Fig. 2.

Variation in the pmx in Geospiza correlates with the expression of TGFβIIr, β-catenin, and Dkk3. At st. 30, the large and medium ground finches have high expression levels of TGFβIIr, β-catenin, and Dkk3 in strong correlation with the volume of the developing pmx. Arrow colors indicate species that have comparable body sizes but differ in beak morphology. (Scale bar, 0.2 mm.) Images of skulls are from ref. 24, with permission from the author. pmx, premaxillary bone; pnc, prenasal cartilage.