Loliginid squid have a unique reflectin protein-based adaptive (i.e., tunable) biophotonic system organized in specialized cells called iridocytes. Reflectin proteins were initially discovered in static iridocytes. In this dissertation I seek to define the molecular and cellular mechanisms governing the neurotransmitter induced tunable changes in color and brightness of light reflected by adaptive iridocytes. Applications to adaptive optics may be envisioned.

I have uncovered salient aspects of this system that allow for and drive adaptive iridescence by making observations at the molecular, macromolecular, cellular and organismal levels in the squid, Doryteuthis opalescens . I dispelled previous misinformation about the unique membrane architecture of the iridocytes and the important water flux associated with color transition. I have further characterized the unique reflectin proteins correlated with adaptive function as well as changes in post-translational modifications commensurate with changes in color. I have explored some of the self-assembly properties of the reflectins. I have also made observations at the organismal level; in particular, the sexually dimorphic adaptive structural color. My studies present insights into the mating behavior of this animal and, more pertinently, open new routes for exploration and understanding of this biophotonic system. I have discovered a new cell type (adaptive leucophores) that function to produce adaptive broadband scattering. This work provides an advanced understanding of dynamic iridocytes and opens the door to potential insights through future work in (but not limited to): bionanophotonics, reversible protein self-assembly, protein phosphorylation, bionanofabrication, membrane organization, protein-protein interactions, and cell signaling.