Studies On The Morphology And Genetics Of Trachidermus Fasciatus Populations And Four Species Of Gadidae Fish

Roughskin sculpin,Trachidermus fasciatus,which belongs to Scorpaeniformes,Cottidae, is a ClassⅡof the National Key Protected Wildlife List and in China Red Data book of Endangered Animals-Pisces.It feeds on zooplankton,fish and shrimp,and has a catadromous life style.Three geographical groups of T.fasciatus,collected from Dandong, Qinhuangdao and Wendeng,are described and compared on morphological characteristics and sequence comparison analysis of mtDNA and ISSR.Seven meristic characters and twenty morphometric characters are measured and the data are analyzed by principie component analysis method,multivariate analysis method and one-way ANOVA to study the morphological variations among 3 groups of T.fasciatus. There are no significant differences among the three groups on mefistic characters except the number of caudal fin rays,for morphometric characters there are significant difference (P＜0.05) among the three groups in seven morphological characters,which are still within the population level.By amplyfing with PCR technique,86 partial mitochondrial control reigion sequences are determined from 3 groups,including Dandong,Qinhuangdao(aquacultured) and Wendeng. Sequence length of the control region in individuals of T.fasciatus is 512bp.Genetic structure analysis showed a high level genetic diversity of Dandong group(h=0.997,π=0.01228),while other two groups is not very high.The distance between groups is equvaliant to that within groups.The AMOVA analysis indicated that the T.fasciatus have obviously genetic variance,a molecular phylogenetic tree constructed using the neighbor-joining(NJ) method suggested that the 48 haplotypes are not assigned to three clades associated with geographic regions.Both mismatch distribution analyses and neutrality tests suggested a late population expansion for T.fasciatus population.402 bp sequence which encode the cytochrome b gene of mitochondrial DNA are amplified successfully.5 haplotypes are found in 13 individuals,including 5 variable sites.The nucleotide diversity(π) is 0.3%and haplotype diversity(h) is 0.628.The Cyt b gene is more conservative compared to the control region.Mitochondrial 16S rRNA gene is amplified and sequenced,4 haplotypes are detected in 11 individuals of T.fasciatus.Of the 572 base pairs in the 16S rRNA gene,3 sites were polymorphic.The results shows that 16S rRNA is the most conservative part among the three parts in mtDNA.Inter-Simple Sequence Repeat(ISSR) systems are used to detect the genetic diversity in T. fasciatus.Eighty-five individuals from three populations are used 6 ISSR primers screened, 22～27 clear and reproducible bands are generated.A total of 324 reproducible loci ranging from 0.2 to 2.5kp were amplified from all the 85 individuals.The Shannon's diversity indices are 0.3507 in wild population(Dandong population) and 0.2769 in cultured population (Qinhuangdao population).Shannon's index and the Gst showed that the wild stock in Dandong and Wendeng have the highest genetic variation.Apparently the inter-stock's Gst (0.34900;0.39646) are higher than the wild population(0.07240).And the gene flow between wild populations(Dandong and Wendeng)(6.40608) are higher than the reared groups of Qinhuangdao(0.93266;0.76116),indicating that the genetic difference between wild and reared stocks hasn't reached the population level yet.In order to identify differentiation of species of Cradidae fishes and evaluate the genetic variance,sequence comparison of mtDNA 16S rRNA,COI and Cyt b gene fragments are employed for Theragra chalcogramma,Gadus macrocephalus,Micromesistius poutassou and Eleginus gracilis.539 bp nucleotide sequences for 16S rRNA gene,601 bp for COI gene and 385 bp for Cyt b gene are obtained,respectively.One hundred and eighty-nine nucleotide substitutions are detected among the four species,most of which are synonymous transitions at the third codon positions.The percentage of A+T is high.Nucleotide composition analysis reveal that the four species investigation shows a strong bias against guanine(G) in the two protein-coding genes and particularly at the third codon positions.Sequence analysis indicated that the variation level of intra-species is low.The nucleotide substitution rates of three gene segments arranged from high to low was Cyt b＞COI＞16S rRNA.The estimated divergence time between G.macrocephalus and T.chalcogramma based on Cyt b gene sequence is about 2.19 million years,which is apparently lower than that between E.gracilis and M.poutassou (about 6.53 million years).The result indicate a Miocene divergence and a Pliocene divergence of the four species.Based on the genetic distances,NJ phylogenetic tree is made and indicated that there is a closer relationship between G.macrocephalus and T. chalcogramma.