Table 1.

Evolution of Animal Body Plans as Change and Conservation of Developmental Gene Regulatory Network (dGRN) Structure: Mechanistic Consequences

Premise	Consequence
Since dGRN structure depends on cis-regulatory linkages at nodes:	1. Change in dGRN structure occurs by co-optive redeployment of cis-regulatory modules controlling regulatory gene expression
Since co-optive cis-regulatory redeployments are gain of function changes:	2. Co-optive redeployment of regulatory gene expression will generally be haplosufficient and act dominantly
Since dGRNs are deeply hierarchical:	3. Effects of given cis-regulatory mutations (including co-options) depend specifically on their location in dGRN
Since dGRNs are deeply hierarchical:	4. Subcircuits operating at upper levels (early in developmental process) preclude certain downstream linkages, and mediate others, i.e., canalize dGRN structure (and developmental process).
Since dGRNs are deeply hierarchical:	5. Conserved upper level subcircuits should produce patterns of canalization that reflect phylogenetic distribution of the developmental processes that generate clade specific body parts (prediction of Kernels)
Since flexibility at given dGRN nodes depends on their upstream and downstream linkages:	6. dGRN structure should contain information for prediction of evolutionary hotspots vs. evolutionarily conserved structural features
Since dGRNs are modular, i.e., given functions are executed by given subcircuits:	7. Evolution of new developmental outcomes must often involve co-optive gain of function changes that cause redeployment of whole dGRN subcircuits
Since redeployment of dGRN subcircuits is a mechanism of evolution of developmental novelty:	8. Evolutionary change must occur in dGRN linkages controlling subcircuit deployment, i.e., in signal presentation and reception, regulatory switches, and inter-subcircuit inputs.