Study On The Phylogeography And Adaptive Differentiation Of Octopus Minor Along The Coast Of China

Octopus minor is an important marine fishery resource in China and is widely distributed in the inner bay and shallow seas of Bohai Sea,Yellow Sea,East China Sea and South China Sea.At present,there is no large-scale artificial breeding of O.minor in China.The demand for its resources in China mainly comes from the fishing of wild groups.Therefore,in order to manage and protect its fishery resources more effectively and scientifically,it is necessary to study the genetic structure and adaptive differentiation pattern of O.minor population.In this study,the population genetic structure and adaptive differentiation pattern of O.minor were analyzed from three aspects: morphology,mitochondrial genome and RADseq(Restriction-site associated DNA sequencing).We hope to study the population of O.minor in the coastal area of China more comprehensively and accurately.On the basis of morphological parameters measurement,principal component analysis and cluster analysis were used to study the morphological variation and population pattern of O.minor in China.Afterwards,at the mitochondrial genome level,the complete mitochondrial genome sequences and partial gene sequences were combined to analyze the population genetic pattern and geographic differentiation of O.minor,and the historical effects of geographical and historical events and environmental factors on population differentiation were discussed.Finally,the nucleotide polymorphic loci of O.minor populations in China were further scanned by using 2b-Rad technique,and the integrity and accuracy of the complete genome information of nuclear genes were used.To explore the geographical genetic pattern of O.minor population in China and analyze the possible environmental factors and ecological processes driving the population differentiation.The potential adaptive evolutionary sites and evolutionary driving forces in O.minor populations were revealed,and the effects of adaptive evolution on the population differentiation pattern of O.minor were discussed.The main research results obtained are as follows:1.The data of 8 wild populations(including Dalian,Qingdao,Yancheng,Nantong,Shanghai,Zhoushan,Wenzhou,Dongshan)collected from the coastal areas of China were measured and analyzed by multivariate morphological measurement.The data including the length of the body,the length of the mantle,the length of the head,the width of the head,the length of the funnel,the width of the funnel,the length of the first pair of tentacle,the length of the second pair of tentacle,the length of the third pair of tentacle,the length of the fourth pair of tentacle,the length of the intercarpal membrane was mesured.Firstly,the morphological differences were analyzed based on principal component analysis(PCA),and three principal components were constructed,with a cumulative contribution rate of 69.263%.The scatter plot and cluster analysis chart based on PCA can clearly see Dongshan and Wenzhou populations are pretty different with other lacation samples.The results of cluster analysis showed that the differentiation of Dongshan population was the largest.The degree of differentiation needs to be further studied at the gene level.2.Using complete mitochondrial genome sequencing,the genetic geography of 12 representative individuals from eight geographic populations of O.minor(Dalian,Liaoning,Shandong,Shandong,Nantong,Shanghai,Zhoushan,Zhejiang,Wenzhou,Zhejiang,Xiamen,Fujian,and Dongshan,Fujian)was analyzed.The results show that the genetic diversity of O.minor is rich.The total mitochondrial genome sequence including 13 encoded protein genes,22 transfer RNA sequences,2 ribosomal RNA sequences and one control region.The sequence length was 15992 bp-16019 bp with a nucleotide frequency of A = 42.51%,T = 33.83%,C = 16.32%,and G = 7.54%.The proportion of base pairs A + T(76.14%)was significantly higher than that of the base pair G + C(23.86%).A total of 1612 variable informative sites were detected in the 12 mitochondrial genomes,of which 1 533 were minimal informational sites.The nucleotide diversity index(pi)was 0.0342 and the average number of nucleotide differences(k)was 567.139.Using the mitochondrial genome to analyze the genetic distribution of O.minor,we found that there was a clear genetic differentiation in the O.minor population of the Chinese coast,and the Dongshan population had the largest difference with other groups,with a genetic distance of 7.4%.The genetic difference of Wenzhou,Xiamen,and other groups were 2.6%.The results of multi-sample analysis based on the ATPase6 gene fragment sequence also supported the results of complete mitochondrial genome analysis.The genetic differentiation between the Dongshan population and other populations was the largest,and the genetic differentiation coefficient reached above 0.9,both of which were significant levels.By comprehensively judging the mitochondrial COI gene and controlregion,the differentiation rate of interspecies or subspecies of similar species,the differentiation of Dongshan and other groups may have reached the level of subspecies differentiation.The low Ka/Ks value showed that these differentiations were mainly from neutral evolution and were not found to be affected by natural selection.The analysis of the differentiation time based on the molecular clock theory shows that the differentiation time between the Dongshan population and other populations was 1.717 million years ago.It is estimated that this is a relatively large genetic difference caused by the unique life history of the O.minor population.The genetic differentiation between Wenzhou and Xiamen groups and Dalian,Qingdao,Nantong,Shanghai,Zhoushan is presumed to be due to the influence of the glacial-interglacial period during the Pleistocene.3.A total of 123 samples from eight O.minor populations collected from Dalian,Yantai,Yancheng,Nantong,Shanghai,Zhoushan,Wenzhou,and Dongshan were scanned for each genome using RADseq(Restriction-site associated DNA sequencing)technology.A total of 5721 polymorphic loci were found.Genetic differentiation Fst and STRUCTURE analysis further confirmed the results of morphological and mitochondrial genome analysis.The Dongshan population and other populations had the most significant differentiation,followed by the Wenzhou population.Adaptive evolution analysis shows that except for neutral evolution,adaptive evolution may play an important role in population differentiation.By using BAYESCENV and LFMM methods,489 outlier sites were found,of which 5 sites were found by comparing with the complete genome of the relative species Octopus bimaculatus.The blast alignment analysis showed that these selected genes are mostly related to osmoregulation and energy metabolism.It is speculated that the adaptability of O.minor to salinity in different sea areas plays an important role in the population differentiation.