A new perspective on biogeographic barrier in the flathead grey mullet (Pisces: Mugilidae) from the northwest Pacific.

BACKGROUND: The flathead grey mullet, Mugil cephalus has a global distribution in tropical, subtropical and temperate seas worldwide. Previous studies proposed that globally distributed M. cephalus comprises at least 14 different lineages, and divided into two or three groups in the northwest Pacific. Therefore, we hypothesized that there may exist at least two lineages in Korea. OBJECTIVE: The aim of this study was to determine the number of lineages of flathead grey mullet in Korea, and detail their biogeographic boundaries, and taxonomic implications using various molecular markers. METHODS: Two partial mitochondrial DNA (mtDNA) gene sequences (COI and 16S rRNA) and nine microsatellite loci were analyzed in 260 individuals from ten locations. RESULTS: Phylogenetic trees from two partial mtDNA gene sequences revealed two distinct lineages of flathead grey mullet (P distance = 0.016-0.021). Lineage 1 (L1) consisted of mullets from all locations except for the Pacific coasts of Japan, while lineage 2 (L2) consisted of mullets from the Jeju Island, Shanghai, and the Pacific coasts of Japan. The STRUCTURE analyses of msat data also revealed two distinct groups. CONCLUSION: This study was the first to reveal the coexistence of two lineages of flathead grey mullet in Korea. L2 was confined to the Jeju Island in Korea, implying a biogeographic boundary between the two lineages. The allopatric distribution and genetic heterogeneity between lineages may be affected by an ancient geographic isolation during the glacial period and maintained due to adaptation to oceanic characteristics. Collectively, the two lineages may be comprised of distinct species.

Cryptic diversity in the inshore hagfish, Eptatretus burgeri (Myxinidae, Pisces) from the northwest Pacific.

The fishery of inshore hagfish (Eptatretus burgeri) is particularly important from the perspective of the eel-skin leather industry in the northwest Pacific. In order to reveal the genetic diversity and population structure of E. burgeri in the northwest Pacific, we analyzed partial nucleotide sequences of three mitochondrial DNA regions (523 bp in COI, 712 bp in ND4 and 617 bp in Cytb) based on specimens collected from six locations in Korea and Japan. The genetic diversities of E. burgeri were higher in Korean locations compared to Japanese ones. AMOVA showed that E. burgeri was completely separated into two groups (group A: southern coast of Korea and western coast of Japan vs. group B: eastern coast of Japan). Furthermore, groups A and B were divided into each two lineages (lineage I: west southern coast of Korea, lineage II: east southern coast of Korea and western coast of Japan, lineage III and IV: eastern coast of Japan). Our molecular results suggest that these two groups and lineages of E. burgeri may be different evolutionary significant unit and management unit, respectively.

Evidence of shallow mitochondrial divergence in the slender armorhead, Pentaceros wheeleri (Pisces, Pentacerotidae) from the Emperor Seamount Chain.

Competitive overexploitation of the slender armorhead, Pentaceros wheeleri, a deep-sea fish inhabiting the Emperor Seamount Chain caused a serious population decline. Therefore, it is urgently necessary to clarify its genetic diversity and connectivity among populations of P. wheeleri for appropriate stock management. For this, we compared 677 base pairs (bp) of mitochondrial (mt) DNA control region (CR) sequences of 80 individuals from three seamounts (the Milwaukee, Kinmei, and Koko Seamounts) in the southern part of the Emperor Seamount Chain. Contrary to our expectation, the three seamount populations showed high genetic diversity, not yet reflecting effects from the recent population decline or due to mixed two clades. Analysis of molecular variance indicated no significant genetic differentiation between seamount populations, however, the neighbour-joining tree and minimum spanning network showed significant separation into two clades (K2P distance= 1.2-3.2%, ϕst = 0.5739, p < .05) regardless of seamount. The divergence time between the two clades was estimated to be 0.3-0.8 Mya, during the period of Pleistocene glacial cycles, suggesting that associated environmental changes and the unique life history traits of Pentaceros spp. might have resulted in the initiation of divergence between these clades.

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.