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Intersexuality in the burrowing crayfish, Parastacus pilimanus (Von Martens, 1869) (Decapoda, Parastacidae)

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Various authors have reported the occurrence of supernumerary gonopores in many species of Parastacus, which has generated discussion about their sexual system. In this study, we examine the external and internal sexual characters of 102 specimens of the burrowing crayfish, Parastacus pilimanus, captured in the province of Maldonado in southeast Uruguay, with the aim of clarifying its sexual system. In this study, we show that in all the specimens analysed, female and male gonopores co-existed externally, and we verified the presence of only one type of gonad internally: either ovary (intersex females) or testis (intersex males), from which one pair of oviducts and another of sperm ducts originated, connecting the gonad to the respective gonopores. We also verified that all specimens smaller than 27.2 mm cephalothorax length (CL) (N = 73) had the same external morphology. Nevertheless, dissection revealed that their gonads were already differentiated. We established that 54.8% of these specimens were intersex females, while the remaining percentage corresponded to intersex males. Twenty-nine specimens were found with a CL equal to, or above, 27.2 mm. Of these, 34.5% (N = 10) were intersex males with the same external morphological traits that characterize all specimens smaller than 27.2 mm CL. The remaining 19 specimens (65.5%) were intersex females, 15 of which presented secondary sexual characters, probably associated with egg incubation. The evidence gathered suggests that Parastacus pilimanus has permanent intersexuality, similar to Parastacus pugnax and Parastacus varicosus in Uruguay. We conclude by identifying some topics that require further study, in order to understand the adaptive value of this type of intersexuality. Varios autores han reportado la ocurrencia de gonoporos supernumerarios en muchas especies de Parastacus, lo que ha generado discusión acerca del sistema sexual de ellas. En este trabajo nosotros examinamos los caracteres sexuales externos e internos de 102 especimenes del camarón excavador Parastacus pilimanus capturados en el Departamento de Maldonado, sureste de Uruguay, con el objetivo de clarificar su sistema sexual. Aquí nosotros demostramos que todos los especimenes analizados presentaron externamente coexistencia de gonoporos de hembra y de macho, e internamente una gónada única — ya sea ovario (hembras intersexo) o testículo (machos intersexo) — desde la cual se originan un par de oviductos y otro de espermiductos que la conectan a los respectivos gonoporos. También comprobamos que todos los especimenes de tallas menores a 27,2 mm de longitud cefalotorácica (LCT) (N = 73), tienen la misma morfología externa. No obstante, las disecciones demostraron que sus gónadas ya estaban diferenciadas. En ellos comprobamos que el 54,8% eran hembras intersexo y el porcentaje restante machos intersexo. De tallas iguales o superiores a 27,2 mm de LCT, encontramos 29 especimenes. De ellos, el 34,5% (N = 10) eran machos intersexo los que presentaron los mismos rasgos morfológicos externos que caracterizan a todos los especimenes de tallas inferiores a 27,2 mm de LCT. Los 19 especimenes restantes (65,5%) eran hembras intersexo, en 15 de las cuales comprobamos la presencia de caracteres sexuales secundarios, probablemente asociados a la incubación de los huevos. Las evidencias reunidas sugieren que Parastacus pilimanus, al igual que Parastacus pugnax y Parastacus varicosus de Uruguay, presenta intersexualidad permanente. Nosotros concluimos sugiriendo algunos tópicos que necesitan de mayores estudios para comprender el valor adaptativo de este tipo de intersexualidad.

Affiliations: 1: Departamento de Ciencias Básicas, Universidad de Los Lagos, Casilla 933, Osorno, Chile; 2: Sección Entomología, Facultad de Ciencias, Universidad de la República, P.O. Box 10773, Montevideo, Uruguay


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