Identifying the selective pressures underlying offspring sex-ratio adjustments: a case study in a wild seabird

• Published in: Behavioral Ecology
• Main Authors: Merkling, Thomas, Welcker, Jorg, Hewison, Mark, Hatch, Scott A., Kitaysky, Alexander S., Speakman, John R., Danchin, Etienne, Blanchard, Pierrick
• Other Authors: Evolution et Diversité Biologique (EDB), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS), Norwegian Polar Institute, University of Alaska Fairbanks (UAF), Unité de recherche Comportement et Ecologie de la Faune Sauvage (CEFS), Institut National de la Recherche Agronomique (INRA), United States Geological Survey (USGS), Institute for Searbird Research and Conservation, Institute of Biological and Environmental Sciences, University of Aberdeen, Chinese Academy of Sciences (CAS), The North Pacific Research Board (Project No. 320, BEST-BSIERP Projects B74, B67, and B77 to A.S.K.), the Research Council of Norway (project 197192/V40 to J.W.), by a grant from the Institut Polaire Français Paul-Emile Victor (IPEV “Programme 1162 SexCoMonArc” to E.D. and P.B.), and by the French Laboratory of Excellence project “TULIP” (ANR-10-LABX-41; ANR-11-IDEX-0002-02), ANR-11-IDEX-0002,UNITI,Université Fédérale de Toulouse(2011)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: cost of reproduction hypothesis; daily energy expenditure; investment capacity; trivers willard hypothesis; corticosterone; [SDV]Life Sciences [q-bio]; rissa tridactyla
• Online Access: https://hal.inrae.fr/hal-02636465; https://doi.org/10.1093/beheco/arv032

International audience Sex allocation theory predicts that parents should bias offspring sex according to the costs and benefits associated with producing either sex in a given context. Accurately interpreting sex-ratio biases, therefore, requires a precise identification of these selective pressures. However, such information is generally lacking. This may partly explain the inconsistency in reported sex allocation patterns, especially in vertebrates. We present data from a long-term feeding experiment in black-legged kittiwakes (Rissa tridactyla) that allowed us to increase investment capacity for some breeding pairs. Previous findings showed that these pairs then overproduced sons compared with control parents. Here, our aim was to test the underlying assumptions of the 2 appropriate sex allocation models for our context: the "cost of reproduction hypothesis" and the "Trivers-Willard hypothesis." The former assumes a sex difference in rearing costs, whereas the latter assumes a difference in fitness returns. 1) Independent of feeding treatment, rearing sons was energetically more demanding for parents (as revealed by higher energy expenditure and higher baseline corticosterone levels) than rearing daughters, thereby corroborating the underlying assumption of the "cost of reproduction hypothesis." 2) Evidence supporting the assumptions of the "Trivers-Willard hypothesis" was less convincing. Overall, our results suggest that drivers of parental sex allocation decisions are probably more related to offspring sex-specific energetic costs than to their future reproductive success in our study species. Assessing the adaptive value of sex-ratio biases requires precise investigation of the assumptions underlying theoretical models, particularly as long as the mechanisms involved in sex-ratio manipulation remain largely unknown.