The influence of exotic salmonids on native host-parasite dynamics Rachel A. Paterson A thesis submitted for the degree of Doctor of Philosophy at the University of Otago, Dunedin, New Zealand December 2010 ii Summary Native parasite acquisition provides introduced species with the potential to modify native host-parasite dynamics by acting as parasite reservoirs (with the ‘spillback’ of infection increasing the parasite burdens of native hosts) or sinks (with the ‘dilution’ of infection decreasing the parasite burdens of native hosts) of infection. Exotic salmonids are frequently shown to acquire native parasites; however, as research into the threats posed by exotic salmonids has largely focused on predation and competition, threats posed by shared native parasites are poorly understood. I used a multiple-pronged approach combining field observations, experimental infections and dynamic population modelling to investigate whether native parasite acquisition by exotic salmonids alters host-parasite dynamics in native fish populations from streams and lakes in New Zealand and Argentina. I also used a meta-analysis approach to investigate which trait(s) influence native parasite acquisition by exotic freshwater fish. My research demonstrated that two key factors strongly influence whether the dynamics of native parasites will be affected by exotic fish. On one hand, the competency of exotic fish for native parasites is an important determinant of whether native parasite populations are likely to increase or decrease. On the other hand, the relative abundance of the exotic species determines whether its competency for a native parasite will actually translate into altered native host-parasite dynamics, with highly abundant exotic species more likely to induce changes in native parasite dynamics. I also demonstrated how exotic species may be able to override the influence of low host abundance, or competency by altering native host behaviour. The meta-analysis suggested that traits known to influence parasite richness in native fish or invasion success of exotic species are not reliable predictors of native parasite acquisition by exotic fish. Instead, it is more likely that complex interactions between a variety of biological, geographical and historical factors govern parasite acquisition by exotic species, making it difficult to predict whether native parasites will be acquired. iii Acknowledgements This thesis would not have completed without the support and encouragement of many wonderful people. First, I would like to thank Dan Tompkins, Robert Poulin and Colin Townsend for the outstanding supervision they provided me. Your prompt feedback and constructive advice greatly shaped my research, and I have learned so much from you all. I am especially grateful to Dan, who first suggested this doctorate to me - otherwise I might be still trapping possums. I was fortunate to belong to both the Aquatic and Parasitology lab groups and wish to thank lab members for interesting discussions, feedback and support. I also have greatly appreciated assistance from the following Department of Zoology staff: Kim Garrett, Ken Miller, Murray McKenzie, Ronda Peacock, Wendy Shanks, Vivienne McNaughton and Esther Sibbald. I would especially like to thank Nicky McHugh, who made the Aquatic lab a fantastic place to work. I would also to thank the following people who assisted with field and laboratory work: Tina Bayer, Marcia Dale, Kim Garrett, Mya Gaby, Ruth Goldsmith, Kristin Herrmann, Andy Hicks, Dave Kelly, Allison Koone, Clement Lagrue, Aparna Lal, Karen Ludwig, Francis Magbanua, Dean O’Connell, Bronwyn Presswell and Cynthia Winkworth. I also wish to thank Frank Wilhelm for providing Paracalliope fluviatilis life history information that contributed to the Acanthocephalus galaxii research. I am also grateful to landowners from the Manuherikia and Taieri River catchments for access to streams on their properties, and in particular wish to thank Robert Scott (Swin Burn) and Dave Crutchley (Old Hut Creek). I wish to thank Landcare Research for their continued assistance, especially Elly Lang for logistical support. I am grateful to the following people from Fish and Game, who provided valuable advice and assistance: Morgan Trotter, Niall Watson (Otago), Maurice Rodway (Southland), Ross Millichamp and Davor Bejakovich (Canterbury). From Argentina, I wish to thank the Laboratorio de Parasitología, Universidad Nacional del Comahue, Bariloche, and in particular Liliana Semenas, Gustavo Viozzi and Carlos Rauque, for hosting me in their lab. I would like to thank Marcelo Alonso, Pepe Di Gusto, Oscar Quatrin and Mauricio Ugoccioni for assistance in fish collection, and am grateful to Victor Baez and the staff of Centro de Salmonicultura Bariloche for providing experimental infection facilities. Special thanks to Celi and Luciana Harran, Ricardo Albarino iv and Beth Chang Reissig for welcoming me into their families and making my stay Argentina very enjoyable. My doctoral work was generously funded by the Royal Society of New Zealand Marsden Fund, Elman Poole Travelling Fellowship, Department of Zoology and Landcare Research. The Division of Sciences, the Department of Zoology, Ecological Research Group and the Claude McCarthy Fellowship sponsored my attendance at conferences in New Zealand, Australia (2) and Argentina. All research was carried out with the approval of the University of Otago Ethics Committee. Finally, I wish to thank my friends and family, especially my parents, Clive and Anne Paterson, for their continued encouragement and support during my studies. v Table of Contents Summary ..................................................................................................................................... ii Acknowledgements ................................................................................................................... iii List of Tables ............................................................................................................................. ix List of Figures ............................................................................................................................ xi Chapter 1 General Introduction 1.1 Exotic species introductions .............................................................................................. 2 1.2 Disease associated with exotic species.............................................................................. 2 1.3 Disease associated with exotic freshwater fish ................................................................. 3 1.4 Salmonid introductions ..................................................................................................... 3 1.5 Thesis outline .................................................................................................................... 4 Chapter 2 Has the introduction of brown trout altered disease patterns in native New Zealand fish? 2.1 Introduction ....................................................................................................................... 7 2.2 Materials and Methods ...................................................................................................... 8 2.2.1 Fish sampling .............................................................................................................. 8 2.2.2 Intermediate host sampling ......................................................................................... 9 2.2.3 Statistical Analyses ..................................................................................................... 9 2.3 Results ............................................................................................................................. 10 2.3.1 Infection of native fish in relation to trout presence ................................................. 11 2.4 Discussion ....................................................................................................................... 12 Chapter 3 Introduced brown trout alter native acanthocephalan infections in native fish 3.1 Introduction ..................................................................................................................... 23 3.2 Materials and Methods .................................................................................................... 25 3.2.1 Study system ............................................................................................................. 25 vi 3.2.2 Field surveys ............................................................................................................. 25 3.2.3 Infection experiment ................................................................................................. 26 3.2.4 Statistical analyses .................................................................................................... 27 3.2.5 Population model ...................................................................................................... 27 3.3 Results ............................................................................................................................. 32 3.3.1 Field survey ............................................................................................................... 32 3.3.2 Infection experiment ................................................................................................. 32 3.3.3 Population model .....................................................................................................