The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. Polyploidy occurs when mitotic or meiotic accidents induce the formation of gametes with more than one set of chromosomes. Triploidy results from the fusion of haploid and diploid gametes and can occur among all animal species. In mammals and birds, the odd number of chromosomes severely impacting mitosis and meiosis, frequently leads to lethal abnormalities,, making triploids less common in the wild. In invertebrates, amphibians and fishes, triploids are often difficult to distinguish from diploids, however, in some species, they have a larger body size and faster growth than diploids. This is often however at the expense of gonadal development,, since in most species, triploids are either sterile or infertile. Since its first induction in the early 1980’s, triploidy has become an important innovation in the oyster aquaculture industry.ĭifferences in growth and reproductive capacity between diploid and triploids have often been used in aquaculture to increase production or to reduce genetic impact of escapes from cultured stock. ![]() Triploid oysters can be produced by two methods: by inhibiting polar body formation after fertilization or by mating diploid and tetraploid broodstock. Recently, in the Pacific oyster Crassostrea gigas (Thunberg, 1793) and the American oyster Crassostrea virginica (Gmelin, 1791), triploid oysters have been produced and grown in large quantities using the second method. They present an important aquacultural benefit mainly by virtue of their faster growth,, their strong reduction of gonad development,, and their better survival. The Pacific oyster is an alternating and irregular protandrous hermaphrodite, meaning that most (≈20% ) individuals mature first as males and then change sex several times. ![]() While sex ratio is not affected by triploidy in C. gigas (resulting either from chemical induction or from crosses between tetraploid and diploid parents), the number of simultaneous hermaphrodites and undifferentiated individuals is significantly higher. Most triploid oysters display highly reduced gonadal development compared with diploid oysters, and thus are commonly referred to as being sterile and are considered as genetically confined. However, 25% of triploid oysters have been shown to produce a significant number of gametes,, and revert to diploid-triploid mosaics.
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