AimGenetic data were used to measure the phylogeographic distribution of the limpet, Cellana toreuma along the China coast in order to acsertain impacts of historic events, ocean currents and especially freshwater discharge from the Yangtze River on the connectivity of intertidal species with limited larval dispersal capability.Methodology/Principal FindingsGenetic variation in 15 populations of C. toreuma (n = 418), ranging from the Yellow Sea (YS), East China Sea (ECS) and South China Sea (SCS), were determined from partial mitochondrial cytochrome c oxidase subunit I gene. Genetic diversity and divergence based on haplotype frequencies were analyzed using CONTRIB, and AMOVA was used to examine genetic population structure. Historic demographic expansions were evaluated from both neutrality tests and mismatch distribution tests. Among the 30 haplotypes identified, a dominant haplotype No. 1 (H1) existed in all the populations, and a relatively abundant private haplotype (H2) in YS. Pairwise FST values between YS and the other two groups were relatively high and the percentage of variation among groups was 10.9%.ConclusionsThe high nucleotide and gene diversity in the YS, with large pairwise genetic distances and relatively high percentages of variation among groups, suggests that this group was relatively isolated from ECS and SCS. This is likely driven by historic events, ocean currents, and demographic expansion. We propose that freshwater discharge from the Yangtze River, which may act as physical barrier limiting the southward dispersal of larvae from northern populations, is especially important in determining the separation of the YS group from the rest of the Chinese populations of C. toreuma.

Pearl oyster, Pinctada martensii, is a marine bivalve species widely distributed in tropic and subtropic marine coasts. Mantle is the special tissue of P. martensii that secretes biomineralization proteins inducing shell deposition as well as iridescent nacre both in the inner shell and artificial nucleus. The pearl oyster is very efficient for artificial pearl production and is therefore an ideal organism for studies into the processes of biomineralization. However, deficiency of transcriptome information limits the insight into biomineralization mechanisms and pearl formation. In this study, we sequenced and characterized the P. martensii mantle transcriptome using 454 pyrosequencing. A total of 25,723 unique transcripts were assembled from 220,824 quality reads, followed by annotation and Gene Ontology classification analysis. A total of 146 unique transcript segments homologous to 49 reference biomineralization genes were identified, including calcineurin-binding protein, amorphous calcium carbonate binding protein 1, calmodulin, calponin-like protein, carbonic anhydrase 1, glycine-rich shell matrix protein, lysine-rich matrix protein, mantle gene or protein, nacrein, pearlin, PIF, regucalcin, and shematrin. The sequence data enabled the identification of 10,285 potential single nucleotide polymorphism loci and 7,836 putative indels, providing a resource for molecular biomarker, population genetics, and functional genomic studies. A large number of candidate genes for biomineralization were identified, considerably enriching resources for the study of shell formation. These sequence data will notably advance biomineralization and transcriptome study in pearl oyster and other Pinctada species.

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Pearl sac is the tissue that secretes proteins resulting into artificial pearl formation, a highly controlled biomineralization process similar to development of inner shell regulated by the mantle. We present here the pearl sac transcriptome of Pinctada fucata martensii using massively parallel pyrosequencing. A total of 21 729 putative unique transcripts were assembled and annotated. Twenty-three candidate biomineralization genes were identified, such as calmodulin, calponin-like protein (CLP), mantle gene, pearlin, nacrein and Pif. The sequence data contained 4303 potential SNP loci and 4291 probable indels, providing a resource for molecular biomarker, population genetics and gene function. Expression levels of six potential biomineralization genes were also characterized with real-time PCR. The expression level of mantle gene 4 was the highest, followed by lysine-rich matrix protein 4. Nearly all detected genes maintained the highest expression levels in mantle edge and the lowest in pearl sac. In both tissues of mantle centre and pearl sac, the six genes had an obvious higher expression activity in host oyster producing nacre pearls than those producing plain nuclei, but the expression level of CLP was similar in the two host groups. These results will notably advance biomineralization and transcript-wide study in P. fucata martensii and other Pinctada species.

Eleven novel microsatellite markers were isolated from small abalone, Haliotis diversicolor Reeve. These loci were tested on 22 individuals from two different geographic populations. We identified a total of 162 alleles from the 11 microsatellite loci. All of the loci were highly polymorphic. Polymorphism information content (PIC) is ranging from 0.7276 to 0.9163. Observed and expected heterozygosities ranged from 0.2727 to 1.0000 and from 0.7738 to 0.9429, respectively. Three loci deviated significantly from Hardy-Weinberg equilibrium. No pairs of loci displayed linkage disequilibrium. These polymorphic markers will be used to analyze population structure, genetic diversity and construct a genetic linkage map.National High Technology Research and Development Program of China [2006AA10A407

Small abalone, Haliotis diversicolor, is naturally distributed along the coastal waters of East Asia from Japan to the Philippines. It is an economically important maricultured species in southern China and Taiwan. Genetic linkage maps for small abalone were constructed using a total of 308 simple sequence repeat markers including 297 novel markers. Segregation data on 96 progeny were genotyped using a pseudo-testcross strategy. Sixteen linkage groups were identified in both female and male maps, consistent with the haploid chromosome number. The female linkage map covered 758.3 cM, with an average interval of 5.2 cM. The male linkage map spanned a total genetic distance of 676.2 cM, with an average interval of 4.5 cM. An integrated map was constructed by incorporating the homologous parental linkage groups, resulting in 16 linkage groups with a total of 762.1 cM. Genome coverage of the integrated linkage map was approximately 80.7%. The genetic linkage maps of small abalone may facilitate marker-assisted selection and quantitative trait loci mapping.

The effect of low salinity levels on byssal re‐attachment behavior in Pteria penguin juveniles was observed in the laboratory. Juvenile pearl oysters were submerged in seawater blended to 8.0, 12.0, 16.0, 20.0, 24.0, 28.0, and 32.0 salinity levels for a period of 48 hr. The sub‐lethal salinity level was greater than 20.0 psu. Although salinity levels of 20.0 and 24.0 psu did not affect the oyster survival, the observed byssogenesis activity was significantly reduced and locomotion activity was delayed. Description of the effects of low salinity levels on the byssal re‐attachment behavior of P. penguin juveniles provides a foundation for the design of more complex experiments and approaches to further the exploration and development of improved pearl production techniques.