title: Sex differences in yolk hormones depend on maternal social status in Leghorn chickens (Gallus gallus domesticus).
abstract: Maternal hormones are known to be present in avian eggs and can have beneficial effects on chick development. Recently, differences in avian yolk steroid concentrations between the sexes have been demonstrated, and in this context steroids have been proposed to be part of the avian sex-determining mechanism. In our study, we show that it is very unlikely that androgen concentrations alone are the decisive part of the sex-determining mechanism. We found that sex-specific differences in the yolk hormones strongly depend on the social rank of the mother. First, dominant females, but not subdominant females, allocated significantly more testosterone to male eggs than to female eggs. Second, subordinate females increased the testosterone concentrations of female eggs. This pattern of yolk hormone deposition can be functionally explained. In polygynous species such as the chicken, reproductive success is more variable in males than in females. Parental investment in sons or daughters is therefore expected to occur in direct relation to parental rearing capacities. We found that the social status of a hen was indeed negatively correlated with her maternal capacities (for example, body mass, egg mass). Differential androgen deposition might thus provide a mechanism for adaptive maternal investment depending on both the sex of the egg and the social status of the mother.
authors.affiliation: Department of Animal Behavior, University of Groningen, PO Box 14, 9750 AA Haren, Groningen, The Netherlands. w.mueller@biol.rug.nl
authors.forename: Wendt
authors.initials: W
authors.lastname: Müller
authors.forename: Corine M
authors.initials: CM
authors.lastname: Eising
authors.forename: Cor
authors.initials: C
authors.lastname: Dijkstra
authors.forename: Ton G G
authors.initials: TG
authors.lastname: Groothuis
mesh_terms: D000728:Androgens / Q000502:physiology; D000818:Animals; D002642:Chick Embryo; D002645:Chickens / Q000254:growth & development / Q000502:physiology*; D005260:Female; D008297:Male; D008425:Maternal Behavior; D012098:Reproduction / Q000502:physiology; D012727:Sex Characteristics; D019849:Sex Determination Processes; D012744:Sex Ratio; D012919:Social Behavior; D015017:Yolk Sac / Q000502:physiology
chemical_list: D000728:Androgens