The Mechanism of the Dart's Influence on Paternity in the Snail
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The mechanism of the dart's influence on paternity in the snail, Cantareus aspersus Katrina C. Blanchard Department of Biology McGill University Montreal October 2005 A thesis submitted to McGill University in the partial fulfillment of the requirements of the degree of Master of Science © Katrina C. Blanchard, 2005 Library and Bibliothèque et 1+1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de l'édition 395 Wellington Street 395, rue Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada Your file Votre référence ISBN: 978-0-494-24619-1 Our file Notre référence ISBN: 978-0-494-24619-1 NOTICE: AVIS: The author has granted a non L'auteur a accordé une licence non exclusive exclusive license allowing Library permettant à la Bibliothèque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par télécommunication ou par l'Internet, prêter, telecommunication or on the Internet, distribuer et vendre des thèses partout dans loan, distribute and sell th es es le monde, à des fins commerciales ou autres, worldwide, for commercial or non sur support microforme, papier, électronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriété du droit d'auteur ownership and moral rights in et des droits moraux qui protège cette thèse. this thesis. Neither the thesis Ni la thèse ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent être imprimés ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission. ln compliance with the Canadian Conformément à la loi canadienne Privacy Act some supporting sur la protection de la vie privée, forms may have been removed quelques formulaires secondaires from this thesis. ont été enlevés de cette thèse. While these forms may be included Bien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. ••• Canada TABLE OF CONTENTS Abstract............................................................................................... .i Résumé .......................................................................................................ü Acknowledgements ................................................................................ .iii Chapter 1: Introduction ..................................................................................1 The research problem .............................................................................2 Reproduction in Cantareus aspersus ........................................................... 4 The function of the dart ................................................................................. 8 Sexual conflict in hermaphrodites ............................................................. 13 Dart shooting and cryptic female choice ...................................................... 16 Experimental design ................................................................................... 17 Figure 1........................................................................................... 20 Figure 2 ...........................................................................................21 Chapter 2: Methods ...............................................................................22 Snail care and maintenance ..................................................................... 23 Removal ofthe dart sac and digitiform mucus glands ......................................23 Digitiform gland mucus homogenate ...........................................................24 Mating trials ......................................................................................25 Egg laying ........................................................................................27 DNA extraction and genotyping ...............................................................27 Statistical analysis ...............................................................................30 Chapter 3: Results ................................................................................. 32 Sample size .......................................................................................33 Success of samples .............................................................................. 33 Spenn precedence ................................................................................34 The mucus effect .................................................................................35 Relationship between maternaI shell volume and the mucus injection ...................36 Table 1 ............................................................................................38 Figure 3 ...........................................................................................39 Figure 4 ...........................................................................................40 Figure 5 ...........................................................................................42 Figure 6 ...........................................................................................43 Chapter 4: Discussion .............................................................................44 Digitiform gland mucus carried on the dart increases paternity ......................... .45 Increased detection of outside fathers ........................................................ .45 Spenn precedence .............................................................................. 46 Mucus injection and maternaI shell volume ................................................ 46 Mating order and maternaI shell volume ................................................... .48 Future experimentation ........................................................................ 49 Dart shooting drives sexual selection ........................................................ 51 References ......................... " ................................................................53 Abstract The courtship behavior of the brown garden snail, Cantareus aspersus, inc1udes 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 conformation al changes to the reproductive tract causing sperm to be stored rather than digested. In addition, successful dart shooters have an increased relative patemity compared to unsuccessful shooters. 1 have tested whether this increased patemity 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. 1 conc1ude that the mucus carried on the dart is responsible for increased patemity levels in Cantareus aspersus. Résumé Les comportements de séduction de l'escargot de jardins brun, le Cantareus aspersus, inclus une composante assez bizarre où l'escargot essaie de percer son partenaire avec un dard à la fois pointu, aiguisé, calcaire et couvert de mucus. In vitro, ce mucus cause des changements de conformation au niveau des voies reproductives causant ainsi l'entreposage plutôt que la digestion du sperme. De plus, celui qui insère son dart avec succès voit son taux de paternité augmenter par rapport à celui qui a moins de succès. J'ai cherché à savoir si le taux élevé de paternité observé est causé par le mucus qui couvre le dard ou bien si il est tout simplement causé par l'action mécanique du dard lui-même. Des essais d'accouplement ont été faits en utilisant des escargots sans dard et sans glande productrice de mucus. La future mère était donc accouplé avec deux pères potentiels différents recevant une injection de mucus avec le premier et une injection saline avec le second. Les pères accompagnés d'une injection de mucus produisèrent significativement plus de progénitures que les pères accompagnés d'une injection saline. Je conclue donc que le mucus recouvrant le dard de l'escargot est responsable pour les taux élevés de paternité chez les Cantareus aspersus. 11 Acknowledgements Foremost, 1 would like to thank Dr. Chase for rus continuing support and dedication to this project. His enthusiasm was always a constant, which made work more stimulating and exciting. He would come to lab in the morning with additional insight or new ideas making his love of scholarship apparent. His critical evaluation was both challenging and essential to the leaming process. He was an excellent supervisor, 1 truly feel lucky to have been his student. Donald Kramer and Laura Nilson, the other two members of my supervisory committee, provided invaluable guidance, suggestions, and critical insights. Angus Davison suggested modifications for the DNA extraction protocol reported by Doyle and Dickson (1987). Advice from Jim Ramsay regarding statistical procedures was also much appreciated. In addition, 1 want to thank Geoff Conrad and Julie Bernard, who provided the translation of the abstract to