Looking at invisibility anti-reflective structures and strategies in hyperiid amphipods

Meeting Abstract

P2.55  Saturday, Jan. 5  Looking at invisibility: anti-reflective structures and strategies in hyperiid amphipods BAGGE, L.E.*; JOHNSEN, S.; Duke University; Duke University laura.bagge@duke.edu

Transparency is a common camouflage strategy for animals inhabiting marine pelagic environments. Transparent species are almost perfectly invisible when viewed under ambient light conditions in the mesopelagic zone; however, at shallower depths, and under the bioluminescent searchlights of potential predators, transparent species may become visible due to reflections from their body surface. No study has yet explored whether any pelagic, transparent animals have developed specific adaptations to minimize surface reflections, though anti-reflection cuticular nanoprotuberances, which optically function as a gradient refractive index material, have been found in the eyes of butterflies and moths, and in transparent wings of moths. Our study uses scanning electron (SEM) and transmission electron (TEM) microscopy to investigate the cuticle of several species of pelagic, transparent hyperiid amphipods, Phronima spp. and Cystisoma spp. Preliminary results show that the appendages of Cystisoma spp. (n=2) are covered with an ordered array of papillae, 200-300nm in height. Interestingly, the dorsal surfaces of Phronima sedentaria (n=4) and Cystisoma spp. (n=2) are covered with a biofilm of densely aggregated sphere-shaped bacteria. Preliminary analysis suggests that the biofilm could effectively function to reduce reflectance of 500nm blue-green bioluminescent light, though future work is needed to further characterize and determine the refractive index of the biofilm.

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