Mantis Shrimp Oratosquilla Oratoria Research Articles

Time-Course and Tissue-Specific Molecular Responses to Acute Thermal Stress in Japanese Mantis Shrimp Oratosquilla oratoria.

Current understanding of adaptability to high temperatures is increasingly important as extreme weather events that can trigger immediate physiological stress in organisms have occurred more frequently. Here, we tracked transcriptomic responses of gills, hepatopancreas, and muscle to acute thermal exposure at 30 °C for 0.5, 6, and 12 h in an economically important crustacean, Oratosquilla oratoria, to gain a preliminary understanding of the tissue-specific and dynamic physiological regulation process under acute heat stress. The unique physiological responses of muscle, hepatopancreas, and gills to acute thermal stress were associated with protein degradation, lipid transport, and energy metabolism in O. oratoria, respectively. Functional enrichment analysis of differentially expressed transcripts and heat-responsive gene clusters revealed a biphasic protective responsiveness of O. oratoria developed from the early responses of signal transduction, immunity, and cytoskeleton reorganization to the responses dominated by protein turnover and energy metabolism at the mid-late stages under acute heat stress. Noteworthy, trend analysis revealed a consistently upregulated expression pattern of high molecular weight heat shock protein (HSP) family members (HSP60, HSP70, and HSP90) during the entire thermal exposure process, highlighting their importance for maintaining heat resistance in O. oratoria. Documenting the whole process of transcriptional responses at fine temporal resolution will contribute to a far-reaching comprehension of plastic responses to acute heat stress in crustaceans, which is critical in the context of a changing climate.

Long-term and monthly changes in abundance, size composition and spatial distribution of the mantis shrimp Oratosquilla oratoria in the Bohai Sea

Long-term and monthly changes in abundance, size composition and spatial distribution of the mantis shrimp Oratosquilla oratoria in the Bohai Sea

Cryptic diversity and population genetic structure of the mantis shrimp Oratosquilla oratoria in South Korea.

The Japanese mantis shrimp Oratosquilla oratoria has two genetic lineages in its Chinese and Japanese populations, which are considered cryptic species. However, the Korean O. oratoria populations have only been studied morphologically, and their genetic diversity pattern remains unknown. To examine the genetic diversity of the Korean O. oratoria populations to explore its cryptic diversity and underlying processes. We sequenced the mitochondrial cytochrome c oxidase I gene of 107 O. oratoria individuals from 8 sampling sites in South Korea. Their genetic diversity and haplotype data were compared to previously reported data from 16 Chinese and 6 Japanese populations. The haplotype network, analysis of molecular variance, FST values, and Bayesian skyline plot of the Korean O. oratoria populations confirmed that they were divided into two genetic lineages corresponding to the two previously identified cryptic species, which might be correlated to ocean currents and water temperature. In addition, the population genetic analysis indicated that both lineages had high genetic diversity. Although the Geoje region belongs to the southern group, it only contained lineage N, which could be related to the specific environmental characteristics of Geoje or the hybridization of the two lineages of O. oratoria. Korean O. oratoria populations have enough cryptic diversity to be described as cryptic species and are correlated with ocean currents and water temperatures. Lineage N dominance in Geoje might be related to environmental characteristics or hybridization.

Insights into adaptive divergence of Japanese mantis shrimp Oratosquilla oratoria inferred from comparative analysis of full-length transcriptomes

The heterogeneous seascapes in the northwestern Pacific (NWP) can be important selective forces driving adaptive divergence of marine coastal species distributed along the gradients. Here, we tested this hypothesis in Japanese mantis shrimp (Oratosquilla oratoria) with a wide distribution in the NWP and a significant north-south population structure. To this end, the full-length (FL) transcriptomes of northern and southern O. oratoria were firstly sequenced using PacBio single molecule real-time sequencing technology. Based on the FL transcriptome data, we captured large-scale FL transcripts of O. oratoria and predicted the FL transcriptome structure, including coding region, transcription factor and long noncoding RNA. To reveal the divergence between northern and southern O. oratoria, we identified 2,182 pairs of orthologous genes and inferred their sequence divergences. The average differences in coding, 5’ untranslated and 3’ untranslated region were 1.44%, 2.79% and 1.46%, respectively, providing additional support to previous proposition that northern and southern O. oratoria are two species. We provided further evolutionary context to our analysis by identifying positive selected genes (PSGs) between northern and southern O. oratoria. In total, 98 orthologs were found evolving under positive selection and involved several environmentally responsive genes associated with stress response, immunity and cytoskeletal organization, etc. Furthermore, we found PSGs also diverged in gene expression response of northern and southern O. oratoria to heat stress. These findings not only highlight the importance of genetic variation in these genes in adapting to environmental changes in O. oratoria, but also suggest that natural selection may act on the plasticity of gene expression to facilitate O. oratoria adaptation to environmental gradients. Overall, our work contributes to understanding how marine coastal species has evolved to adapt to heterogeneous seascapes in the NWP.

Metabolomic Alterations in the Digestive System of the Mantis Shrimp Oratosquilla oratoria Following Short-Term Exposure to Cadmium.

Mantis shrimp Oratosquilla oratoria is an economically critical aquatic species along the coast of China but strongly accumulates marine pollutant cadmium (Cd) in its digestive system. It is necessary to characterize the toxicity of Cd in the digestive system of mantis shrimp. The metabolic process is an essential target of Cd toxicity response. In this work, we used ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC-TOF-MS) for untargeted metabolomics to characterize the metabolic changes in the digestive system of O. oratoria, exposed to 0.05 mg/L for 96 h. The aim of this study was to further investigate the effect of O. oratoria on Cd response to toxicity and develop biomarkers. Metabolomics analysis showed the alteration of metabolism in the digestive system of mantis shrimp under Cd stress. A total of 91 metabolites were differentially expressed and their main functions were classified into amino acids, phospholipids, and fatty acid esters. The enrichment results of differential metabolite functional pathways showed that biological processes such as amino acid metabolism, transmembrane transport, energy metabolism, and signal transduction are significantly affected. Based on the above results, the Cd-induced oxidative stress and energy metabolism disorders were characterized by the differential expression of amino acids and ADP in mantis shrimp, while the interference of transmembrane transport and signal transduction was due to the differential expression of phospholipids. Overall, this work initially discussed the toxicological response of Cd stress to O. oratoria from the metabolic level and provided new insights into the mechanism.

Evaluating Impacts of Trophic Interactions on the Effectiveness of Single-Species Fisheries Management

Single-species fisheries management (SSFM) is applied to many fisheries ecosystems around the world. The associated ecological impacts are usually not well understood due to the lack of considering trophic interactions among species in the ecosystem. This impedes the implementation of SSFM in an ecosystem context and reduces our ability to understand the possible ecological impacts of fishing activities. This study focuses on two economically important species in the Jiaozhou Bay, China: the short-lived, fast-growing, and relatively abundant Japanese mantis shrimp (Oratosquilla oratoria) and the long-lived, slow-growing, and less abundant Korean rockfish (Sebastes schlegelii). We evaluated how varying trophic interactions influenced O. oratoria and S. schlegelii (i.e., target-species) who were managed under constant fishing pressure. The increase of fishing pressure to other species (i.e., non-target species) was beneficial to O. oratoria and S. schlegelii. O. oratoria was more sensitive to the decrease of fishing pressure to other species. The predation mortality of age-0 O. oratoria increased with the increased fishing pressure to other species. The predation mortality of age-1 O. oratoria and age-0 S. schlegelii had negative relationships with the fishing pressure to other species. Age-1 S. schlegelii seemed not to be sensitive to the changes in trophic interactions. The predation mortality of O. oratoria and S. schlegelii had bigger changes than the starvation mortality after fishing changed. It suggested the prey-predator relationship had a bigger impact than the food competition. The increase of high-trophic-level fish Johnius belangerii fishery positively impacted O. oratoria, but negatively impacted S. schlegelii. S. schlegelii was more sensitive to the changes of the low-trophic-level fish Pholis fangi fishery. Given the complex dynamics of ecosystems, this study highlights the importance of species-specific responses of fishes to shifting trophic interactions in fisheries management.

Reproductive biology and biochemical changes in female mantis shrimp Oratosquilla oratoria (Stomatopoda) with ovary development from the Tianjin coastal zone of Bohai Bay

Overexploitation and preliminary artificial breeding have led to an increasing interest in studying the reproductive biology and biochemical changes during gonad development in Oratosquilla oratoria. In this study, we established an accurate one-to-one correspondence between physical (and ovarian) morphology and ovarian histology during different maturity stages and improved the understanding of trophic dynamics with the progress of maturation, which will aid the aquaculture and artificial breeding techniques for this commercially important species. Based on ovarian histology and morphology, the ovaries were differentiated into six developmental stages, with five changes in color: immature stage (black), previtellogenesis (black), primary vitellogenesis (faint yellow), secondary vitellogenesis (golden yellow), maturation (light orange) and spent stage (brownish yellow). The visible colors of the median triangular structure of the telson can be used as an external morphological indicator of ovarian development status, and indicates that the females are near-ripe broods stocks when median triangular structure is almost filled with yellow. The gonadosomatic index (GSI) showed a statistically significant inverse correlation with the hepatopancreatic index (HPI) and muscle-somatic index (MSI). GSI significantly increased until stage III and HPI significantly decreased at stage II and recovered slowly thereafter. Nevertheless the MSI increased during the first two stages and decreased thereafter. A continuous decline in feeding intensity of females with ovarian development was found. The protein level in the muscle and hepatopancreas increased with protein accumulation in the ovary. Ovarian lipid concentration continued to increase, while, as in the hepatopancreas and muscle, lipid content decreased significantly at stage II and then recovered rapidly, followed by a sharp decline. Glycogen concentrations in the ovary kept steady, while in the hepatopancreas and muscle, there was a downward trend after a rise to the highest value. In conclusion, the energy for supporting ovarian development inevitably relies on energy reserves in the hepatopancreas and muscle and attention should be given to how to promote the transfer of organic reserves and energy to the ovaries during stock culture.

Evaluation of trace metals and rare earth elements in mantis shrimp Oratosquilla oratoria collected from Shandong Province, China, and its potential risks to human health

This study provided the primary data of selected trace elements and rare earth elements from 120 samples of mantis shrimp Oratosquilla oratoria (O. oratoria) caught from three sites in the Shandong Province, China and evaluated the potential health risk of shrimp consumption from this region. The calculation of estimated daily intake (EDI), target hazard quotient (THQ) and total target hazard quotient (TTHQ) showed that the contents of all target TREs were below respective permitted limits recommended by China, with the exceptions of Cd and iAs levels. In addition to pollution, results indicated that TREs concentrations in O. oratoria were also impacted by characteristics of O. oratoria. The distribution patterns of REEs in O. oratoria did not differ from those in the sediment and other marine organisms, following the abundance rule. Consumption of O. oratoria from Shandong Province is potentially harmful to human health due to high levels of Cd and iAs.

Nuclear microsatellites reveal population genetic structuring and fine-scale pattern of hybridization in the Japanese mantis shrimp Oratosquilla oratoria.

The interplay between historical and contemporary processes can produce complex patterns of genetic differentiation in the marine realm. Recent mitochondrial and nuclear sequence analyses revealed cryptic speciation in the Japanese mantis shrimp Oratosquilla oratoria. Herein, we applied nuclear microsatellite markers to examine patterns and causes of genetic differentiation in this morphotaxon. Population structure analyses revealed two genetically divergent and geographically structured clades in O. oratoria, one dominating the temperate zone of the Northwestern (NW) Pacific and the other occurring in the subtropical and tropical waters where are influenced by the Kuroshio Current. Two sympatric zones, one around the Changjiang Estuary in China coast and the other in the northern Japan Sea, were demonstrated to be hybrid zones where introgressive hybridization occurred asymmetrically. The interaction between historical climate shifts and contemporary factors (e.g., freshwater discharge, temperature gradient and isolation by distance) may contribute to the present-day genetic architecture in the Japanese mantis shrimp. Range shift induced by climate changes and oceanographic factors may promote hybridization and gene flow between the O. oratoria complex. Our results provide insights into the interacting mechanisms that give rise to diversification and speciation of coastal species in the NW Pacific.

Molecular identification and phylogenetic relationship of Erugosquilla massavensis (Kossmann, 1880) from the Mediterranean Sea, Egypt

The Erythraean species of mantis shrimp, Erugosquilla massavensis, has been reported as the first Lessepsian migrant stomatopod to the Mediterranean Sea in 1933, off Alexandria, Egypt via the Suez Canal. Currently, it extended to the middle and western Mediterranean competing with the native spot-tail mantis shrimp Squilla mantis (Linnaeus, 1758). The continuous increase of invasive species to the Mediterranean claimed the necessity to update and revise the identification of those early migrants. The present study aimed to confirm the morphological identification of E. massavensis from the coast of the Egyptian Mediterranean Sea using the DNA barcoding gene cytochrome oxidase subunit I (COI) and conducting a phylogenetic analysis. Genomic DNA of samples collected from the Mediterranean Sea at Port Said in 2016 was extracted and COI was amplified and sequenced. Our phylogenetic analysis revealed that E. massavensis (MH447072 and MH447073) constitutes a single monophyletic clade and appeared more linked with E. woodmasoni than the Japanese mantis shrimp Oratosquilla oratoria (divergence value < 3%). The phylogenetic relationship between E. massavensis, E. woodmasoni, and O. oratoria was confirmed by the Neighbor-Joining tree. The present study confirmed the morphological identification and document, for the first time in GenBank/EMBL/ DDBJ genetic databases, the genetic status of E. massavensis from the Mediterranean of Egypt using COI.

Optimization of environmental variables in habitat suitability modeling for mantis shrimp Oratosquilla oratoria in the Haizhou Bay and adjacent waters

Habitat suitability index (HSI) models have been widely used to analyze the relationship between species abundance and environmental factors, and ultimately inform management of marine species. The response of species abundance to each environmental variable is different and habitat requirements may change over life history stages and seasons. Therefore, it is necessary to determine the optimal combination of environmental variables in HSI modelling. In this study, generalized additive models (GAMs) were used to determine which environmental variables to be included in the HSI models. Significant variables were retained and weighted in the HSI model according to their relative contribution (%) to the total deviation explained by the boosted regression tree (BRT). The HSI models were applied to evaluate the habitat suitability of mantis shrimp Oratosquilla oratoria in the Haizhou Bay and adjacent areas in 2011 and 2013–2017. Ontogenetic and seasonal variations in HSI models of mantis shrimp were also examined. Among the four models (non-optimized model, BRT informed HSI model, GAM informed HSI model, and both BRT and GAM informed HSI model), both BRT and GAM informed HSI model showed the best performance. Four environmental variables (bottom temperature, depth, distance offshore and sediment type) were selected in the HSI models for four groups (spring-juvenile, spring-adult, fall-juvenile and fall-adult) of mantis shrimp. The distribution of habitat suitability showed similar patterns between juveniles and adults, but obvious seasonal variations were observed. This study suggests that the process of optimizing environmental variables in HSI models improves the performance of HSI models, and this optimization strategy could be extended to other marine organisms to enhance the understanding of the habitat suitability of target species.

Feeding intensity and molecular prey identification of the mantis shrimp, Oratosquilla oratoria (De Haan, 1844), in the Tianjin coastal zone of Bohai Bay

AbstractBohai Bay, a representative semi‐enclosed bay of China, has been severely impacted in recent decades by rapid human development. Although the mantis shrimp Oratosquilla oratoria plays an important role in the Bohai Bay ecosystem and fishery, its feeding ecology and the impact of habitat changes on its feeding habits are poorly known. In this study, we sought to identify its feeding strategy through the separation of stomach contents, and to describe its trophic ecology during maturation in the Tianjin coastal zone of Bohai Bay by the DNA barcoding method using a fragment (about 690 bp) of the mitochondrial cytochrome oxidase I (CO I) gene. A total of 594 specimens were collected from March to July 2018, and 347 (58.42%) stomachs were found to have food remains. More than half of the O. oratoria individuals had poor feeding activity, and the degree of feeding of females was higher than that of males, but there was no significant difference in the visual fullness index and the fullness weight index (FWI) between sexes for each month. In addition, the feeding activity of O. oratoria was consistent across the months, suggesting in artificial breeding programs it is not worried too much about the accessional diet supplied to the female bloodstocks except maintaining their normal food. A total of 167 retrieved prey items yielded 187 readable sequences; 86.63% of these sequences could be assigned to the species level. Consequently, 25 different prey taxa covering all readable sequences were identified, showing O. oratoria is a generalist predator. In terms of percent composition by frequency of occurrences (%N), crustaceans and fishes accounted for the same and highest percentage (35.83%) in the mantis shrimp diet, followed by mollusks (24.59%) and the remaining marine organisms (3.73%) including Polychaeta (2.67%), Sagittoidea (0.53%), and Chromadorea (0.53%). The result shows the benthic fish Oxudercidae (family) appears to be an especially important food supply for O. oratoria during maturation. The degree of cannibalism decreased with an increase in diet species and the frequencies of cannibalism in this study was noticeably higher than that in previous studies, suggesting that cannibalism may be a significant feeding strategy in the mantis shrimp O. oratoria in the Tianjin coastal zone of Bohai Bay, and because of the frequently cannibalistic behavior, the high stocking density of broodstocks should be avoided.

Effect of salinity fluctuation on the transcriptome of the Japanese mantis shrimp Oratosquilla oratoria

Salinity fluctuation may detrimentally affect the composition and biological processes of crustaceans. As a euryhaline crustacean, Oratosquilla oratoria can survive at salinities ranging from 20 psu to 40 psu. Therefore, we designed five salinity gradients (20, 25, 30, 35, and 40 psu) and 66.39 Gb clean transcriptome data were obtained after O. oratorias were exposed to each gradient for 24 h. All clean data were spliced into 50,482 unigenes and 17,035 unigenes were annotated in at least one database. Compared with 30 psu, 1010, 851, 1733 and 2188 differentially expressed genes were obtained at 20, 25, 35 and 40 psu, respectively. Results also showed that the osmoregulation of O. oratoria is primarily regulated by lipid and amino acid metabolism, amongst others. No significant up-regulated pathways were enriched at 25 psu and 35 psu, although more significant down-regulated pathways were obtained at 35 psu. Therefore, we assumed that the optimum survival salinity of O. oratoria may range from 25 psu to 35 psu. However, 35 psu may be more suitable for O. oratoria. In addition, 55 unigenes that encode putative inorganic ion exchanges were identified. This study aims to provide fundamental information for understanding the osmoregulation mechanisms of crustaceans.

Ultrastructure of spermiogenesis and the distribution of spermatozoal nuclear histones in the Japanese mantis shrimp, Oratosquilla oratoria (Crustacea: Stomatopoda).

The Japanese mantis shrimp Oratosquilla oratoria (Stomatopoda; Crustacea) is one of the most economically important aquatic species of Pacific shrimp and it is distributed from Japan to the coast of China, the Philippines, the Malay Peninsula, and the Hawaiian Islands. Early studies described certain characteristics of spermatogenesis and the sperm ultrastructure in Stomatopoda, but the composition of sperm basic nuclear proteins (SBNPs) remains completely unknown. We studied the sperm ultrastructure of O. oratoria using transmission electron microscopy and the histone composition using immunofluorescence and immunoelectron microscopy. We found that the spherical nucleus is adjacent to the electron translucent external coat, which occurs in early spermatids. The acrosomal structure begins to form at the junction of the nucleus and the external coat. At the mid‐spermatid stage, part of the chromatin appears to be more electron‐dense than the external coat side. The aflagellate sperm of O. oratoria, are rounded or slightly ovoid in shape and have a consistent granular nucleus, an acrosome structure of pushpin shape and a spherical vesicular body in which faintly granular material is scattered. The acrosome consists of an acrosomal vesicle, perforatorium, and subacrosomal material. The sperm contains histones H2A, H2B, H3, H4, H3.3, H2AX, and H2AZ as well as some histone modifications, that is, H3K9me3, H3K4me2, H3S10ph, H4Kac, and H2A + H4S1ph. Histones are localized not only in the nucleus of the sperm but also in other structures outside the nucleus. The results may provide new perspectives for systematic studies of crustaceans and their sperm chromatin components. These findings extend the study of the sperm structure of Stomatopoda and provide basic data to elucidate the epigenetic mechanism of fertilization.

Isolation and characterization of microsatellite markers for exploring introgressive hybridization between the Oratosquilla oratoria complex.

The Japanese mantis shrimp Oratosquilla oratoria is one of the most dominant stomatopod species found in coastal waters of the northwestern Pacific. We previously reported cryptic speciation and hybridization in this taxon by integrating mitochondrial and nuclear evidence. The present study aims at developing potential useful microsatellite markers for the O. oratoria complex through transcriptome sequencing, with a view to reveal the occurrence of hybridization. Of the 100 tested microsatellites, 55 were experimentally validated. 24 of these microsatellites were transferable across different species of the O. oratoria complex and showed polymorphic among individuals. The average number of alleles, observed and expected heterozygosity per locus was 6.125, 0.446 and 0.577 for the temperate species, and 6.083, 0.444 and 0.578 for the subtropical and tropical species. We also explore genetic differentiation and hybridization between O. oratoria cryptic species using these 24 microsatellite loci. The pairwise FST values and phylogenetic tree indicated a strong genetic differentiation between the two cryptic species. In addition, Bayesian analysis provided evidence for the presence of hybridization between the O. oratoria complex. These markers provide valuable genomic resources for exploring introgressive hybridization and expanding understanding of evolution in the O. oratoria complex.

Genetic structure analysis of mantis shrimp Oratosquilla oratoria based on mitochondrial DNA control region sequence.

The genetic relationships of mantis shrimp Oratosquilla oratoria between the coastal waters of China and Japan were not well studied. To reveal the genetic differentiation and genetic structure among populations, we collected populations of mantis shrimp O. oratoria from the coastal waters of China and Japan to analyze the mtDNA control region variation. A total of 309 individuals of O. oratoria were collected from 13 localities (11 from China and 2 from Japan) and a segment of mitochondrial DNA control region was sequenced. Three hundred nine haplotypes were defined, yielding a very high haplotype diversity and nucleotide diversity. Two lineages of O. oratoria were revealed and displayed strong differences in the geographical distribution. In the coastal waters of China, the geographic distribution of the two lineages was completely separated by the Yangtze River estuary; however, the lineages showed geographic sympatry in two populations from Japan. Based on the lineage distribution, three groups were defined. There was no significant genetic differentiation among the populations within the three groups, indicating high gene flow within each group. Significant and negative values for Tajima D and Fu's Fs tests, and mismatch distributions for two lineages indicated population expansion. The present result confirmed that the freshwater outflow from the Yangtze River formed a physical barrier and affected gene exchange. The different distribution patterns of the two lineages in coastal waters of China and Japan indicated that the larvae of O. oratoria were transferred from China to the coastal waters of Japan with a one-way gene flow.

Population genetic structure of the mantis shrimp Oratosquilla oratoria (Crustacea: Squillidae) in the Yellow Sea and East China Sea

The mantis shrimp Oratosquilla oratoria is an ecologically and economically important species in the Western Pacific. In present study, the population genetic structure of Oratosquilla oratoria from the Yellow Sea and East China Sea was examined with mitochondrial DNA control region sequences. In total, 394 samples were collected from 18 locations and 102 haplotypes were obtained. For the Yellow Sea, the overall nucleotide diversity and haplotype diversity were 0.006 9 and 0.946 8, respectively; while across all the East China Sea locations, the overall nucleotide diversity and haplotype diversity were 0.027 94 and 0.979 0, respectively. The results of AMOVA and pairwise FST (0.145 2, P < 0.001) revealed moderate differentiation between the Yellow Sea and East China Sea populations of O. oratoria. However, neither the neighbor-joining tree nor haplotype network showed clades with geographic pattern, which indicated considerable gene flow was existed between the Yellow Sea and East China Sea, and supporting the high larval dispersal ability in this species. Mismatch distribution analysis and neutrality tests suggested that O. oratoria has undergone population expansion event, and the Pleistocene glacial cycles might have an impact on the historical demography of O. oratoria. The genetic information obtained in this study can provide useful information for sustainable improvements for capture fisheries management strategies.

De novo transcriptome analysis and differentially expressed genes in the ovary and testis of the Japanese mantis shrimp Oratosquilla oratoria by RNA-Seq

The mantis shrimp Oratosquilla oratoria is a widely distributed, commercially important crustacean species. Although its conservation and the development of successful artificial breeding technologies have recently received considerable attention, there are currently no available data regarding the molecular mechanisms in controlling reproduction. In this study, we performed transcriptome sequencing of the testis, ovary, female and male eyestalks and the androgenic gland of O. oratoria, and compared the expression pattern of transcripts from the testis and ovary libraries to identify genes involved in gonadal development. A total of 147,130,937 clean reads were retrieved after removing the adapters in reads and filtering out low-quality data. All the reads were assembled into 94,990 unigenes (23,133 in testis and ovary) with an average length of 783 base pairs (bp) and N50 of 1502 bp. A search of all-unigenes against COG, GO, KEGG, KOG, Pfam, Swiss-Prot and Nr databases resulted in a total of 19,404 annotated unigenes. Comparison of the sequences in the ovary and testis libraries revealed that 1188 unigenes were up-regulated in the ovary and 2732 were up-regulated in the testis. Twenty ovary-up-regulated and 21 testis-up-regulated unigenes were confirmed by quantitative real-time PCR. Additionally, 13,437 simple sequence repeats (SSRs) and 275,799 putative single nucleotide polymorphisms (SNPs) were identified. The important functional genes and pathways identified here provide a valuable dataset for understanding the molecular mechanisms controlling gonad development in O. oratoria, and the numerous (13,437 SSRs and 275,799 SNPs) molecular markers obtained here will provide fundamental basis for functional genomic and population genetic studies of O. oratoria.

Cryptic diversity in the Japanese mantis shrimp Oratosquilla oratoria (Crustacea: Squillidae): Allopatric diversification, secondary contact and hybridization

Mounting evidence of cryptic species in the marine realm emphasizes the necessity to thoroughly revise our current perceptions of marine biodiversity and species distributions. Here, we used mitochondrial cytochrome oxidase subunit I (mtDNA COI) and nuclear ribosomal internal transcribed spacer (nrDNA ITS) to investigate cryptic diversity and potential hybridization in the Japanese mantis shrimp Oratosquilla oratoria in the Northwestern (NW) Pacific. Both mitochondrial and nuclear gene genealogies revealed two cryptic species in this morphotaxon, which was further confirmed by extensive population-level analyses. One cryptic species is restricted to cold waters with a distribution range corresponding to temperate affinities, while the other dwelled warm waters influenced by the Kuroshio Current. Their divergence was postulated to be attributable to the vicariant event which resulted from the isolation of the Sea of Japan during the middle Pliocene (c. 3.85 Mya, 95% HPD 2.23–6.07 Mya). Allopatric speciation was maintained by limited genetic exchange due to their habitat preferences. Furthermore, the observation of recombinant nrDNA ITS sequence and intra-individual ITS polymorphism suggested recent hybridization event of the two cryptic species occurred in sympatric areas. Our study also illustrated that the Changjiang River outflow might act as an oceanic barrier to gene flow and promoted allopatric diversification in O. oratoria species complex.

Energy reserves and gonad steroid levels during the reproductive cycle of the Japanese mantis shrimp Oratosquilla oratoria De Haan, 1844 (Stomatopoda: Squillidae) in Pikou Bay, Dalian, China

Energy reserves and gonad steroid levels during the reproductive cycle of the Japanese mantis shrimp Oratosquilla oratoria De Haan, 1844 (Stomatopoda: Squillidae) in Pikou Bay, Dalian, China