Demographic causes of adult sex ratio variation and their consequences for parental cooperation

• Published in: Nature communications 2018-04, Vol.9 (1), p.1651-8, Article 1651
• Main Authors: Eberhart-Phillips, Luke J., Küpper, Clemens, Carmona-Isunza, María Cristina, Vincze, Orsolya, Zefania, Sama, Cruz-López, Medardo, Kosztolányi, András, Miller, Tom E. X., Barta, Zoltán, Cuthill, Innes C., Burke, Terry, Székely, Tamás, Hoffman, Joseph I., Krüger, Oliver
• Format: Article
• Language: English
• Subjects: 631/158/1745; 631/158/856; 631/181/2470; Animal Communication; Animals; Aquatic birds; Biological evolution; Charadriiformes; Cooperation; Cooperative Behavior; Demographics; Fecundity; Female; Gender aspects; Humanities and Social Sciences; Life assessment; Male; Models, Biological; multidisciplinary; Parenting - psychology; Population biology; Populations; Reproduction - physiology; Science; Science (multidisciplinary); Sex; Sex Characteristics; Sex differences; Sex Ratio; Sexual behavior; Sexual selection; Social behavior; Survival; Variation
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-03833-5

The adult sex ratio (ASR) is a fundamental concept in population biology, sexual selection, and social evolution. However, it remains unclear which demographic processes generate ASR variation and how biases in ASR in turn affect social behaviour. Here, we evaluate the demographic mechanisms shaping ASR and their potential consequences for parental cooperation using detailed survival, fecundity, and behavioural data on 6119 individuals from six wild shorebird populations exhibiting flexible parental strategies. We show that these closely related populations express strikingly different ASRs, despite having similar ecologies and life histories, and that ASR variation is largely driven by sex differences in the apparent survival of juveniles. Furthermore, families in populations with biased ASRs were predominantly tended by a single parent, suggesting that parental cooperation breaks down with unbalanced sex ratios. Taken together, our results indicate that sex biases emerging during early life have profound consequences for social behaviour. Biases in adult sex ratio (ASR) are common, yet their causes and consequences are not well understood. Here, the authors analyse data from >6000 individuals of five shorebird species, showing that sex differences in juvenile survival drive ASR variation and biased ASR is associated with uniparental care.