Fluorescence is widespread in marine organisms but uncommon in terrestrial tetrapods. We here show that many chameleon species have bony tubercles protruding from the skull that are visible through their scales, and fluoresce under UV light. Tubercles arising from bones of the skull displace all dermal layers other than a thin, transparent layer of epidermis, creating a ‘window’ onto the bone. In the genus Calumma, the number of these tubercles is sexually dimorphic in most species, suggesting a signalling role, and also strongly reflects species groups, indicating systematic value of these features. Co-option of the known fluorescent properties of bone has never before been shown, yet it is widespread in the chameleons of Madagascar and some African chameleon genera, particularly in those genera living in forested, humid habitats known to have a higher relative component of ambient UV light. The fluorescence emits with a maximum at around 430 nm in blue colour which contrasts well to the green and brown background reflectance of forest habitats. This discovery opens new avenues in the study of signalling among chameleons and sexual selection factors driving ornamentation.

The kinetics of the addition reaction of O 2 to the ethyl radical has been investigated as a function of temperature (259-425 K) and pressure (1.5-60 bar) using the muon spin relaxation technique in longitudinal magnetic fields. Within this temperature range at 1.5 bar, the chemical reaction is represented by an Arrhenius rate law with an activation energy of -4.4(4) kJ mol -1 and an apparent frequency factor of 1.3(2) × 10 -12 cm 3 molecule -1 s -1 . The high-pressure limit of the rate constant at 294 K amounts to k ch ∞ ) 8.7(8) × 10 -12 cm 3 molecule -1 s -1 . Within error, this limit has been reached at 1.5 bar. The rate coefficient for spin exchange, k ex ) 2.8(2) × 10 -10 cm 3 molecule -1 s -1 , is collision controlled. The results for k ch agree well with experimental literature values, but the temperature dependence is more pronounced than that predicted on the basis of a RRKM extrapolation from low-pressure data. The theoretical basis for the analysis of experimental data is given, and the results are discussed.

Avoided level crossing muon spin resonance spectra are reported for the muon substituted cyclohexadienyl radical which is formed on irradiation of benzene adsorbed on porous silica and in NaZSM-5. The shapes of the resonances are discussed in terms of the reorientation dynamics of the adsorbed radical and of freezing of the pore-confined benzene.

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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.