Determining genetic contributions to host oyster shell growth: Quantitative trait loci and genetic association analysis for the silver-lipped pearl oyster, Pinctada maxima

The silver-lipped pearl oyster, Pinctada maxima, is of high economic importance to the global pearling industry. However, pearling industries worldwide have reported declines in gross pearl production values over the last decade, leading to the establishment of several genetic breeding programmes aiming to improve commercially important pearl production traits within pearl oyster stock. Even though the value of a pearl is directly determined by its graded quality, production traits such as host oyster shell growth and shell width define the timing of seeding operations and the size of the implanted nuclei, and therefore have considerable influence on the production of a pearl. In this study, the genetic architecture of complex oyster growth traits (i.e. shell height, length, width and weight) is explored and putative QTL and marker associations are identified.Heritability estimates for pearl oyster shell growth traits ranged from 0.18 to 0.33 indicating the potential for moderate response to genetic selection. A total of six QTL and four genetic associations were detected for four oyster shell growth traits (shell height, length, width and weight). These QTL are estimated to explain a minimum of 32.5%, 20.7% and 30.1% of the phenotypic variation observed in shell height (2 QTL), width (3 QTL) and weight (1 QTL) respectively within the 11 half-sib families (n= 342). In addition, three of the four genetic associations detected for shell length (effect sizes from 3.3 to 4.3) are co-localised on LG4 near the mapped biomineralisation genes PFMG1, Pif177 and CS1.This study confirms previous quantitative genetic studies that oyster growth traits are polygenic, and provides additional evidence that these traits have sufficient genetic basis for improvement in animal selective breeding programmes. The preliminary QTL and genetic associations identified here also serve as prime candidates for ongoing analysis aiming to unravel the complex biological processes involved in pearl oyster growth and shell formation (i.e. biomineralisation). Furthermore, selection programmes incorporating marker information for growth traits with large QTL effects should further accelerate genetic gains within the P. maxima pearling industry.