Fucun Wu

The oyster genome reveals stress adaptation and complexity of shell formation

The Pacific oyster Crassostrea gigas belongs to one of the most species-rich but genomically poorly explored phyla, the Mollusca. Here we report the sequencing and assembly of the oyster genome using short reads and a fosmid-pooling strategy, along with transcriptomes of development and stress response and the proteome of the shell. The oyster genome is highly polymorphic and rich in repetitive sequences, with some transposable elements still actively shaping variation. Transcriptome studies reveal an extensive set of genes responding to environmental stress. The expansion of genes coding for heat shock protein 70 and inhibitors of apoptosis is probably central to the oyster’s adaptation to sessile life in the highly stressful intertidal zone. Our analyses also show that shell formation in molluscs is more complex than currently understood and involves extensive participation of cells and their exosomes. The oyster genome sequence fills a void in our understanding of the Lophotrochozoa.

A novel shell color variant of the Pacific abalone Haliotis discus hannai Ino subject to genetic control and dietary influence.

ABSTRACT Molluscan shells may display a variety of colors, which formation, inheritance, and evolutionary significance are not well understood. Here we report a new variant of the Pacific abalone Haliotis discus hannai that displays a novel orange shell coloration (O-type) that is clearly distinguishable from the wild green-shelled abalone (G-type). Controlled mating experiments between O- and G-type abalones demonstrated apparent Mendelian segregations (1:1 or 3:1) in shell colors in F2 families, which support the notion that the O- and G-types are under strict genetic control at a single locus with a recessive o (for orange shell) allele and a dominant G (for green shell) allele. Feeding with different diets caused modifications of shell color within each genotype, ranging from orange to yellow for O-type and green to dark-brown for the G-type, without affecting the distinction between genotypes. A previously described bluish-purple (B-type) shell color was found in one of the putative oo × oG crosses, suggesting that the B-type may be a recessive allele belonging to the same locus. The new O-type variant had no effect on the growth of Pacific abalone on the early seed-stage. This study demonstrates that shell color in Pacific abalone is subject to genetic control as well as dietary modification, and the latter probably offers selective advantages in camouflage and predator avoidance.

Molecular characterization of a mollusk chicken-type lysozyme gene from Haliotis discus hannai Ino, and the antimicrobial activity of its recombinant protein

A chicken-type lysozyme was obtained and characterized from the abalone Haliotis discus hannai Ino (HdLysC). The full-length cDNA of HdLysC was 586 bp, and it contained an open reading frame of 441 bp, encoding a 147-amino acid protein with a calculated molecular mass of 15.64 kDa and an isoelectric point of 4.87. The amino acid sequence of HdLysC possessed all conserved features critical for the fundamental structure and function of c-type lysozymes, including the two catalytic residues, Glu54 and Asp70. The genomic length of HdLysC was 2865 bp, with four exons interrupted by three introns. The genomic structure of HdLysC was more similar to vertebrates than invertebrates. Many putative transcription factor binding sites involved in the immune system and cancer were found in the promoter region of HdLysC. Quantitative real-time RT-PCR detected HdLysC expression in all examined tissues, as well as in an expression profile of abalone gills challenged with bacteria Vibrio anguillarum. HdLysC transcripts were found to be most abundantly expressed in mantles, and weakly expressed in hemocytes, and increased expression of HdLysC also observed after bacterial stimulation. HdLysC was expressed in Escherichia coli, and the recombinant protein showed bacteriolytic activity against both Gram-positive and Gram-negative bacteria. Of the Vibrio species tested, more effective activity was detected against V. anguillarum.

Pacific Abalone Farming in China: Recent Innovations and Challenges

ABSTRACT Recently, cultivation of the Pacific abalone Haliotis discus hannai (Ino, 1953) in China has developed rapidly, boosted by innovations in low-cost seed production and highly efficient sea-based culture systems. Seed production of Pacific abalone differs between northern and southern China and is dependent on sufficient quantities of broodstock, excess quantities of freshly cultured diatoms during the nursery phase, and tank hygiene and newly designed attachment methodology during the intermediate culture phase. Innovations in grow-out systems for Pacific abalone, such as stock enhancement in northern regions and commercial application of cage culture methods in southern regions, have further contributed to the success of Pacific abalone farming in China. There are still challenges in Pacific abalone-farming industry in China. First, mass mortality during the nursery and postlarval culture stages hinders seed production in northern and southern regions. Second, extreme weather events, including cold waters in northern regions and typhoons and red tides in southern regions, have occurred more frequently during recent years, and these events often cause high mortality of adult abalone during the grow-out phase. Finally, Pacific abalone H. discus hannai is an introduced species from northern regions, and, therefore, summer mortality remains a major problem in most bays of southern China; moreover, the survival rate from seed to market size varies widely among growing areas. The future direction in development of Pacific abalone farming in China will be also discussed.

Yield trait improvement of bay scallops following complete diallel crosses between different scallop stocks

This study describes the complete diallel hybridization between newly introduced bay scallop stock (W) from Canada and local commercial stock (D) grown under laboratory conditions, in China. Larval survival and growth during all life stages (larvae, spat, and adult) were compared among hybrid (DW, WD) and purebred (DD, WW) populations. Significant heterosis was detected for survival during the larval stage (>1% of the mid-parent values). The mean heterosis (Hm) varied in growth throughout the life span. More than 50% of the Hm values were positive and negative in the DW and WD groups, respectively. The influence of maternal effects and mating types (intrapopulation vs. interpopulation crosses) on growth for all life stages was not consistent. Larval survival did not differ significantly (P>0.05) with maternal effect or mating type. In the harvest stage, shell length (SL), shell height (SH), shell width (SW), and total weight (TW) were larger in the hybrid compared with the inbred groups. Positive Hm values were observed in SL (1.5%), SW (5.8%), and TW (12.3%), and were more significant in the DW groups (6.1%, 4.5%, 6.8%, and 27.2%). These results suggest that hybridization between two geographic populations is a good tool for improving bay scallop growth. However, unstable heterosis between the two populations requires further study.

The effects of feeding Lactobacillus pentosus on growth, immunity, and disease resistance in Haliotis discus hannai Ino

ABSTRACT To study the effects of probiotic‐added food on the survival and growth of abalone (Haliotis discus hannai Ino), the expression levels of nonspecific immune genes and the anti‐Vibrio parahaemolyticus infection were examined. During an 8‐week culturing experiment in an indoor aquarium and a 2‐week V. parahaemolyticus artificial infection experiment, the control group was fed with untreated food once a day, while the experimental groups (L1, L2 and L3) were fed with Lactobacillus pentosus added food. The concentration of probiotics in the experimental food was 103cfu/g (L1), 105cfu/g (L2) and 107cfu/g (L3), respectively. The results showed that the survival rate, shell length‐specific growth rate, and the food conversion rate (FCR) of abalones in L1 and L2 were significantly higher than the control group. The food intake of abalones in L3 was significantly lower than that in L1, L2 and the control group, but there was no significant difference in FCR identified between L1, L2 and L3. In the L. pentosus‐added groups, the total number of blood lymphocytes, lysozyme activity, acid phosphatase, superoxide dismutase, and expression levels of Mn‐superoxide dismutase (Mn‐SOD) and thioredoxin peroxidase (TPx) were significantly higher than the control group, while the malondialdehyde (MDA) content was significantly lower than the control group. The phagocytic activity of blood lymphocytes, catalase activity and the expression levels of heat shock protein 70 (HSP70) of abalones in the control group were significantly lower than that in L1 and L2, but there was no significant difference when compared with L3. The levels of O2−, NO produced by respiratory burst of blood lymphocytes and the expression levels of catalase (CAT) in L1 and L2 were significantly higher than both L3 and the control group. Seven days after infection with V. parahaemolyticus, all abalones in the control group were dead. After 14 days the cumulative mortality rate of abalones in the L. pentosus‐added groups was significantly lower than that in the control group. Therefore, the 103cfu/g and 105cfu/g L. pentosus‐added food not only promoted food intake and growth of abalones, but also improved their non‐specific immunity and reduced V. parahaemolyticus infection, indicating that this strain is a good potential candidate for probiotic added food in the aquaculture industry. HIGHLIGHTSThree different concentrations of L. pentosus were added to the abalones basal feed.Dietary supplementation with L. pentosus for 8 weeks enhanced abalones growth.Dietary L. pentosus at 103cfu/g and 105cfu/g significantly improved immunity in abalones.L. pentosus enhanced disease resistance to Vibrio parahemolyticus in abalones.

Broadening the Genetic Basis of the Atlantic Bay Scallop Argopecten Irradians after Interspecific Hybridization and Backcrossing

The above noted paper is being officially retracted as a publication in the Journal of Shellfish Research. The paper was originally published in Marine Sciences, Volume 36 (8) in 2012 in Chinese with an English Abstract. This constitutes duplicate publication. The authors have agreed to this retraction. The paper is no longer citeable.

Divergence and plasticity shape adaptive potential of the Pacific oyster

The interplay between divergence and phenotypic plasticity is critical to our understanding of a species’ adaptive potential under rapid climate changes. We investigated divergence and plasticity in natural populations of the Pacific oyster Crassostrea gigas with a congeneric oyster Crassostrea angulata from southern China used as an outgroup. Genome re-sequencing of 371 oysters revealed unexpected genetic divergence in a small area that coincided with phenotypic divergence in growth, physiology, heat tolerance and gene expression across environmental gradients. These findings suggest that selection and local adaptation are pervasive and, together with limited gene flow, influence population structure. Genes showing sequence differentiation between populations also diverged in transcriptional response to heat stress. Plasticity in gene expression is positively correlated with evolved divergence, indicating that plasticity is adaptive and favoured by organisms under dynamic environments. Divergence in heat tolerance—partly through acetylation-mediated energy depression—implies differentiation in adaptive potential. Trade-offs between growth and survival may play an important role in local adaptation of oysters and other marine invertebrates.Adaptive differentiation is poorly understood in marine systems. Here, the authors combine genome sequencing with gene expression and physiology to show that genetic divergence and plasticity contribute to local adaptation of Pacific oyster populations.

Potential of Abalone Shells as Vectors for Exotic Oyster Species in the Abalone Farming Practice in China

ABSTRACT Pacific abalone Haliotis discus hannai (Ino, 1953) aquaculture is a thriving and prosperous industry in China, producing more than 110,000 metric tons in 2013. In recent years, Fujian in the southern region of China has become the chief abalone farming center, accounting for 85% of the total Pacific abalone yield. The practice of transferring abalone to northern regions to oversummer emerged because of challenges in Fujian, such as fouling, high temperature stress, and unexpected extreme weather events. From the view of ecology and conservation biology, however, the potential ecological risks of this practice should be considered as the abalone shells could act as vectors of exotic organisms. In this study, oyster samples from the shells of live, farmed abalones were collected in Fujian in southern and Rongcheng in northern China. The oysters were identified using a recently developed molecular method. In addition, the fouling oysters on Pacific abalone transferred to the northern region were monitored in a field trial. Survivorship and growth performance of the fouling oysters on the transferred abalones were determined through investigation of digital images taken at 2-wk intervals during the oversummering period. Results of the molecular analysis showed that fouling oysters collected from southern and northern regions are Crassostrea angulata and Crassostrea gigas, respectively. The field trial demonstrated that approximately half of the C. angulata, from the southern region, were still alive after a 6-mo oversummering period in the northern region. Findings from this study have important implications for aquaculture, the management and monitoring of cultured populations of Pacific abalone, and the conservation of wild oyster species in China.