Gamete Biology

Sex of Bovine Embryos May Be Related to Mothers' Preovulatory Follicular Testosterone

Abstract
Although the sex of the offspring in mammals is commonly viewed as a matter of chance (depending on whether an X- or a Y-chromosome-bearing spermatozoon reaches the ovum first), evolutionary biologists have shown that offspring sex ratios are often significantly related to maternal dominance, a characteristic which has been shown to be linked to testosterone in female mammals, including humans. Hence we hypothesized that variations in female testosterone might be related to reproductive mechanisms associated with sex determination, with higher levels of follicular testosterone being associated with a greater likelihood of conceiving a male. To investigate this hypothesis we collected follicular fluid and cumulus oocyte complexes from bovine antral follicles. Individual matched samples of follicular fluid were assayed for testosterone, while the oocytes were matured, fertilized and cultured in vitro. The resultant embryos were sexed by polymerase chain reaction. The level of testosterone in the follicular fluid was then compared with sex of the embryo (n=171). Results showed that follicular testosterone levels were significantly higher for subsequently male embryos. (Mann Whitney U = 2823, p (one-tailed) = 0.016). When we excluded embryos from follicles in which the oestradiol to testosterone ratio was more than 1, (leaving a sample size of 135) the same result held, (Mann Whitney U = 1667, p (one-tailed) = 0.009). Thus bovine ova that developed in follicular fluid with high concentrations of testosterone in vivo were significantly more likely to be fertilized by Y-chromosome-bearing spermatozoa.

Key words: Embryo • Fertilization • Follicle • Oocyte development • Testosterone

This article has been cited by other articles:

				P. Bermejo-Alvarez, D. Rizos, D. Rath, P. Lonergan, and A. Gutierrez-Adan Can Bovine In Vitro-Matured Oocytes Selectively Process X- or Y-Sorted Sperm Differentially? Biol Reprod, October 1, 2008; 79(4): 594 - 597. [Abstract] [Full Text] [PDF]