Does traumatic secretion transfer manipulate mating roles or reproductive output in a hermaphroditic sea slug?
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Copulation in the simultaneous hermaphrodite Siphopteron sp. involves injection of prostate fluids into the mating partner with a stylet-shaped penile appendage before insemination. It has been hypothesised that such traumatic secretion transfer manipulates sex roles or the recipient’s short-term reproductive output. To test manipulative effects of traumatic secretion transfer, we ablated the stylet of male-acting individuals and then paired them to untreated focal individuals. Mating behaviour and egg output of focal individuals was then compared between this ‘no injection group’ and a ‘control group’ with sham-treated mating partners. We found that penile stylets were inserted at different areas prior to and during insemination, but prostate fluid injection was restricted to the first phase. Here, injections were into the anterior foot region, indicating that prostate secretions target the nearby male or female copulatory tracts. Our experimental manipulation of traumatic secretion transfer did not affect the exhibited mating roles. Matings in both treatments were usually reciprocal so that both partners acted in the male as well as female mating role. Moreover, sperm recipient reproductive output did not differ between treatments. We conclude that traumatic secretion transfer in this species either affects currently unmeasured traits, for instance the donor’s paternity share, or that these sea slugs are so well-adapted to traumatic secretion transfer that the effects were too subtle to be detected in our current assays.
KeywordsGastropteridae Sexual conflict Traumatic insemination Traumatic mating Offspring size Maternal size
The authors thank Anne Hoggett, Marianne & Lance Pearce and Lyle Vail from Lizard Island Research station for invaluable support during field work. Comments by Jack O’Connor, Katja Heubel and three anonymous referees helped to improve earlier versions of this manuscript. The German Science Foundation (DFG) provided funds for field work and manuscript preparation (AN549/2-1).
The experiment reported in this article complies with the current laws of Australia and a permit had been acquired to collect and perform experiments on Siphopteron sp. (GBRMPA permit no G09/30973.1).
Conflict of interest
The authors declare that they have no conflict of interest.
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