EFFECTS OF PREDATOR-RELATED CHEMICAL CUES ON THE ACTIVITY LEVEL OF HOUSTON TOAD (BUFO [ANAXYRUS] HOUSTONENSIS) AND COASTAL PLAIN TOAD (BUFO [INCILIUS] NEBULIFER) TADPOLES THESIS Presented to the Graduate Council of Texas State University – San Marcos in Partial Fulfillment of the Requirements for the Degree Master of SCIENCE by Devin Preston, B. S. San Marcos, Texas May 2013 EFFECTS OF PREDATOR-RELATED CHEMICAL CUES ON THE ACTIVITY LEVEL OF HOUSTON TOAD (BUFO [ANAXYRUS] HOUSTONENSIS) AND COASTAL PLAIN TOAD (BUFO [INCILIUS] NEBULIFER) TADPOLES Committee Members Approved: ________________________________________________ Michael R. J. Forstner, Chair _________________________________________________ Caitlin R. Gabor __________________________________________________ Joseph Veech Approved: __________________________________________________ J. Michael Willoughby Dean of the Graduate College COPYRIGHT by Devin Bruce Preston 2013 FAIR USE AND AUTHOR’S PERMISSION STATEMENT Fair Use This work is protected by the Copyright Laws of the United States (Public Law 94-553, section 107). Consistent with fair use as defined in the Copyright Laws, brief quotations from this material are allowed with proper acknowledgement. Use of this material for financial gain without the author’s express written permission is not allowed. Duplication Permission As the copyright holder of this work I, Devin Bruce Preston, authorize duplication of this work, in whole or in part, for educational or scholarly purposes only. ACKNOWLEDGMENTS Firstly I thank Michael Forstner, my major advisor, for giving me a chance and much-needed kicks off the dock. He has given me many opportunities I never would have had otherwise. I thank my committee members, Caitlin Gabor and Joseph Veech as well for their guidance and input on this project. I thank Paul Crump at the Houston Zoo, without whose assistance this experiment would not have happened. I thank Floyd Weckerly, whose door was always open for me to solicit statistical assistance. I thank all my lab mates, especially Melissa Jones for helping to assimilate me into the Forstner lab and being a friendly face when I first arrived at Texas State. I thank Emrah Ozel, who helped me with odonate identification. I thank Donald Brown, who showed me the ropes, stimulated more research for me, and answered all of my questions about graduate school. I thank Clarissa Starbuck for supporting me throughout my undergraduate career and beyond. I thank Amanda Moore for making me wash the dirt off of my clothes and myself and for letting me use (and break) all of her expensive electronic equipment. I thank my brother for the blunt head trauma that surely led to me getting into biology. I thank my sister being the academic forerunner in our generation of Prestons. I thank my dad for his selflessness and always putting his children first, and I thank my mom for always believing in me and pulling me out of the hole I dug myself into while getting my bachelor’s degree. This manuscript was submitted on 04/02/2013. v TABLE OF CONTENTS Page ACKNOWLEDGMENTS ................................................................................................... v LIST OF FIGURES ........................................................................................................... viii ABSTRACT......................................................................................................................... ix CHAPTER I. SOLITARY AND AGGREGATED COASTAL PLAIN TOAD (BUFO [INCILIUS] NEBULIFER) LARVAE DECREASE THEIR ACTIVITY IN RESPONSE TO KAIROMONE AND DIET CUES ..................................1 Abstract .........................................................................................................1 Introduction ..................................................................................................2 Materials and Methods ..................................................................................9 Cue Production .................................................................................9 Cue Exposure ..................................................................................10 Statistical Analyses ...........................................................................11 Results.........................................................................................................12 Discussion ...................................................................................................14 Acknowledgments .......................................................................................16 Literature Cited ...........................................................................................16 vi II. HOUSTON TOADS (BUFO [ANAXYRUS] HOUSTONENSIS) DECREASE THEIR ACTIVITY IN RESPONSE TO PREDATION OF CONSPECIFICS AND THE COASTAL PLAIN TOAD, BUFO (INCILIUS) NEBULIFER .........................................................................27 Abstract .......................................................................................................27 Introduction ................................................................................................28 Materials and Methods ................................................................................30 Cue Production ...............................................................................31 Cue Exposure ..................................................................................32 Statistical Analyses ...........................................................................33 Results.........................................................................................................34 Discussion ...................................................................................................36 Acknowledgments .......................................................................................40 Literature Cited ...........................................................................................41 vii LIST OF FIGURES Figure Page 1. Mean activity events (±SE) of individuals and groups of Bufo nebulifer tadpoles per aquarium per tadpole before (pre) and after (post) exposure to three chemical cues. .....................................................12 2. Mean response strength of individual Bufo nebulifer tadpoles (±SE) in response to three chemical cues. ..................................................13 3. Mean response strength of groups of five Bufo nebulifer tadpoles (±SE) in response to three chemical cues. ..................................................14 4. Mean activity events (±SE) of Bufo houstonensis tadpoles per aquarium per tadpole before (pre) and after (post) exposure to three chemical cues ...............................................................................35 5. Mean response strength of groups of five Bufo houstonensis tadpoles (±SE) in response to four chemical cues ....................................................35 viii ABSTRACT EFFECTS OF PREDATOR-RELATED CHEMICAL CUES ON THE ACTIVITY LEVEL OF HOUSTON TOAD (BUFO [ANAXYRUS] HOUSTONENSIS) AND COASTAL PLAIN TOAD (BUFO [INCILIUS] NEBULIFER) TADPOLES by Devin Preston, B.S. Texas State University-San Marcos May 2013 SUPERVISING PROFESSOR: MICHAEL R. J. FORSTNER Predation is a strong ecological force and plays a role in shaping communities. In response to predation, many prey species have evolved predator avoidance mechanisms. One such avoidance mechanism is the detection of chemical cues from predators. This mechanism of predator detection is especially important in aquatic systems. Many anuran larvae can detect chemical cues created by the presence of aquatic invertebrate predators and consumption of conspecific and/or concurrent anurans by these same predators. A ix commonly documented larval anuran response to the presence of predator-related chemical cues is the reduction of activity. Two species that have not been tested for antipredator response in the presence of chemical cues during their larval stage are the coastal plain toad (Bufo [Incilius] nebulifer) and the federally endangered Houston toad (Bufo [Anaxyrus] houstonensis). I conducted two experiments. In the first, I tested if B. nebulifer exhibited a reduction of activity (antipredator response) in the presence of chemical cues produced from the presence of an invertebrate predator (kairomone cues) or chemical cues produced from the predation of conspecifics by an invertebrate predator (conspecific diet cues). I also examined whether aggregation status (solo tadpoles vs. groups of tadpoles) mediated the response of B. nebulifer to both cues. In the second experiment, I tested if B. houstonensis exhibited a reduction of activity (antipredator response) in the presence of kairomone cues, conspecific diet cues, or congeneric diet cues produced from the predation of larval B. nebulifer. I found that individuals and groups of B. nebulifer tadpoles reduced their activity level when exposed to conspecific diet cues, but only individuals reduced their activity level when exposed to kairomone cues. I found that B. houstonensis larvae lowered their activity in the presence of conspecific diet cues and congeneric diet cues, but not in the presence of kairomone cues. Taken together, these results imply a stronger response by both bufonids to predation than to the presence of a predator alone. I propose some possible hypotheses for the disparity in activity levels between solo and group treatments, diet and kairomone cues, and discuss the ecological implications