A chromosome-level genome of Portunus trituberculatus provides insights into its evolution, salinity adaptation and sex determination.

Portunus trituberculatus (Crustacea: Decapoda: Brachyura), commonly known as the swimming crab, is of major ecological importance, as well as being important to the fisheries industry. P. trituberculatus is also an important farmed species in China due to its rapid growth rate and high economic value. Here, we report the genome sequence of the swimming crab, which was assembled at the chromosome scale, covering ~1.2 Gb, with 79.99% of the scaffold sequences assembled into 53 chromosomes. The contig and scaffold N50 values were 108.7 kb and 15.6 Mb, respectively, with 19,981 protein-coding genes. Based on comparative genomic analyses of crabs and shrimps, the C2H2 zinc finger protein family was found to be the only gene family expanded in crab genomes, suggesting it was closely related to the evolution of crabs. The combination of transcriptome and bulked segregant analysis provided insights into the genetic basis of salinity adaptation and rapid growth in P. trituberculatus. In addition, the specific region of the Y chromosome was located for the first time in the genome of P. trituberculatus, and three genes were preliminarily identified as candidate genes for sex determination in this region. Decoding the swimming crab genome not only provides a valuable genomic resource for further biological and evolutionary studies, but is also useful for molecular breeding of swimming crabs.

QTL mapping and marker identification for sex determination in the ridgetail white prawn, Exopalaemon carinicauda.

Sex determination is an important and intriguing research topic in the field of evolutionary and developmental biology. Quantitative trait locus (QTL) mapping for sex is helpful in clarifying the sex determination system of species. In this study, a second high-resolution genetic linkage map was constructed for the ridgetail white prawn, Exopalaemon carinicauda, which included 9280 markers, covering 99.98% of the complete genome. Based on the linkage map, a highly significant sex-related QTL was first mapped to a single linkage group (LG3, LOD > 55.6). Fifty-two markers in the QTL region were significantly associated with sex (p ≤ 10-40), of which heterogametic genotypes in females supported the ZW sex determination mechanism. Six markers were verified to be significantly associated with sex in the wild population. Some sex-related genes were identified, including phospholipase D, protein kinase shaggy, and longitudinals lacking protein. These results inform our understanding of the mechanisms of sex determination in E. carinicauda.

Quantitative Trait Loci Mapping and Marker Identification for Low Salinity Tolerance Trait in the Swimming Crab (Portunus trituberculatus).

Low salinity is one of the most important abiotic factors that directly affect the abundance of the swimming crab, Portunus trituberculatus. Quantitative trait loci (QTL) mapping could be helpful in identifying the markers and genes involved in low salinity tolerance. In this study, two QTLs of low salt tolerance were mapped on linkage group 17 (LG17, 2.6-5.2 cM) based on a high-density linkage map. Ninety-five markers related to low salinity tolerance were identified via association analysis, and seventy-nine low salt-related candidate genes (including ammonium transport, aldehyde dehydrogenase, and glucosyltransferase) were screened from draft genome of the species via these markers. This represents the first report of QTL mapping for low salinity tolerance in the swimming crab, which may be useful to elucidate salinity adaptation mechanisms.