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

Abstract

The pearl oyster Pinctada margaritifera has the specific ability to produce pearls with the widest range of colours among all pearl oyster species. This pearl colour diversity originates from the mantle biomineralising tissue (graft) of the donor oyster, which is originally responsible for the variety of colours of the inner shell surface. This study aimed to: 1) assess the geographic distribution and establish a first stocklist of the colourful oyster phenotypes used as donors in French Polynesia, and 2) investigate the phenotypic relation between inner shell colouration and the corresponding colour of harvested pearls. With the support of a pearl farmers' network, we investigated the different donor phenotype frequencies among five collection sites (Ahe, Apataki, Takaroa, Takume and Mangareva). This donor evaluation was made during grafting of pearl oysters (N = 49,938) obtained from collector stations. Results showed that pearl production is mainly based on six common colourful donor phenotypes classified as monochromatic and polychromatic profiles, which shown different frequencies among the collection sites. Experimental grafts (N = 4640) were then realised and subsequent culture conducted at a single site in order to avoid pearl colour variation due to environmental influences. Traceability between donors (N = 232) and pearls (N = 2776), revealed that: 1) yellow (gold) and aubergine (reddish) pearls could be mostly obtained by using the monochromatic yellow and red donor phenotypes, respectively, and 2) one third to one quarter of grey pearls was inevitably harvested, whatever the polychromatic phenotype chosen as the donor, which leaves at least half the harvest composed of the attractive green and peacock colours. This preliminary stocklist of colour range together with analysis of the colour phenotype transmission between inner shell and pearl provide the basis for producing multiple pearl oyster "colour lines" through hatchery propagation and would be helpful for future selective breeding programs.

Potential combinations of mabé, keshi and cultured pearl production from colourful hatchery-produced Pinctada margaritifera

“…This was done by using selected hatchery-produced oysters to maximise the occurrence of colourful individuals that could be used both as donor and recipient. In French Polynesia, occurrence of colourful oysters from wild are rare (Ky et al, 2017a). Production of cultured round pearls and mabé are usually dissociated in terms of mollusc species and genus (i.e.…”

“…Other countries of the Pacific region, such as the Cook Islands, Fiji or Micronesia, do not have this advantage of wild settlement, which constrains the development of P. margaritifera pearl farming industries in these areas (Cartier et al 2013). Like species from the Pteria genus (P. penguin and P. sterna) (Acosta-Salmón, 2003), P. margaritifera has one of the largest ranges of nacre and pearl colours of any pearl oyster species across all its developmental stages (Ky et al, 2017a, Ky et al, 2018aand 2018b. Some countries and companies produce both cultured pearls and mabé, mainly using different species.…”

“…Pteria species are not present and highly colourful individuals of P. margaritifera are rare and mostly used as donors for cultured pearl production (Ky et al, 2017a). As the Polynesian pearl industry matures and larval culture ceases to be a bottleneck, massive hatchery production, begun in 2015, will assume a role in the supply of colourful pearl oysters to the industry (Ky and Devaux, 2016a).…”

Donor effect on cultured pearl nacre development and shell matrix gene expression inPinctada margaritiferareared in different field sites

“…These are first inspected to assess health and the quality and colour of the nacre lining the inside of their shells (Ky, Lo & Planes, ). Most evidence reported to date in P. margaritifera suggests that, while many pearl characteristics (such as colour and lustre) are dictated by the graft donor (Ky et al., ; Ky, Lo et al., ; Ky, Le Pabic et al., McGinty, Evans, Taylor & Jerry, ; Tayale et al., ), the eventual size of the pearl is mainly dictated by biometric parameters of the recipient (Ky, Cabral & Lo, ; Le Pabic et al., ). In P. fucata , the phenotypic correlation between recipient shell weight and pearl size was examined and a positive relationship was found whereby recipient oysters with heavier valves produced larger pearls (Wada & Komaru, ).…”

“…The quality of cultured pearls depends greatly on the selection of appropriate donor oysters (Taylor, 2002). These are first inspected to assess health and the quality and colour of the nacre lining the inside of their shells (Ky, Lo & Planes, 2017). Most evidence reported to date in P. margaritifera suggests that, while many pearl characteristics (such as colour and lustre) are dictated by the graft donor (Ky et al, 2013;Ky, Le Pabic et al, 2017McGinty, Evans, Taylor & Jerry, 2010Tayale et al, 2012), the eventual size of the pearl is mainly dictated by biometric parameters of the recipient (Ky, Cabral & Lo, 2017;Le Pabic et al, 2016).…”