ON THE STRUCTURE AND FUNCTION OF TAILS IN SNAKES: RELATIVE LENGTH AND ARBOREALITY By COLEMAN MATTHEW SHEEHY III A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006 1 Copyright 2006 By Coleman Matthew Sheehy III 2 To the increased understanding, respect, and conservation of snakes worldwide 3 ACKNOWLEDGMENTS I thank my committee members Harvey B. Lillywhite (chair), James Albert, and Max A. Nickerson for their guidance and support. Harvey B. Lillywhite first inspired this work by suggesting a link between snake tails and the gravitational hypothesis. I thank Harvey B. Lillywhite and Michael B. Harvey for providing unpublished snake length data, Florida Museum of Natural History (FLMNH) curators F. Wayne King and Max A. Nickerson for access to the Herpetology collection, Roy McDiarmid and George Zug at the United States National Museum (USNM) for permission to use the Herpetology collection, and Steve Gotte at the USNM and Kenney L. Krysko at the FLMNH for supplying data from the Herpetology collection databases. I thank Michael B. Harvey, Laurie Vitt, James McCranie, Rom Whitaker, Bob Henderson, Bob Powell, Blair Hedges, Ming Tu, Max A. Nickerson, Richard Sajdak, Bill Love, and John Rossi for providing difficult to find snake natural history information. I thank Michael B. Harvey and Ron Gutberlet for information on snake phylogenies, Michael McCoy for assistance with various statistical programs and analyses, and Kent Vliet for the use of a Macintosh computer. I thank Andres Lopez and Griffin Sheehy for help with illustrating programs, Andres Lopez for help with phylogenetic programs, and Jason Neville for computer assistance. I thank Glades Herp Inc. for permission to measure live snakes and, perhaps more importantly, I am grateful to Russel L. Anderson, Sam D. Floyd and Ryan J. R. McCleary for assistance in handling and measuring live snakes, many of which were large, highly venomous, and uncooperative. In addition to my committee members, I thank Ryan J. R. McCleary, David A. Wooten, Leslie Babonis, Chris Samuelson, Bruce Jayne, and Roy McDiarmid for stimulating discussions regarding snake natural history and evolution. I thank Griffin E. Sheehy and Andrea Martinez for all their patience, love and support. Finally, I want to 4 thank my parents Coleman M. Sheehy, Jr. and Ellen R. Sheehy for never failing to support and encourage a young boy’s endless passion for snakes. I could not have been more lucky. 5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES...........................................................................................................................8 LIST OF FIGURES .........................................................................................................................9 ABSTRACT...................................................................................................................................10 CHAPTER 1 INTRODUCTION ..................................................................................................................12 Gravitational Influence on Tail Morphology..........................................................................13 Length Limitations..................................................................................................................14 Relative Tail Length and Macrohabitat Use...........................................................................15 Multiple Functions of Tail Use...............................................................................................17 Locomotion......................................................................................................................17 Caudal Luring..................................................................................................................20 Defense............................................................................................................................21 Morphology and Reproduction........................................................................................24 Sexual Dimorphism and Ontogenetic Shifts ...................................................................25 2 MATERIALS AND METHODS............................................................................................27 Categorizing Climbing in Snakes: Gravitational Habitat .......................................................27 Analyses..................................................................................................................................31 Frequency Distribution....................................................................................................31 Gravitational Habitat and Total Body Length.................................................................31 Gravitational Habitat and Tail Length.............................................................................32 Constructing the Phylogeny ............................................................................................32 Relative Tail-Length, Gravitational Habitat, and Phylogeny..........................................34 3 RESULTS...............................................................................................................................48 Frequency Distribution ...........................................................................................................48 Gravitational Habitat and Total Body Length ........................................................................48 Gravitational Habitat and Tail Length....................................................................................49 Relative Tail-Length, Gravitational Habitat, and Phylogeny .................................................49 4 DISCUSSION.........................................................................................................................63 Relative Tail Length, Gravity, and Climbing in Snakes.........................................................63 Snake Tails and Defense: Speed and Pseudautotomy ............................................................67 APPENDIX STENOTOPICALLY ARBOREAL SPECIES........................................................71 6 LIST OF REFERENCES...............................................................................................................73 BIOGRAPHICAL SKETCH .........................................................................................................85 7 LIST OF TABLES Table page 2-1 Taxa and associated data sources for 227 snake species included in this study................36 2-2 Total variation in relative tail-lengths of 26 species of snakes..........................................43 3-1 The 227 species included in this study ..............................................................................50 A-1 Stenotopically arboreal species..........................................................................................71 8 LIST OF FIGURES Figure page 2-1 Composite phylogeny of 227 snake taxa. ..........................................................................44 3-1 Snake total length frequency distribution. .........................................................................56 3-2 Coefficients of variation of log10 transformed total length................................................58 3-3 Regression of log10 tail length on log10 total length...........................................................59 3-4 Analysis of covariance (ANCOVA) on corrected tail-length for 227 species of stenotopically arboreal.......................................................................................................60 3-5 Analysis of covariance (ANCOVA) on corrected tail-length for 227 species of scansorial............................................................................................................................61 3-6 Independent contrasts.........................................................................................................62 4-1 Regression of absolute tail length on relative tail-length...................................................70 9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ON THE STRUCTURE AND FUNCTION OF TAILS IN SNAKES: RELATIVE LENGTH AND ARBOREALITY By Coleman Matthew Sheehy III December 2006 Chair: Harvey B. Lillywhite Major Department: Zoology The pervasive effect of gravity on blood circulation is an important consequence for elongate animals such as snakes that utilize arboreal habitats. Upright postures create vertical gradients of hydrostatic pressures within circulatory vessels, and the magnitude of the pressure change is proportional to the total length of the blood column. In air, this potentially induces blood pooling and edema in dependent tissues and a decrease in the volume of blood reaching the head and vital organs of animals that are tall or elongate. Arboreal snakes exhibit a suite of behavioral, morphological, and physiological adaptations for countering the effects of gravity on blood circulation including relatively non-compliant tissue compartments in the tail. Comparative studies involving arboreal, terrestrial, and aquatic species have demonstrated that blood pooling in dependent