Meeting Abstract

P2.123  Friday, Jan. 4  Mechanism of sex ratio manipulation: Effects of testosterone in homing pigeons (Columba livia) GOERLICH, V.*; SCHAAFSMA, S.; DIJKSTRA, C.; GROOTHUIS, T.G.G.; Univ. of Groningen V.Goerlich@rug.nl

Birds are able to influence the primary and secondary sex ratio of their offspring. This has attracted substantial attention because of its functional and evolutionary implications, but the underlying mechanisms remain elusive. As the egg formation process is under control of maternal plasma hormones, which are also transferred to the oocyte, it is conceivable that the hormonal state of the mother contributes to changes in sex ratio. Maternal hormones in plasma or oocytes could affect the primary sex ratio by sex specific follicle development, fertilization, resorption, and by meiotic distortion. Maternal hormones in the egg could affect the secondary sex ratio by sex specific allocation and effects on embryonic development. Manipulating testosterone levels in the breeding female resulted in a male biased primary offspring sex ratio in starlings and zebra finches but not in Japanese quail. We studied the effect of testosterone in homing pigeons, which are known to be able to adjust the sex ratio of their offspring. Compared to sham treated control (C) females, primary offspring sex ratio produced by testosterone (T) females was significantly male biased. Plasma levels of T females were elevated but yolk T levels were not different between T and C clutches, suggesting that maternal plasma levels rather than yolk levels affect sex ratio. T females initiated their clutches later than C females but autopsies revealed no indication of additional ovulation nor post meiotic absorption. Since other aspects of the maternal physiology (corticosterone, body condition, and blood glucose) have been implicated in primary sex ratio adjustment we are currently analyzing the effect of testosterone treatment on these parameters too.