Sex identification in the eastern blue-tongued lizard (Tiliqua scincoidesWhite, ex Shaw, 1790) using morphometrics

Sex identification in Australian skinks (Egernia stokesii, E. hosmeri, E. striolata) using cloacoscopy

Thirteen adult healthy captive skinks, six Gidgee spiny-tailed skinks (Egernia stokesii), three Hosmer's spiny-tailed skinks (Egernia hosmeri) and four tree crevice-skinks (Egernia striolata), were submitted to the study. The weight of the animals ranged from 28 g to 146 g. All skinks were explored during their putative mating season, which is December. Lizards were restrained manually and positioned in ventral recumbence. Cloacoscopy was performed with the rigid endoscope, protecting channel, endocamera and recording system Telepack-Pal (Karl Storz Endoskope, Tuttlingen, Germany). While the endoscope was gently introduced into the cloaca and advanced into the coprodeum sterile saline was flushed into the cloaca through the protecting channel. The endoscope was then slowly withdrawn to allow visualization of the main structures of the urodeum and proctodeum. Male skinks are characterized by the presence of urethral papillae and only one horizontal septum which divides the chamber of the urodeum into two subchambers. Female skinks are characterised by the presence of two septa. The central-dorsal fold that divides the urodeum into two pouches in female skinks is absent in males. Cloacoscopy proved an effective method of sex identification and can be considered a valuable method for breeding and conservation in monomorphic skink lizards.

Using morphometrics to identify sex in the eastern blue-tongued skink (Tiliqua scincoides)

INTRODUCTION

Tiliqua scincoides coexists with human activity and is frequently presented for rehabilitation due to injury. The correct identification of sex is important as animals identified as female should be subject to a different decision-making matrix for rehabilitation. However, identification of sex is notoriously difficult in Tiliqua scincoides. We describe a reliable, safe and cost-effective morphometry-based method.

MATERIALS AND METHODS

Adult and sub-adult, wild Tiliqua scincoides dead on presentation or euthanased due to their presenting injuries were collected in South-East Queensland (SE Qld). Head-width to snout-vent length ratio (H:SV) and head-width to trunk length ratio (H:T) were measured and sex was defined at necropsy. Similar data were obtained from a previous study in Sydney, New South Wales (NSW). H:SV and H:T were assessed for accuracy of sex prediction by the area under the receiver operating characteristic curve (AUC-ROC). Optimal cut-points were identified.

RESULTS

The AUC-ROC for the H:T test was for NSW adults, 0.99 (n = 29), NSW sub-adults, 0.95 (n = 10), Qld adults, 0.90 (n = 35) and Qld sub-adults, 0.79 (n = 25). In all cases, H:T was as good or superior to H:SV. H:T cut-points optimized for female sexing or both sexes ranged from 0.20 to 0.23 depending on State and adult status. Sensitivities and specificities of the test at suggested optimal cut-points ranged from 0.54 to 1.0.

CONCLUSION

We describe how H:T can be used as an accurate method to determine sex in Tiliqua scincoides. However, it is more accurate in adults than sub-adults and more accurate in NSW skinks than in SE Qld skinks.

A comparison of two techniques to identify the sex of the eastern blue-tongue skink (Tiliqua scincoides scincoides)

INTRODUCTION

The eastern blue-tongued skink (Tiliqua scincoides scincoides), native to eastern Australia, is commonly kept as both a pet and for breeding. As a sexually monomorphic species, it is important to develop reliable techniques for sex identification, both for breeding and health purposes. Numerous techniques have been developed for the identification of sex in other reptile species but, other than possibly morphometric analysis, none have proven to be reliable in this species. Two techniques showing promise are contrast radiography of the hemepenes/hemeclitores, and morphometrical analysis. This study looks at both techniques and compares them for accuracy.

METHODS AND MATERIALS

Twenty captive eastern blue-tongued skinks (of known sex) were sedated, contrast radiography of their hemepenes /hemeclitores was performed, and physical measurements were taken for morphometric analysis. The radiographs were examined by a panel of three researchers (blinded to the known sex) to identify sex. The morphometric data were statistically analysed, following a previously published methodology, and the individual sex identified. Again, the researchers were blinded to the known sex.

RESULTS

The contrast radiography technique was 100% accurate in correctly identifying the sex of all the skinks. Morphometric analysis was, by contrast, only 70% accurate.

CONCLUSION AND CLINICAL RELEVANCE

Physical differences between wild and captive skinks, as well as different environmental and nutritional factors, may have contributed to the lower accuracy of morphometric analysis in identifying the sex of eastern blue-tongued skinks. While contrast radiography was more accurate, the need for specialised equipment may render this technique impractical for field researchers, but more suitable for owned animals. More research is needed to assess the impact of captivity on eastern blue-tongued skinks' physical morphometrics.

Are lizards capable of inhibitory control? Performance on a semi-transparent version of the cylinder task in five species of Australian skinks

Abstract

Inhibitory control, the inhibition of prepotent actions, is essential for higher-order cognitive processes such as planning, reasoning, and self-regulation. Individuals and species differ in inhibitory control. Identifying what influences inhibitory control ability within and between species is key to understanding how it evolved. We compared performance in the cylinder task across five lizard species: tree skinks (Egernia striolata), gidgee skinks (Egernia stokesii), eastern blue-tongue skinks (Tiliqua s. scincoides), sleepy lizards (Tiliqua r. asper), and eastern water skinks (Eulamprus quoyii). In our task, animals had to inhibit the prepotent motor response of directly approaching a reward placed within a semi-transparent mesh cylinder and instead reach in through the side openings. Additionally, in three lizard species, we compared performance in the cylinder task to reversal learning to determine the task specificity of inhibitory ability. Within species, neither sex, origin, body condition, neophobia, nor pre-experience with other cognitive tests affected individual performance. Species differed in motor response inhibition: Blue-tongue skinks made fewer contacts with the semi-transparent cylinder wall than all other species. Blue-tongue skinks also had lower body condition than the other species which suggest motivation as the underlying cause for species differences in task performance. Moreover, we found no correlation between inhibitory ability across different experiments. This is the first study comparing cylinder task performance among lizard species. Given that inhibitory control is probably widespread in lizards, motor response inhibition as exercised in the cylinder task appears to have a long evolutionary history and is likely fundamental to survival and fitness.

Significance

The study of lizard cognition is receiving increasing attention. Lizards are a diverse group with a wide range of ecological attributes and represent a model system through which we can test a wide range of hypotheses relating to cognitive evolution. Furthermore, considering their evolutionary history, studying non-avian reptile cognition can help understand the evolution of different cognitive abilities including inhibitory control. Here, we provide a comparison of inhibitory control ability in five lizard species. Consequently, we are able to, firstly, validate a method (the cylinder task) initially developed for the use in mammals and birds, for use in lizards, and secondly, collect valuable data on inhibitory control in a poorly studied group with respect to cognitive ability. Our study suggests non-cognitive factors as a major influence on cylinder task performance, which is in agreement with previous studies of other vertebrates.

Do lizards have enhanced inhibition? A test in two species differing in ecology and sociobiology

Waiting for the right moment to strike, avoiding the ingestion of harmful foods, or ignoring stimuli associated with ephemeral or depleted resources requires the inhibition of prepotent responses. Good response inhibition facilities flexibility in behaviour which is associated with survival in unpredictable environments. To investigate differences in behavioural flexibility in lizards, we tested reversal learning in the sleepy lizard (Tiliqua rugosa asper) and compared its performance to the relatively closely related eastern blue-tongue skink (Tiliqua scincoides scincoides). We presented both species with a choice between either a light and dark blue stimulus or a triangle and X shape. Both species were able to learn to discriminate between these stimuli and showed similar learning ability during the acquisition of the discrimination. Sleepy lizards, however, demonstrated a higher probability of making a correct choice at the start of the reversal, hinting towards enhanced stimulus response inhibition. Sleepy lizards and blue-tongue skinks inhabit different environments and show differences in ecology and sociobiology, all of which could possibly lead to adaptive specialisation in cognitive ability. Although further research is required, we propose that selection might have led to a change in stimulus response inhibition in the arid-adapted sleepy lizard, because better response inhibition may help them avoid the costs of repeated choices towards stimuli which no longer predict a beneficial outcome.