Taxonomic And Genetic Status Of Lancelet In The Coastal Waters Of Weihai And Qingdao Based On The Studies Of Cyt B Gene And CO Ⅰ Gene

Lancelet is widely distributed in tropical and temperate seas. It has so far been assumed to be the closest relative to vertebrates, and has been intensely investigated for clue as the origin of vertebrates. In China, lancelet was first reported in Xiamen Bay, and had been found in Qingdao, Changli, Maoming and the other coastal waters. Its habitat has been becoming gradually lost, leading to demographic declining tendency due to the environmental change since 1960s, and thus, lancelet was listed in OrderⅡunder the Wild Animal Protection Law in China.Cytochrome b (Cyt b) and cytochrome oxidase c subunitⅠ(COⅠ) genes are located in the functional area of mtDNA. The evolutionary rates of the two genes are higher than that of other functional areas. As Cyt b and CO I genes exist in most species and could reveal phylogenetic information of high-definition, they are considered to be good markers for examining phylogenetic relationships among species with close relationships.Lancelet in Weihai coastal waters was first documented in 2002, while there is still no accurate information about its taxonomy and genetic diversity. In this study, we analyzed cytochrome b (Cyt b) and cytochrome oxidase c subunit I (CO I) genes for samples in Weihai and Qingdao waters with previously reported sequences from other geographic regions. The genetic data show that:(1) Lancelets in Weihai and Qingdao belong to the same species Branchiostoma japonicus, and have a high level of genetic diversity, with relatively large values of haplotype diversity (h) and nucleotide diversity (π) based on both Cyt b and CO I genes;(2) Based on Cyt b and CO I genes, Fst andΦst values between lancelets in Weihai and Qingdao are very small (Fst< 0.025,Φst< 0.026), while Nm values between them are large (Nm> 9), indicating the high gene flow and low genetic differentiation between the two populations;(3) Using Cyt b gene as the DNA marker, it is estimated that the possible time of demographic expansion was 1.1 million years ago (Mya) (the middle Pleistocene) for lancelets in Weihai-Qingdao waters;(4) The divergence time between B. belcheri and B. japonicus was estimated roughly at 37.75 (early Oligocene) and 46.5 (late Eocene) Mya based on Cyt b and CO I genes, respectively.