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 generations, which allows for selection to continue late in life. By contrast, the IV populations are maintained on a discrete 14-day generation culture cycle in vials at a controlled density of approximately 100 eggs per vial, which prevents selection from acting beyond that time point. This difference in culturing conditions could potentially alter sexual conflict-mediated selection on female ageing in Dahomey versus IV populations. However, there have been no direct tests of this hypothesis. It will be important for future studies to explore, via the fully factorial design applied here, whether relatedness and familiarity among males similarly interact to affect female harm in the IV and other Drosophila populations.

More generally, one implication of these studies is that local relatedness among male competitors may represent a possible modulator of the ´sexual tragedy of the commons´ and population viability. An important avenue of future research, therefore, will be to explore whether the ecology of D. melanogaster across different laboratory and wild populations (e.g. fine-grained population structure) may be more or less conducive to kin-selected sexual cooperation.

Data accessibility. The datasets supporting this article can be accessed at the Oxford University Research Archive: https://doi.org/10.5287/bodleian:mq112gn2P.

Authors' contributions. S.W. and P.C. conceived of the study. S.L.P., P.C. and S.W. designed the study. S.L.P. and E.F. generated the experimental flies. S.L.P. and I.S. collected behavioural data. S.L.P. collected offspring data and carried out the statistical analyses. S.L.P., S.W., P.C. and T.P. drafted the manuscript. All authors gave their final approval for publication.

Competing interests. We have no competing interests.

Funding. S.L.P. is funded by a BBSRC studentship award (BB/J014427/1). S.W. and I.S. are funded by a BBSRC fellowship to S.W. (BB/K014544/1). P.C. is funded by a Ramón y Cajal research fellowship and by Spanish Research Grants (CGL2014-58722-P and CGL2016-81894-ERC) from the Spanish Ministry of Economy and Competitiveness (MINECO). T.P. is funded by a BBSRC-LINK grant with Aviagen Ltd (BB/L009587/1).

Acknowledgements. Thanks are expressed to Ju Morimoto and Eleanor Bath for their assistance in generating the experimental flies, Florian Klimm for assisting in writing a program to randomly assign larvae, George Nicholson, Dan Lunn and Nico Kist for their assistance in the statistical analyses, and to two anonymous reviewers for their constructive suggestions.