TACTILE DISCRIMINATION IN THREE SPECIES OF GARTER SNAKE, (THAMNOPHIS) The members of the Committee approve the doctoral dissertation of Vicki Lynne Keathley Roger L. Mellgren Supervising Professor Veme C. Cox Raymond L. Jackson Martha A. Mann Yuan B. Peng Dean of the Graduate School Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TACTILE DISCRIMINATION IN THREE SPECIES OF GARTER SNAKE, (THAMNOPHIS) by VICKI LYNNE KEATHLEY Presented to the Faculty of tiie Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT ARLINGTON MAY 2004 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Copyright ©by Vicki Lynne Keathley 2004 All RightsReserved Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS This research was conducted under the supervision of Roger L. Meligren. I appreciate Ms instruction and guidance throughout tMs very long process. I also very much appreciate the other members of my cominlttee, Veme C. Cox, Raymond L. Jackson, Martha M. Mann and Yuan B, Peng for their time, patience and many contributions to tMs project I would also like to acknowledge the technical help and si^port provided by Golden Strader. Thank you for your many rescues. I could not have acMeved tMs goal without the constant and unwavering support of my family and friends. Not once did they ever question my motivation or resolve, or tempt me to do something else when I needed to work. appreciateI their understanding and forgiveness for the times I was mentally and/or physically checked out Thank you to my parents, Beverly and Darrell Keathley,my sister, Alane Mulleo, and my son. Hunter M. Davis, who wasespecially understanding. My dear husband, Rodney A. Carver, colleague, friend and life companion has trulybeen a life saver over these last few intense years. On tough days, he was always there to encourage and restore my confidence and on gooddays ready to celebrate my accomplishments. Priceless. Aprill2,2004 IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT TACTILE DISCRIMINATION IN THREE SPECIES OF GARTER SNAKE, {THAMNOPHIS) Publication No. Vicki Lynne Keathley, Ph.D. The University o f Texas at Arlington, 2004 Supervising Professor; Roger L. Mellgren Tactile perception and the utilization of tactile information has been little studied in snakes. Three questions were addressed in this study. 1) When given the choice, would subjects choose one type of tactily differentiated substrate over another? 2) If tactile sensations are a factor in the discrimination of a preferred substrate, would compromising the cephalicmechanorecqjtors disrupt that discrimination? 3) Could snakes demonstrate acquisition of a behavior by utilizing tactile information from the environment? Three species of gartersnake served as subjects, JhammpMs: marcimms, radix and sirtalis. In Phase 1 of Experiment 1, each half of a rectangular box was covered with one o f three substrates: large, medium or small irregularly shaped black Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rocks. Results revealed that all subjects preferred large over medium and medium over small rocks. Phase 2 was identical to Phase 1, except the cephalic mechanoreceptora were covered with plastic wrap. In each substrate combination, less time was spent on the preferred side when the mechanoreceptors were covered (Phase 2)tiran when they were not covered (Phase 1). Experiment 1 supports the hypothesis that compromising the cephalic mechanoreceptors interferes with the ability to discriminate a preferred side. In Experiment 2, subjects were trained in a Y-maze with tactily different substrates (large vs. medium rocks) in each arm for a food reward. Medium size rocks were the only cue to the correct arm (going against their preferred substrate as determined in Experiment 1). After meeting a criterion of 70% correct in 20 trials, probe trials were conducted in the dark. Five of eight subjects reached criterion: all witihin 65 trials or less. Subjects as a group, performed significantly better in the last twenty trials. Three of the four subjects on which probes were run met or exceeded the 70% criterion. Five of the eight showed a reduction in running time across trials. There were no species differences. Evidence iftom this study suggests tactile cues from the substrate may be acquired and used by snakes to navigate the environment. VI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ACKNOWLEDGEMENTS ...... iv ABSTRACT ................. v LIST OF ILLUSTRATIONS ................ ix LIST OF TABLES .......... xi Ch^ter 1. INTRODUCTION AND BACKGROUND ........ 1 1.1 Mechanoreceptors ...... 12 2. EXPERIMENT 1—SUBSTRATE PREFERENCE ....... 27 2.1 Phases ofExjwriment 1 ............... 29 2.1.1 Phase 1 ..... 29 2.1.2 Phase 2 ..... 29 2.1.3 Phase 3 ........ 30 2.1.4 Phase 4 ........ 31 2.2 Method of lavestigatioe ........ 31 2.2.1 Subjects.... .............. 31 ■ 2.2.2 Appratus ......... 32 2.2.3 Procedure ................. 32 2.3 Results—^Experimeat 1.......... 35 2.3.1 Time on preferred side......................... 35 vii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.3.2 Time on preferred side under cover, no-cover conditions............... 36 2.4 Discussion—Experiment 1 ............ 40 2.4.1 Substrate preference............................. 40 2.4.2 Effect o f the cover variable .... 44 3. EXPERIMENT 2—TACTE.E DISCRIMINATION IN A Y-MAZE.......... 46 3.1 Method of Investigation ........ 50 3.1.1 Subjects............... 50 3.1.2 Apparatus ....... 51 3.1.3 Procedure ............... 51 3.2 Results—^Experiment 2 ....... 55 3.2.1 drorce..........a............................................................................ 55 3.2.2 Running time.. ............ 63 3.3 Discussion—^Experiment 2 ..... 67 3.3.1 ^^rm c l s o r c e 67 3.3.2 Running time.. ............. 72 4. SUMMARY AND CONCLUSIONS.. ................. 78 ................... a....................................................................................... 8^1 BIOGRAPHICAL INFORMATION., ............................... 99 V lll Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF ILLUSTRATIONS Figure Page 1.1 Papilla and sunrounding tissues of a mechanoreceptor .... ...... 14 1.2 Stippled areas depict the distribution of mechanoreceptors on the head o f a typical coluhrid snake ......... ................. ...................... 15 2.1 Head scales of atypical garter snake ......................................... ............ 30 2.2 Shadowed areas depict the qjproximate scale area covered by the plastic wrap .... .................................... ............... ....... 34 2.3 Total mean time spent on large and medium rocks in the no-cover and cover conditions .......... ......... ............................ 37 2.4 Total mean time spent on large and small rocks in the no-cover and cover conditions .......... ........... ............... ......... ......... 38 2.5 Total mean time spent on medium and small rocks in the no-cover and cover conditions ...... ...................... ...................... 38 2.6 Total mean time spent on preferred and non-preferred substrates (cover vs. co-cover) .... ....................... ........ ................... ...... 40 3.1 Y-maze as it would appear if left was the correct side (medium rocks)......... 47 3.2 Cumulative successes for subject M l............................................................. 59 3.3 Cumulative successes for subject M 2 ... ................................... 60 3.4 Cumulative successes for subject M 3 ..... ............. 60 3.5 Cumulative successes for subject R 1 ........................................................... 61 3.6 Cumulative successes for subject R 2 ... ...................................................61 3.7 Cumulative successes for subject M 4 ........ ......... 62 IX Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.8 Cmmilative successes for subject MS ....... 62 3.9 Cumulative successes for subject SL................ .... .....63 3.10 Correct and incorrect running times (RT) for those that made criterion and those that did not ...... 66 X Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Table Page 2.1 Substrate preference data for each species...... ..... ....... ............ 36 2.2 Total time (sec.) and percent spent on preferred side for each of the four phases.... ............ .............................. ....... 36 3.1 Comparisons between first twenty and last twenty trials.................................56 3.2 Subject performance across all trials ..... ........................... ...................... 58 3.3 RT summary statistics for the two trial blocks. ............. ....... 64 3.4 Post hoc RT comparisons......................... ............... ...................... ........ 66 XI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 1 INTRODUCTION AND BACKGROUND Herpeton, root of the word, herpetology,