Where and how to build? Influence of social and environmental cues on nest building behavior in leaf-cutting ants Dissertation zur Erlangung des Naturwissenschaftlichen Doktorgrades der Bayerischen Julius-Maximilians-Universität Würzburg Vorgelegt von Daniela Römer, Diplom Biologin aus Bad Mergentheim Würzburg, Dezember 2014 Photo title page: Cement cast of Atta laevigata nest in Botucatu, Brazil; source: W. Thaler Würzburg, Dezember 2014 Eingereicht am: 18. Dezember 2014 Mitglieder der Promotionskommission: Vorsitzender: Prof. Dr. Markus Engstler Gutachter: Prof. Dr. Flavio Roces Gutachter: Prof. Dr. Christian Jost Tag des Promotionskolloquiums: 10. Februar 2015 Doktorurkunde ausgehändigt am: ……………………………………………… Table of Contents Summary .................................................................................................................................... 1 Zusammenfassung ..................................................................................................................... 4 1. General Introduction ......................................................................................................... 9 1.1 Natural history and nesting behavior of leaf-cutting ants ........................................... 9 1.2 Nest building mechanisms ......................................................................................... 10 1.3 Thesis aim and experimental approach ..................................................................... 13 2. Nest enlargement in leaf-cutting ants: relocated brood and fungus trigger the excavation of new chambers ................................................................................................... 17 2.1 Introduction ............................................................................................................... 18 2.2 Materials and Methods .............................................................................................. 21 (a) Determination of relocation preference for brood or fungus ................................................... 22 (b) Brood as a cue for fungus relocation ....................................................................................... 25 (c) Chamber excavation as a response to the presence of brood and fungus ................................ 27 (d) Shape of excavated structures .................................................................................................. 28 2.3 Results ........................................................................................................................ 29 (a) Determination of relocation preference for brood or fungus ................................................... 29 (b) Brood as a cue for fungus relocation ....................................................................................... 30 (c) Chamber excavation as a response to the presence of brood and fungus ................................ 32 (d) Shape of excavated structures .................................................................................................. 33 2.4 Discussion .................................................................................................................. 36 (a) Determination of relocation preference for brood or fungus ................................................... 37 (b) Brood as a cue for fungus relocation ....................................................................................... 39 (c) Chamber excavation as a response to the presence of brood and fungus ................................ 40 (d) Mechanism of chamber emergence ......................................................................................... 42 3. Available space, symbiotic fungus and colony brood influence excavation and lead to the regulation of nest size in leaf-cutting ants ....................................................................... 47 3.1 Introduction ............................................................................................................... 48 3.2 Materials and Methods .............................................................................................. 50 (a) Regulation of nest size: effects of available space and brood presence ............................ 50 (b) Regulation of nest size: influence of fungus and brood .................................................... 52 (c) Measured variables ............................................................................................................ 53 3.3 Results ........................................................................................................................ 53 (a) Regulation of nest size: effects of available space and brood presence ............................ 54 (b) The effect of brood on cavity area ..................................................................................... 56 (c) Regulation of nest size: effects of fungus and brood ......................................................... 57 3.4 Discussion .................................................................................................................. 59 (a) Feedback mechanisms during nest excavation .................................................................. 61 (b) The formation of nest chambers and tunnels ..................................................................... 64 4. Underground carbon dioxide levels: Preferences for fungus culturing by leaf-cutting ants …………………………………………………………………………………………...68 4.1 Introduction ............................................................................................................... 69 4.2 Materials and Methods .............................................................................................. 71 (a) Animals ............................................................................................................................. 71 (b) Experimental Setup ........................................................................................................... 71 (c) General Procedure ............................................................................................................. 72 (d) Experimental series ........................................................................................................... 73 4.3 Results ........................................................................................................................ 74 4.4 Discussion .................................................................................................................. 78 (a) Preferences for carbon dioxide levels for fungus rearing .................................................. 78 (b) Implication of CO2-preference for nest location and architecture ..................................... 80 5. Underground carbon dioxide levels: The effect on digging behavior of leaf-cutting ants …………………………………………………………………………………………...84 5.1 Introduction ............................................................................................................... 85 5.2 Materials and Methods .............................................................................................. 86 (a) Study animals .................................................................................................................... 86 (b) Experimental setup ............................................................................................................ 86 (c) Experimental procedure ..................................................................................................... 88 5.3 Results ........................................................................................................................ 89 5.4 Discussion .................................................................................................................. 90 6. Waste management in leaf-cutting ants: The use of environmental cues in the selection of a dumpsite ............................................................................................................................ 95 6.1 Introduction ............................................................................................................... 96 6.2 Materials and Methods .............................................................................................. 98 (a) Study animals .................................................................................................................... 98 (b) Temperature choice experiment: setup and procedure ...................................................... 98 (c) Humidity choice experiment: setup und procedure ........................................................... 99 (d) CO2 concentration choice experiment: setup and procedure ........................................... 101 (e) Statistical analysis ........................................................................................................... 102 6.3 Results ...................................................................................................................... 102 (a) Temperature-dependent waste deposition ....................................................................... 102 (b) Humidity-dependent waste deposition ............................................................................ 103 (c) Carbon dioxide dependent worker aggregation and waste deposition ............................ 104 6.4 Discussion ................................................................................................................ 105 7. Waste management