De novo assembly of trachidermus fasciatus genome by nanopore sequencing

Trachidermus fasciatus is a roughskin sculpin fish widely located at the coastal areas of East Asia. Due to the environmental destruction and overfishing, the populations of this species have been under threat. It is important to have a reference genome to study the population genetics, domestic farming, and genetic resource protection. However, currently, there is no reference genome for Trachidermus fasciatus, which has greatly hurdled the studies on this species. In this study, we proposed to integrate nanopore long reads sequencing, Illumina short reads sequencing and Hi-C methods to thoroughly de novo assemble the genome of Trachidermus fasciatus. Our results provided a chromosome-level high quality genome assembly with a total length of about 543 Mb, and with N50 of 23 Mb. Based on de novo gene prediction and RNA sequencing information, a total of 38728 genes were found, including 23191 protein coding genes, 2149 small RNAs, 5572 rRNAs, and 7816 tRNAs. Besides, about 23% of the genome area is covered by the repetitive elements. Furthermore, The BUSCO evaluation of the completeness of the assembled genome is more than 96%, and the single base accuracy is 99.997%. Our study provided the first whole genome reference for the species of Trachidermus fasciatus, which might greatly facilitate the future studies on this species.

Population Genomic Signatures of Genetic Structure and Environmental Selection in the Catadromous Roughskin Sculpin Trachidermus fasciatus

Understanding the patterns of genetic diversity and adaptation across species’ range is crucial to assess its long-term persistence and determine appropriate conservation measures. The impacts of human activities on the genetic diversity and genetic adaptation to heterogeneous environments remain poorly understood in the marine realm. The roughskin sculpin (Trachidermus fasciatus) is a small catadromous fish, and has been listed as a second-class state protected aquatic animal since 1988 in China. To elucidate the underlying mechanism of population genetic structuring and genetic adaptations to local environments, RAD tags were sequenced for 202 individuals in nine populations across the range of T. fasciatus in China. The pairwise FST values over 9,271 filtered SNPs were significant except that between Dongying and Weifang. All the genetic clustering analysis revealed significant population structure with high support for eight distinct genetic clusters. Both the minor allele frequency spectra and Ne estimations suggested extremely small Ne in some populations (e.g., Qinhuangdao, Rongcheng, Wendeng, and Qingdao), which might result from recent population bottleneck. The strong genetic structure can be partly attributed to genetic drift and habitat fragmentation, likely due to the anthropogenic activities. Annotations of candidate adaptive loci suggested that genes involved in metabolism, development, and osmoregulation were critical for adaptation to spatially heterogenous environment of local populations. In the context of anthropogenic activities and environmental change, results of the present population genomic work provided important contributions to the understanding of genetic differentiation and adaptation to changing environments.