Maternal investment in last-laid eggs does not compensate for hatching asynchrony in a seabird
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Maternal and environmental effects can have profound effects on offspring performance by generating variation in offspring phenotypes, independent of genetic effects. Within avian broods, differential maternal investment of resources across the laying sequence is thought to be an adaptive strategy to modulate competitive hierarchies induced by hatching asynchrony. In this study, we evaluated the relative importance of maternally derived within-clutch variation and the asymmetric post-hatching environment for growth and survival of common tern (Sterna hirundo) siblings. We experimentally manipulated hatching order, resulting in chicks from last-laid eggs hatching first and vice versa. Although both initial age and size asymmetries were larger within experimental than control broods, the early survival of last-hatched chicks was similar between groups. Initial positive effects of egg size disappeared as siblings approached fledging. Ultimately at fledging, both within-brood growth and cumulative survival patterns were similar between experimental and control broods, suggesting that the effects of systematic variation of egg constituents (e.g., maternally derived yolk hormones) and egg size are too subtle and largely overwhelmed by the effects of hatching asynchrony. Therefore, we conclude that variation in offspring phenotypes is pre-dominantly determined by the social environment experienced post-hatching. Maternal effects may further fine-tune phenotypic variation in response to varying environmental conditions, but this needs to be tested through empirical studies in which multiple maternal effects are measured simultaneously under different environmental conditions.
KeywordsEgg quality Maternal effects Hatching asynchrony Sibling competition Egg size Phenotypic variation Laying order Sterna hirundo
We thank Götz Wagenknecht for data processing and molecular sex determination, and Christina Bauch, Jana Sprenger, and Luis Schmidt for help with field work. We thank Gerold Gembler, Götz Wagenknecht, and Tom Ezard for constructing the breeding raft. We are grateful for constructive criticism on a previous draft of the manuscript by Oscar Vedder. We thank Oliver P. Love and three anonymous reviewers whose helpful comments greatly improved the paper. For technical support and the permission to work in otherwise restricted areas, we thank the Standortverwaltung and Marinearsenal of the Bundeswehr Wilhelmshaven. Funding for this project was provided by the German Research Foundation Deutsche Forschungsgemeinschaft (DFG, BE/916-8-2).
Author contribution statement
AB and PHB conceived and designed experiments. AB performed experiments. AB and PHB collected data. AB analyzed the data. AB wrote the manuscript. PHB provided editorial advice.
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