SAFER, A.B.*; GRACE, M.S.; Florida Institute of Technology, Melbourne: Pits within pits: Are nanopit arrays functional components of snake infrared imaging systems?

Some members of the snake families Pythonidae and Boidae (pythons and boas) and all of the viperid subfamily Crotalinae (pit vipers) possess infrared (IR) sensitive pit organs which allow these snakes to form detailed images of their thermal environments. IR imaging species can utilize pit organs to target homeothermic prey in the absence of visual cues, find suitable sites for thermoregulation, and to defend against predators. Microstructural analyses have revealed characteristic arrays of epidermal surface nanopits in the pit organ epidermis in pythonid and crotaline snakes, and on IR sensitive areas of labial scales in the boid, Boa constrictor. Nanopit arrays also occur in epidermal regions not associated with IR reception (ocular spectacle and interscale epidermis), but the arrays in pit organs and related labial regions have unique and distinct dimensions. The fact that all IR imaging species investigated thus far possess nanopit arrays suggests that nanopits are important for sensing and imaging IR radiation. In an effort to better understand the mechanisms involved in IR reception and the evolution of IR imaging in snakes, we performed a detailed dimensional analysis of nanopit arrays, comparing known IR imaging species, species suspected to be IR imagers, and non-IR imaging species. We also tested the hypothesis that nanopit arrays may serve as selective spectral filters, enhancing IR photon absorption. We used scanning electron microscopy to investigate the epidermal microstructure of pit organ and non-pit organ epidermis and investigated the IR transmittance properties of these epidermal regions using Fourier Transform Infrared Spectroscopy (FTIR). Our results provide a comprehensive analysis of how nanopit arrays may be involved in infrared imaging.