Mating behaviour, dart shape and spermatophore morphology of the Cuban tree snail Polymita picta (Born, 1780)

Abstract

Hermaphroditic animals display a remarkable range of complex mating behaviours that are frequently related to the transfer of accessory-gland products. Here, we describe the use of the dart, an accessory reproductive device, and the mating behaviour of the hermaphroditic Cuban tree snail Polymita picta. Mating can be divided into three stages: courtship, copulation and post-copulation. Polymita picta has the longest mating duration of all Polymita species investigated so far. During courtship, a partial genital eversion exposes the sensitive zone, genital lobes and dart apparatus. During all mating stages, three uses of the dart apparatus can be distinguished: wiping, rubbing and stabbing, all of which mainly target the anterior region of the body, usually without loss of the dart. Morphological variation in the dart involves the extent of curvature, irregularities along the length and total length. These characteristics possibly provide a larger contact surface and deeper penetration through the body wall, which could result in increased sperm storage and paternity. The spermatophore is equipped with spines and we suggest that these might slow down spermatophore uptake into the bursa copulatrix. Overall, the general mating pattern, the presence of the sensitive zone, repeated use of the dart and its shape diversity support the idea that in more ancestral dart-possessing snails the dart apparatus is used to transfer accessory gland secretions, not only by stabbing but also through wiping and rubbing.