Levels of inbreeding in group mating captive broodstock populations of Common sole, (Solea solea), inferred from parental relatedness and contribution

In this paper, we estimate levels of inbreeding with parental relatedness and contribution inferred from microsatellites in groups of Common sole that reproduce by natural mating. We present results on spawning patterns during one entire reproductive season of wild Common sole, Solea solea, kept in two broodstock groups (28 animals in broodstock A; 20 animals in broodstock B) under semi-natural conditions. Batches of eggs were collected daily and incubated separately. First, we performed a parentage analysis on parents and samples of 24 newly hatched larvae from all batches, using 10 polymorphic microsatellite markers. As expected, contribution of parents to offspring was highly skewed. In both broodstocks, five or less parental pairs produced more than half of the total progeny. Natural spawning and unequal contributions of parents to offspring resulted in significant deviations from Hardy–Weinberg equilibria. Furthermore, few alleles were lost and levels of heterozygosity in offspring population increased. Next, we calculated relatedness between parents that mated successfully based on estimates of molecular similarity. Mean coefficients of coancestry in offspring were determined using parental relatedness and contributions. Levels of coancestry in progeny were substantially high. These results show that due to different parental contributions, natural mating in groups can result in significant inbreeding in future generations despite of limited loss of alleles and high levels of heterozygosity in first generation progeny. This shows that using loss of alleles and levels of heterozygosity alone can be misleading for estimation of genetic diversity.