THE flatworm Pseudoceros bifurcus is no romantic. When it wants sex,
it simply rears up and stabs its mate with its penis. Because it is a
hermaphroditic species, its mate has a penis too, so it may get a jab in return.
This leads to an unusual foreplay ritual that its discoverers in Germany have
dubbed 鈥減enis fencing鈥�.
Nicolaas Michiels and Leslie Newman of the Max Planck Institute for
Behavioural Physiology in Seewiesen stumbled upon the 6-centimetre worm in the
sea off Heron Island at the southern end of Australia鈥檚 Great Barrier Reef. For
20 hours they observed 16 pairs of worms, which they had housed in ice-cream
tubs. At first, the animals did nothing. 鈥淭hey can鈥檛 smell, so they couldn鈥檛
find each other,鈥� says Michiels.
But when the worms happened to meet, they started sexual fencing bouts that
lasted up to an hour. The two animals would sit up, evert their penises and try
to inject sperm into each other. Only about one out of six strikes leads to
successful insemination, says Michiels, who calls the behaviour 鈥渂rutally
inefficient鈥�. The animals are left severely wounded, with prominent
punctures.
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Michiels says each worm may be trying to inseminate others and avoid being
stabbed itself so that others have to bear the energetic costs of reproducing
its genes. 鈥淚t鈥檚 hard to know whether the individuals are really trying to avoid
being hit,鈥� comments Janet Leonard of Oregon State University in Newport. 鈥淚t鈥檚
an interesting hypothesis.鈥�