Developmental timing scales wing patterning between avian species

How development is timed between differently sized species is a fundamental question in biology. To address this problem, we compared wing development in the quail and the larger chick. We reveal that developmental timing is faster in the quail than in the chick, and is associated with pattern specification, proliferation, organiser duration, differentiation and apoptosis. However, developmental timing is independent of the growth rate, which is equivalent between both species, and therefore scales pattern to the size of the wing. We reveal that developmental timing can be either maintained or reset in interspecies tissue grafts, and we implicate retinoic acid as the resetting signal. Accordingly, retinoic acid can switch species developmental timing and rescale pattern, both between the quail and chick, and the chick and the larger turkey. We suggest that the scaling of pattern to wing bud size is achieved by the modulation of developmental timing against a comparable rate of growth. Summary - We show that developmental timing scales wing patterning