Feminizing turtle embryos as a conservation tool

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 phenotype adult females of 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 Mullerian 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-biased-a result contrary to that expected-and 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.