Chromosome-scale genome assembly of brown-spotted flathead Platycephalus sp.1 provides insights into demersal adaptation in flathead fish.

Flatheads are valuable commercial fish species endemic to the Indo-West Pacific. Due to their economic value and unique biological traits, such as metamorphosis and camouflage, they serve as ideal marine organisms for studies on demersal adaptation and evolution. The brown-spotted flathead (Platycephalus sp.1) is the most widely distributed in the northwestern Pacific. Despite the lack of a valid scientific name, it has been long recognized and exploited in the marine fisheries of China, Japan, and Korea. In the current study, we applied Illumina, PacBio, and Hi-C sequencing to assemble a chromosome-scale genome for this species. The assembled genome was 660.63 Mb long with a scaffold N50 of 28.65 Mb and 100% of the contigs were anchored onto 24 chromosomes. We predicted 22 743 protein-coding genes, 94.8% of which were functionally annotated. Comparative genomic analyses suggested that Platycephalus sp.1 diverged from its common ancestor with Gasterosteus aculeatus ~88.4 million years ago. The expanded gene families were significantly enriched in immune, biosynthetic, and metabolic pathways. Furthermore, three shared Gene Ontology terms and 377 common positively selected genes were identified between flathead and flatfish species, suggesting that these genes may contribute to demersal adaptation in flatheads. The assembled genomic data provide a valuable molecular resource for further research on the biological and adaptive evolution of flathead species.

Whole-genome resequencing of Japanese whiting ( Sillago japonica) provide insights into local adaptations.

The genetic adaptations of various organisms to heterogeneous environments in the northwestern Pacific remain poorly understood. Heterogeneous genomic divergence among populations may reflect environmental selection. Advancing our understanding of the mechanisms by which organisms adapt to different temperatures in response to climate change and predicting the adaptive potential and ecological consequences of anthropogenic global warming are critical. We sequenced the whole genomes of Japanese whiting ( Sillago japonica) specimens collected from different latitudinal locations along the coastal waters of China and Japan to detect possible thermal adaptations. Using population genomics, a total of 5.48 million single nucleotide polymorphisms (SNPs) from five populations revealed a complete genetic break between the Chinese and Japanese groups, which was attributed to both geographic distance and local adaptation. The shared natural selection genes between two isolated populations (i.e., Zhoushan and Ise Bay/Tokyo Bay) indicated possible parallel evolution at the genetic level induced by temperature. These genes also indicated that the process of temperature selection on isolated populations is repeatable. Moreover, we observed natural candidate genes related to membrane fluidity, possibly underlying adaptation to cold environmental stress. These findings advance our understanding of the genetic mechanisms underlying the rapid adaptations of fish species. Species distribution projection models suggested that the Chinese and Japanese groups may have different responses to future climate change, with the former expanding and the latter contracting. The findings of this study enhance our understanding of genetic differentiation and adaptation to changing environments.

Description of a new species, Sillago nigrofasciata sp. nov. (Perciformes, Sillaginidae) from the southern coast of China.

A new Sillago species, the black-banded sillago, Sillago nigrofasciata sp. nov., is described based on 302 specimens sampled from the southern coast of China. Morphological comparisons have been conducted between the new species and ten other Sillago species. The results show that the new species is characterized by a black mid-lateral band below the lateral line when fresh; other characteristics are similar to those of Sillago sihama but subtle differences exist on the swim bladder between Sillago nigrofasciata sp. nov. and S. sihama. A detailed description and illustrations are provided for the new species. The validity of this new species is also supported by a genetic comparison using sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene.

Genomic characteristics and profile of microsatellite primers for Acanthogobius ommaturus by genome survey sequencing.

Acanthogobius ommaturus is one of the suitable species to study the genetic mechanism of adaptive evolution, but there are few reports on its genetics. In the present study, the genomic survey sequencing method was used to analyze the genome characters of A. ommaturus. A total of 50.50 G high-quality sequence data were obtained in the present study. From the 19-mer distribution frequency, the estimated genome size was 928.01 Mb. The calculated sequence repeat rate was about 38.31%, the heterozygosity was approximately 0.17%, and the GC% content was approximately 40.88%. Moreover, 475,724 simple sequence repeats (SSRs) were identified. Among them, dinucleotide repeats were the most (53.70% of the total SSRs), followed by tri- (35.36%), hexa- (4.59%), tetra- (4.57%) and penta- (1.77%) nucleotide repeats type. This is the first genome-wide feature of this species to be reported.

Whole genome survey analysis and microsatellite motif identification of Sebastiscus marmoratus.

The marbled rockfish Sebastiscus marmoratus is an ecologically and economically important marine fish species distributed along the northwestern Pacific coast from Japan to the Philippines. Here, next-generation sequencing was used to generate a whole genome survey dataset to provide fundamental information of its genome and develop genome-wide microsatellite markers for S. marmoratus. The genome size of S. marmoratus was estimated as approximate 800 Mb by using K-mer analyses, and its heterozygosity ratio and repeat sequence ratio were 0.17% and 39.65%, respectively. The preliminary assembled genome was nearly 609 Mb with GC content of 41.3%, and the data were used to develop microsatellite markers. A total of 191,592 microsatellite motifs were identified. The most frequent repeat motif was dinucleotide with a frequency of 76.10%, followed by 19.63% trinucleotide, 3.91% tetranucleotide, and 0.36% pentanucleotide motifs. The AC, GAG, and ATAG repeats were the most abundant motifs of dinucleotide, trinucleotide, and tetranucleotide motifs, respectively. In summary, a wide range of candidate microsatellite markers were identified and characterized in the present study using genome survey analysis. High-quality whole genome sequence based on the "Illumina+PacBio+Hi-C" strategy is warranted for further comparative genomics and evolutionary biology studies in this species.

Levels and patterns of genetic variation in Japanese whiting (Sillago japonica) based on mitochondrial DNA control region.

Japanese whiting (Sillago japonica) is a commercially important demersal fish distributed along the coasts of East Asia and becomes recently an aquaculture species. Despite its commercial importance, the levels and patterns of population genetic variation remain poorly understood. In this study, 346 specimens were collected from 14 localities along the coastal waters of China, Korea and Japan and their genetic variation was analyzed with mtDNA control region (D-loop) sequences. A total of 131 polymorphic sites were detected which determined 294 haplotypes. A pattern with high levels of haplotype diversity (h = 0.999 ± 0.001) and nucleotide diversity (л = 0.030 ± 0.015) was detected in the examined range. Analyses of analysis of molecular variance (AMOVA) and Fst showed that no significant genetic differentiation existed among China, Korea and Japan populations, excepting for the populations between Ise Bay (IBP) sample and the other ones. Minimum spanning tree (MST), neutrality tests, mismatch distribution and Bayesian skyline analyses indicated that the species along coastline of China, Korea and Japan have experienced population expansions originated in its most recent history at about 106-423 kya during the late Pleistocene glaciations and deglaciations periods.

Genetic signatures of polymorphic microsatellite loci in the Ambiguous silver pomfret, Pampusargenteus (Teleostei, Stromateidae).

Pampusargenteus is a broadly exploited pelagic fish species, commonly misidentified as Pampusechinogaster. Genetic variation and population structure in Pampusargenteus was studied based on seven microsatellite loci. The observed high average allele number, heterozygosity values, and polymorphism information content of P.argenteus suggested high genetic diversity. No population genetic differentiation was detected based on the results of pairwise F st, three-dimensional factorial correspondence analysis (3D-FCA) and STRUCTURE analysis, which implied continuous gene flow. Wilcoxon signed rank tests did not indicate significant heterozygosity excess, and recent genetic bottleneck events were not detected. Coupled with previous mitochondrial DNA results, the findings presented here indicate that high gene flow characterizes the current phylogeographic pattern of the species.

Restricted Gene Flow for Gadus macrocephalus from Yellow Sea Based on Microsatellite Markers: Geographic Block of Tsushima Current.

The Pacific cod Gadus macrocephalus is a demersal, economically important fish in the family Gadidae. Population genetic differentiation of Pacific cod was examined across its northwestern Pacific range by screening variation of eight microsatellite loci in the present study. All four populations exhibited high genetic diversity. Pairwise fixation index (Fst) suggested a moderate to high level of genetic differentiation among populations. Population of the Yellow Sea (YS) showed higher genetic difference compared to the other three populations based on the results of pairwise Fst, three-dimensional factorial correspondence analysis (3D-FCA) and STRUCTURE, which implied restricted gene flow among them. Wilcoxon signed rank tests suggested no significant heterozygosity excess and no recent genetic bottleneck events were detected. Microsatellite DNA is an effective molecular marker for detecting the phylogeographic pattern of Pacific cod, and these Pacific cod populations should be three management units.

Population Structure and Adaptive Divergence in a High Gene Flow Marine Fish: The Small Yellow Croaker (Larimichthys polyactis).

The spatial distribution of genetic diversity has been long considered as a key component of policy development for management and conservation of marine fishes. However, unraveling the population genetic structure of migratory fish species is challenging due to high potential for gene flow. Despite the shallow population differentiation revealed by putatively neutral loci, the higher genetic differentiation with panels of putatively adaptive loci could provide greater resolution for stock identification. Here, patterns of population differentiation of small yellow croaker (Larimichthys polyactis) were investigated by genotyping 15 highly polymorphic microsatellites in 337 individuals of 15 geographic populations collected from both spawning and overwintering grounds. Outlier analyses indicated that the locus Lpol03 might be under directional selection, which showed a strong homology with Grid2 gene encoding the glutamate receptor δ2 protein (GluRδ2). Based on Lpol03, two distinct clusters were identified by both STRUCTURE and PCoA analyses, suggesting that there were two overwintering aggregations of L. polyactis. A novel migration pattern was suggested for L. polyactis, which was inconsistent with results of previous studies based on historical fishing yield statistics. These results provided new perspectives on the population genetic structure and migratory routes of L. polyactis, which could have significant implications for sustainable management and utilization of this important fishery resource.

Description and DNA Barcoding of a New Sillago Species, Sillago shaoi (Perciformes: Sillaginidae), in the Taiwan Strait.

Jia-Guang Xiao, Na Song, Zhi-Qiang Han, and Tian-Xiang Gao (2016) Reliance only on morphology to identify fishes to the species level is challenging when the diagnostic characters are similar among related taxa. Within the genus Sillago, differences among some nominal species are generally small and restricted to a few characters. In this study, a new species of Sillago (Sillago shaoi sp. nov.) was described using morphology and genetic analysis of DNA barcoding. The morphological results differentiated S. shaoi sp. nov. from eight other Sillago spp. Genetic analysis verified both the validity of the current taxonomy and the relationships between the new species and other Sillago species. S. shaoi sp. nov. formed a monophyletic group as a distinct phylogenetic species and showed strong genetic divergence from others. The present study also revealed that the COI gene was an effective molecular marker for identifying Sillago species.

The possible physical barrier and coastal dispersal strategy for Japanese grenadier anchovy, Coilia nasus in the East China Sea and Yellow Sea: evidence from AFLP markers.

In order to ascertain the taxonomic status of the Ariake Sea population of Japanese grenadier anchovy, Coilia nasus, and assess the contemporary possible genetic barrier between the west and east coastal waters of the East China Sea, we used amplified fragment length polymorphism (AFLP) markers to detect the genetic structure of C. nasus, in the East China Sea and Yellow Sea. Eighty-one individuals of C. nasus were collected from five locations and 12 individuals of Coilia mystus were sampled from the Yangtze River Estuary. A total of 371 loci were detected by five primer combinations, 310 of which were polymorphic (83.56%). Analysis of molecular variation (AMOVA) and pairwise fixation index (FST) revealed significant genetic differentiation among five samples, indicating limited gene flow among populations. The dendrogram for populations by neighbor-joining (NJ) cluster analysis provided evidence of a clear relationship between genetic and geographic patterns, supporting significant genetic differentiation between China coastal populations and Ariake Sea populations. Compared to the genetic divergence between C. nasus and C. mystus, the level of genetic differentiation between China and the Ariake Sea populations of C. nasus is obvious below the species level, indicating isolated populations of C. nasus in the Ariake Sea. Isolation by distance analysis revealed that direct ocean distance with deep-water at the continental slope and high salinity between west and east coastal waters of the East China Sea served as major physical barrier to C. nasus, supporting the coastal dispersal pattern in this estuarine species, and rejecting offshore dispersal strategy.

Population genetic structure of chub mackerel Scomber japonicus in the Northwestern Pacific inferred from microsatellite analysis.

Marine pelagic fishes are usually characterized by subtle but complex patterns of genetic differentiation, which are influenced by both historical process and contemporary gene flow. Genetic population differentiation of chub mackerel, Scomber japonicus, was examined across most of its range in the Northwestern Pacific by screening variation of eight microsatellite loci. Our genetic analysis detected a weak but significant genetic structure of chub mackerel, which was characterized by areas of gene flow and isolation by distance. Consistent with previous estimates of stock structure, we found genetic discontinuity between Japan and China samples. Local-scale pattern of genetic differentiation was observed between samples from the Bohai Sea and North Yellow Sea and those from the East China Sea, which we ascribed to differences in spawning time and migratory behavior. Furthermore, the observed homogeneity among collections of chub mackerel from the East and South China Seas could be the result of an interaction between biological characteristics and marine currents. The present study underlies the importance of understanding the biological significance of genetic differentiation to establish management strategies for exploited fish populations.

Complete mitochondrial genome sequence of bighead croaker Collichthys niveatus (Perciformes, Sciaenidae): a mitogenomic perspective on the phylogenetic relationships of Pseudosciaeniae.

The monophyly and phylogenetic relationships of Pseudosciaeniae have long been controversial. Here we describe the mitochondrial genome (mitogenome) sequence of Collichthys niveatus. It is a circular double-stranded DNA molecule of 16,450 base pairs (bp) in length with a standard set of 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs), 13 protein-coding genes as well as a non-coding control region. The mitogenome of C. niveatus shared common features with those of other bony fishes in terms of gene arrangement, base composition, and tRNA structures. The C. niveatus mitogenome exhibited pronounced strand-specific asymmetry in nucleotide composition, which was also reflected in the codon usage of genes oriented in opposite directions. Contrary to the typical structure of the control region, the central conserved blocks (CSB-D, -E, and -F) could not be detected in C. niveatus mitogenome. Phylogenetic analysis based on whole mitogenome sequences provided strong support for the monophyly of Pseudosciaeniae, and sister-group relationships of C. niveatus+Collichthys lucidus and Larimichthys crocea+Larimichthys polyactis, which was consistent with the traditional taxonomy. Unexpected divergence was found in two C. niveatus mitogenomes and several hypotheses were proposed to explain this observation including misidentification and introgressive hybridization between C. niveatus and L. polyactis, and polyphyletic origin of C. niveatus. We considered species misidentification to be the main hypothesis. However, additional data is essential to test these proposed hypotheses.

Complete mitochondrial genome sequence of the spinyhead croaker Collichthys lucidus (Perciformes, Sciaenidae) with phylogenetic considerations.

The complete mitochondrial genome of the spinyhead croaker Collichthys lucidus was determined using long-PCR and primer walking methods. It is a circular molecule of 16,451 bp in length with a standard set of 22 tRNAs, 2 rRNAs, 13 protein-coding genes as well as a non-coding control region in the same order as those of the other bony fishes. C. lucidus mitogenome exhibited a clear strand-specific bias in nucleotide composition, as evidence by a GC- skew of the H-strand of -0.319. The strand-specific bias was also reflected in the codon usage of genes oriented in opposite directions. All tRNA genes except for tRNA( Ser(AGY)) harbored the typical cloverleaf secondary structures and possessed anticodons that matched the vertebrate mitochondrial genetic code. Contrary to the typical structure of control region consistig of TAS, central, and CSB domains, there were no central conserved blocks available in C. lucidus mitogenome. Despite extensive studies based on both morphology and molecules, phylogenetic position of C. lucidus with Sciaenidae is still controversial. Our phylogenetic results provided more evidence to support previous morphological studies and consistently placed C. lucidus as a sister taxon to Collichthys niveatus, with both of these taxa forming the monophyletic Collichthys.

Pleistocene isolation in the Northwestern Pacific marginal seas and limited dispersal in a marine fish, Chelon haematocheilus (Temminck & Schlegel, 1845).

The Northwestern Pacific has a unique tectonic and geographical history with several marginal seas separating Asia from the Pacific Ocean. During low sea level periods of Pleistocene glaciations, populations might have been isolated in three marginal seas: the Sea of Japan, East China Sea and South China Sea. Following postglacial sea level rise, we would expect the populations isolated in the three regions to have been homogenized by high dispersal potential. To assess these hypotheses, we explore the intraspecific phylogeographical patterns in redlip mullet, Chelon haematocheilus. Fragments of 435 bp at the 5' end of mitochondrial DNA control region were sequenced for 272 individuals from nine localities over most of the species' range. Three distinct lineages were detected, which might have diverged in the three marginal seas during Pleistocene low sea levels. Contrary to homogenization expectation, there were strong differences in the geographical distribution of the three lineages. Analyses of molecular variance and the population statistic Phi(ST) also revealed significant genetic structure among populations of the three marginal seas. These results indicate that gene flow in Chelon haematocheilus is far more restricted spatially than predicted by the potential dispersal capabilities of this species. The lack of phylogeographical structure in East China Sea may reflect a recent range expansion after the last glacial maximum and insufficient time to attain migration-drift equilibrium.

Late Pleistocene divergence and subsequent population expansion of two closely related fish species, Japanese anchovy (Engraulis japonicus) and Australian anchovy (Engraulis australis).

Climatic oscillations during the Pleistocene ice ages produced great changes in species' geographical distribution and abundance, which could be expected to have genetic consequences. Living in the temperate upwelling zones of the northwestern Pacific, Japanese anchovy (Engraulis japonicus) might have been affected by these severe climatic oscillations. To investigate the effects of Pleistocene climatic changes on the evolution in Japanese anchovy, fragments of 522 bp at the 5' end of mitochondrial DNA control region were sequenced for 241 individuals from 13 localities and 37 individuals of Australian anchovy. Japanese anchovy and Australian anchovy are reciprocally monophyletic and a late Pleistocene transequatorial divergence between the two species was indicated. High levels of haplotype diversity (>0.99) were found for all samples, indicating a high level of genetic diversity. Analyses of molecular variance and the conventional population statistic F(ST) revealed no significant genetic structure throughout the range of Japanese anchovy. Both mismatch distribution analyses and neutrality tests suggested a late Pleistocene population expansion for both Japanese anchovy (79,000-317,000 years ago) and Australian anchovy (45,000-178,000 years ago).

Differential population structuring and demographic history of two closely related fish species, Japanese sea bass (Lateolabrax japonicus) and spotted sea bass (Lateolabrax maculatus) in Northwestern Pacific.

The Quaternary cold periods in the Northwestern Pacific are thought to have heavily influenced the amount and distribution of intraspecific genetic variation in marine fishes. To estimate the demographic history and genetic structure of Lateolabrax maculatus and L. japonicus in the Northwestern Pacific, 256 individuals were sampled from 19 localities throughout the distribution range of the two species. Mitochondrial DNA variation was analyzed using DNA sequence data from the cytochrome b gene and control region. Nucleotide diversity was much higher in L. japonicus (0.030) than in L. maculatus (0.012). The demographic history of the two species was examined using neutrality tests and mismatch distribution analyses and results indicated Pleistocene population expansion in both species. Estimates of population expansion time suggested earlier population expansion in L. japonicus than in L. maculatus. Molecular variance analyses showed differential genetic structuring for these two closely related species. The results indicated that L. japonicus is panmictic throughout its range. In contrast, populations of L. maculatus showed statistically significant levels of genetic structuring. Pattern of isolation by distance was observed in L. maculatus, suggesting that L. maculatus is in genetic equilibrium. In contrast, L. japonicus did not exhibit isolation by distance.

[Chemical constituents from the mangrove plant Ceriops tagal].

AIM: To investigate the secondary metabolites of the mangrove plant Ceriops tagal. METHODS: Column chromatography techniques including HPLC were used for the separation and purification, and extensive spectral analysis including various 2D NMR spectra were employed for structure elucidation. RESULTS: Nine compounds, namely, tagalsins A (1), ent-5alpha-dolabr-4 (18) -ene-15S,16-diol (2), squalene (3), betulinic acid (4), lup-20 (29) -en-3-on-28-oic acid (5), betulin (6), lup-20 (29) -en-3-on-28-ol (7), beta-sitosterol (8), n-hexacosanylferulate (9) were obtained. Of which 1 and 2 belong to dolabrane diterpene. CONCLUSION: Compound 1 is a new compound, and 2 to 9 are isolated from this species for the first time.