Separate effects of triploidy, parentage and genomic diversity upon feeding behaviour, metabolic efficiency and net energy balance in the Pacific oyster Crassostrea gigas

Abstract

Triploid oysters were induced using cytochalasin B upon retention of either the first (meiosis I triploids) or the second (meiosis II triploids) polar body in embryos from a single cohort derived from mixed parentage. Allozyme and microsatellite assays enabled the confirmation of both parentage and triploidy status in each oyster. Comparison of meiosis I triploids, meiosis II triploids and diploid siblings established that improved physiological performance in triploids was associated with increased allelic variation, rather than with the quantitative dosage effects of ploidy status. An unidentified maternal influence also interacted with genotype. Among full sibs, allelic variation measured as multi-locus enzyme heterozygosity accounted for up to 42% of the variance in physiological performance; significant positive influences were identified upon feeding rate, absorption efficiency, net energy balance and growth efficiency (= net energy balance divided by energy absorbed). Whilst allelic variation was greater in both meiosis I and meiosis II triploids than in diploid siblings, both allelic variation and net energy balance were highest in triploids induced at meiosis I. This suggests that it may be preferable to induce triploidy by blocking meiosis I, rather than meiosis II as has traditionally been undertaken during commercial breeding programmes.

Responses of diploid and triploid Pacific oysters Crassostrea gigas to Vibrio infection in relation to their reproductive status

“…However, previous studies have proposed that improved growth in triploid molluscs could be explained by an increase in net energy budget (Hawkins et al, 2000(Hawkins et al, , 1994Wang et al, 2002), a phenomenon independent of energetic re-allocation from reproduction to other functions. Such results have been thought to be due to increased heterozygosity in polyploid individuals, suggesting that triploidy could confer an advantage per se on growth and survival through the increase of intra-individual allelic diversity and the optimisation of energy balance (Hawkins et al, 2000).…”

Reproductive effort and growth in Crassostrea gigas: comparison of young diploid and triploid oysters issued from natural crosses or chemical induction

“…The 2 groups of triploid oysters were obviously more similar to one another than either was to the diploid group, despite the common parents used for the 3nCB and 2n groups. The method of triploid induction used (chemical induction or mating between diploid and tetraploid broodstock) may lead to genetic differences at several levels, as mentioned in previous studies: unbalanced contribution of parental genetic values (Blanc et al 2005), higher heterozygosity of 3nDT individuals (Hawkins et al 2000), effects of unintentional selection during the production of tetraploid oysters (i.e. selection of fertile triploid females, Guo & Allen 1994b), as well as long-term toxic effects of chemical cytoblocking molecules such as cytochalasin B (Goulletquer et al 1996).…”

“…zero gametogenesis controls) and may be detrimental to their saleability for human consumption and risky for their use in genetic confinement. Numerous hypotheses have been suggested to explain the difference in growth and survival between diploid and triploid bivalves, including polyploid gigantism (Guo & Allen 1994a), heterozygosity (Stanley et al 1984, Hawkins et al 2000, gene dosage (Zouros et al 1996) and, of course, sterility (Allen & Downing 1986), which would allow energy reallocation from gonadic development to somatic growth. However, probably due to the relative technical difficulty of quantifying reproductive allocation in oysters, this factor has seldom been recorded when comparing growth performance between diploid and triploid oysters (e.g.…”

Cadmium accumulation and loss in the Pacific oyster Crassostrea gigas along the west coast of the USA

“…Amiard et al (2005) in fact hypothesized that the higher energy available for growth in triploid oysters may have a positive impact on the metal detoxification and excretion since transcription is faster with 3 copies of each gene. The positive role of heterozygosity on feeding rate and absorption efficiency has also been emphasized by Hawkins et al (2000). However, the triploid Crassostrea gigas had a lower Ag, Cd, and copper (Cu) accumulation in the study by Amiard et al (2005), probably due to the physiological changes associated with the reproductive development of the diploids.…”