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Sound Source Segregation in the Acoustic Parasitiod Fly Ormia Ochracea

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Sound Source Segregation in the Acoustic Parasitiod Fly Ormia Ochracea Sound Source Segregation in the Acoustic Parasitiod Fly Ormia ochracea by Norman Lee A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Cell and Systems Biology University of Toronto © Copyright by Norman Lee 2012 Sound Source Segregation in the Acoustic Parasitoid Fly Ormia ochracea Norman Lee Doctor of Philosophy Cell and Systems Biology University of Toronto 2012 Abstract Sound source localization depends on the auditory system to identify, recognize, and segregate elements of salient sources over distracting noise. My research investigates sensory mechanisms involved in these auditory processing tasks of an insect hearing specialist, to isolate individual sound sources of interest over noise. I first developed quantitative methods to determine signal features that the acoustic parasitoid fly Ormia ochracea (Diptera: Tachinidae) evaluate for host cricket song recognition. With flies subjected to a no-choice paradigm and forced to track a switch in the broadcast location of test songs, I describe several response features (distance, steering velocity, and angular orientation) that vary with song pulse rate preferences. I incorporate these response measures in a phonotaxis performance index that is sensitive to capturing response variation that may underlie song recognition. I demonstrate that Floridian O. ochracea exhibit phonotaxis to a combination of pulse durations and interpulse intervals that combine to a range of accepted pulse periods. Under complex acoustic conditions of multiple coherent cricket songs that overlap in time and space, O. ochracea may experience a phantom source illusion and localize a direction between actual source locations. By varying the temporal overlap between competing sources, I demonstrate that O. ochracea are able to resolve this illusion via the precedence effect: exploitation of small time differences between competing sources to selectively localize the leading over lagging sources. An increase in spatial separation between cricket song and masking noise does not reduce song detection thresholds nor improve song localization accuracy. Instead, walking responses are diverted away from both song and noise. My findings support the idea that the ears of O. ochracea function as bilateral symmetry ii detectors to balance sound intensity, sound arrive time differences, and temporal pattern input to both sides of the auditory system. Asymmetric acoustic input result in corrective turning behaviour to re-establish balance for successful source localization. iii Acknowledgments I owe my deepest gratitude to my supervisor Dr. Andrew Mason for his contributions, and endless support in nurturing me as an independent scientist. Andrew provided me with the opportunity and resources to explore my own research interests independently, but was always available to provide invaluable input critical to the success of this dissertation. I would like to thank my thesis advisory committee members Drs. Maydianne Andrade and John Peever for their experimental advice and for pointing out my weaknesses so that I may grow as a scientist. I thank Andrew and Maydianne for being sources of inspiration that has sparked my passion for pursuing academia. I am grateful for Dr. Thomas Walker who has provided me with support for field experiments and fly collection. I would also like to thank Drs. Damian Elias, Michael Kasumovic, Mark Fitzpatrick, Kevin Judge, Jeff Stoltz, Patrick Guerra, Paul De Luca, Daniel Howard, Carrie Hall, and Fernando Montealegre for helpful discussions and feedback on projects. I thank my fellow graduate students Dean Koucoulas, Jenn Van Eindhoven, Matt Jackson, Sen Sivalinghem, Maria Modanu, Emily MacLeod and Luciana Baruffaldi for their support. I thank Michelle Leung and numerous Mason Lab volunteers that have contributed to maintaining a stable colony of Ormia ochracea for this research endeavor to be possible. I am grateful for the support from my closest friends that include: David Pham, Gary Yan, Fang Zhao, Paul Pan, Steven Wong, Takeshi Ishii, Jeongkyo Jang, Eunji In, and Min Ok Choi. I would like to show my sincere gratitude to John Ko and Phoebe Choe for their love and generosity in providing me with a place to stay during my transition to work in the laboratory of Dr. Mark Bee at the University of Minnesota. I thank John and Phoebe for their provisions that have assisted me in the final stages of completing my dissertation. I would also like to thank my mother Tung Moy Lee, and my father Chee Wing Lee, for teaching me to be diligent at an early age. I am indebted to my wife Mijung Kim and our ‘Somang’ for their love, encouragement, and sacrifices that they have made to provide me with the opportunity to pursue my dreams. Lastly, I would like to thank my mother-in-law Heo Nam Soon and our family in Busan, South Korea for believing in me and entrusting their precious Mijung to my care. iv Table of Contents Contents Abstract ........................................................................................................................................... ii Acknowledgments.......................................................................................................................... iv Table of Contents .............................................................................................................................v List of Tables ................................................................................................................................. ix List of Figures ..................................................................................................................................x Chapter 1 General Introduction .......................................................................................................1 1.1 Evaluating Features of Acoustic Signals .............................................................................1 1.2 Spectral Features of Acoustic Signals Evaluated for Species Recognition .........................1 1.3 Temporal Features of Acoustic Signals Evaluated for Species Recognition .......................2 1.4 Directional Hearing in Small Insects ...................................................................................3 1.5 Hearing in Complex Acoustic Conditions ...........................................................................4 1.6 Acoustically Orienting Parasitoid Flies (Diptera: Tachinidae) ............................................5 1.7 Directional Hearing in O. ochracea .....................................................................................6 1.8 Thesis Outline ......................................................................................................................8 References ......................................................................................................................................10 Chapter 2 Deriving a Sensitive Measure of Walking Phonotaxis Performance in the Acoustic Parasitoid Fly Ormia ochracea .................................................................................................14 2.1 Abstract ..............................................................................................................................14 2.2 Introduction ........................................................................................................................15 2.3 Materials and Methods .......................................................................................................18 2.3.1 Animals ..................................................................................................................18 2.3.2 Acoustic Stimuli.....................................................................................................18 v 2.3.3 Spherical treadmill .................................................................................................18 2.3.4 Protocol ..................................................................................................................19 2.3.5 Data Analysis .........................................................................................................19 2.4 Results ................................................................................................................................20 2.5 Discussion ..........................................................................................................................23 2.6 Acknowledgements ............................................................................................................27 References ......................................................................................................................................28 Figure Legends...............................................................................................................................31 Chapter 3 Convergent Temporal Features Evaluated for Song Recognition in a Host- Parasitoid Relationship .............................................................................................................39 3.1 Abstract ..............................................................................................................................39 3.2 Introduction ........................................................................................................................40 3.3 Materials and Methods .......................................................................................................43 3.3.1 Animals ..................................................................................................................43
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