of D and FST were highly correlated whether from RAPD (r=0.9706, P=0.009) or ISSR data (r=0.9161, P=0.009). AMOVA indicated that variations among populations were higher than those within populations, being 55.82% verse 44.18% by RAPD and 55.21% verse 44.79% by ISSR respectively. Mantel test suggested that genetic differentiation among S. muticum populations also conformed to the IBD model (r>0.6), as expected from UPGMA cluster analysis. On the whole, the high genetic structuring among the four S. muticum populations along the distant locations was clearly indicated in RAPD and ISSR analyses (r>0.9, P<0.05) in the study.Early development studies on germlings of S. thunbergii were conducted under controlled laboratory conditions. It was shown that the development of embryonic germlings belongs to the classic"8 nuclei 1egg"type in Sargassaceae, and young germlings with one or two leaflets reached 2-3 mm in length in two months under the given conditions. Temperature (10, 15, 20, 25℃) and irradiance variations (9, 18, 44, 88μEm-2s-1) significantly influenced germling growth in 1 week (ANOVA, P<0.01). The germlings showed a broad tolerance to the two environmental parameters during the 8 weeks culture, with growth recorded from 10℃to 25℃, and 9 to 88μEm-2s-1, and the optimal growth occurred at 25℃and 44μEm-2s-1. Low temperature (10℃) had remarkably negative effects on its growth. Besides, different light qualities affected the growth significantly (P<0.01), the blue light apparently cannot meet the need of the growth of young germlings compared to the white light with same intensity.