Veiled Chameleons (Chamaeleo calyptratus) 2021 Environmental Summary, Reptile & Aquatics, Stowers Institute for Medical Research v1

Veiled Chameleons (Chamaeleo calyptratus) are an increasingly popular model organism, and we have maintained a colony at the Stowers Institute since 2010. Due to the poikilothermic nature of these animals, achieving the correct macro and microenvironments plays an important role in successful long term colony maintenance. Despite being bred in captivity for many generations, relatively little husbandry information has been published regarding housing in a research environment. Recognizing that husbandry conditions and environmental parameters can impact research results we provide information about the housing, husbandry, maintenance, nutrition, and health for our colony of Veiled Chameleons. This information will be applicable to any chameleon housed in the facility in 2021.

Chemotherapy-Responsive Acute Myeloid Leukemia in a Veiled Chameleon (Chamaeleo calyptratus)

A 4-year-old captive-bred male veiled chameleon (Chamaeleo calyptratus) presented with anorexia, weight loss, and stomatitis. Complete blood count revealed pancytopenia and a marked leukocytosis (197 x103/µL) composed of blast cells (195 x103/µL) that had oval to irregular nuclei with finely stippled chromatin and occasional nucleoli. The diagnosis was acute leukemia of presumptive myeloid origin. Treatment with prednisone (1.5 mg/kg once daily orally) and cytosine arabinoside (300 mg/m2 subcutaneously) was initiated. Post-treatment hematologic analysis revealed decreased blast count (88.5 x103/µL) and improved mentation. Additional doses of cytosine arabinoside were given two and three weeks after the initial diagnosis with marked improvement in circulating blast concentration (15.3 x103/µL). During the course of treatment, which included the chemotherapeutics, fluid therapy, and oral supportive care, the chameleon’s weight increased 32.5% (199 g to 295 g). Unfortunately, the animal died 33 days after presentation. Histopathologic evaluation revealed hypocellular bone marrow with rare blast-like cells within vessels and mycotic granulomatous hepatitis with intralesional hyphae and fructiferous bodies. The blast cells expressed Iba1 but not CD3, CD79a, or lysozyme, suggesting a myeloid origin. Cell morphology further reinforced an acute myeloid leukemia. The authors surmised that the chameleon was responding to treatment, but ultimately succumbed to the mycotic hepatitis. This report describes the first case of acute myeloid leukemia with response to chemotherapeutic intervention in a veiled chameleon.

Predicting The Invasion Risk of Non-Native Reptiles as Pets in The Middle East

Wildlife trade for non-native pets is an important and increasing driver of biodiversity loss and often compromises the standards required for protection. However, the growing interest in non-native pets has posed the issue of invasive non-native species to wildlife managers and conservationists. Instituting effective policies regarding non-native species requires a thorough understanding of the potential range of the species in new environments. In this study, we used an ensemble of ten species distribution models to predict the potential distribution for 23 commonly traded species of reptiles across the Middle East. We used ten modeling techniques implemented in the Biomod2 package and ensemble forecasts. Final models contained fourteen environmental variables, including climatic, topographic, and land cover/land use variables. Our results indicate that all Middle Eastern countries included suitable habitats for at least six species, except Qatar, Kuwait and Bahrain for which the models did not predict any suitable habitats. Our study showed that Lebanon, Palestine, Turkey, and Israel face the highest risk of biological invasion by the species on the whole. Also, the results showed that Centrochelys sulcata, Chamaeleo calyptratus, and Trachemys scripta posed the highest risk of spreading in this area. Information on which species pose a greater danger as invaders and the possible impacts of their introduction will be a valuable contribution to the development of conservation plans and policies.

Two novel bornaviruses identified in colubrid and viperid snakes

We present the complete genome sequences of Caribbean watersnake bornavirus (CWBV) and Mexican black-tailed rattlesnake bornavirus (MRBV), which we identified in archived raw transcriptomic read data of a Caribbean watersnake (Tretanorhinus variabilis) and a Mexican black-tailed rattlesnake (Crotalus molossus nigrescens), respectively. The genomes of CWBV and MRBV have a length of about 8,900 nucleotides and comprise the complete coding regions and the untranslated regions. The overall genomic makeup and predicted gene content is typical for members of the genus Orthobornavirus within the family Bornaviridae. Alternative splicing was detected for the L and M genes. Based on a phylogenetic analysis of all viral proteins, we consider both viruses to be members of a single novel species within the genus Orthobornavirus. Both viruses form a distinct outgroup to all currently known orthobornaviruses. Based on the novel virus genomes, we furthermore identified closely related endogenous bornavirus-like nucleoprotein sequences in transcriptomic data of veiled chameleons (Chamaeleo calyptratus) and a common lancehead (Bothrops atrox).

Do substrate roughness and gap distance impact gap-bridging strategies in arboreal chameleons?

Chameleons are well equipped for an arboreal lifestyle, having “zygodactylous” hands and feet as well as a fully prehensile tail. However, to what degree tail use is preferred over autopod prehension has been largely neglected. Using an indoor experimental set-up, where chameleons had to cross gaps of varying distances, we tested the effect of substrate diameter and roughness on tail use in Chamaeleo calyptratus. Our results show that when crossing greater distances, C. calyptratus is more likely to use its tail for additional stability. The animals were able to cross greater distances (up to 1.75 times the shoulder-hip length) on perches with a rougher surface. We saw that depending on the distance of the gap, chameleons would change how they use their prehensile tails when crossing. With shorter gaps the tails either do not touch, or only touch the perch without coiling around it. With larger distances the tails are fully coiled around the perch, and with the largest distances additionally they reposition the hind legs, shifting them towards the end of the perch. Males were able to cross relatively greater distances than females, likely due to their larger size and strength.

Ocular elongation and retraction in foveated reptiles

BackgroundPronounced asymmetric changes in ocular globe size during eye development have been observed in a number of species ranging from humans to lizards. In contrast, largely symmetric changes in globe size have been described for other species like rodents. We propose that asymmetric changes in the three-dimensional structure of the developing eye correlate with the types of retinal remodeling needed to produce areas of high photoreceptor density. To test this idea, we systematically examined three-dimensional aspects of globe size as a function of eye development in the bifoveated brown anole, Anolis sagrei.ResultsDuring embryonic development, the anole eye undergoes dynamic changes in ocular shape. Initially spherical, the eye elongates in the presumptive foveal regions of the retina and then proceeds through a period of retraction that returns the eye to its spherical shape. During this period of retraction, pit formation and photoreceptor cell packing are observed. We found a similar pattern of elongation and retraction associated with the single fovea of the veiled chameleon, Chamaeleo calyptratus.ConclusionsThese results, together with those reported for other foveated species, support the idea that areas of high photoreceptor packing occur in regions where the ocular globe asymmetrically elongates and retracts during development.Key FindingsThe eyes of the brown anole, Anolis sagrei, and veiled chameleon, Chamaeleo calyptratus undergo dynamic asymmetrical changes in ocular shape during development.In both species, asymmetric elongation and retraction of the ocular globe is associated with fovea morphogenesis.Pit formation and photoreceptor cell packing in the foveal area occur when the corresponding region of the ocular globe is retracting relative to adjacent regions.