Different mechanisms and their impact over time. A) Performance of parent populations and hybrids in an example run. The parent populations evolved separately from generation 2000 onwards. Hybrids showed heterosis until generation 2150 followed by the collapse of fitness in the hybrids. Hybridization was performed every 20 generations; red and black: average fitness of parent populations, green circles: average fitness of hybrid population B) Effect of local heterozygosity mechanisms relative to each other; light blue: over-dominance, orange: dominance, black: under-dominance. C) Effect of epistatic mechanisms relative to each other; dark blue: positive epistasis, yellow: negative epistasis, gray: epistatic incompatibility.