Genetic diversity and variation in wild populations of dark sleeper (Odontobutis potamophila) in China inferred with microsatellite markers

Population Structure, Genetic Diversity, and Conservation Strategies of a Commercially Important Sleeper Fish, Odontobutis potamophilus (Gobiiformes: Odontobutidae) Based on Gene-Capture Data

Odontobutis potamophilus is a popular food fish in China, distributed mainly in the middle and lower reaches of the Yangtze River, where it is a famous delicacy and a newly focused species for aquaculture. The wild populations of O. potamophilus are facing the problem of overfishing and habitat degradation. Therefore, it is very necessary to investigate and protect the wild populations of O. potamophilus. In this study, 72 fish were sampled from 18 different sites over its distribution range. Nuclear sequence data of 4,267 loci were collected using a gene-capture method. Phylogenetic reconstruction revealed that there were three major clades: Oujiang clade (OJ), Qiantang and lower Yangtze clade (QY), and middle Yangtze clade (MY). The discriminant analysis of principal components (DAPC) and a STRUCTURE analysis confirmed that there are three major groups within O. potamophilus. A fastsimcoal2 analysis corroborated the population history and suggested that there was discernible gene flow among these three groups, especially between QY and MY. Estimated pairwise F ST suggested that Linhai (LH) and Shexian (SX) populations were the most divergent pair (F ST = 0.7077). Taking the nucleotide diversity, population divergence, and admixture status altogether into consideration, we recommend that the LH, Gaoyou (GY) and Chaohu (CH) populations could be protected as the preferred resource for breeding projects. According to the results of genetic analyses, all populations of O. potamophilus should be protected due to low genetic diversity.

Evolutionary conservation and divergence of Vasa, Dazl and Nanos1 during embryogenesis and gametogenesis in dark sleeper (Odontobutis potamophila)

Germline-specific genes, Vasa, Dazl and Nanos1, have highly conserved functions in germline development and fertility across animal phyla. In this study, the full-length sequences of Opvasa, Opdazl and Opnanos1 were cloned and characterized from the dark sleeper (Odontobutis potamophila). Gonad-specific expression patterns of Opvasa and Opdazl were confirmed in adult tissues by quantitative real-time PCR (qRT-PCR). Different from Opvasa and Opdazl, the expression of Opnanos1 was ubiquitously detected in all examined tissues except for the liver and spleen. Time-course dynamic expressions during embryogenesis were assessed, and all three genes (Opvasa, Opdazl and Opnanos1) persisted at a high level until gastrulation. qRT-PCR and Western blotting analyses revealed that all three genes were highly expressed throughout gametogenesis. In testis, the expressions of all three genes at the mRNA and protein levels were down-regulated during spermatogenesis. In ovary, different expression patterns were found, and all three genes had a differential role in translational regulation during oogenesis. The expressions of Opvasa, Opdazl and Opnanos1 at the mRNA but not the protein level were high in stage IV. Different expression patterns were found in premeiotic gonads treated by HPG axis hormones (HCG and LHRH-A). Immunolocalization analysis demonstrated that in testis, Opvasa, Opdazl and Opnanos1 were detected in spermatogonia and spermatocytes but absent in the meiotic products, such as spermatids and spermatozoa. In ovary, Opvasa, Opdazl and Opnanos1 persisted at a high level throughout oogenesis. These findings indicated that Opvasa, Opdazl and Opnanos1 played an important role in mitotic and early meiotic phases of oogenesis and spermatogenesis, and they functioned as maternal factors in early embryogenesis. Their proteins could be used as three new markers for germ cells during gametogenesis in O. potamophila gonad. Our data laid a good foundation for improving the breeding efficiency of O. potamophila.