How different types of pattern formation mechanisms affect the evolution of form and development.

Here we investigate how development and evolution can affect each other by exploring what kind of phenotypic variation is produced by different types of developmental mechanisms. A limited number of developmental mechanisms are capable of pattern formation in development. Two main types have been identified. In morphodynamic mechanisms, induction events and morphogenetic processes, such as simple growth, act at the same time. In morphostatic mechanisms, induction events happen before morphogenetic mechanisms, and thus growth cannot influence the induction of a pattern. We present a study of the variational properties of these developmental mechanisms that can help to understand how and why a developmental mechanism may become involved in the evolution and development of a particular morphological structure. Using existing models of pattern formation in teeth, an extensive simulation analysis of the phenotypic variation produced by different types of developmental mechanisms is performed. The studied properties include the amount and diversity of the phenotypic variation produced, the complexity of the phenotypic variation produced, and the relationship between phenotype and genotype. These variational properties are so different between different types of mechanisms that the relative involvement of these types of mechanisms in evolutionary innovation and in different stages of development can be estimated. In addition, type of mechanism affects the tempo and mode of morphological evolution. These results suggest that the basic principles by which development is organized can influence the likelihood of morphological evolution.