Incidence of dart shooting, sperm delivery, and sperm storage in natural populations of the simultaneously hermaphroditic land snailArianta arbustorum

Abstract

In several families of terrestrial pulmonates, simultaneously hermaphroditic animals form a sharp, hard, calcified or chitinous structure (the so-called love dart) in the female part of their reproductive organs. The dart is used to pierce the body of the mating partner during courtship. The adaptive significance of this peculiar behaviour is still little understood. We examined dart shooting, autosperm delivery, and allosperm storage in three natural populations of the simultaneously hermaphroditic land snail Arianta arbustorum in the Austrian Alps. Twenty-six (30.2%) of 86 copulating snails used their dart. The frequency of dart shooting tended to vary among populations. There was no reciprocity in dart shooting: individuals shot their dart independently of the behaviour of the mating partner. The number of spermatozoa delivered ranged from 522 000 to 4 238 000 (mean 1 706 000). The occurrence of dart shooting was related to neither the number of sperm delivered nor the number received from the partner. The occurrence of dart shooting was not influenced by the amount of allosperm from previous matings stored in the spermatheca of the dart shooters in two populations. In the third population, however, dart shooters had stored more allosperm in their spermatheca than non-shooters. The number of sperm received was not correlated with the size of the donor or the size of the recipient, indicating that snails do not allocate more sperm to larger partners. Experimental results showed that snails which mated under laboratory conditions did not differ in dart-shooting frequency from snails which mated in the wild.