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Intrasexual competition and sexual selection in cooperative mammals

Abstract

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most1,2. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males3,4,5. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group6. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection.

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Figure 1: Dominance and breeding success in males and females.
Figure 2: Sex differences in aggression and
Figure 3: The acquisition and maintenance of dominance status.

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Acknowledgements

We thank H. Kotze, J. Kotze and Northern Cape Conservation for allowing us to work in the Kalahari; G. McIlrath for his contribution to habituating meerkat groups; T. Flower, F. Dalerum, M. Haupt, J. d. Toit and E Cameron of the University of Pretoria and P. Roth of the University of Cambridge for logistical support. We are grateful to the many volunteers, PhD students and post-docs who have assisted with data collection. We also thank A. Young, K. Isvaran and J. Hoogland for comments on previous drafts; P. Sherman and J. Shellman-Reeve for discussion; and the Natural Environmental Research Council, the Royal Society and the Earthwatch Institute for financial support.

Author Contributions T.H.C.B. and S.J.H. were responsible for the organisation and management of the project, drafting the manuscript and conducting most of the statistical analyses. Additional analyses were conducted by A.F.R. and L.L.S. G.S. was responsible for the genotyping and N.C.B. conducted all hormonal analyses. N.R.J. and M.B.M. contributed to the organisation and management of data collection in the field.

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Correspondence to T. H. Clutton-Brock.

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This file contains Supplementary Methods describing details of the methods used to calculate variance in the breeding success of male and female meerkats.

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Clutton-Brock, T., Hodge, S., Spong, G. et al. Intrasexual competition and sexual selection in cooperative mammals. Nature 444, 1065–1068 (2006). https://doi.org/10.1038/nature05386

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