Figure 7: A multi-module regulatory model of feather diversification.

(a) Schematic representation of the infrastructure of the multi-module regulatory feather (MRF) model and the corresponding transformative events of feather shapes in evolution. Dashed lines denote crosstalk relationships not fully confirmed. The differential equations for quantifying the crosstalk relationships are listed in the Methods. (b) Representative simulations of vane shape variations using the MRF model either without RA module, with high RA (CRABP1 level set at 1.1, CYP26B1 at 0.02, artificial unit), or with low RA (CRABP1 at 0.005, CYP26B1 at 0.2). (c) Representative simulations of feathers with different levels of vane asymmetry by changing the slope of RA gradient (CRABP1 at 0.006, CYP26B1 at 5 for the steeper RA gradient, CRABP1 at 0.03, CYP26B1 at 0.5 for the intermediate RA gradient, CRABP1 at 0.06, CYP26B1 at 0.3 for the shallower RA gradient), (d) Simulations of RCAS-GREM1 and RCAS-DNRARb infected feathers in which the BGZ expands without significantly shortening of barbs.