Sea slugs let sex go to their heads...

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Humans are encouraged to say it with flowers, but a small marine slug prefers to inject his mate in the head with prostate secretions while making love.

The Siphopteron species mates in the usual way, placing sperm inside the female’s genital tract – while also using a special cannula to deposit proteins close to her central nervous system.

While this kind of cephalo-traumatic secretion transfer has been observed in a number of species, this particular shot to the head is something new.

Dr. Rolanda Lange and her team of researchers from the Institute of Evolution and Ecology at Tübingen University suspect that the secretion contains bioactive proteins which can enter the female’s nervous system to manipulate reproduction — possibly increasing the number of eggs laid or ensuring that the most recent sperm are preferred to those of earlier mates.

And if that sounds a little below the belt, bear in mind that Siphopteron is a hermaphrodite — any 'female' manipulated in this way will get a chance to wear the trousers next time round.

Nudibranchs do seem to display some unusual behaviour when it comes to breeding. Earlier this year we reported on another species of sea slug that discards its penis after sex — then it just grows a new one to use the following day.

Dr. Rolanda Lange, Johanna Werminghausen and Dr. Nils Anthes of the Institute of Evolution and Ecology at Tübingen University describe the process used by Siphopteron in the current online edition of Proceedings of the Royal Society B.

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