Assessment of parental contribution and effective population size from a 3×3 diallel cross of clam Meretrix meretrix

Unbalanced parental contribution and small effective population size (N (e)) are common issues during the artificial breeding of marine bivalves. The impact of hatchery-spawning practices on parental contribution, effective population size, the N (e)/N ratio, and genetic diversity are largely unknown. To address this, we conducted a parentage analysis on a complete 3x3 diallel cross of clam M eretrix meretrix using eight microsatellite markers. The genetic diversity of the parents was higher than that of their respective offspring in most crosses (8/9). Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross, and the same parent clam exhibited large variation in parental contribution among different crosses. The variance in male contribution was higher than that of the female contribution in most crosses, suggesting that male contribution was more skewed than for females. The N (e)/N ratio for nine crosses ranged from 0.58 to 0.86. There was no linear relationship between the sex ratio and the N (e)/N ratio (P > 0.05). Moreover, a sex ratio closer to one-to-one does not necessarily mean a larger effective population size. A solution to small effective population size in commercial breeding programs is increasing broodstock numbers and attempting to maintain a balanced sex ratio.