Neon-green fluorescence in the desert gecko Pachydactylus rangei caused by iridophores.

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.

Rising from the ashes: resurrection of the Malagasy chameleons Furcifer monoceras and F. voeltzkowi (Squamata: Chamaeleonidae), based on micro-CT scans and external morphology.

The taxonomy of the Malagasy chameleon Furcifer rhinoceratus (Gray, 1845) is poorly resolved. The aim of this study is to clarify the taxonomic status of Chamaeleon voeltzkowi Boettger, 1893 and Chamaeleon monoceras Boettger, 1913 both only known from single or very few specimens mostly collected more than 100 years ago and currently considered as synonyms of Furcifer rhinoceratus. Using osteological data from micro-X-ray computed tomography (micro-CT) combined with traditional morphological characters and morphometrics we resurrect both taxa from the synonymy of F. rhinoceratus as F. voeltzkowi and F. monoceras, respectively. Compared to F. rhinoceratus, F. monoceras is smaller, has a relatively shorter tail, a longer and thinner rostral appendage, a poorly developed gular crest and no ventral crest, whereas F. voeltzkowi has a smaller rostral appendage, higher casque and the dorsal crest is continuous with the tail crest. Compared to the broad rostral appendage formed by the anterior protuberance of the premaxillary process of the maxilla, which has serrated edges in F. rhinoceratus, F. monoceras presents a long rostral appendage with a smooth dorsal edge that progressively narrows, and the nasal aperture is extended along the elongated appendage; F. voeltzkowi presents a smaller but curved rostral appendage with a crenate edge. The prefrontal and postorbitofrontal approach one another forming a large, laterally closed supraorbital fontanelle in F. rhinoceratus while in F. monoceras they do not approach, leaving a laterally open fontanelle, and in F. voeltzkowi the fontanelle is diminutive. Furcifer voeltzkowi also differs from the similar F. labordi by a smaller size of the rostral appendage, less bulging casque and body pholidosis. The former exhibits a conspicuous white lateral band comprising heterogeneous scalation. Furcifer labordi, on the other hand, has a homogeneous scalation with a remarkable reticulate pattern. Osteologically, the shape of the prefrontal and the connection of the postorbitofrontal with the parietal also differ greatly between the two. Using micro-CT scans we detected key differences that would be otherwise impossible to determine. We also provide a brief morphological and osteological description of the species and strongly recommend efforts to rediscover these two poorly known taxa in order to enable additional studies and to assess their conservation status.

Widespread bone-based fluorescence in chameleons.

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.

Systematic revision of the Malagasy chameleons Calumma boettgeri and C. linotum (Squamata: Chamaeleonidae).

We revise the taxonomic status of two species of Madagascan chameleons in light of a recent molecular phylogenetic study on the Calumma nasutum group. The investigation of morphological and osteological characters led to a clear delineation between two species within the C. boettgeri complex, C. boettgeri and C. linotum. Calumma linotum has been considered either a synonym of C. boettgeri or a dubious, poorly defined taxon. So far it has only been known from the male holotype with the imprecise locality 'Madagascar'. Based on pholidosis, morphological measurements and characters of the skull that were analyzed using micro-X-ray computed tomography (micro-CT) scans, we ascribe the population of chameleons from Montagne d'Ambre, formerly assigned to C. boettgeri, to C. linotum. Calumma linotum differs from C. boettgeri in the larger size of tubercle scales on the extremities and rostral appendage, the larger diameter of the extremities relative to the body size, the presence of a parietal crest as well as the form of the nasal bones and the anterior tip of the frontal. The life colouration of the males is also characteristic, with a blue rostral appendage and greenish turquoise extremities. The body and rostral appendage of C. boettgeri in contrast are inconspicuously yellowish brown coloured. All confirmed distribution records of C. boettgeri are confined to the biogeographic Sambirano region whereas C. linotum is only known from Montagne d'Ambre and a locality at the base of the Tsaratanana massif. Additional literature records of C. boettgeri and C. linotum from northeastern Madagascar are in need of confirmation. We also confirm the synonymy of Chamaeleo macrorhinus (described from a female holotype with an unknown locality) with Calumma boettgeri. The use of micro-CT exposed further characteristics for species delimitation in an integrative taxonomic approach. In addition to the skull, we also micro-CT scanned the hemipenes of C. boettgeri and C. linotum, using an iodine-based tissue stain, and provide 3D PDF models of these organs. This method enables detailed illustration and the detection of variation in particular characters, and might be an important tool in further taxonomic studies on the C. nasutum group and other squamate reptiles.