Here still harmless swimming around: C. reticulata - whether with or without penis, is not known. Image: Thinkstock
There are propagation strategies in which one wonders if nature was drunk when she invented it. A particularly beautiful example of this category has now been discovered by Japanese researchers: a sea snail called Chromodoris reticulata. Not only does she play the male and the female role in sex - as a hermaphrodite no problem for the animal - she also relies on a kind of disposable penis: Once the act is completed, she simply drops off the annoying genital organ. Never before has such bizarre behavior been observed, even researchers around Ayami Sekizawa of Osaka City University wonder about their discovery. They had come across the disposable penises as they collected some of the magnificent star snails in coral reef off the coast of the Ryukyu Islands in western Japan and observed them in the lab. There, the snails also made the same diligent to produce offspring: Whole 31 pairs, the scientists could watch during sex.

Give and take

And it has it all, because the nudibranchs follow the motto "double coupled keeps better": The two partners lie side by side and put out a kind of appendages, each containing both sex organs. Then one snail introduces her penis into the vagina of the other and vice versa. So each animal transmits its semen when paired, and on the other hand, it also receives some from the partner - a very effective strategy for reproduction.

However, the biologists experienced a real surprise after the mating: For a while, the snails still swam around with the well-visible, elongated penis - and then they simply threw it off. This happened on average 20 minutes after the two partners had split up, the team reported. However, this was by no means all over: Just under 24 hours later, the snails ran again - only to subsequently repel their penis again. display

Replacement is always included

Only a more detailed anatomical investigation told the researchers then the secret of the nudibranchs: In her body is, spirally rolled up, tubular replacement tissue for the penis. However, it basically seems to be in an immature form, in which only the foremost part develops into the ready-to-use sex organ. If this part is repelled after copulation, the next piece needs said 24 hours to fully mature. However, the snails do not possess infinite reserves. Researchers estimate that after three penis replacements, it would have to be over. You have never seen more than three pairings, they report.

But that's not enough of the peculiarities of C. reticulata's love life: When the scientists took a closer look at the discarded genitals, they discovered that they were littered with tiny barbs pointing backwards - and that there was a considerable amount of sperm attached to these hooks, It could be with the check mark so a kind of insurance that actually their own seed comes into play, the team speculates. Because C. reticulata mates not only with a conspecific, but usually with several and preserves their sperm. If a partner succeeds in removing the unwanted seeds of the competition from the body of the chosen one with the help of the check mark, the own chances increase. However, the researchers have not yet evidence for this scenario - they must first perform a kind of paternity test on the found sperm.

Ayami Sekizawa (Osaka City University, Osaka) et al .: Journal of the Royal Society: Biology Letters, doi: 10.1098 / rsbl.2012.1150 © science.de - Ilka Lehnen-Beyel

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