Genetic Diversity and Variation in Mitochondrial COI Gene in Wild and Hatchery Populations of Saxidomus purpuratus

To investigate the genetic diversity and genetic variations of four wild (Geoje, Jinhae, Yeosu, and Boryeong) and two hatchery (Goheung and Geoje) populations of purplish Washington clam (Saxidomus purpuratus), 421 bp sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene were analyzed. A total of 149 haplotypes were identified from 358 individuals from the four wild and two hatchery populations with 109 substitutions. The genetic diversity of the wild populations and Geoje hatchery population were high, whereas the total number of haplotypes, population-specific haplotypes, and haplotype diversity were comparatively low in the Goheung hatchery population. The fixation index (F_ST) indicated that there was no significant genetic difference between the four wild populations. However, the Goheung hatchery population was significantly different from that of the Geoje hatchery, exhibiting the most pronounced difference, and two wild populations (Jinhae and Yeosu). The low genetic diversity indices exhibited by the Goheung hatchery population might have resulted from farm propagation using a limited parental stock. Therefore, to maintain genetic diversity, a proper breeding management program using more progenitors is required in hatcheries, in addition to regular monitoring of both hatchery and wild populations.

Transcriptome profiling suggests roles of innate immunity and digestion metabolism in purplish Washington clam

The purplish Washington clam (Saxidomus purpuratus) in the family Veneridae is distributed widely along the intertidal zones of northeast Asia and is increasingly being utilized as a commercially important food resource. Bivalves maintain homeostasis by regulating their food intake and digestion, innate immunity, and biotransformation in a mollusk-specific organ, the digestive gland. To understand digestive gland-specific pathways, we generated a high-quality de novo assembly of the digestive gland transcriptome of this clam using the Illumina Miseq platform. A total of 9.9 million raw reads were obtained and assembled using the Oases assembly platform, resulting in 27,358 contigs with an N50 of 433 bp. Functional gene annotations were performed using Gene Ontology, Eukaryotic Orthologous Groups, and Kyoto Encyclopedia of Genes and Genomes pathway analyses. In the transcriptome, many crucial genes involved in innate immunity and digestion metabolism were detected. A number of enzymes associated with drug metabolism were annotated, as much as that identified from the whole transcriptome of the Pacific oyster Crassostrea gigas. We provide valuable sequence information of S. purpuratus to predict functional understandings of the bivalve-specific digestive gland. This resource will be valuable for researchers comparing gene compositions and their expression levels in the digestive glands of bivalves.

Geographical Variations and Genetic Distances of Three Saxidomus purpuratus Populations ascertained by PCR Analysis

Genomic DNA samples isolated from geographical purplish Washington clam (Saxidomus purpuratus) were obtained from three different regions in the Korean Peninsula: Geoje (Geoje population; GJP), Gunsan (Gunsan population; GSP) and a site of North Korea (North Korea population; NKP). The seven primers generated the total 369 loci that can be scored from the GSP clam population. 356 fragments were generated from the NKP clam population. The complexity of the banding patterns varies dramatically between the primers and three localities. In this study, 319 loci were identified in the purplish Washington clam from Geoje and 369 in the clam population from Gunsan: 221 specific loci (69.3%) in the GJP clam population and 300 (81.3%) in the GSP population. These results demonstrate that the primer detected a large quantity of specific fragments, suggesting that the genetic variation in the GSP is higher than in the GJP population. In particular, the BION-28 primer gave DNA profiles with more fragments than the other six primers in the NKP population. The oligonucleotides primer BION-75 produced 21 unique loci to each population, which were ascertaining each population, approximately 250 bp, 300 bp and 400 bp, in the GJP population. Outstandingly, the primer BION-50 detected 21 shared loci by the three populations, major and/or minor fragments of sizes 150 bp, which were matching in all samples. With regard to average bandsharing value (BS) results, individuals from GJP population (0.743) displayed higher bandsharing values than did individuals from GSP population (0.606). In the present study, the dendrogram gained by the seven oligonucleotides primers indicates three genetic clusters: cluster 1 (GEOJE 01 ~ GEOJE 07), cluster 2 (GUNSAN 08 ~ GUNSAN 14), cluster 3 (N.KOREA 15 ~ N.KOREA 21). Among the twenty one clams, the shortest genetic distance that revealed significant molecular differences was between individuals 08 and 09 from the NKP population (genetic distance = 0.073), while the longest genetic distance among the twenty-one individuals that demonstrated significant molecular differences was between individuals GEOJE no. 03 and GUNSAN no. 09 (genetic distance = 0.669). Comparatively, individuals of GJP population were properly closely related to that of NKP population, as revealed in the hierarchical dendrogram of genetic distances. In due course, PCR analysis has revealed the significant genetic distance among three purplish Washington clam populations. PCR fragments discovered in this study could be valuable as a DNA marker of the three geographical clam populations to distinguish.

The complete mitochondrial genome of Saxidomus purpuratus (Veneroida: Veneridae)

In this study, the complete mitochondrial genome of Saxidomus purpuratus is determined, which is the first complete mitochondrial genome in the genus Saxidomus. The genome was of 19 637 bp in length, including 2 rRNAs, 22 tRNAs and 12 protein-coding genes with the order of ND3 and ND5 reversed. Maximum likelihood tree based on nucleotide sequences of 12 mitochondrial PCGs was constructed, in which S. purpuratus was clustered with 3 Meretrix species. The results are expected to provide useful data for species identification and further studies of the genus Saxidomus.