Loliginid squid use tunable multilayer reflectors to modulate the optical properties of their skin for camouflage and communication. Contained inside specialized cells called iridocytes, these photonic structures have been a model for investigations into bio-inspired adaptive optics. Here, we describe two distinct sexually dimorphic tunable biophotonic features in the commercially important species Doryteuthis opalescens: bright stripes of rainbow iridescence on the mantle just beneath each fin attachment and a bright white stripe centered on the dorsal surface of the mantle between the fins. Both of these cellular features are unique to the female; positioned in the same location as the conspicuously bright white testis in the male, they are completely switchable, transitioning between transparency and high reflectivity. The sexual dimorphism, location and tunability of these features suggest that they may function in mating or reproduction. These features provide advantageous new models for investigation of adaptive biophotonics. The intensely reflective cells of the iridescent stripes provide a greater signal-to-noise ratio than the adaptive iridocytes studied thus far, while the cells constituting the white stripe are adaptive leucophores – unique biological tunable broadband scatterers containing Mie-scattering organelles activated by acetylcholine, and a unique complement of reflectin proteins.
D.G.D. discovered the tunable photonic structures discussed in this paper and conducted the microscopic, spectrophotometric and protein measurements and data analyses; A.G. provided additional expertise with the spectrophotometric measurements and analyses; E.P. and A.T.W assisted with the microscopy and protein analyses; M.B. contributed biological expertise and data analysis; D.G.D. and D.E.M. wrote the manuscript; all authors contributed to editing and revising the manuscript; and D.E.M. supervised all aspects of the project.
Supplementary material available online at http://jeb.biologists.org/cgi/content/full/216/19/3733/DC1
No competing interests declared.
This research was supported by the Army Research Office [through contract W911NF-09-D-0001 to the Institute for Collaborative Biotechnologies and grant W911NF-10-1-0139 to D.E.M.] and by a subcontract from the Office of Naval Research via a MURI award to Duke University [no. N00014-09-1-1053]. Electron microscopy made use of instrumentation and facilities provided by UCSB's Materials Research Laboratory, a Materials Research Science and Engineering Center supported by the National Science Foundation [through grant DMR-0080034].
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