Penguin chicks benefit from elevated yolk androgen levels under sibling competition.

Maud Poisbleau,Ton G G Groothuis,Jeff Van Camp,David Carslake,Laurent Demongin,Marcel Eens,Wendt Müller

doi:10.1371/journal.pone.0042174

Maud Poisbleau, Ton G G Groothuis + Show 5 more

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https://doi.org/10.1371/journal.pone.0042174

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Abstract

Crested penguins (genus Eudyptes) have a peculiar hatching pattern, with the first-laid egg (A-egg) hatching after the second-laid egg (B-egg) and chicks from A-eggs typically having a much lower survival probability. Maternal yolk androgens have been suggested to contribute to the competitive superiority of the B-chick in southern rockhopper penguins Eudyptes chrysocome, given their important role in mediating sibling competition in other species. We therefore increased the yolk androgen levels in freshly-laid eggs and examined the consequences for sibling competition - via effects on embryonic developmental times, chick growth and early survival. We placed one androgen-treated egg and one control egg into each foster nest, matching them for mass, laying date and laying order. The androgen treatment did not significantly affect embryonic developmental times or chick measurements at hatching. However, elevated yolk androgen levels benefitted chick growth in interaction with the number of siblings in a brood. Chicks from androgen-treated eggs had faster growth in the presence of a sibling than chicks from control eggs. Under these circumstances they also had a higher survival probability. Thus maternal androgens appear to reinforce the observed hatching pattern, facilitating brood reduction. This contrasts to most previous studies in other species where yolk androgens have been shown to compensate for the negative consequences of delayed hatching within the brood hierarchy.

Highlights

In most bird species, parents initially produce more offspring than they are able to raise [1,2,3,4]
Given the role that maternal yolk androgens play in mediating sibling competition, we previously suggested that yolk androgens reinforce the competitive superiority of the chick hatched from B-egg (B-chick) when the survival of both chicks becomes unlikely [30]
We examined the consequences of embryonic exposure to elevated yolk androgen levels on embryonic developmental times, chick growth and early survival, controlling for chick sex and the presence of a sibling during growth

Summary

Introduction

Parents initially produce more offspring than they are able to raise [1,2,3,4] This overproduction commonly results in an intense competition between siblings that may lead to the elimination of part of the brood. During poor years, hatching asynchrony may serve as a mechanism to adjust brood size to food availability during the nestling period (‘‘brood reduction hypothesis’’ [1]). It is typically the smallest/youngest siblings that die, those in which parents have invested the least in terms of time and energy [7]

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