On the evolution and development of morphological complexity: A view from gene regulatory networks
Fig 6
Developmental mechanisms producing complex morphologies occupy smaller regions of the parameter space than developmental mechanisms producing simple morphologies.
The figure shows the number of accepted steps in each iso-morphological random walk of each developmental mechanism (Y axis) versus the complexity of the morphology produced by each developmental mechanism. The Y axis, thus, is a measure of the region of the parameter space where a morphology forms. We performed an iso-morphological random walk for the developmental mechanisms in the parental set that are very stable developmentally (i.e. EMD distance between parental twins less than 0.3). In each walk we mutated, one at a time and chosen randomly, gene-gene interactions or gene-cell behavior interactions in each developmental mechanism. If a mutation did not change in a significant way the phenotype (when compared to the original parental morphology in the walk) the mutation was kept, and a new mutation was applied. If the mutation did change the phenotype, this mutation was reversed. This process of mutation was iterated 200 times per developmental mechanism (see Methods 2.3 for details). This way we calculated the proportion of mutations that changed the phenotype: the more mutations changed the parental phenotype, the smaller the region of the parameter space where a developmental mechanism can produce its parental phenotype. We performed 10 random walks per developmental mechanisms. To minimize the effect of random developmental noise in our results each mutant was simulated 5 times (see S1 Text for details). The morphological distance between the final morphology of each of these 5 simulations and the parental was measured using CMD. The average of these distances was used to evaluate whether a mutation was accepted or not. In order to be considered different to the parent, the CMD had to be 0.01 higher than the developmental instability of the parental (measured in CMD). Spearman: pval<0.0001, rs = 0.65, n = 422. See—Methods 2.3. for further details.