Article Dans Une Revue Conservation Biology Année : 2008

Feminizing Turtle Embryos as a Conservation Tool

Résumé

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-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.

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‐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. Feminización de Embriones de Tortugas Como una Herramienta de Conservación La mayoría de las tortugas poseen determinación sexual dependiente de la temperatura. Con la intención de preservar especies en peligro o amenazadas, dos herramientas de manejo han sido sugeridas: Incubación artificial a temperaturas tanto productoras de machos como de hembras y la introducción de mucho mas hembras que machos es las poblaciones mediante la manipulación de las temperaturas de incubación para facorecer la producción de embriones de hembras. El uso de estrógenos durante la incubación ha sido propuesto para inducir el desarrollo de hembras. Nosotros argumentamos que en la naturaleza, la incubación de huevos alrededor de temperaturas pivotes es probablemente mas frecuente de lo que en general se ha reconocido, tendiendo a producir organismos adultos fenotípicamente hembras o fenotípicamente machos, aunque los testículos podrían presentar diversos grados d intersexualidad, incluyendo ovotestis, como se ha documentado en incubaciones artificiales. Observaciones en la tortuga Emys orbicularis muestran que después de la eclosión los ovotestis tienden a evolucionar hacia testículos por regresión total o parcial de la corteza de tipo ovárica. En algunos organismos adultos se han observado testículos con algunos ovocitos inmaduros en la superficie, sin embargo estos producen espermatozoides. Por lo tanto, la intersexualidad gonadal aparentement no inhibe la función reproductiva del macho en adultos. Nosotros pusimos atención en el riesgo de producir embriones de hembras mediante trataminetos estrogénicos. En muchos casos, estos tratamientos indujeron gonadas pequeñas (Hipogónadas) en las cuales el volúmen tanto de la corteza como de la médula son muy reducidos. Estrógenos exógenos pueden también resultar en el arresto del elongamineto de los condutos Müllerianos y algunas veces de su apertura final en los conductos de Wolff, cualquiera de estos procesos imposibilita a los organismos adultos para la evacuación de huevos de los oviductos. Modelamos los efectos a largo plazo de la introducción en una población de sexos fuertemente sesgados hacis hembras (20 hembras; 1 macho) por 30 años. Tomando en consideración un componente genético de la determinación sexual, como se ha ejemplificado en los resultados de incubaciones a temperaturas pivote, favoreciendo los alelos masculinizantes. Cuando la manipulación es detenida, la proporción sexual primaria, así como la proporción sexual de los adultos se torna sesgada hacia machos. Un resultado contrario a lo esperado, disminuyendo el tamaño poblacional. Recommendamos acciones para proteger las poblaciones de adultos y los sitios de anidamiento para mejorar las condiciones de incubación natural, en lugar de llevar a cabo intentos de manipulación de las proporciones de sexos.

Dates et versions

hal-04424160 , version 1 (29-01-2024)

Identifiants

Citer

Marc Girondot, Hélène Fouillet, Claude Pieau. Feminizing Turtle Embryos as a Conservation Tool. Conservation Biology, 2008, 12 (2), pp. 353-362. ⟨10.1111/j.1523-1739.1998.96382.x⟩. ⟨hal-04424160⟩
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