Abstract
The European clam, Ruditapes decussatus is a species with a high commercial importance in Portugal and other Southern European countries. Its production is almost exclusively based on natural recruitment, which is subject to high annual fluctuations. Increased knowledge of the natural reproductive cycle of R. decussatus and its molecular mechanisms would be particularly important in providing new highly valuable genomic information for better understanding the regulation of reproduction in this economically important aquaculture species. In this study, the transcriptomic bases of R. decussatus reproduction have been analysed using a custom oligonucleotide microarray representing 51,678 assembled contigs. Microarray analyses were performed in four gonadal maturation stages from two different Portuguese wild populations, characterized by different responses to spawning induction when used as progenitors in hatchery. A comparison between the two populations elucidated a specific pathway involved in the recognition signals and binding between the oocyte and components of the sperm plasma membrane. We suggest that this pathway can explain part of the differences in terms of spawning induction success between the two populations. In addition, sexes and reproductive stages were compared and a correlation between mRNA levels and gonadal area was investigated. The lists of differentially expressed genes revealed that sex explains most of the variance in gonadal gene expression. Additionally, genes like Foxl2, vitellogenin, condensing 2, mitotic apparatus protein p62, Cep57, sperm associated antigens 6, 16 and 17, motile sperm domain containing protein 2, sperm surface protein Sp17, sperm flagellar proteins 1 and 2 and dpy-30, were identified as being correlated with the gonad area and therefore supposedly with the number and/or the size of the gametes produced.
Highlights
The European clam, Ruditapes decussatus (Linnaeus, 1758) is a bivalve mollusc of the family Veneridae, native to the European Atlantic and Mediterranean coastal waters
We identified several differentially expressed probes, which led us to a specific pathway involved in the recognition signals and binding between the oocyte and components of the sperm plasma membrane
We believe that these results can be useful to R. decussatus hatchery production program management
Summary
The European clam, Ruditapes decussatus (Linnaeus, 1758) is a bivalve mollusc of the family Veneridae, native to the European Atlantic and Mediterranean coastal waters. Its production is almost exclusively based on natural recruitment, which is subject to high annual fluctuations due to pollution and other environmental factors. To address this situation, artificial spawning and larval rearing programs were developed to provide an alternative source of seed [2], but still need improvement to gain robustness of seed production. During the second stage of gametogenesis (II) follicles and gonadal acini begin to appear in females and males, respectively They increase in size, and appear filled with oocytes in the growth phase in the females and with immature gametes (spermatogonia and spermatocytes) in the males. Throughout this period partial spawning may occur, and it concludes with the total emission of gametes [4]
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