David Prötzel,corresponding author1 Martin Heß,2 Martina Schwager,3 Frank Glaw,1 and Mark D. Scherz1
1Zoologische Staatssammlung München (ZSM-SNSB), Munich (Germany); 2Department Biologie II, Ludwig-Maximilians-Universität München, Planegg-Martinsried (Germany); 3Department of Applied Sciences and Mechatronics, Munich University of Applied Sciences, Munich (Germany).
Biofluorescence is widespread in the natural world, but only recently discovered in terrestrial vertebrates. Here, we report on the discovery of iridophore-based, neon-green flourescence in the gecko Pachydactylus rangei, localised to the skin around the eyes and along the flanks. The maximum emission of the fluorescence is at a wavelength of 516 nm in the green spectrum (excitation maximum 465 nm, blue) with another, smaller peak at 430 nm. The fluorescent regions of the skin show large numbers of iridophores, which are lacking in the non-fluorescent parts. Two types of iridophores are recognized, fluorescent iridophores and basal, non-fluorescent iridophores, the latter of which might function as a mirror, amplifying the omnidirectional fluorescence. The strong intensity of the fluorescence (quantum yield of 12.5%) indicates this to be a highly effective mechanism, unique among tetrapods. Although the fluorescence is associated with iridophores, the spectra of emission and excitation as well as the small Stokes shifts argue against guanine crystals as its source, but rather a rigid pair of fluorophores. Further studies are necessary to identify their morphology and chemical structures. We hypothesise that this nocturnal gecko uses the neon-green fluorescence, excited by moonlight, for intraspecific signalling in its open desert habitat.
Stained and unstained slices were photographed with a Leica DM 750 fluorescence microscope, equipped with Leica DMC 4500 digital camera, a CoolLED pE-300 white light-source using the GFP filter cube (excitation wavelength at 475 nm; objectives Leica HI Plan 10 × NA 0.25 and 40 × NA 0.65) or in transmission bright field.
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