DIPTERAN LARVAE INFESTATION OF LEATHERBACK TURTLE (DERMOCHELYS CORIACEA) NESTS ON GANDOCA BEACH, COSTA RICA A Thesis Presented to The Faculty of Graduate Studies of The University of Guelph by SONIA GAUTREAU In partial fulfillment of requirements for the degree of Master of Science February, 2007 © Sonia Gautreau, 2007 ABSTRACT DIPTERAN LARVAE INFESTATION OF LEATHERBACK TURTLE (DERMOCHELYS CORIACEA) NESTS ON GANDOCA BEACH, COSTA RICA Sonia Gautreau Co-Advisor: Dr. Ronald J. Brooks University of Guelph, 2007 Co-Advisor: Dr. Steve A. Marshall We examined the ecological characteristics of dipteran larvae infesting Leatherback nests on Gandoca Beach, Costa Rica in 2005-2006. Fly infestation exceeded 75% of nests, but levels were much lower when evaluated as the percent of the clutch infested. Fly larvae seemed to act mostly as scavengers, but a few live hatchlings were attacked indicating that flies also act opportunistically as predators. Several dipteran species were recorded with the sarcophagid Eumacronychia sternalis being dominant. Back-calculations from the development timeframe for E. sternalis showed that infestation happened shortly after hatchling emergence, suggesting that flies are attracted to the nest because of emanating odours of decomposing material brought to the surface by emerging hatchlings. Sampling year, bacteria or fungus invasion, and the interaction between nest depth and the number of dead hatchlings best predicted the incidence of larvae within nests. Infestation levels in egg hatcheries were not higher, possibly because of protective baskets. Our results suggest that flies do not seriously threaten Leatherback turtle populations in Gandoca, but they can cause incidental mortality and measures should be taken to protect nests against larval infestation. i ACKNOWLEDGMENTS I would like to thank my charismatic advisor, Dr. Ronald Brooks for believing in me and allowing me to pursue my dreams of working with Leatherbacks in Costa Rica. I will be forever grateful to you. I extend a warm thanks to the members of my advisory committee: Dr. Steve Marshall and Dr. Jinzhong Fu for providing insight and guidance throughout this work. Steve, thanks for initiating me to the world of flies. An enormous thanks goes to Didiher Chacón-Chaverri for his turtle expertise and for letting me join the ANAI team. This work would not have been possible without the help and encouragement of Jormmy Machado Hernández, your determination and devotion will forever amaze me. To my field assistant Yoela Matute López, thanks for your hard work, free spirit, and for putting humour in the gory job of nest excavations. I would not have survived in the Costa Rican jungle without the knowledge of my good friend Luis Corea Baltodano. Luis, gracias por tu amistad y tu ayuda durante todo mi tiempo en Gandoca. Me enseñaste muchas cosas sobre las tortugas que no habría podido aprender en libros. Thanks to Adelina López, la familia Velásquez, Claudio Quesada and to the rest of ANAI’s staff for their hospitality, support and friendship throughout my stay in Costa Rica. I am very grateful for the relentless work of the research assistants and the volunteers, all of you made my field work more enjoyable and successful. A la gente de Gandoca, nunca les voy a olvidar y espero verlos todos algún día. ¡Muchas gracias por todo! I give many thanks to all of my labmates and my other friends in Guelph for their friendship and assistance. Although my time in Guelph was relatively short, I am glad I had the opportunity to meet, work and just hang out with such an amazing group of people. I would like to acknowledge everyone who has helped me with fly identification, statistics and thesis editing: Dr. Mehrdad Parchami-Araghi, Dr. Matthias Buck, Manuel ii Zumbado, Dr. Thomas Pape, Michelle Edwards, Matt Partridge, Dr. Thomas Nudds, Joe Crawley and Njal Rollinson. I want to recognize all of my biology professors at Université de Moncton, especially Dr. François Fournier, Dr. Céline Bérubé, Patrick Maltais and Dr. Stéphane Reebs for initiating me to research and for always being available to me when I needed advice. Vous avez énormément contribué à mon cheminement en sciences et j’en suis très reconnaissante. To my family, a special thanks for encouraging me to reach my goals in life and for providing endless support. Je vous aime beacoup! Thanks to my mom who is always there for me whenever I need her, I could not have accomplished so much without you. Deep gratitude is extended to my late father for his love and wisdom. I will forever remember all of our camping trips and it is because of his love of nature that I am a biologist today. An enormous thanks goes to all of my friends at home and around the world, and to all the wonderful people I met travelling in Central America. Although you may not always have understood why I wanted to spend months “in the middle of nowhere” chasing turtles on the beach at night, you were always supportive and listened to hours of stories I had to tell. You have truly made my life more enjoyable. This research was possible thanks to the generous funding of WWF-Canada, NSERC, OGS and several scholarships provided through U of Guelph. iii TABLE OF CONTENTS ABSTRACT ....................................................................................................................... I ACKNOWLEDGMENTS................................................................................................II TABLE OF CONTENTS............................................................................................... IV LIST OF TABLES.........................................................................................................VII LIST OF FIGURES........................................................................................................ IX GENERAL INTRODUCTION 1.1. SPECIES INFORMATION.................................................................................................. 1 1.2. DISTRIBUTION ............................................................................................................... 1 1.3. STATUS ......................................................................................................................... 2 1.4. REPRODUCTION............................................................................................................. 3 1.5. INCUBATION AND THE NEST ENVIRONMENT ................................................................. 4 1.6. HATCHING AND EMERGENCE OF SEA TURTLE HATCHLINGS........................................... 5 1.7. DECOMPOSITION AND SAPROPHAGOUS FLIES ............................................................... 6 1.8. EFFECTS OF DIPTERAN INFESTATION ON SEA TURTLE NESTS ....................................... 9 1.9. FLY SPECIES RECORDED FROM SEA TURTLE NESTS.................................................... 12 1.10. MECHANISMS OF DIPTERAN INFESTATION OF SEA TURTLE NESTS ............................ 12 1.11. OBJECTIVES OF STUDY.............................................................................................. 16 GENERAL METHODOLOGY 2.1. STUDY SITE................................................................................................................. 17 2.2. BEACH PREPARATION AND NEST TRANSLOCATION..................................................... 19 2.3. COMMUNAL EGG HATCHERIES ................................................................................... 20 2.4. NEST IDENTIFICATION................................................................................................. 21 2.5. POST-EMERGENCE NEST EXCAVATIONS...................................................................... 22 iv CHAPTER I VARIATION IN LEATHERBACK TURTLE NEST SUCCESS ON GANDOCA BEACH DUE TO INFESTATION BY DIPTERAN LARVAE 3.1. INTRODUCTION .......................................................................................................... 24 3.2. MATERIALS AND METHODS ...................................................................................... 26 Effects of infestation on nest success........................................................................ 26 Larval feeding preferences........................................................................................ 28 3.3. RESULTS..................................................................................................................... 29 Effects of infestation on nest success........................................................................ 29 Larval feeding preferences........................................................................................ 32 3.4. DISCUSSION................................................................................................................ 37 Effects of infestation on nest success........................................................................ 37 Larval feeding preferences........................................................................................ 40 CHAPTER II MECHANISMS OF DIPTERAN LARVAE INFESTATION OF LEATHERBACK TURTLE NESTS: WHO, WHEN AND HOW? 4.1. INTRODUCTION .......................................................................................................... 44 4.2. MATERIALS AND METHODS ...................................................................................... 47 Dipteran species recorded......................................................................................... 47 Timing of infestation................................................................................................