Sexually Dimorphic Growth in the Western Swamp Tortoise, Pseudemydura umbrina (Testudines: Chelidae)
Keywords:
Growth, development, sexual dimorphism, carapace length, tortoise, Pseudemydura umbrinaAbstract
Captive breeding of the critically endangered Western Swamp Tortoise (WST: Pseudemydura umbrina) has occurred at Perth Zoo as part of the species’ recovery plan since 1988. The first release of captive bred individuals took place in 1994. Individuals are primarily released into protected wild reserves at approximately three years of age, when they typically reach the mandatory minimum body mass of 100g. They are sexually immature at this age, and gender determination is not possible by external physical examination. For sustainable reintroduction programs, it is desirable to know the sex ratio of individuals prior to release, and the sex of individuals being retained for future captive breeding purposes. Utilising body mass and size morphometrics from zoo bred individuals retained until sexual maturity, we evaluated sex related changes in growth rates and body size over time. Sexual dimorphism in favour of males was first detected at four years of age, with significant differences (P < 0.05) observed in both the body mass (121.9±6.8 g vs 105.0±4.4 g) and carapace length (89.5±2.0 mm vs 83.2±1.4 mm). Age at which sexual maturity was attained varied between 5 to 13 years, but on average occurred earlier in males (8.0±0.5 yr) than females (8.7±0.4 yr). Data confirm a faster growth rate and earlier age of sexual maturity in males than females, as well as a smaller size (carapace length) at sexual maturity (~110 mm for males and ~100 mm for females) than previously reported for wild WST (110 – 131 mm). We suggest that using growth rate data, body size (mass and length) and plastron shape may be useful to determine sex at 4-5 years of age, and prior to release to the wild, to better monitor sex ratios at release and during future in situ monitoring.
Downloads
Published
How to Cite
Issue
Section
License
Authors who publish with this journal agree to the following terms:
- Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.
- Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
- Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as it can lead to productive exchanges, as well as earlier and greater citation of published work (See The Effect of Open Access).