Maternal androgens in black-headed gull (Larus ridibundus) eggs: consequences for chick development.

• Main Authors: Corine M Eising, Cas Eikenaar, Hubert Schwabl, Ton G G Groothuis
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2001
• Subjects: Black-headed Gull; Larus ridibundus
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1084.5658; http://behav.zoology.unibe.ch/sysuif/uploads/files/esh/CUSO_LIT/Eising_2001.pdf

We tested the hypothesis that mother birds counterbalance the negative e¡ects of hatching asynchrony for later-hatched chicks by increasing the yolk androgen concentrations in consecutive eggs of their clutch. In doing so, they may adaptively tune each o¡spring's competitive ability and, thus, growth and survival. However, evidence in support of this hypothesis is contradictory. The yolk concentrations of maternal androgens in the eggs of black-headed gulls increase signi¢cantly with the laying order of the eggs in a clutch. We experimentally tested the functional consequences of this increase on chick development under natural conditions by injecting eggs with either an oil or androgen solution. We created experimental clutches in which androgen levels either stayed constant or increased with laying order while controlling for di¡erences in egg quality by using only ¢rst-laid eggs. We then compared development, growth and survival between these broods. Androgen treatment enhanced embryonic development because androgentreated eggs hatched half a day earlier than controls, while their size at hatching was similar to oil-treated controls. Androgen treatment did not increase chick survival, but it enhanced growth. Androgen-treated, third-hatched chicks had a higher body mass and longer legs than third-hatched chicks that hatched from oil-treated eggs. At the same time, growth of ¢rst chicks (which were all oil treated) was reduced by the presence of two androgen-treated siblings, suggesting that yolk androgens enhance the competitive ability of later-hatched chicks. Our results support the hypothesis that transfer of di¡erent amounts of androgens to the eggs of a clutch is a mechanism by which mothers maximize their reproductive output.