Abstract
There are nearly 300 species belonging to the order Testudines. Over half are listed by CITES as either threatened or endangered, many are maintained in captivity as pets, zoological exhibits or research animals, and a few are farmed for commercial purposes. The gender of most species is determined by temperature-dependent sex determination during incubation, with males predominating at lower and females at higher temperatures (although genetically determined gender has been documented for a couple of species).1,2,5-13 Unfortunately, precise incubation parameters have only been determined for a handful of species. For most hatchings gender will not be reliably known until secondary characteristics become obvious, which may take several years. This delay in identifying gender prevents the refinement of incubation practices and may result in gender-biased clutches. Such phenotypic bias could have obvious deleterious effects on head-start or conservation programs, and so a means of confirming gender in neonates and hatchlings is beneficial.
Unlike most birds there is no commercially available DNA probe to identify gender for chelonians. However, endoscopy has proven effective in determining gender in monomorphic birds, and more recently, similar techniques have been developed for reptiles.3,4 Under anesthesia, prefemoral insertion of 1.9-mm or 2.7-mm rigid telescopes combined with CO2, air, or sterile saline insufflation enables visualization of the immature reproductive tract, even in hatchling turtles. Given the small size of the animals involved, a single injection can often achieve sufficient insufflation. In some species, the ovary or testis may be differentiated at a very early age, especially when the terminal telescope lens is held against the gonad to facilitate a 15–20x magnification of the tissue. However, in those species that appear to undergo significant post-hatching gonadal differentiation, the identification of the immature oviduct can also lead to accurate gender identification. Endoscopy offers a fast, reliable and immediate means of determining gender that can be used to monitor and adjust incubation parameters more quickly than waiting for secondary characteristics to develop. In addition, the advent of portable equipment makes this system appropriate for use in the field as well as the hospital.
Literature Cited
1. Booth, D.T., and K. Astill. 2001. Incubation temperature, energy expenditure and hatchling size in the green turtle (Chelonia mydas), a species with temperature-sensitive sex determination. Australian J Zool. 49: 389–396.
2. Du, W.G., L.J. Hu, J.L. Lu, and L.J. Zhu. 2007. Effects of incubation temperature on embryonic development rate, sex ratio and post-hatching growth in the Chinese three-keeled pond turtle, Chinemys reevesii. Aquaculture. 272: 747–753.
3. Hernandez-Divers, S.J. 2004. Diagnostic and surgical endoscopy. In: P. Raiti and S. Girling, eds. Manual of Reptiles. 2nd ed. British Small Animal Veterinary Association, Cheltenham, England. Pp. 103–114.
4. Hernandez-Divers, S.J., S.M. Hernandez-Divers, G.H. Wilson, and S.J. Stahl. 2005. A review of reptile diagnostic coelioscopy. J Herp Med Surg. 15: 16–31.
5. Lescure, J., F. Rimblot, J. Fretey, S. Renous, and C. Pieau. 1985. Influence of the incubation temperature of eggs on the hatchling sex-ratio in the leatherback, Dermochelys coriacea. Bulletin De La Societe Zoologique De France-Evolution Et Zoologie. 110: 355–359.
6. Lewis-Winokur, V., and R.M. Winokur. 1995. Incubation temperature affects sexual differentiation, incubation time, and posthatching survival in desert tortoises (Gopherus agassizii). Canadian J Zool., Revue Canadienne De Zoologie. 73: 2091–2097.
7. Madge, D. 1994. Temperature and sex determination in reptiles with reference to chelonians. Testudo 2: 9–14.
8. Pieau, C., T.M. Mignot, M. Dorizzi, and A. Guichard. 1982. Gonadal steroid levels in the turtle Emys orbicularis—a preliminary study in embryos, hatchlings, and young as a function of the incubation temperature of eggs. Gen Comp Endocrinol. 47: 392–398.
9. Thompson, M.B. 1988. Influence of incubation temperature and water potential on sex determination in Emydura macquarii (Testudines, Pleurodira). Herpetologica. 44: 86–90.
10. Vogt, R.C., J.J. Bull, C.J. McCoy, and T.W. Houseal. 1982. Incubation temperature influences sex determination in kinosternid turtles. Copeia. 480–482.
11. Vogt, R.C., and O. Floresvillela. 1992. Effects of incubation temperature on sex determination in a community of neotropical freshwater turtles in Southern Mexico. Herpetologica. 48: 265–270.
12. Wyneken, J., S.P. Epperly, L.B. Crowder, J. Vaughan, and K.B. Esper. 2007. Determining sex in posthatchling loggerhead sea turtles using multiple gonadal and accessory duct characteristics. Herpetologica. 63: 19–30.
13. Yntema, C.L. 1979. Temperature levels and periods of sex determination during incubation of eggs of Chelydra serpentina. J Morphol. 159: 17–27.