Sociobiology of the hypogaeic army ant Dorylus (Dichthadia) laevigatus Fr. Smith Dissertation zur Erlangung des naturwissenschaftlichen Doktorgrades der Bayerischen Julius-Maximilians-Universität Würzburg vorgelegt von Stefanie M. Berghoff Geb. in Heessen Würzburg 2002 Eingereicht am: 17. Dezember 2002 Mitglieder der Promotionskommission: Vorsitzender: Dekan Prof. Dr. Rainer Hedrich Gutachter: Prof. Dr. K. Eduard Linsenmair Gutachter: Prof. Dr. Ulrich Maschwitz Tag des Promotionskolloquiums: .................................................................................... Doktorurkunde ausgehändigt am: ..................................................................................... For my parents The awe of army ants “Even man, styled “Lord of creation,” bows to this more numerous foe; for let the Drivers enter one door and he quickly escapes at the other.” (Savage, 1849) “I lost all sense of proportion, forgot my awkward human size, and with a new perspective became an equal of the ants, looking on, watching every passer-by with interest, straining with the bearers of the heavy loads, and breathing more easily when the last obstacle was overcome and home attained.” (Beebe, 1919) Contents Index SUMMARY.................................................................................................................................................................... 1 ZUSAMMENFASSUNG................................................................................................................................................. 3 1. INTRODUCTION........................................................................................................................................................... 5 2. ARMY ANTS – A LIFE HISTORY STRATEGY............................................................................................................ 8 SUMMARY.................................................................................................................................................................... 8 ARMY ANT TRAITS ...................................................................................................................................................... 8 Foraging habits.................................................................................................................................................... 8 Prey....................................................................................................................................................................... 9 Migrating behavior............................................................................................................................................. 9 Nesting habits..................................................................................................................................................... 10 Castes within the colony................................................................................................................................... 10 Workers........................................................................................................................................................ 10 Queens.......................................................................................................................................................... 10 Males............................................................................................................................................................ 11 Brood............................................................................................................................................................ 11 Colony reproduction.......................................................................................................................................... 11 Hypogaeic vs. epigaeic species........................................................................................................................ 12 Army ants – a vague definition........................................................................................................................ 12 3. SETTING THE SCENE: STUDY SITES, STUDIED SPECIES, AND METHODS EMPLOYED.................................... 14 SUMMARY.................................................................................................................................................................... 14 INTRODUCTION............................................................................................................................................................ 14 STUDY SITES................................................................................................................................................................. 14 STUDIED SPECIES......................................................................................................................................................... 16 STUDY METHODS......................................................................................................................................................... 16 Field methods...................................................................................................................................................... 17 Soil baits....................................................................................................................................................... 17 Sieve buckets................................................................................................................................................ 17 Sieve cavities............................................................................................................................................... 18 Bucket baits................................................................................................................................................. 18 Random and search sampling.................................................................................................................. 18 Night observations...................................................................................................................................... 19 Food-choice experiments.......................................................................................................................... 19 Trail excavations........................................................................................................................................ 19 Large-scale excavations............................................................................................................................ 19 Male collections.......................................................................................................................................... 19 Laboratory methods........................................................................................................................................... 20 Keeping D. laevigatus................................................................................................................................ 20 Formicary experiments.............................................................................................................................. 20 Morphological measurements.................................................................................................................. 21 Genetic analyses......................................................................................................................................... 21 4. FORAGING OF A HYPOGAEIC ARMY ANT: A LONG NEGLECTED MAJORITY................................................... 22 SUMMARY.................................................................................................................................................................... 22 INTRODUCTION............................................................................................................................................................ 22 MATERIALS AND METHODS........................................................................................................................................ 23 Study sites........................................................................................................................................................... 23 Ant baiting........................................................................................................................................................... 25 Laboratory observations................................................................................................................................... 26 RESULTS....................................................................................................................................................................... 26 Bait acceptance................................................................................................................................................... 26 Types of trails and raiding patterns................................................................................................................. 27 The stable hypogaeic trail system............................................................................................................ 27 Column raids on exploratory and secondary trails.............................................................................. 27 Epigaeic swarm raid.................................................................................................................................. 28 Trail establishment and use............................................................................................................................... 29 Prey....................................................................................................................................................................... 30 DISCUSSION.................................................................................................................................................................. 30 ACKNOWLEDGEMENTS............................................................................................................................................... 33 5. NESTING HABITS AND COLONY COMPOSITION OF THE HYPOGAEIC ARMY ANT DORYLUS (DICHTHADIA) LAEVIGATUS FR. SMITH.............................................................................................................. 34 SUMMARY.................................................................................................................................................................... 34 INTRODUCTION............................................................................................................................................................ 34 I Contents Index MATERIALS AND METHODS........................................................................................................................................ 35 Study site............................................................................................................................................................. 35 Nest excavation and laboratory observations................................................................................................ 35 Morphological measurements........................................................................................................................... 36 RESULTS....................................................................................................................................................................... 36 Nest excavations................................................................................................................................................. 36 Nest site 0..................................................................................................................................................... 36 Nest site 1..................................................................................................................................................... 37 Nest site 2..................................................................................................................................................... 37 Morphology and colony composition............................................................................................................. 38 Workers........................................................................................................................................................ 38 Queen............................................................................................................................................................ 38 Colony size................................................................................................................................................... 40 Laboratory observations................................................................................................................................... 40 Emigration and bivouac............................................................................................................................ 40 Feeding......................................................................................................................................................... 41 DISCUSSION.................................................................................................................................................................. 41 Nest and emigration............................................................................................................................................ 41 Colony population and composition............................................................................................................... 42 ACKNOWLEDGEMENTS............................................................................................................................................... 43 6. SOCIOBIOLOGY OF HYPOGAEIC ARMY ANTS: DESCRIPTION OF TWO SYMPATRIC DORYLUS SPECIES ON BORNEO AND THEIR COLONY CONFLICTS...................................................................................................... 44 SUMMARY.................................................................................................................................................................... 44 INTRODUCTION............................................................................................................................................................ 44 MATERIALS AND METHODS........................................................................................................................................ 45 Study sites........................................................................................................................................................... 45 Field and laboratory observations................................................................................................................... 45 Morphological and genetic analyses............................................................................................................... 46 DNA-Extraction, amplification, purification, and phylogenetic analysis......................................... 47 RESULTS....................................................................................................................................................................... 47 Morphological and genetic characterization.................................................................................................. 47 Life history traits of D. laevigatus and D. cf. vishnui................................................................................... 49 Foraging strata........................................................................................................................................... 49 Occurrence and bait utilization............................................................................................................... 49 Feeding habits............................................................................................................................................. 50 Intra- and interspecific interactions................................................................................................................. 50 Field observations...................................................................................................................................... 50 Morphological description of interspecific fights................................................................................. 50 Interactions between laboratory worker samples................................................................................. 52 DISCUSSION.................................................................................................................................................................. 53 Morphological and genetic characterization.................................................................................................. 53 Niche differences................................................................................................................................................ 53 Intra- and interspecific interactions................................................................................................................. 54 ACKNOWLEDGEMENTS............................................................................................................................................... 55 7. INFLUENCE OF THE HYPOGAEIC ARMY ANT DORYLUS (DICHTHADIA) LAEVIGATUS ON GROUND ARTHROPOD COMMUNITIES, WITH SPECIAL EMPHASIS ON SELECTED ANT SPECIES.............................. 56 SUMMARY.................................................................................................................................................................... 56 INTRODUCTION............................................................................................................................................................ 56 MATERIAL AND METHODS......................................................................................................................................... 57 Study sites........................................................................................................................................................... 57 Baits...................................................................................................................................................................... 57 Census areas........................................................................................................................................................ 58 Interactions.......................................................................................................................................................... 58 RESULTS....................................................................................................................................................................... 59 Arthropod communities..................................................................................................................................... 59 Ant communities................................................................................................................................................. 60 Interactions between D. laevigatus and selected ground ant species....................................................... 63 Lophomyrmex bedoti.................................................................................................................................. 63 Odontoponera denticulata and O. transversa....................................................................................... 63 Pachycondyla sp. 2..................................................................................................................................... 64 Pheidologeton affinis................................................................................................................................. 64 II Contents Index DISCUSSION.................................................................................................................................................................. 65 ACKNOWLEDGEMENTS............................................................................................................................................... 67 8. BAITED SIEVE BUCKETS: AN EASY METHOD TO INCLUDE HYPOGAEIC ANT SPECIES INTO GROUND ANT DIVERSITY STUDIES........................................................................................................................................... 68 SUMMARY.................................................................................................................................................................... 68 INTRODUCTION............................................................................................................................................................ 68 MATERIALS AND METHODS........................................................................................................................................ 69 Study sites........................................................................................................................................................... 69 Baits...................................................................................................................................................................... 69 Ant identifications.............................................................................................................................................. 70 RESULTS....................................................................................................................................................................... 70 DISCUSSION.................................................................................................................................................................. 73 ACKNOWLEDGEMENTS............................................................................................................................................... 75 9. MYRMECOPHILOUS STAPHYLINIDAE (COLEOPTERA) ASSOCIATED WITH DORYLUS (DICHTHADIA) LAEVIGATUS (HYMENOPTERA: FORMICIDAE) IN MALAYSIA WITH STUDIES OF THEIR BEHAVIOR........ 76 SUMMARY.................................................................................................................................................................... 76 INTRODUCTION............................................................................................................................................................ 76 MATERIALS AND METHODS........................................................................................................................................ 76 TRIBE LOMECHUSINI................................................................................................................................................... 77 Zyras (Rhynchodonia) praedabunda Kistner New species................................................................. 77 Genus Trachydonia Bernhauer........................................................................................................................ 80 Trachydonia dichthadiaphila Kistner New species.............................................................................. 82 RELATIONSHIPS AMONG THE MYRMEDONIINA....................................................................................................... 84 TRIBE DORYLOGASTRINI WASMANN....................................................................................................................... 85 Genus Berghoffia Kistner New genus............................................................................................................. 85 Berghoffia spectabilis Kistner New species........................................................................................... 87 RELATIONSHIPS AMONG THE DORYLOGASTRINI.................................................................................................... 88 TRIBE PYGOSTENINI FAUVEL.................................................................................................................................... 88 Genus Doryloxenus Wasmann......................................................................................................................... 89 Doryloxenus groveri Kistner & Jacobson.............................................................................................. 89 Doryloxenus coecus Kistner New species.............................................................................................. 93 Genus Pseudolydorus Kistner New genus..................................................................................................... 96 Pseudolydorus linsenmairi Kistner New species.................................................................................. 98 Genus Pygoplanus Kistner New genus.......................................................................................................... 100 Pygoplanus subterraneus Kistner New species..................................................................................... 103 Genus Micropolemon Wasmann..................................................................................................................... 104 Micropolemon malayensis Kistner & Jacobson.................................................................................... 104 Micropolemon sabahensis Kistner New species................................................................................... 107 THE RELATIONSHIPS OF THE PYGOSTENINE GENERA............................................................................................. 108 ACKNOWLEDGEMENTS............................................................................................................................................... 112 10. GENERAL DISCUSSION.............................................................................................................................................. 114 METHODOLOGY........................................................................................................................................................... 114 SOCIOBIOLOGY OF D. LAEVIGATUS............................................................................................................................ 115 Occurrence and abundance............................................................................................................................... 116 Foraging behavior............................................................................................................................................... 116 Migrating behavior............................................................................................................................................. 117 Nesting habits..................................................................................................................................................... 117 The colony and its castes.................................................................................................................................. 118 INTERACTIONS OF D. LAEVIGATUS............................................................................................................................. 118 Interspecific army ant interactions................................................................................................................... 118 Prey....................................................................................................................................................................... 119 Predators.............................................................................................................................................................. 119 Intranidal guests................................................................................................................................................. 120 CONCLUSIONS.............................................................................................................................................................. 121 11. POSSIBLE FUTURE METHODS TO STUDY HYPOGAEIC (ARMY) ANTS............................................................... 122 12. REFERENCES............................................................................................................................................................... 124 III Contents Index APPENDIX A - ASIAN DORYLINAE – A GUIDE TO MORPHOLOGY AND DISTRIBUTION................................ 131 DORYLUS (DICHTHADIA) LAEVIGATUS....................................................................................................................... 132 Diagnosis of heaviest worker............................................................................................................................ 132 Diagnosis of lightest worker............................................................................................................................. 132 Diagnosis of the queen...................................................................................................................................... 133 Diagnosis of males.............................................................................................................................................. 133 Diagnosis of brood............................................................................................................................................. 134 Relationships and biogeography..................................................................................................................... 134 DORYLUS (ALAOPONE) CF. VISHNUI......................................................................................................................... 135 Diagnosis of heaviest worker............................................................................................................................ 135 Diagnosis of lightest worker............................................................................................................................. 136 Other castes......................................................................................................................................................... 136 Relationships and biogeography..................................................................................................................... 136 DORYLUS (TYPHLOPONE) LABIATUS......................................................................................................................... 137 Diagnosis of heaviest worker............................................................................................................................ 137 Other castes......................................................................................................................................................... 138 Relationships and biogeography..................................................................................................................... 138 DORYLUS (ALAOPONE) ORIENTALIS......................................................................................................................... 139 Relationships and biogeography..................................................................................................................... 139 APPENDIX B................................................................................................................................................................ 140 CURRICULUM VITAE................................................................................................................................................... 140 LIST OF PUBLICATIONS............................................................................................................................................... 141 ACKNOWLEDGEMENTS............................................................................................................................................... 142 ERKLÄRUNG................................................................................................................................................................. 143 IV Contents Figures Figures FIGURE 2.1: Army ant raiding forms: Swarm and column raids........................................................................... 9 FIGURE 3.1: Main study sites in Malaysia................................................................................................................ 15 FIGURE 3.2: Two major and one minor D. laevigatus workers............................................................................ 16 FIGURE 3.3: Soil bait.................................................................................................................................................... 17 FIGURE 3.4: Sieve bucket............................................................................................................................................ 17 FIGURE 3.5: Sieve cavity............................................................................................................................................. 18 FIGURE 3.6: Bucket bait............................................................................................................................................... 18 FIGURE 3.7: Setup of formicary experiments........................................................................................................... 20 FIGURE 4.1: Studied palm oil plantation (Plot 12).................................................................................................. 24 FIGURE 4.2: Baiting devices to monitor hypogaeic army ants: sieve bucket and sieve cavity........................ 26 FIGURE 4.3: Schematic trail and raiding systems of D. laevigatus...................................................................... 29 FIGURE 5.1: Position of nest sites (NS0, 1, and 2) within the plantation............................................................ 37 FIGURE 5.2: Dry weight distributions of D. laevigatus worker samples from a nest, baits, and an exploratory raiding trail.......................................................................................................................... 39 FIGURE 5.3: Morphology of the D. laevigatus queen............................................................................................ 39 FIGURE 5.4: Vertical, soil filled, 1cm wide glass formicary showing a cavity excavated and used by D. laevigatus as bivouac site and associated tunnels........................................................................... 39 FIGURE 6.1: One of six parsimonious trees of D. laevigatus (West-Malaysia, Borneo, and Java), D. cf. vishnui (Borneo) and D. nigricans (Ivory Coast).............................................................................. 48 FIGURE 6.2: Approximate extent of neighboring D. laevigatus and D. cf. vishnui colonies on Plot 8............ 51 FIGURE 6.3: Head width distributions of D. laevigatus and D. cf. vishnui workers collected foraging at baits and engaged in interspecific fights............................................................................................ 52 FIGURE 7.1: Trap arrangement in each of 12 1m² census areas (squares) to which D. laevigatus was attracted.................................................................................................................................................... 58 FIGURE 7.2: Abundance of Pheidologeton affinis and D. laevigatus co-occurring at a single bait............... 65 FIGURE 9.1: Zyras (Rhynchodonia) praedabunda. Dorsal view of male and female........................................ 78 FIGURE 9.2: Zyras (Rhynchodonia) praedabunda. Abdominal segments of male and female....................... 79 FIGURE 9.3: Zyras (Rhynchodonia) praedabunda. Male and female genitalia................................................. 80 FIGURE 9.4: Trachydonia anommatis, T. rufoflavus, and T. aenictophila.......................................................... 81 FIGURE 9.5: Trachydonia dichthadiaphila. Dorsal view of male and female..................................................... 81 FIGURE 9.6: Trachydonia dichthadiaphila. Morphology of the head................................................................ 82 FIGURE 9.7: Trachydonia dichthadiaphila. Morphology of the thorax............................................................. 83 FIGURE 9.8: Trachydonia dichthadiaphila. Morphology of the abdomen........................................................ 83 FIGURE 9.9: Berghoffia spectabilis. Dorsal view and morphology of the head................................................. 86 FIGURE 9.10: Berghoffia spectabilis. Leg and genitalia morphology..................................................................... 87 FIGURE 9.11: Berghoffia spectabilis. Morphology of the abdomen...................................................................... 88 FIGURE 9.12: Doryloxenus groveri. Dorsal view and morphology of the genitalia............................................. 90 FIGURE 9.13: Doryloxenus groveri. Morphology of the head................................................................................ 91 FIGURE 9.14: Doryloxenus groveri. Morphology of the thorax.............................................................................. 92 FIGURE 9.15: Doryloxenus groveri. Morphology of the abdomen......................................................................... 93 FIGURE 9.16: Doryloxenus coecus. Morphology of the head................................................................................. 94 FIGURE 9.17: Doryloxenus coecus. Morphology of the thorax............................................................................... 95 FIGURE 9.18: Doryloxenus coecus. Morphology of the abdomen.......................................................................... 96 FIGURE 9.19: Pseudolydorus linsenmairi. Dorsal and lateral view........................................................................ 97 FIGURE 9.20: Pseudolydorus linsenmairi. Morphology of the head..................................................................... 98 FIGURE 9.21: Pseudolydorus linsenmairi. Morphology of the thorax................................................................... 99 FIGURE 9.22: Pseudolydorus linsenmairi. Morphology of the abdomen............................................................. 100 FIGURE 9.23: Pygoplanus subterraneus. Dorsal and ventral view......................................................................... 101 FIGURE 9.24: Pygoplanus subterraneus. Morphology of the head....................................................................... 101 FIGURE 9.25: Pygoplanus subterraneus. Morphology of the thorax..................................................................... 102 FIGURE 9.26: Pygoplanus subterraneus. Morphology of the abdomen................................................................ 103 FIGURE 9.27: Micropolemon malayensis. Dorsal view............................................................................................. 104 FIGURE 9.28: Micropolemon malayensis. Morphology of the head...................................................................... 105 FIGURE 9.29: Micropolemon malayensis. Morphology of the thorax and abdomen........................................... 106 FIGURE 9.30: Micropolemon sabahensis. Dorsal view and morphology of the abdomen.................................. 107 FIGURE 9.31: Cladogram of the Pygostenini derived from the data published by Jacobson & Kistner (1980)......................................................................................................................................................... 111 FIGURE 9.32: Cladogram of the Pygostenini using the same characters but incorporating the 2 new genera. 111 V Contents Figures APPENDIX FIGURE A.1: Dorylus (Dichthadia) laevigatus major worker................................................................................ 132 FIGURE A.2: D. laevigatus Side view of major worker............................................................................................. 132 FIGURE A.3: D. laevigatus Petiole of major worker.................................................................................................. 132 FIGURE A.4: D. laevigatus Frontal lobes of major worker....................................................................................... 132 FIGURE A.5: D. laevigatus Head of major worker..................................................................................................... 132 FIGURE A.6: D. laevigatus Minor worker.................................................................................................................. 133 FIGURE A.7: D. laevigatus Minor worker side view................................................................................................. 133 FIGURE A.8: D. laevigatus Head of minor worker.................................................................................................... 133 FIGURE A.9: D. laevigatus Queen............................................................................................................................... 133 FIGURE A.10: D. laevigatus Queen side view............................................................................................................. 133 FIGURE A.11: D. laevigatus Head of queen................................................................................................................ 133 FIGURE A.12: D. laevigatus Male................................................................................................................................. 134 FIGURE A.13: D. laevigatus Male side view................................................................................................................ 134 FIGURE A.14: D. laevigatus Head of male................................................................................................................... 134 FIGURE A.15: D. laevigatus Young larva..................................................................................................................... 134 FIGURE A.16: D. laevigatus Larvae and young pupae.............................................................................................. 134 FIGURE A.17: D. laevigatus Pupae............................................................................................................................... 134 FIGURE A.18: Proposed distribution of D. laevigatus............................................................................................... 135 FIGURE A.19: Dorylus (Alaopone) cf. vishnui Major worker................................................................................... 136 FIGURE A.20: D. cf. vishnui Side view of major worker............................................................................................. 136 FIGURE A.21: D. cf. vishnui Petiole of major worker.................................................................................................. 136 FIGURE A.22: D. cf. vishnui Frontal lobes of major worker....................................................................................... 136 FIGURE A.23: D. cf. vishnui Head of major worker..................................................................................................... 136 FIGURE A.24: Proposed distribution of D. cf. vishnui............................................................................................... 137 FIGURE A.25: Dorylus (Typhlopone) labiatus major worker................................................................................... 138 FIGURE A.26: D. labiatus Side view of major worker................................................................................................. 138 FIGURE A.27: D. labiatus Petiole of major worker...................................................................................................... 138 FIGURE A.28: D. labiatus Frontal lobes of major worker........................................................................................... 138 FIGURE A.29: D. labiatus Head of major worker......................................................................................................... 138 FIGURE A.30: Proposed distribution of D. labiatus................................................................................................... 138 FIGURE A.31: Proposed distribution of D. orientalis................................................................................................ 139 VI Contents Tables TABLES TABLE 3.1: Study plot data............................................................................................................................................ 15 TABLE 3.2: Collection sites of Dorylus males at UV-light sources in Sabah......................................................... 20 TABLE 4.1: Study plots from Borneo and West-Malaysia........................................................................................ 24 TABLE 5.1: Morphological measurements of a queen and 350 D. laevigatus workers........................................ 39 TABLE 6.1: Study plot data............................................................................................................................................ 45 TABLE 6.2: Morphological measurements of 50 D. laevigatus and 50 D. cf. vishnui workers collected from baits and their statistical comparison............................................................................................. 48 TABLE 6.3: Trait comparison of the sympatric D. laevigatus and D. cf. vishnui.................................................. 49 TABLE 7.1: Collected individuals of the most common taxa in epigaeic and hypogaeic pitfall traps before and after D. laevigatus recruited to the squares.................................................................................... 59 TABLE 7.2: Ant individuals collected with epigaeic and hypogaeic pitfall traps before and after D. laevigatus was attracted to the study plots........................................................................................... 61 TABLE 7.3: Life history traits of five common ground foraging ant species.......................................................... 63 TABLE 7.4: Interspecific fights between Pheidologeton affinis and D. laevigatus at baits............................... 64 TABLE 8.1: Taxonomic composition of ants recorded at palm oil baits.................................................................. 70 TABLE 8.2: Ant diversity recorded at sieve buckets baited with palm oil.............................................................. 71 TABLE 8.3: Ant species found at sieve buckets baited with tuna or cookie crumbs............................................ 73 TABLE 9.1: List of characters used to investigate the phylogeny of the Pygostenini by Jacobson & Kistner (1980)............................................................................................................................................................. 109 TABLE 9.2: Coding of the characters given in Table 1.............................................................................................. 110 TABLE 9.3: Pygostenini genera together with their hosts at the subgeneric level............................................... 112 VII