Relative effects of heterosis mechanisms on the fitness of hybrids. Data of 11 runs is pooled. Data from each run was shifted so the fitness collapse coincides after the 5th hybridization (red dashed line). A) Effects of local heterozygosity mechanisms. B) Effect of epistatic mechanisms. Please note that only gene pairs were considered for epistasis, allowing multiple counting of effects in cases of epistasis involving several genes. For this reason, epistatic and local heterozygosity mechanisms cannot be directly compared.