title: Androgens during development in a bird species with extremely sexually dimorphic growth, the brown songlark, Cinclorhamphus cruralis.
abstract: In birds, early exposure to androgens has been shown to influence offspring growth and begging behaviour, and has been proposed as a mechanism for the development of sexual size dimorphism (SSD). Sex specific effects during development can occur due to sex-specific allocation of maternal androgens, sensitivity to, or synthesis of, androgens. In addition, maternal hormones have been suggested as a mechanism to skew brood sex ratio. This study uses one of the world's most extreme SSD species, the brown songlark Cinclorhamphus cruralis, to investigate (1) sex-specific differences of androgens in yolk and chick plasma and (2) the relationship between androgens and sex ratio bias. The study reveals no indication of sex-specific maternal allocation, but a modest sex effect during the later stages of incubation when the embryo starts to produce its own androgens. Moreover, there was a strong seasonal sex ratio bias: female-biased early and male-biased later in the season, but yolk testosterone (T) did not show a seasonal trend. Taken together these results suggest that if androgens, from any source, have a significant role in development of SSD in this species it is most likely via sex-specific sensitivity or synthesis rather than differential maternal transfer to the egg.
authors.affiliation: Centre for Ecological and Evolutionary Studies, University of Groningen, Haren, The Netherlands. caroline.isaksson@zoo.ox.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Isaksson
authors.forename: M J L
authors.initials: MJ
authors.lastname: Magrath
authors.forename: T G G
authors.initials: TG
authors.lastname: Groothuis
authors.forename: J
authors.initials: J
authors.lastname: Komdeur
mesh_terms: D000818:Animals; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008297:Male; D046109:Passeriformes / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D011863:Radioimmunoassay; D012727:Sex Characteristics; D012744:Sex Ratio; D013739:Testosterone / Q000378:metabolism*
chemical_list: D013739:Testosterone