The consequences of differential family survival rates and equalizing maternal contributions on the effective population size (Ne) of cultured silver-lipped pearl oysters, Pinctada maxima

摘要

The effective population size (N_e) is a critical gauge of how efficiently an aquaculture operation is capturing or maintaining genetic diversity and can govern the long-term success of genetic selection programmes. In communally reared pearl oysters (Pinctada maxima), high variance in family sizes is a significant contributor towards low N_e and its severity may be compounded by differential survival rates of individual families. To determine the effect of variable survival on N_e in cultured P. maxima, families from two commercial populations were analysed using DNA parentage analyses to monitor survival and changes in relative contributions. Significant shifts in relative contributions were observed between 72 days and 18 months of age in both commercial cohorts (P0.001). Survival rates were found to be highly variable among families (ranging from 2.5% to 49.5%) when reared in a common environment. Additionally, we investigated whether equalizing maternal family sizes before communal rearing will reduce family size variance, and increase N_e, compared with stocking at naturally produced proportions. Family equalization (E) significantly improved N_e (P=0.013) compared with rearing at natural (N) proportions (E: N_e=7.18±0.34; N: N_e=5.60±0.15); however, this practice may unintentionally magnify negative influences of poor performing families if survival is correlated with other commercially important traits. It is concluded that highly variable family survival will affect N_e in communally reared P. maxima, and the practice of equalizing family sizes in order to maximize N_e may only become consistently beneficial once further progress is made towards understanding, and then reducing variation in family survival rates.