Genetic diversity of <italic>Platycephalus</italic> sp.1 in coastal waters of China based on mtDNA <italic>cox</italic>1 sequence

Abstract

<italic>Platycephalus</italic> sp.1 is a commercially important trawling fish species widely distributed in the northwestern Pacific. For better protection and sustainable exploitation of this valuable fishery resource, sequences of partial mitochondrial <italic>cox</italic>1 gene of 155 individuals from 7 populations were determined to analyze genetic diversity of <italic>Platycephalus</italic> sp.1 in coastal waters of China. In total, 28 variable sites in the aligned 652 bp sequences determined 28 haplotypes, indicating low haplotype diversity (<italic>H</italic>_d = 0.428) and low nucleotide diversity (π=0.001 02). Fangchenggang, Lianyungang and Fuzhou population possessed the highest (<italic>H</italic>_d = 0.864), the second (<italic>H</italic>_d = 0.489) and the lowest (<italic>H</italic>_d = 0.298) haplotype diversity, while Fangchenggang, Lianyungang and Nantong population had the the highest (π=0.003 02), the second (π=0.001 24) and the lowest (π=0.000 61) nucleotide diversity respectively. Significant genetic differentiation existed between Fangchenggang population and other populations (east of Qiongzhou Strait population, composed of Dalian, Weifang, Lianyungang, Nantong, Fuzhou and Jieyang). The pairwise <italic>F</italic>_st between Fangchenggang population and east of Qiongzhou Strait population were significantly different, ranging from median to high level(0.088 61-0.189 29). Meanwhile, the result of AMOVA showed that molecular variation between Fangchenggang population and east of Qiongzhou Strait population explained 24.19 % of variance within the whole population. A star-like haplotype network indicated weak phylogenetic lineage and a possible recent fast population expansion. Furthermore, negative neutrality test result (<italic>D</italic> = -1.024, <italic>P</italic> = 0.152; <italic>F</italic>_s =-2.60, <italic>P</italic>=0.015) and unimodal mismatch distribution curve indicated a possible population expansion in Fangchengguang population around 167-56 Ka B.P. in the last interglacial period. Significant negative neutrality test result (<italic>D</italic>=-2.468, <italic>P</italic>= 0.000; <italic>F</italic>_s = - 34.02, <italic>P</italic>=0.000) and the nearly Z-shaped Bayesian skyline plot suggested a population expansion in east of Qiongzhou Srait population around 25-30 Ka B.P. in the late last glacial period. It is hypothesized that ancient <italic>Platycephulas</italic> sp.1 population had expanded in the last interglacial period, then returned to refuge in the last glacial period because of sea level drop. In the late last glacial period, it spreaded out in coastal waters of China with rising sea level and achieved population expansion. Simultaneously, Fangchenggang population gradually adapted to its environment and differentiated from east of Qiongzhou Strait population because Qiongzhou Strait had separated each other and restricted their exchange of eggs, larvae and juveniles via currents. By contrast, east of Qiongzhou Strait population was more homogeneous under the influence of current cycle and possible reproductive migration. Due to significant genetic differentiation on either side of Qiongzhou Strait, Fangchenggang population and east of Qiongzhou Strait population should be set as two independent management units respectively. As Fangchenggang population owned the highest genetic diversity, it should be protected in priority for exploitation. It is also recommended to protect Dalian population and to take measures to avoid the decrease of genetic diversity of Nantong population since they owned the highest and the lowest nucleotide diversity in east of Qiongzhou Strait population respectively.