title: Broadband and polarization reflectors in the lookdown, Selene vomer.
abstract: Predator evasion in the open ocean is difficult because there are no objects to hide behind. The silvery surface of fish plays an important role in open water camouflage. Various models have been proposed to account for the broadband reflectance by the fish skin that involve one-dimensional variations in the arrangement of guanine crystal reflectors, yet the three-dimensional organization of these guanine platelets have not been well characterized. Here, we report the three-dimensional organization and the optical properties of integumentary guanine platelets in a silvery marine fish, the lookdown (Selene vomer). Our structural analysis and computational modelling show that stacks of guanine platelets with random yaw angles in the fish skin produce broadband reflectance via colour mixing. Optical axes of the guanine platelets and the collagen layer are aligned closely and provide bulk birefringence properties that influence the polarization reflectance by the skin. These data demonstrate how the lookdown preserves or alters polarization states at different incident polarization angles. These optical properties resulted from the organization of these guanine platelets and the collagen layer may have implications for open ocean camouflage in varying light fields.
authors: Department of Integrative Biology, University of Texas, Austin, TX 78712, USA szhao@utexas.edu.
authors: Shulei
authors: S
authors: Zhao
authors: Department of Integrative Biology, University of Texas, Austin, TX 78712, USA.
authors: Parrish Clawson
authors: PC
authors: Brady
authors: Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA.
authors: Meng
authors: M
authors: Gao
authors: Department of Integrative Biology, University of Texas, Austin, TX 78712, USA.
authors: Robert Ian
authors: RI
authors: Etheredge
authors: Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA.
authors: George W
authors: GW
authors: Kattawar
authors: Department of Integrative Biology, University of Texas, Austin, TX 78712, USA.
authors: Molly E
authors: ME
authors: Cummings
mesh_terms: D000818:Animals; D003094:Collagen / Q000737:chemistry; D003198:Computer Simulation; D003460:Crystallization; D017753:Ecosystem; D005399:Fishes / Q000502:physiology*; D006147:Guanine / Q000737:chemistry; D008027:Light; D008853:Microscopy; D008855:Microscopy, Electron, Scanning; D016011:Normal Distribution; D009792:Oceans and Seas; D055095:Optics and Photonics; D010858:Pigmentation; D011235:Predatory Behavior; D012867:Skin / Q000378:metabolism*; D013472:Sunlight
chemical_list: D006147:Guanine; D003094:Collagen
keywords: broadband reflectance; camouflage; guanine platelets; iridophores; polarization; the lookdown