14 February 2007

Love darts for you my love


What could better express a malacologist's love on Valentine's Day than a box of love darts painstakingly isolated from scores of Helix aspersa* sacrificed in the name of love (and science)?

During mating of hermaphrodite land snails, each partner places a spermatophore, a bag of spermatozoa (sperm cells), in their partner's bursa copulatrix (BC). The spermatophore is digested in the BC and only a small fraction of the spermatozoa escapes to the higher parts of the female reproductive system to fertilize the partner's eggs.

Diagrammatic representation of the reproductive organs of a pulmonate snail. All pulmonates are hermaphrodites, but not all of them have darts. P, penis; D, dart; S, dart sac; V, vagina; MG, mucus glands; BC, bursa copulatrix; G, genital opening. Original by Koene, copy from Schilthuizen.

The so-called love darts are sharp needles of calcium carbonate that are stored one at a time in a special bag-like organ, the dart sac, and thrust inside the body of a snail's partner during mating. Studies have demonstrated that darts transfer mucus from the mucus glands (MG), which, probably by reducing sperm digestion in the BC, increases fertilization success of the sperm.

*Also known as Cantareus aspersus.

Recent papers on love darts:
Schilthuizen, M. 2005. The darting game in snails and slugs. TRENDS in Ecology and Evolution 20:581-584.
Joris M. Koene & Satoshi Chiba. 2006. The Way of the Samurai Snail. American Naturalist 168:553-555. copy and movie on Koene's web page


Snail said...

Those darts really are weird structures. Snails are fascinating!

Anonymous said...

ow! Imagine if humans had sex like that! But they had to reproduce somehow!