Sex differentiation of somatic tissue in the unsexualised gonad primordia of the embryos of three species of poeciliid fish
Kramer, C.R.; Kallman, K.D.
Journal of Anatomy 140: 269-277
1985
ISSN/ISBN: 0021-8782 PMID: 4077690 Document Number: 266367
The developing gonads in male and female embryos of poeciliid fish (Xiphophorus maculatus, X. pygmaeus, X. nigrensis, Poecilia formosa) were examined for somatic differences prior to sexualization of the germ cells. All-male broods were generated in X. maculatus by mating XX++ with YY'' and all-female broods were obtained from P. formosa which reproduces by gynogenesis. Both males and females were produced by X. nigrensis. Thus, in 2 species the sex of the embryos was ascertained by independent methods. The gonads of male embryos were characterized by the presence of a hilar stalk or by being thinly connected to the peritoneum. This was the condition in all embryos of X. maculatus (n=16) and in 14 of 30 embryos of the X. pygmaeus-nigrensis complex. The gonads of female embryos were always broadly attached to the peritoneum and never exhibited a hilar stalk. This condition was observed in all embryos of P. formosa (n=15) and in 16 embryos of X. pygmaeus-nigrensis. The somatic elements of the gonad differentiate first and represent the earliest morphological sign of sex differentiation.