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

Abstract

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.

Social Stimuli, Testosterone, and Aggression in Gull Chicks: Support for the Challenge Hypothesis

“…Schwabl (1993Schwabl ( , 1996 showed in canaries that egg yolk contains maternal androgens that influence the competitive abilities of the chicks after hatching. Eggs of the blackheaded gull have been shown to contain high levels of androgens too (Groothuis and Schwabl, 2002;Eising, Eikenaar, Schwabl, and Groothuis, 2001) and the relatively high levels around hatching in a period that the chick is still using yolk may still be of maternal origin.…”

Yolk androgens do not appear to mediate sexual conflict over parental investment in the collared flycatcher Ficedula albicollis

“…Groothuis et al, 2005a). In some bird species, androgens deposited in the egg yolk have been found to increase competitive ability of chicks (correlative data in Schwabl, 1993; experimental data in Eising et al, 2001), chick begging (experimental data : Schwabl, 1996;Schwabl and Lipar, 2002;Eising and Groothuis, 2003;Boncoraglio et al, 2006;von Engelhardt et al, 2006) and growth (experimental data: Schwabl, 1996;Eising et al, 2001;Pilz et al, 2004;Navara et al, 2005Navara et al, , 2006Tschirren et al, 2005). In other studies, however, no positive effect of elevated yolk androgens on begging or growth was found (experimental data: Sockman and Schwabl, 2000;Andersson et al, 2004;Pilz et al, 2004;Uller et al, 2005;Saino et al, 2006), or the effect depended on offspring sex (e.g.…”

Maternal androgens in egg yolks: relation with sex, incubation time and embryonic growth

“…It has been suggested that yolk hormone levels correlate with circulating plasma hormone levels in the female (Canary, Schwabl, 1996a) and may vary adaptively with the speciesÕ reproductive strategy and social requirements (Cattle egret, Schwabl et al, 1997, Black-headed gulls: Eising et al, 2001Groothuis and Schwabl, 2002). Maternal yolk hormones influence the offspringÕs embryonic development (Eising et al, 2001), development of the hatching muscle (Redwinged blackbird, Lipar and Ketterson, 2000), begging behavior (Canary, Schwabl, 1996b, Eising and Groothuis, submitted), and nestling growth rate (Eising et al, 2001). Recently it has also been found that male and female producing eggs differ in the content of maternal androgens (Petrie et al, 2001).…”