Insights into genetic variation and demographic history of sharpnose rays: examinations of three species of Telatrygon (Elasmobranchii, Dasyatidae) from the Indo-West Pacific.

Coastal and demersal chondrichthyans (sharks, rays, and skates) are expected to exhibit high levels of genetic differentiation in areas of complex geomorphology. Population genetic studies investigating the extent to which demographic history shapes the genetic structure of these fishes are rare. Here, we combined mitochondrial DNA (Cytb and ND2) and 8 nuclear microsatellite loci from 244 individuals to examine the population genetic structure and demographic history of the 3 Indo-West Pacific species of sharpnose rays (Telatrygon zugei, Telatrygon biasa, and Trygon crozieri). High levels of genetic variation both within and between species were identified. Phylogenetic analysis partitioned haplotypes into 2 lineages supporting divergence of T. zugei from T. crozieri and T. biasa during the Pleistocene. Furthermore, microsatellite-based clustering analyses identified 4 genetic groups (i.e. T. zugei from Japan, T. zugei from coastal China, T. biasa from Gulf of Thailand, and T. crozieri from the Andaman Sea). Measurements of genetic differentiation also support these 4 groups. Additionally, Pleistocene demographic expansions were examined in all genetic groups. The climate oscillations and current hydrologic cycles in the Indo-West Pacific appear to coincide with the hypothesis regarding speciation and the observed demographic history trends of the sharpnose rays. Considering the species group has, until recently, been thought to be one species, these results are critical for defining management units and guiding conservation efforts to preserve stingray biodiversity.

Mitochondrial genome of Japanese angel shark Squatina japonica (Chondrichthyes: Squatinidae).

Squatina japonica belonging to the monogenetic family Squatinidae is endemic to the Northwest Pacific. The complete mitochondrial genome sequence of S. japonica is 16,689 bp long and comprises 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 control region. The base composition of the genome is 31.10% A, 31.04% T, 24.42% C, and 13.43% G. The geographic clade and phylogenetic relationship of S. japonica are ambiguous. Therefore, studying the complete mitochondrial genome of S. japonica is highly important to understand the aforementioned aspect and to analyze the conservation genetics in the genus Squatina.

Mitochondrial genome of longheaded eagle ray Aetobatus flagellum (Chondrichthyes: Myliobatidae).

The complete mitochondrial genome sequence of the Aetobatus flagellum is 20,201 bp long and consists of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and 1 control region (CR). The base composition of the genome is 30.9% A, 28.2% T, 27.1% C and 13.8% G. Comparing mtDNA of elasmobranchs submitted in NCBI, our study not only identified the longest mitochondrial genome with 4490 bp CR in A. flagellum, but also strongly revealed that records in the northwest Pacific may belong to a separate species from those distributed in Indonesia.

A new species of eagle ray Aetobatus narutobiei from the Northwest Pacific: an example of the critical role taxonomy plays in fisheries and ecological sciences.

Recent taxonomic and molecular work on the eagle rays (Family Myliobatidae) revealed a cryptic species in the northwest Pacific. This species is formally described as Aetobatus narutobiei sp. nov. and compared to its congeners. Aetobatus narutobiei is found in eastern Vietnam, Hong Kong, China, Korea and southern Japan. It was previously considered to be conspecific with Aetobatus flagellum, but these species differ in size, structure of the NADH2 and CO1 genes, some morphological and meristic characters and colouration. Aetobatus narutobiei is particularly abundant in Ariake Bay in southern Japan where it is considered a pest species that predates heavily on farmed bivalve stocks and is culled annually as part of a 'predator control' program. The discovery of A. narutobiei highlights the paucity of detailed taxonomic research on this group of rays. This discovery impacts on current conservation assessments of A. flagellum and these need to be revised based on the findings of this study.