Valentine's Day is upon us, and once again love is in the air. In a quiet third floor laboratory of the Stewart Biology building, garden snails Helix aspersa are courting….in slow-motion. The snails belong to Dr. Ron Chase, who has spent the past 30 years using these organisms as subjects for his study of neurobiology, behaviour and evolution.
Snail reproduction is a curious tale. Snails are hermaphrodites, but although individuals contain both male and female sex organs, they do not self-fertilize. The two to six hour marathon session that is snail copulation is actually an exchange of sperm between two individuals, combined with plenty of rubbing, biting and 'eye-stalk' waving. Individuals use the received sperm to fertilize their own eggs — a process that is necessary to maintain genetic diversity in the population.
What makes some snail species particularly interesting to Dr. Chase is their use of 'love darts' during copulation. About one third of snail species manufacture hard, sharp darts which they 'fire' at the object of their affections (i.e. other snails).
"The love dart phenomenon has been documented in the literature as far back as the mid-17th century," noted Dr. Chase. "Love dart snails were known to the ancient Greeks, and it wouldn't be surprising to find that they influenced the creation of the cupid myth".
Dr. Chase became intrigued with snails' 'love darts.'
"It was incorrectly believed that these darts were a nuptial gift of calcium —a major constituent of snail shells—from one snail to another. Like a bunch of flowers or a box of chocolates in humans," explained Dr. Chase. "Another belief was that the dart was intended to arouse the receiver and indicate the shooters readiness to mate."
Research conducted by Dr. Chase has uncovered the real reason for dart shooting in snails, and the truth is much more sinister than previously thought.
The answer lies in Darwin's theory of sexual selection. Basically, snails want to reproduce as much as possible. Snails that have a way of ensuring that their sperm, rather than another's, is used to fertilize eggs will therefore sire more offspring. This is known as sperm competition.
