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

Abstract

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 MaterialsTwenty 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. ResultsThe 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 ClinicalRelevance 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.Keywords contrast radiography; eastern blue-tongued; hemeclitores; hemepenes; morphometrics; sex identification; skink Abbreviations H, widest point of the head; H/SVL%, head width divided by snout-vent length; H/T%, head width divided by trunk length.; HL, head length from the rostral tip of the head to the back of the ears; SVL, snout-vent length from the rostral tip of the head to the middle of the vent; T, trunk length from the middle of the forelimbs to the middle of the hindlimbs; TBL, total body length from the rostral tip of the head to the distal tip of the tail; TW, tail width at the widest point of the proximal tail

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

“…In conclusion, in addition to morphometry, 11,12,14 a variety of methods have been reported for sexing in Tiliqua scincoides [8][9][10][11]13 but none are entirely adequate in the rehabilitation setting.…”

“…The accuracy of these procedures is yet to be determined from large studies though McKenzie et al recently reported 100% accuracy using contrast radiography in 20 captivebred Blue Tongues. 9,10,12 Cytogenetic analysis is also accurate but is a very specialized technique. 13 We have, thus, presented a practical and relatively accurate, morphometry-based procedure for sexing Eastern Blue Tongued Skinks that is applicable to the rehabilitation setting as it can be used to eliminate the need to radiograph (or use another more definitive means of sexing) a substantial proportion of rescued Blue Tongues who are most probably male.…”

“…However, in large lizards such as Tiliqua scincoides both techniques may cause injury and, particularly if the operator is inexperienced, are unreliable. [8][9][10][11][12] Transillumination of the base of the tail region with bright light can identify the presence or absence of hemipenes though this method is ineffective if the specimen is dark in colour. 8,10 Radiography (plain and using contrast media instilled into the cloaca), ultrasonography and computed tomography, have also been used though such methods are more commonly used for pet lizards or breeding.…”

“…8,10 Radiography (plain and using contrast media instilled into the cloaca), ultrasonography and computed tomography, have also been used though such methods are more commonly used for pet lizards or breeding. [9][10][11][12] These techniques are generally more difficult and less accurate in smaller animals or, for ultrasound, due to ultrasound impenetrable osteoderms. [8][9][10]12 Finally, it has been shown that Tiliqua scincoides can be accurately sexed cytogenetically as the X chromosome exhibits an accumulation of ribosomal DNA loci in contrast to the Y chromosome.…”

“…[9][10][11][12] These techniques are generally more difficult and less accurate in smaller animals or, for ultrasound, due to ultrasound impenetrable osteoderms. [8][9][10]12 Finally, it has been shown that Tiliqua scincoides can be accurately sexed cytogenetically as the X chromosome exhibits an accumulation of ribosomal DNA loci in contrast to the Y chromosome. 13 This, however, is a very specialized, primarily research technique and not easily available to wildlife rescuers.…”