THE LOVE DART OF HELIX ASPERSA MÜLLER IS NOT A GIFT OF CALCIUM

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Abstract
The phenomenon of dart shooting in several species of land snails has still not been explained. We were interested in whether the dart can function as a nuptial gift of calcium, as previously proposed. Donating calcium would increase the fitness of the offspring and thereby result in a higher reproductive success for the donor. We confirmed in Helix aspersa that the developing embryo takes up calcium from the egg shell for the formation of its embryonic shell. However, other results from behavioural observations and calcium measurements in various reproductive structures do not support the calcium hypothesis. We found that the dart penetrated the skin in 91.7% or the shootings, but it was internalized by the recipient in only 6.3% of the shootings. The amount of calcium in one dart is roughly equal to that of one egg, and thus it would not contribute significantly to an average clutch of 59 eggs. The spermatophore contains virtually no calcium, and therefore it is unlikely that the dart signals a donation of calcium with the sperm. The dart is also unlikely to influence egg laying since dart shooting does not predict either the latency or the productivity of egg laying in the shooter or the recipient. We conclude that the love dart of Helix aspersa is not a gift of calcium. Instead, we suggest that it is a vehicle to introduce a substance into the partner to influence the fate of the donated sperm.

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