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Proc Biol Sci. 2013 Nov 13;281(1774):20132694. doi: 10.1098/rspb.2013.2694. Print 2014 Jan 7.

Sexual conflict over mating in red-sided garter snakes (Thamnophis sirtalis) as indicated by experimental manipulation of genitalia.

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Department of Zoology, Oregon State University, , Cordley Hall 3029, Corvallis, OR 97330, USA, Department of Biology, Texas A&M University, , 3258 TAMU, College Station, TX 77843, USA, School of Biological Sciences, University of Sydney, , Heydon-Laurence Building AO8, Science Road, New South Wales 2006, Australia, Biology Department, University of Massachusetts, , 221 Morrill Science Center, Amherst, MA 01003, USA.


Sexual conflict over mating can result in sex-specific morphologies and behaviours that allow each sex to exert control over the outcome of reproduction. Genital traits, in particular, are often directly involved in conflict interactions. Via genital manipulation, we experimentally investigated whether genital traits in red-sided garter snakes influence copulation duration and formation of a copulatory plug. The hemipenes of male red-sided garter snakes have a large basal spine that inserts into the female cloaca during mating. We ablated the spine and found that males were still capable of copulation but copulation duration was much shorter and copulatory plugs were smaller than those produced by intact males. We also anaesthetized the female cloacal region and found that anaesthetized females copulated longer than control females, suggesting that female cloacal and vaginal contractions play a role in controlling copulation duration. Both results, combined with known aspects of the breeding biology of red-sided garter snakes, strongly support the idea that sexual conflict is involved in mating interactions in this species. Our results demonstrate the complex interactions among male and female traits generated by coevolutionary processes in a wild population. Such complexity highlights the importance of simultaneous examination of male and female traits.


copulation duration; copulatory plugs; genitalia; hemipene; sexual selection

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