Meeting Abstract

S5-1.4  Saturday, Jan. 5  The role of maternal hormones in avian sex ratio manipulation GROOTHUIS, T.G.G.*; GOERLICH, V.C.; DIJKSTRA, C.; University of Groningen, NL; University of Bielefeld D; University of Groningen, NL a.g.g.groothuis@rug.nl

Avian species can manipulate the sex ratio of their offspring before these offspring hatch. In birds, mothers can not only affect the secondary sex ratio, but also the primary sex ratio of their offspring as the mother is the heterogametic sex. Avian sex ratios vary in relation to environmental or maternal condition. The production of maternal steroid hormones is sensitive to those conditions, and the hormones are also involved in reproduction and deposited in the egg before meiosis. Therefore, we explored to what extend and how maternal steroid hormones may be involved in affecting clutch primary or secondary sex ratio. We showed in the rock pigeon, as well as in a related wild pigeon species, the wood pigeon, both producing clutches of two eggs, a clear case of seasonal change in sex ratio in first eggs. In the homing pigeon, domesticated from the rock pigeon, testosterone treatment induced a clear male bias in first eggs, and corticosterone a female bias and we argue that this is in line with sex allocation theory. We next analysed treatment effects on follicle formation, yolk mass and yolk hormones, the latter both pre- and post-ovulatory, in order to test a diversity of potential mechanisms related to both primary and secondary sex ratio manipulation. In addition, we review the existing avian literature on correlative and experimental evidence for effects of maternal steroids on the primary and secondary sex ratio. We conclude that hormone levels in the mother may affect several pre-ovulatory mechanisms affecting offspring sex ratio, whereas egg hormones are probably involved in secondary sex ratio manipulation only.