Literaturdatenbank
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Girondot, M., Fouillet, H., & Pieau, C. (1998). Feminizing turtle embryos as a conservation tool. Conservation Biology, 12(2), 353.
Added by: Admin (17 Aug 2008 18:17:17 UTC) |
| Resource type: Journal Article BibTeX citation key: Girondot1998 View all bibliographic details  |
Categories: General Keywords: Emydidae, Emys, Emys orbicularis, Habitat = habitat, Schildkröten = turtles + tortoises, Zeitigung = incubation Creators: Fouillet, Girondot, Pieau Collection: Conservation Biology |
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| Abstract |
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Most turtles have temperature-dependent sex determination. With the intention to preserve endangered and threatened species, two management tools have been suggested: artificial incubation at either male- or female-producing temperatures and introduction of many more females than males into populations by manipulating incubation temperatures to favor the production of female embryos. The use of estrogens during incubation has also been proposed to induce the development of females. We argue that in nature the incubation of eggs around the pivotal temperature is probably more frequent than generally recognized and leads to either phenotypic adult females or phenotypic adult males, even though the embryonic testis may present various degrees of intersexuality, including ovotestes as documented in artificial incubation. Observations of the turtle Emys orbicularis show that, after hatching, ovotestes tend to evolve into testes by regression, total or partial, of the ovarian-like cortex. Testes with some immature oocytes at their surface have been observed in adult turtles, and they produce spermatozoa. Therefore, gonadal intersexuality apparently does not hinder the reproductive male function in adults. We draw attention to the danger of estrogenic treatment of embryos to produce females. In many cases, such treatment induces thin gonads ("hypogonads") in which the volume of both cortex and medulla are reduced. Exogenous estrogens may also result in the arrest of lengthening of the Müllerian ducts and sometimes in the opening of their caudal end in the Wolffian ducts. Either process results in the inability of adult females to evacuate eggs from oviducts. We modeled the long-term effects of introducing in a population a strongly female-biased primary sex ratio (20 females to 1 male) for 30 years. Taking into account a genetic component of sex determination, as exemplified by the results of incubation at pivotal temperature, such a manipulation favors masculinizing alleles. When the manipulation is stopped, the primary sex ratio, as well as the adult sex ratio, becomes male-biaseda result contrary to that expectedand the population size decreases. We recommend actions that protect adult populations and nesting sites and that improve the natural conditions of incubation in these sites rather than attempts to manipulate sex ratios.
Added by: Admin |