ENDOCRINE CONTROL OF TERRITORIAL AGGRESSION IN THE EUROPEAN STONECHAT (SAXICOLA TORQUATA RUBICOLA) DISSERTATION der Fakultät für Biologie der Ludwig-Maximilians-Universität München Vorgelegt von VIRGINIE CANOINE Andechs, August 2001 1. Gutachter: Prof. Dr. Eberhard Gwinner 2. Gutachter: Prof. Dr. Gerhard Neuweiler Tag der Einreichung der Dissertation: 17. August 2001 TABLE OF CONTENTS 1. INTRODUCTION ...................................................................................... 1 1.1. Territoriality ....................................................................................................................1 1.2. The role of androgens .....................................................................................................2 1.3. The Challenge hypothesis...............................................................................................5 1.4. Hormones other than androgens that might be involved in the control of aggression ...6 1.4.1. Oestrogens ...................................................................................................................7 1.4.2. Glucocorticoids ...........................................................................................................7 1.5. The study species : The European stonechat ..................................................................9 2. AIM OF THE THESIS ............................................................................. 11 3. GENERAL METHODS ........................................................................... 13 3.1. Animal maintenance .....................................................................................................13 3.1.1. Animals ......................................................................................................................13 3.1.2. Aviary .........................................................................................................................13 3.1.3. Implants .....................................................................................................................14 3.1.4. Implantation ..............................................................................................................14 3.2. Measurement of plasma levels of steroids....................................................................14 3.2.1. Reagents ....................................................................................................................15 3.2.2. Extraction of steroids from plasma............................................................................15 3.2.3. Chromatography on celite micro-columns ................................................................16 3.2.4. Radioimmunoassay ....................................................................................................17 3.2.5. Data calculation and quality controls .......................................................................18 4. HORMONAL RESPONSE TO AN INTRUSION IN CAPTIVE MALE STONECHATS .........................................................................................19 4.1. Introduction ..................................................................................................................19 4.2. Methods ........................................................................................................................21 4.2.1. Experimental animals ................................................................................................21 4.2.2. Experimental design ..................................................................................................21 4.2.3. Hormonal analyses ....................................................................................................22 4.2.4. Statistics .....................................................................................................................23 4.3. Results ..........................................................................................................................24 4.3.1. Hormones ..................................................................................................................24 4.3.2. Behaviour ..................................................................................................................24 4.4. Discussion.....................................................................................................................28 4.4.1. Challenge hypothesis .................................................................................................28 4.4.2. Are other androgens involved during an STI?...........................................................30 4.4.3. Seasonal relationship between androgens and aggression/behaviour ......................30 4.4.4. Methodology ..............................................................................................................31 4.4.5. Species differences .....................................................................................................31 4.4.6. Is corticosterone involved? ........................................................................................32 5. DO ANDROGENS CONTROL AGGRESSIVE BEHAVIOUR IN CAPTIVE MALE STONECHATS ......................................................... 34 5.1. Introduction ..................................................................................................................34 5.2. Material and Methods ...................................................................................................36 5.2.1. Animals ......................................................................................................................36 5.2.2. Experimental design ..................................................................................................36 5.2.3. Simulated territorial intrusion test ............................................................................37 5.2.4. Implantation ..............................................................................................................37 5.2.5. Hormonal analyses ....................................................................................................37 5.2.6. Statistical analysis .....................................................................................................38 5.3. Results ..........................................................................................................................38 5.3.1. Behaviour ..................................................................................................................38 5.3.2. Song activity ..............................................................................................................38 5.3.3. Hormones ..................................................................................................................40 5.4. Discussion.....................................................................................................................42 5.4.1. Methodology ..............................................................................................................42 5.4.2. Behaviour ..................................................................................................................43 5.4.2.1. Androgens ...............................................................................................................44 5.4.2.2. Corticosterone ........................................................................................................46 5.4 3. Why is aggressive behaviour reduced in captive stonechats? ...................................47 6. TERRITORIAL AGGRESSION IN FREE-LIVING MALE STONECHATS .........................................................................................49 6.1. Introduction ..................................................................................................................49 6.2. Materials and Methods .................................................................................................50 6.2.1. Study sites ..................................................................................................................50 6.2.2. Monitoring .................................................................................................................51 6.2.3. Experimental design ..................................................................................................52 6.2.4. Simulated territorial intrusion (STI) test ...................................................................53 6.2.5. Behavioural observations ..........................................................................................53 6.2.6. Capture ......................................................................................................................53 6.2.7. Blood sampling ..........................................................................................................54 6.2.8. Hormonal manipulations ...........................................................................................54 6.2.9. Hormonal analyses ....................................................................................................54 6.2.10. Statistical analyses ..................................................................................................55 6.3. Results ..........................................................................................................................55 6.3.1. Behaviour ..................................................................................................................55