Bone labeling experiments and intraskeletal growth patterns in captive leopard geckos (Eublepharis macularius)

An understanding of the dynamics of bone growth is key to interpreting life-history parameters of vertebrates. In this study, we used fluorochrome labels in captive leopard geckos (Eublepharis macularius) to track bone growth and intraskeletal variability from embryonic to adult growth stages. Thirteen individuals were administered fluorochromes from pre-hatching to 4 years of age. The left tibia, fibula, femur, humerus, radius, and ulna were examined histologically and compared for differences in the number of labels within and between individuals at each sampled growth stage, and the amount of bone growth between labels was calculated. Results suggest that limb elements had differing growth rates; the fibula grew the fastest per day on average and the femur grew the slowest per day on average. All labels administered in ovo were still present in all limb elements in adults except for the tibia, suggesting growth marks are not lost in most elements and accurate calculations of growth rates could be performed in individuals up to 3 years old. All ex ovo labels were accounted for; however, when two fluorochromes were administered 3 weeks apart, the labels could not be differentiated from each other due to the new bone not being deposited at a quantifiable level. Overall, the tibia in leopard geckos is the least reliable limb bone to use for skeletochronology and the humerus, radius, and fibula preserve the longest growth record. This research highlights that, as in other extinct and extant animals, patterns of bone growth are not consistent across reptiles. This study adds to the growing body of knowledge on growth variability in reptiles.