Figure 5

Evolution of Robustness to Recombination under Canalization. A Evolution of the average phenotypic hamming distance of offspring to the nearest niche as a function of recombination (crossing over, CO) location. We construct a single measure for the CO locations on the two parental genomes: , with l₁ and l₂ locations on the genomes of parent 1 and 2, respectively, and l relative CO locations (position of gene at which CO occurs normalised to the number of genes in the genome). If the CO locations on both parental genomes lie at the 'begin' of the genomes (eg. l₁ = 0.1 and l₂ = 0.1) a low value arises, if both locations lie at the 'end' of the genomes (eg. l₁ = 0.9 and l₂ = 0.9) a high value arises. Extreme values thus correspond to recombinations between either two genome 'begins' or two genome 'ends', that is two "corresponding" genome ends. Intermediate values arise if CO locations at opposite ends are used (eg. l₁ = 0.2 and l₂ = 0.8) or if CO locations at the middle regions of the genome are used (eg. l₁ = 0.5 and l₂ = 0.5). B Evolution of the average phenotypic HD of offspring to its closest resembling parent as a function of recombination locations on the parental genomes. C Evolution of the average phenotypic HD of offspring to the nearest niche as a function of phenotypic HD between the two parents. D Evolution of the average phenotypic HD of offspring to its closest resembling parent as a function of phenotypic HD between the two parents. E Cartoon showing how conserved genome ends cause robustness to recombination and high hybrid fitness. Two parents adapted to different niches have genomes that are conserved at the ends but differentiated in the middle regions (top). If for recombination a gene is chosen that lies on a genome end, recombination replaces a part of the genome of one parent with a similar part of the genome of the other parent. The offspring genome will thus correspond to the parental genome from which it received the largest, and hence the specific, part (middle). As a consequence, the offspring will be equally well adapted as this parent. If, in contrast, a gene from the middle genome region is chosen, recombination results in the exchange of non-equivalent genome parts between the parental genomes. In this case offspring genomes will contain a mixture of the specific parts of their parental genomes (bottom), causing offspring phenotype to be a non adaptive amalgam of the parental phenotypes. As conserved genome ends take up a considerable part of genome length (here 4 of the 7 genes), a considerable fraction of recombination events will lead to fit hybrid offspring closely resembling one of their parents.