Cm. Eising et al., Maternal androgens in black-headed gull (Larus ridibundus) eggs: consequences for chick development, P ROY SOC B, 268(1469), 2001, pp. 839-846
Citations number
47
Categorie Soggetti
Experimental Biology
Journal title
PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES B-BIOLOGICAL SCIENCES
We tested the hypothesis that mother birds counterbalance the negative effe
cts of hatching asynchrony for later-hatched chicks by increasing the yolk
androgen concentrations in consecutive eggs of their clutch. In doing so. t
he) may adaptively tune each offspring's competitive ability and, thus, gro
wth and survival. However, evidence in support of this hypothesis is contra
dictory. The yolk concentrations of maternal androgens in the eggs of black
-headed gulls increase significantly with the laying order of the eggs in a
clutch. We experimentally tested tile functional consequences of this incr
ease on chick development under natural conditions by injecting eggs with e
ither an oil or androgen solution. We created experimental clutches in whic
h androgen levels either stayed constant or increased with laying order whi
le controlling for differences in egg quality by using only first-laid eggs
. We then compared development, growth and survival between these broods. A
ndrogen treatment enhanced embryonic development because androgen-treated e
ggs hatched half a day earlier than controls: while their size at hatching
was similar to oil-treated controls. Androgen treatment did not increase ch
ick survival, hut it enhanced growth.,Androgen-treated, third-hatched chick
s had a higher body mass and longer legs than third-hatched chicks that hat
ched from oil-treated eggs. At the same time, growth of first chicks which
M ere all oil treated was reduced by tile 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
different amounts of androgens to the eggs of a clutch is a mechanism by wh
ich mothers maximize their reproductive output.