Genome survey on invasive veined rapa whelk (Rapana venosa) and development of microsatellite loci on large scale.

The veined rapa whelk (Rapana venosa) is an economically important gastropod in China, but is considered as an invasive species globally. Only a few studies have examined the R. venosa genome, a genomewide survey is necessary for improving our understanding of the genome structure and size of this organism. Microsatellite markers are powerful tools for characterizing germplasms, genetic diversity and kinship among individuals. The resultant data are applicable to breeding efforts in commercial aquaculture or for understanding invasion mechanisms. Here, we investigated the genome structure of R. venosa on an Illumina Hi-seq platform with ∼92× sequencing depth. We performed a K-mer analysis to estimate genome size, repeat sequences and heterozygosity. Clean reads were de novo assembled for the identification of simple-sequence repeat (SSR) loci that are suitable as markers. The estimated genome size of R. venosa was 2200.07 Mb, with a 1.41% heterozygosity rate and 67.04% repeats. We detected 5,477,450 simple-sequence repeats (SSRs), with 3,400,602 loci present as pure tandem repeats and 2,076,848 as compound motifs. We further selected and characterized 28 polymorphic markers in 78 individuals from Dandong, Laizhou, Weihai and Zhoushan in China. The range of alleles was 2-28 and the observed heterozygosity was 0.2857-0.8676. The data obtained from our genomic survey will aid the design of R. venosa whole-genome sequencing projects and advance the identification of SSR markers. Both these developments are valuable for further studies on ecological, evolutionary and genetic breeding in R. venosa.