Developmental canalization with no part of stabilizing selection

Abstract

Referring the developmental canalization to stabilizing selection may be a bias that results from the ignorance of developmental mechanisms. Considering the morphological evolution of one-cell trichomes in Draba plants makes it clear that the transition from continuous variation in morphological traits to developmental creods occurs in the evolution of remote lineages of the genus irrespective of contribution to the net fitness. Morphological diversification of trichome branching is not under selection control, being a physical consequence of the trichome cell volume growth equilibrated by complication of the cell surface shape. At the start of evolution, the trichome development refers not to an individual trichome, but rather to repetitive trichome modules (branches), whose spatiotemporal order is arbitrary, except that some variants of branching depend on events that occur at earlier developmental stages more than others. Under selection fluctuating at random, or with no selection at all, fixing of these variants leads to the formation of trichome ontogeny, in which earlier developmental stages correspond to later stages of developmental evolution.