Snails’ mating strategies reveal an intriguing corner of evolution
THE complexities of human courtship pale into insignificance when compared with those of snails. For a start, snails are hermaphrodites—meaning each has to size up a potential mate from both the male and the female points of view. And, for snails, Cupid’s arrow is no metaphor. When mating, these molluscs often fire tiny, limestone darts at each other as part of the preliminaries.
Snail darts are covered with a secretion that closes off blind alleys in the egg-fertilising machinery of the dartee, ensuring the sperm of the darter goes to good use. Snails often mate with several partners before laying eggs, and it is thought the dart’s coating also serves to reduce the chance of re-mating, perhaps by causing more sperm to be stored. In this the darts serve a bit like the mating plugs used by many male insects to block the female’s sexual passage after mating. Among hermaphrodites, though, both parties can be affected.
Snail darts seem to cause only superficial damage to those they hit. But Kazuki Kimura of Tohoku University, in Japan, wondered if they create more subtle long-term problems. He therefore did an experiment on Bradybaena pellucida, a local species.