Comparative limb development in insects and crustaceans

Developmental genetics has revealed several molecular players critical for patterning the adult leg in Drosophila. Comparisons throughout insects and crustaceans reveal that some of the molecular mechanisms that initiate limb patterning are conserved: limbs seem to always consist of anterior/posterior compartments, and their initial proximal/distal outgrowth is marked by Distalless expression. It remains unknown whether the developmental mechanisms that subsequently generate differences in limb morphology are themselves diverse. A comparative perspective suggests that one important evolutionary transition in limb development was the evolution of joints and limb segmentation.