Meeting Abstract

P2.167  Monday, Jan. 5  Effect of diet on periovulatory levels of steroid hormones and primary sex ratio in zebra finches OKEKPE, CC*; NAVARA, KJ; HILL, GE; MENDONCA, MT; Auburn Univ., Auburn Al; Univ. of Georgia, Athens Ga; Auburn Univ., Auburn Al; Auburn Univ., Auburn Al

Recently, a number of studies on birds have indicated that females (the heterogametic sex) are capable of using pre-ovulatory mechanisms to skew primary offspring sex ratios; however, no one has conclusively identified the mechanism responsible for this phenomenon. Sex is determined in the first meiotic division when one sex chromosome is retained in the oocyte and the other segregates to the polar body. During this time, follicular steroid production is limited primarily to progesterone (P4) and it has been suggested that maternal steroids, which are sensitive to environmental perturbations, could influence sex chromosome segregation. Experimental studies exploring the relationship of maternal steroids on sex ratio have primarily administered various exogenous hormones but, to date, no one has examined endogenous hormones at ovulation. We manipulated both diet quality and perceived food availability in breeding female zebra finches to examine the effects on natural levels of maternal steroids circulating during meiosis I, the critical time in sex determination and primary offspring sex ratio. We found that females on the low quality diet had significantly lower body condition, but higher P4 and lower CORT levels when compared to females on a higher quality diet. Levels of maternal testosterone do not differ between diet quality or perceived availability. Though we do show an effect of diet on body condition and levels of P4and CORT, factors which have been shown to bias sex ratios, to date, this change in hormone profile at the periovulatory period did not result in a change in the primary sex ratio in clutches produced by females on the different diets.