Research article

Sexual conflict over the duration of copulation in Drosophila montana: why is longer better?

Dominique Mazzi^1,2* , Jenni Kesäniemi¹ , Anneli Hoikkala¹ and Kirsten Klappert^3,4*

¹  Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, FIN-40014, Finland

²  ETH Zurich, Institute of Plant Sciences, Applied Entomology, Schmelzbergstrasse 9, CH-8092 Zurich, Switzerland

³  Evolutionary Biology, Dyer's Brae House, University of St Andrews, St Andrews, Fife, KY16 9TH, UK

⁴  Aquatic Ecology, EAWAG/ETH, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland

author email corresponding author email* Contributed equally

BMC Evolutionary Biology 2009, 9:132doi:10.1186/1471-2148-9-132

Published:	12 June 2009

Abstract

Background

Conflicts of interest between the sexes are increasingly recognized as an engine driving the (co-)evolution of reproductive traits. The reproductive behaviour of Drosophila montana suggests the occurrence of sexual conflict over the duration of copulation. During the last stages of copulation, females vigorously attempt to dislodge the mounting male, while males struggle to maintain genital contact and often successfully extend copulations far beyond the females' preferred duration.

Results

By preventing female resistance, we show that females make a substantial contribution towards shortening copulations. We staged matings under different sex ratio conditions, and provide evidence that copulation duration is a form of male reproductive investment that responds to the perceived intensity of sperm competition as predicted by game theoretical models. Further, we investigated potential benefits to persistent males, and costs to females coerced into longer matings. While males did not benefit in terms of increased progeny production by protracting copulation, female remating was delayed after long first copulations.

Conclusion

Copulation time is a trait subject to sexual conflict. Mating durations exceeding female optima serve males as a form of 'extended mate guarding': by inducing mating refractoriness in the female, a male extends the time over which its sperm is exclusively used to sire progeny and reduces the likelihood of the female being reinseminated by a competitor.