Sexual interactions in so-called cross-fertilizingsimultaneous hermaphrodites, such as earthworms, snails, leeches, andsome fishes, have long challenged researchers' understanding of howestablished theories regarding sexual selection apply in cases ofhermaphroditic species. For example, combining male and female genderin one and the same individual, hermaphrodites have been predicted tofrequently be at conflict (theoretically speaking) about which sexualroles to play, because matings are often more costly, in terms ofevolutionary fitness, to one gender than to the other. In such cases,hermaphrodites are predicted to share a preference to copulate in themore beneficial gender role. This would appear to make the interests ofany two potential mates incompatible. For 20 years, evolutionarybiologists have speculated that hermaphrodites may solve such matingconflicts by "trading sperm," that is, giving sperm only when themating partner follows suit. However, this prediction had never beenproven experimentally.
In the new work, researchers Nils Anthes,Annika Putz, and Nico Michiels generated individual sea slughermaphrodites only capable of performing a "dry" copulation--that is,without sperm transfer. Sea slugs that mated with such a "cheating"partner interrupted sexual intercourse significantly sooner than didcontrol pairs. This supports the concept of sperm trading, where matesnegotiate mating roles in order to balance sexual interactions.
Theresearchers included Nils Anthes, Annika Putz and Nico K. Michiels ofUniversität Tübingen in Tübingen, Germany. This research was supportedby the DFG and DAAD.
Anthes et al.: "Gender trading in a hermaphrodite." Publishing in Current Biology Vol 15, pages R792-R793, October 11, 2005 www.current-biology.com
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