The Mendelian inheritance of rare flesh and shell colour variants in the black‐lipped pearl oyster (Pinctada margaritifera)

Abstract

SummaryPinctada margaritifera is French Polynesia's most economically important aquaculture species. This pearl oyster has the specific ability to produce cultured pearls with a very wide range of colours, depending on the colour phenotypes of donor oysters used. Its aquaculture is still based on natural spat collection from wild stocks. We investigated three rare colour variants of P. margaritifera -orange flesh, and red and white shell colour phenotypes -in comparison with the wild-type black flesh and shell commonly found in this species. The study aimed to assess the geographic distribution and genetic basis of these colour variants. Colour frequencies were evaluated during transfer and graft processes of pearl oyster seed captured at collector stations. Among the collection locations studied, Mangareva Island showed the highest rate of the orange flesh phenotype, whereas Takaroa and Takume atolls had relatively high rates of red and white shell phenotypes respectively. Broodstocks were made of these rare colour variants, and crosses were performed to produce first-and secondgeneration progenies to investigate segregation. The results were consistent with Mendelian ratios and suggest a distinct model with no co-dominance: (i) a two-allele model for flesh trait, whereby the orange allele is recessive to the black fleshed type, and (ii) a three-allele model for shell trait, whereby the black wild-type allele is dominant to the red coloration, which is dominant to the white shell. Furthermore, the proposed model provides the basis for producing selected donor pearl oyster lines through hatchery propagation.

Quality Trait Signature at Archipelago Scale of the Cultured Pearls Produced by the Black-Lipped Pearl Oyster (Pinctada margaritiferaVar.cumingi) in French Polynesia

“…On a broader scale, irrespective of donor phenotype, the archipelago quality trait signatures are also observed in the overall production diversity, as seen at the Tahitian pearl auction exhibition, where these patterns of commercial quality trait signatures have already been observed. This raises questions about the feasibility of achieving homogeneity of pearl quality through the diffusion of homogeneous selected hatchery-produced donor oyster lines from a genetic improvement program, when handling such complex phenotypes (as opposed to a ''simple'' phenotype with Mendelian inheritance as described in Ky et al 2016). In the light of these archipelago-scale quality signatures, different strategies and targeted commercial pearl quality trait selection should be set up to take advantage of the contrasting environments, together with the diffusion of specific pearl oyster phenotypes.…”

Mono- and polychromatic inner shell phenotype diversity in Pinctada margaritifera donor pearl oysters and its relation with cultured pearl colour

“…margaritifera, the Mendelian inheritance of outer shell colour variants has already been demonstrated, with a three-allele model where the black wildtype allele is dominant to the red colouration, which is dominant to the white shell (Ky et al, 2016b). Crossing experiments has been previously done in P. fucata on different outer shell phenotype (prismatic layer colouration), and have shown relatively simple genetic bases for colour trait inheritance.…”

“…A phenotype is the expressed state of a given trait, which may either have distinct categories, as in simple Mendelian qualitative traits or polygenic traits with an underlying threshold that determines the phenotype, or be quantitative, with many possible values along a continuous scale. Some rare colour phenotypes have been recently reported in P. margaritifera, with a Mendelian inheritance for orange flesh, and red and white shell colours, compared with the wildtype black flesh and shell commonly found in this species (Ky et al, 2016b). Some phenotypes can be particularly advantageous because of their local adaptation to the constraints of their specific environment (e.g.…”

Tracing key genes associated with the Pinctada margaritifera albino phenotype from juvenile to cultured pearl harvest stages using multiple whole transcriptome sequencing

“…The whole process, from natural collection or hatchery production of spat, through juvenile growth to the adult stage at which the animals have reached a sufficient size to provide graft tissue or be grafted and finally the culture until pearl harvest, is a long process throughout which the biomineralization properties of specific tissues continue. P. margaritifera produces the largest range of cultured pearl colour in the genus [ 22 , 23 ], including white pearls produced by the rare white albino shell morphotype, when these individuals are used as donors [ 24 ]. These albino individuals are characterised by total or partial absence of coloration resulting in a white shell (periostracum and calcitic layer) [ 14 ].…”