Proteins’s Role in Determining the Optical Properties of the Arthropod Cuticle

The cuticle of arthropods is made of crystalline chitin fibres embedded in an amorphous matrix. It forms the exoskeleton of the animal providing a protective shield as well as a skeleton for structural support and muscle attachment. But the cuticle also serve multiple optical functions, such as providing structural- and pigment-based coloration as well as constructing transparent cornea and lenses. While the role of chitin fibres as well as of pigments are well established, it is not completely clear what is the role of cuticular proteins in determining the optical properties of the cuticle. In this talk we describe the case of the eyes of the horseshoe crab, <i>Limulus polyphemus</i>, in which gradients of RI stem from structural and compositional gradients of cuticular proteins in the cornea, followed by a discussion of the composition of butterfly and beetles reflecting scales.