Individual markings are a reliable non-invasive means of identification over time in Blotched Blue-tongued Lizards, Tiliqua nigrolutea

Pattern is often studied by zoologists who wish to re-identify an individual animal within a population. For pattern to prove a reliable method of identification, it must be unique between individuals and constant throughout time, as has been demonstrated in species such as badgers (Dixon, 2003), polar bears (Anderson and Waterman, 2007) and grey nurse sharks (Bansemer and Bennett, 2008). However, little work has been undertaken on reptiles, which are often identified by injecting or surgically implanting PIT tags (Jemison et al., 1995; Hilterman et al., 2007) or toe-clipped (Sacchi et al., 2007). Pattern is a less intrusive and more potentially reliable method of distinguishing individuals. There is currently no information available on pattern stability in the blotched blue tongue lizard (Tiliqua nigrolutea). Markings displayed by blue tongue lizards are a combination of very dark blotches and bands on a paler background, and differences in these patterns between individuals are immediately distinguishable. However, it is not enough simply to state that these patterns appear unchanged over time, they must be quantified and scored in some way to confirm that this is so. This project has investigated whether pattern remains sufficiently constant over time to be used as a reliable method of individual identification in T. nigrolutea. METHODS We created a key of ten characters, each with multiple possible character states, focusing on features such as the colour shades of the paler regions (e.g. grey/gold/salmon), the arrangement of individual blotches into connected bands (e.g. Figure 1), and particular regions of the body such as neck, pelvis and tail (e.g. Figure 2) (dorsal pattern only). This key allowed a more objective assessment of digital photographs taken over a period of four years as individuals (N=29) from five litters grew in captivity from neonatal (snout to vent (SVL) length ‚Äöv¢v†10 cm to adult body length (SVL > 24 cm in males, SVL > 26 cm in females). Digital images of the dorsal surface of individual lizards taken at 12 and 18 months and 4 years were scored using the key and compared. Not all photos displayed all 10 characters clearly, so only characters that were visible in the photos were scored. Only characters where a score was available for at least two of the sample periods dates were considered. The proportion of characters scored for which each individual achieved an identical character state over time was calculated as a percentage for each litter, and overall.