Meeting Abstract

S5-1.3  Saturday, Jan. 5  Stress, hormones, and sex: How do we solve the puzzle of sex ratio adjustment in birds? NAVARA, KJ; Univ of Georgia knavara@uga.edu

Ecologists and evolutionary biologists have shown time and again that birds have a striking ability to vary the ratios of male and female offspring they produce in response to environmental and social conditions. However, even after decades of similar observations, the physiological mechanisms responsible for the adjustment of offspring sex by birds remain elusive. What we do know is that female birds target hormones to the egg contents and utilize them to program the growth, development, and other phenotypic variables of their offspring for the environment into which they will hatch. It seems logical, then, that they might also use these hormones to adjust the sexes of offspring as well. Indeed, several studies have shown that situations that provoke the release of reproductive and stress hormones also provoke skews in offspring sex ratios, and that direct treatment with these hormones can also induce similar skews. We now need to address how the hormones may be acting, and at what point in the reproductive process offspring sex is being manipulated. We have shown that both testosterone and corticosterone can influence which sex chromosome is donated by the heterogametic female bird, however these effects require exposure at a very specific time during ovulation and at a very specific dosage. In addition, the effects of these hormones are often inconsistent and likely depend upon other factors such as body condition and environmental variables. The adaptive significance of using hormones to mediate sex ratio adjustment depends on both the cellular mechanisms by which the adjustment of offspring sex occurs as well as how the use of those hormones fits into the larger environmental picture.