First draft genome for the sand-hopper Trinorchestia longiramus.

Crustacean amphipods are important trophic links between primary producers and higher consumers. Although most amphipods occur in or around aquatic environments, the family Talitridae is the only family found in terrestrial and semi-terrestrial habitats. The sand-hopper Trinorchestia longiramus is a talitrid species often found in the sandy beaches of South Korea. In this study, we present the first draft genome assembly and annotation of this species. We generated ~380.3 Gb of sequencing data assembled in a 0.89 Gb draft genome. Annotation analysis estimated 26,080 protein-coding genes, with 89.9% genome completeness. Comparison with other amphipods showed that T. longiramus has 327 unique orthologous gene clusters, many of which are expanded gene families responsible for cellular transport of toxic substances, homeostatic processes, and ionic and osmotic stress tolerance. This first talitrid genome will be useful for further understanding the mechanisms of adaptation in terrestrial environments, the effects of heavy metal toxicity, as well as for studies of comparative genomic variation across amphipods.

New insight into hybridization and unidirectional introgression between Ammodytes japonicus and Ammodytes heian (Trachiniformes, Ammodytidae).

Based on northern (NOL) and southern (SOL) mitochondrial lineages, recently, it proposed the new species Ammodytes heian and revived the species name Ammodytes japonicus to describe sand lances from the northwestern Pacific Ocean. This study used molecular methods to investigate genetic relationships between the two sand lance species in Korea and Japan. In total, 154 specimens were collected from four locations in Korea (Baengnyeongdo in the Yellow Sea, Tongyeong in the Korean Strait, and Jumunjin and Gijang in the East Sea), and 50 specimens were collected from a single location in Japan (Wakkanai in the Okhotsk Sea). Mitochondrial DNA analysis demonstrated that the individuals from Baengnyeongdo and Tongyeong all belonged to the SOL, whereas those from Gijang, Jumunjin, and Wakkanai included individuals from both the NOL and SOL (over 75% NOL). Population structure analyses were performed on the same individuals using seven microsatellite DNA markers. The population structure analysis based on 201 specimens identified two clusters (named as northern group and southern group), with the admixture proportion (q) of < 0.1 for the northern group in the Backyeongdo and Tongyeong sand lances and < 0.1 for the southern group in the Wakkanai sand lances. The high heterogeneity indicated that the former was probably A. japonicus and the latter probably A. heian. However, the admixture proportion in the Jumunjin and Gijang sand lances was 0.71-0.75 for the southern group, indicating that hybridization and unidirectional introgression from SOL to NOL occurs in southwestern margin of the East Sea. Our findings illustrate the speciation process based on different patterns of gene flow between Korean and Japanese sand lance, which is strongly influenced by both the paleo-climatic change and the contemporary local oceanic current pattern.