Classical population-genetics theory suggests that reproductive isolation will evolve fastest in small isolated populations1. In contrast, recent theory suggests that divergence should occur fastest in larger allopatric populations2. The rationale behind this is that sexual conflict, potentially the strongest driver of speciation, is greater in larger, higher-density populations. This idea is highly controversial3 and has little experimental support4,5. Here we show, using replicate fly populations with varying levels of sexual conflict, that larger, more dense populations with more sexual conflict diverged to a greater degree than small populations with relaxed conflict. This result strongly suggests that speciation can occur rapidly in large populations through increased sexual conflict.
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We thank the SNF for financial support, and R. Leugger, K. Landergott and M. Eger for laboratory help. We also thank W. Blanckenhorn for statistical advice, F. Balloux for comments on the experimental design, and G. Arnqvist, A. Badyaev, F. Balloux, P. Bauerfeind, J. Evans, T. Garner, B. Holland, L. Keller, T. Pizzari and L. Simmons for valuable comments on this manuscript.
The authors declare that they have no competing financial interests.
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Martin, O., Hosken, D. The evolution of reproductive isolation through sexual conflict. Nature 423, 979–982 (2003). https://doi.org/10.1038/nature01752
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