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Kuchling, G. , Evaluating impacts of temperature dependent sex determination in headstarting and captive breeding projects of critically endangered turtles. Unpublished paper presented at 6th World Congress of Herpetology. 
Added by: Admin (21 Nov 2009 11:59:58 UTC)
Resource type: Conference Paper
BibTeX citation key: Kuchling2008b
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Categories: General
Keywords: Aldabrachelys, Aldabrachelys dussumieri, Astrochelys, Astrochelys yniphora, Batagur, Batagur affinis, Batagur borneoensis, Chitra, Chitra chitra, Erymnochelys, Erymnochelys madagascariensis, Geoemydidae, Podocnemididae, Schildkröten = turtles + tortoises, Testudinidae, Trionychidae, Zeitigung = incubation
Creators: Kuchling
Collection: 6th World Congress of Herpetology
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Abstract     
Testudinidae Temperature dependent sex determination has important implications for tortoise and turtle conservation programs involving captive breeding or nest translocation and head-starting. The standard scientific method to establish sex ratios of hatchlings is to sacrifice them for histological examination of their gonads. The dilemma is that this technique is generally not permissible in conservation programs of critically endangered species, for which however the assessment of sex ratios is particularly imperative. Many tortoise and turtle species take many years or decades to mature. External sexual dimorphism may take as long to develop. Thus, conservation programs often operate for a long time without knowing the sex ratio they produce and the sex ratio of juveniles released into the wild. Unfortunately no non-invasive technique presently allows the accurate sexing of juvenile chelonians. I used endoscopy to sex juvenile Geochelone yniphora and Erymnochelys madagascariensis in the breeding and head-starting programme of the Durrell Wildlife Conservation Trust in Madagascar; to sex juvenile Dipsochelys dussumieri at the breeding program of the La Vanille Crocodile and Tortoise Park in Mauritius; and to sex juvenile Batagur affinis and Batagur borneoensis for the Malaysian Fisheries Department and the University of Malaysia Terengganu. I successfully sexed turtles as small as 60g, but found that gonads and reproductive tracts are better differentiated and the sex is easier to determine in larger juveniles. Intersex conditions do occur in small tortoises and turtles, but three “intersex” D. dussumieri which I re-examined four years later had all turned into females. The conservation programs for G. yniphora, E. madagascariensis and D. dussumieri generally produced female biased sex ratios, those for B. affinis either male or female biased sex ratios, and those of B. borneoensis only females. A captive breeding project for Chitra chitra in Kanchanaburi produced a heavily male biased sex ratio based on dissection of dead juveniles, even though softshell turtles are generally believed to have genetic sex determination. Biased sex ratios from nests constructed by captive mothers demonstrate that the limited nest site choice in captivity does not guarantee that this “natural” incubation provides balanced sex ratios.
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