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Could you gender your reptile?
Animals 2025
Alessandro Vetere 1,*,Michele Capasso 2 and Francesco Di Ianni
Background
Sex determination is a critical aspect of reptile management in veterinary, zoological, and conservation contexts, especially given the minimal sexual dimorphism observed in many species. This review synthesizes the current methodologies for determining reptile sex, emphasizing the importance of accurate techniques to establish breeding groups, reduce aggression, and conserve endangered species. Advances in imaging and molecular tools offer promising non-invasive alternatives to traditional methods.
Methods
The authors reviewed 44 journal articles and five book chapters using databases like Google Scholar, PubMed, and Scopus. Search terms included "sex identification," "sex determination," "reptiles," and related keywords. Only peer-reviewed and relevant articles were included.
Results
The study describes various techniques for sex determination in reptiles, categorized into traditional and advanced methods:
Traditional Methods:
-Probing: Common in snakes and some lizards, using blunt instruments to identify hemipenes in males.
-Eversion and Popping: Applying pressure near the cloaca to evert hemipenes in males; suitable for juveniles.
-Hydrostatic Eversion: Saline injection to evert hemipenes or visualize oviductal papillae in females; invasive and less commonly used.
Imaging Techniques:
-Ultrasound: Useful for visualizing gonads, follicles, or testes; widely applicable but with limitations in accuracy for some species.
-CT Scans: Superior for assessing reproductive structures, particularly in chelonians, though expensive and less available.
-Radiography: Detects mineralized sexual structures like hemibacula in male monitors; effective in mature individuals.
-Contrast Radiography: Highlights differences between male and female reproductive structures using contrast agents.
-Endoscopy and Coelioscopy: Direct visualization of gonads, offering high accuracy but requiring anesthesia or sedation.
Molecular Methods:
-Genotypic Sex Determination (GSD): Includes karyotyping and PCR-based techniques. While promising, molecular methods remain underutilized due to cost and limited availability.
Limitations
The accuracy of techniques varies significantly across species, emphasizing the need for tailored approaches.
Advanced methods, such as imaging and molecular diagnostics, may not be universally accessible due to cost or technical expertise requirements.
Conclusions
Reptile sex determination requires a combination of traditional and advanced techniques, with the choice depending on the species, context, and resources. Non-invasive imaging and molecular methods show potential for improving accuracy and reducing stress but need broader accessibility. Accurate sex determination is vital for breeding programs, preventing aggression, and supporting conservation efforts.

On the left (A), radiograph of a mature male black-headed monitor (Varanus tristis), showing evident mineralized hemibacula (yellow arrows). On the right (B), a mature female of the same species; hemibacula are absent. Courtesy of Dr. Clément Paillusseau.
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