We thank G. Besnard, J. Britton-Davidian, J.-B. Ferdy, S. Glémin, L. D. Hurst, P. Jarne, O. Judson, M. Kirkpatrick, S. P. Otto, J.-M. Prosperi, and C. Vosa for helpful comments, information, and stimulating discussions. This study was supported by the Centre National de la Recherche Scientifique and French Ministry of Research.
Competing interests. The authors have declared that no competing interests exist.