Hanlon Award Aims to Reveal Dynamic Interplay of Pigments & Reflectors in Cephalopod Skin
Roger Hanlon is interested in the expression of color and pattern in the animal kingdom, especially how these features are deployed for camouflage and communication. His MBL lab focuses on animals that can dynamically change their appearance with a combination of skin pigments and reflectors, producing the most diverse color and patterning possible.
The standout animals for these highly evolved capabilities are the cephalopods – squid, cuttlefish and octopus. One hallmark of cephalopod coloration is that it does not create new light, but rather manipulates available light in elegant and sophisticated ways. Learning how biological systems do this at the cellular and nano- levels can inspire the development of materials that are engineered to change appearance, for a wide variety of applications.
Toward that goal, Hanlon has received a new grant from the Air Force Office of Scientific Research to reveal the design principles of combined pigmentary and structural coloration in the dynamic color patterning system of cephalopods. The team seeks the framework for how this system works by teasing out what each part does independently, as well as communally.
Cephalopod skin offers many combinations of interplay between pigmentary and structural optical elements. Hanlon and collaborators will focus on two of these systems: one that produces a tunable spectrum of colors, and another that produces many grades of white.
Their goal is to determine mechanistic insights into how these biological systems work, and to use this information to inform the design of new materials and structures designed to emulate them.
Understanding Novel Mechanisms of Color
Cephalopods produce color and pattern with three basic skin elements: chromatophores (yellow, red, brown), iridophores (all colors) and leucophores (white). Chromatophores are pigmentary organs, while iridophores and leucophores are structural coloration cells that contain reflectin proteins for reflectance.
Combinations of pigmentary and structural coloration can be static (i.e. non-changeable) or dynamic. In most cases, the pigmentary and structural elements are in different dermal layers. Yet in one recently discovered unique system – the squid chromatophore - they are both present and tightly co-located within the same chromatophore organ and a single dermal layer. The optical significance of this is yet unknown.
A major objective of the new grant award is to elucidate the design principles of dynamic and static colorants in cephalopod skin, with an emphasis on the exceptionally tight co-localization of pigments and reflectors in the squid chromatophore.
Deciphering White Structural Coloration
White is extremely important as a “multi-color” for both camouflage and communication, and among other things it helps enhance contrast and brightness of pigmentation in some animal systems. In cephalopods, white is solely a structural color; i.e., no white pigments are known for this group. Cephalopod skin passively produces whites of many shades, including extremely bright coherent white, through the combination of multiple reflectin proteins in its leucophores.
The second major objective for this grant award is to elucidate the design details of refractive index, cell shape and gross morphology of leucophore structural elements. These, in turn, will inform the design of bio-inspired structures that can replicate these functions.
Hanlon’s collaborators for this work include Co-Principal Investigators Leila Deravi of Northeastern University and Caroline Albertin of MBL. Steven Senft of MBL is also a key player on the team.