Dart shooting, a bizarre component of mating behaviour seen in several species of terrestrial snails, has bewildered scientists for centuries. The hermaphroditic snail Helix aspersa pushes a calcareous "love dart", covered with mucus, through the skin of its partner at the end of an elaborate courtship. I address both why this dart shooting behaviour is performed and how it is controlled by the brain. I find that the dart cannot serve as a nuptial gift of calcium because it is rarely internalised by the recipient and contains only a small amount of calcium. However, most shot darts penetrate the skin and come into contact with the blood. I demonstrate that mucus, produced by the digitiform glands and carried on the dart, causes contractions in the female organs. The contractions suggest that more sperm will reach the sperm storage organ as a result of dart shooting, which is important in sperm competition because snails store sperm from several partners before laying eggs. This introduction of a bioactive substance can be explained by either mate choice or mate manipulation. My findings show that dart shooting is an optional component of mating behaviour, which supports the mate manipulation hypothesis. I conclude that the dart transfers a substance to manipulate the storage of the donated sperm. Many species transfer bioactive substances into conspecifics. I propose the term "allohormones" for such substances to distinguish them from hormones and pheromones. / To investigate how the central nervous system controls dart shooting and other mating behaviours, I used an in vivo approach. The right mesocerebrum has been proposed as the control centre for mating behaviour based on in vitro findings. I demonstrate, by electrically stimulating and recording from right mesocerebral neurones in the intact animal, that these neurones are involved in dart shooting and penial eversion. I also test the hypothesis that different neuropeptides mediate different mating behaviours, and I find that APGWamide is responsible for genital eversion. From my results, together with data obtained using other gastropods, I conclude that the anteromedial portion of the right cerebral ganglion is an evolutionarily conserved region for the control of mating behaviour.

During the final stage of courtship, the garden snail Helix aspersa attempts to stab its mating partner with a mucus-coated calcareous "love dart." I present evidence supporting two predictions of the most promising hypothesis for the adaptive significance of this behavior: that the dart serves to increase the reproductive success of the shooter by increasing the numerical representation of its sperm in the recipient's storage organ (the sperm loading hypothesis). First, I demonstrate that once-mated snails store more of the sperm transferred by successful shooters than by unsuccessful shooters. Second, I demonstrate that this biased storage results in higher paternity scores for successful shooters relative to unsuccessful shooters in the clutches of multiply mated recipients. Moreover, I present evidence that body size and mating order influence the outcome of sperm competition in snails. Finally, I propose a novel mechanism to explain the observed pattern of sperm utilization in H. aspersa based on the motility of stored allosperm.

The distribution of APGWamide-like and FMRFamide-like immunoreactive neurons involved in the mating behaviour of the terrestrial snail Helix aspersa have been investigated in the mesocerebrum by retrograde and anterograde labelling and immunostaining techniques. Retrograde labelling shows that 25-40 mesocerebral neurons have an axon in the penis nerve and a similar number of neurons have an axon in the nervus cutaneus pedalis primus dexter (NCPD). It was found that the mesocerebral neurons also project to the nervus cutaneus pedalis secundus dexter (NCSD), the medial lip nerves, the posterior lip nerve, the peritentacular nerve, and the pedal ganglion. Some mesocerebral neurons have multiple projections. Quantitative analysis using confocal laser scanning microscopy indicates that approximately half of the mesocerebral neurons projecting to the penis nerve contain APGWamide-like peptide and half of the mesocerebral neurons projecting to the NCPD contain FMRFamide-like peptide. Some mesocerebral neurons have both peptides. These results are generally in agreement with the hypothesis that the neurons projecting to the penis nerve contain APGWamide, while those projecting to the NCPD contain FMRFamide.

Sexual 'arousal' in Helix aspersa can be divided into 2 components, sexual proclivity (the tendency of a snail to respond to conspecific contact with courtship) and sexual arousal (the intensity with which the snail courts). Sexual proclivity and sexual arousal have different effects on feeding and locomotion and are differentially affected by sexual isolation, daily conspecific contact, and by a courtship pheromone found in the digitiform gland mucus. Therefore sexual arousal and sexual proclivity are probably mediated by 2 separate physiological mechanisms. Behavioural state, or the animal's general level of activity, correlates positively with mating behaviour. However, although a central system controlling behavioural state probably exists, it has no direct effect on either sexual proclivity or sexual arousal. Confusion over the term 'arousal', which impedes neuroethological research in this area, would be decreased by the adoption of the terms used in this thesis.

The courtship behavior of the brown garden snail, Cantareus aspersus , includes a bizarre component where one snail attempts to pierce its mating partner with a sharp, calcareous dart that is covered with mucus. In vitro, the mucus causes conformational changes to the reproductive tract causing sperm to be stored rather than digested. In addition, successful dart shooters have an increased relative paternity compared to unsuccessful shooters. I have tested whether this increased paternity is caused by the mucus delivered on the dart or by the mechanical action of the dart. Mating trials were conducted using dartless and glandless snails, where a future mother was mated to two different potential fathers, receiving an injection of mucus with one mating, and an injection of saline with the second mating. The fathers accompanied by the mucus injection sired significantly more offspring than the fathers accompanied by the saline injection. I conclude that the mucus carried on the dart is responsible for increased paternity levels in Cantareus aspersus.

Thesis (M.Sc.). / Written for the Dept. of Biology. Title from title page of PDF (viewed 2008/05/29). Includes bibliographical references.

No description available.

No description available.

No description available.

No description available.