P3.97 Saturday, 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.; Univ. of Georgia; Auburn Univ.; Auburn Univ. email@example.com
Sex ratio theory predicts that parents will maximize parental investment and production costs by adjusting offspring sex ratio when fitness returns of sons and daughters are differentially influenced by ecological and social circumstances. Recently, a number of studies on birds have indicated that females (being the heterogametic sex) are capable of using pre-ovulatory mechanisms to skew offspring sex ratio; however, no one has conclusively identified the mechanism responsible for this phenomenon. Many have turned to investigating the role of circulating maternal hormones during meiosis I (the time of sex chromosome segregation) as a possible mechanism controlling primary sex ratio adjustment. To date, experimental studies that have demonstrated sex biases in birds have only explored the effects of exogenous administration of various hormones to breeding females. We still do not know whether these exogenous manipulations reflect what may be naturally occurring during ovulation and whether timing of hormones around the periovulatory period influences subsequent sex ratio. In our study, we have manipulated diet quality and perceived availability of food in breeding female zebra finches and measured levels of circulating progesterone, corticosterone, and testosterone in the periovulatory period in relation to primary sex-ratio. Diet affected circulating P and B at ovulation, but, to date, these changes did not relate to a change in sex ratio.