Letter

Within-group male relatedness reduces harm to females in Drosophila

Received:
Accepted:
Published online:

Abstract

To resolve the mechanisms that switch competition to cooperation is key to understanding biological organization1. This is particularly relevant for intrasexual competition, which often leads to males harming females2. Recent theory proposes that kin selection may modulate female harm by relaxing competition among male relatives3,4,5. Here we experimentally manipulate the relatedness of groups of male Drosophila melanogaster competing over females to demonstrate that, as expected, within-group relatedness inhibits male competition and female harm. Females exposed to groups of three brothers unrelated to the female had higher lifetime reproductive success and slower reproductive ageing compared to females exposed to groups of three males unrelated to each other. Triplets of brothers also fought less with each other, courted females less intensively and lived longer than triplets of unrelated males. However, associations among brothers may be vulnerable to invasion by minorities of unrelated males: when two brothers were matched with an unrelated male, the unrelated male sired on average twice as many offspring as either brother. These results demonstrate that relatedness can profoundly affect fitness through its modulation of intrasexual competition, as flies plastically adjust sexual behaviour in a manner consistent with kin-selection theory.

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Acknowledgements

We thank the following funding agencies: Marie Curie fellowship (PIEF-GA-2010-273010 to P.C.), the Wellcome Trust VIP award and NERC fellowship (to S.W.), NERC research grant and the Leverhulme Trust (to T.P.). We thank C. Garroway, J. Perry and S. Michaelides for technical help; and M. Bonsall, A. Buckling, G. McDonald, D. Noble, J. Perry, P. Pizzari, R. Snook and S. West for helpful discussions.

Author information

Author notes

    • Pau Carazo
    •  & Cedric K. W. Tan

    These authors contributed equally to this work.

Affiliations

  1. Edward Grey Institute, Department of Zoology, University of Oxford, Oxford OX1 3PS, UK

    • Pau Carazo
    • , Cedric K. W. Tan
    • , Felicity Allen
    • , Stuart Wigby
    •  & Tommaso Pizzari

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Contributions

Experiment 1 was designed by P.C., S.W. and T.P., conducted by P.C. and F.A., and analysed by P.C. Experiment 2 was designed by P.C., C.K.W.T., S.W. and T.P., and conducted and analysed by P.C. Experiment 3 was designed and conducted by S.W. and P.C., and analysed by P.C. Experiment 4 was designed by C.K.W.T., T.P. and S.W., and conducted and analysed by C.K.W.T. The article was conceived and written by T.P. with input from P.C., C.K.W.T. and S.W.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Tommaso Pizzari.

Data have been deposited in the Dryad Digital Repository at http://dx.doi.org/10.5061/dryad.9c7bq .

Extended data

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