Herdsmen Ants and their Mealybug Partners

About this book

Language: English

The herdsmen symbiosis is an extraordinary life form of Southeast Asian rainforest ants, a life form that shows an amazing parallelism to the habits of human migrating herdsmen. Among the multifarious mutualistic symbioses of tropical ants with plants or other animals the trophobiotic association of the herdsmen ants with their mealybug partners occupy a unique position, particularly regarding the complexity of the mutualistic system, the high degree of mutual behavioural adaptations and interdependence as well as of the species-specificity of the associations.

The herdsmen ants of the genus Dolichoderus cultivate their "livestock", honeydew-producing pseudococcids of the morphologically anomalous tribe Allomyrmococcini. As true migrating nomads the ants move their livestock to always fresh, nutrition-rich pastures using a variety of transport techniques. The tight interdependence of the mutualistic partners has led to many behavioural and morphological adaptations, e. g. the complete abandonment of firm nest structures in favour of flexible bivouac nests (which also give shelter to part of the mealybug colony), well-organized colony relocations towards newly colonized pasture sites of the mealybugs, budding as the mode of colony reproduction to ensure the uninterrupted persistence of the symbiosis, or various behavioural patterns and morphological structures that facilitate mealybug transport.

Hitherto the herdsmen lifestyle has only been described for a single Dolichoderus species. In contrast, the authors found this life form to be a very diverse complex, of symbiotic associations, widely distributed in tropical Southeast Asia, ranging from the Himalayas to the Greater Sunda Islands, effectively occupying a specific ecological niche in the tropical rainforest. The study proves the herdsmen lifestyle for at least 12 Dolichoderus species with over 30 species of Allomyrmococcini from 11 genera.

This monograph comprises the current state of knowledge about the life history, behavioural ecology and evolution of the symbiosis as well as the taxonomy of both partner groups. The approach to combine the results of the ethoecological field studies with the taxonomic revisions of the herdsmen Dolichoderus and the Allomyrmococcini (including keys and descriptions of new species and genera) allows a thorough insight into this fascinating tropical life form.

Contents

Abstract 1 

Kurzfassung 2 

I Introduction 4 

II The migrating herdsmen symbioses of Southeast Asia: Overview and 
geographical distribution 9 
The herdsmen species 9 
Diversity and distribution of the migrating herdsmen symbioses: 
summary of all available data 10 

III Taxonomy of the migrating herdsmen species of the genus 
Dolichoderus LUND, 1831 with remarks on the systematics of other 
Southeast-Asian Dolichoderus 17 

1 Introduction 17 
2 Material, methods, measurements and abbreviations 18 
3 Species groups of the Oriental Dolichoderus (including New Guinea) 21 
4 Revision of species of the Dolichoderus cuspidatus group (species 
with herdsmen lifestyle) 30 
5 Annotated checklist and bibliography of the described species of the 
other species groups of Oriental Dolichoderus (incl. New Guinea) 57 
6 Overview of all species group taxa of the genus Dolichoderus 
(Oriental Region, incl. New Guinea) 68 
7 Figures 70 

IV The mealybug tribe Allomyrmococcini and its association with herdsman ants 
of the genus Dolichoderus in southeast Asia 115 

Introduction 115 
Material and Methods 115 
Habit and Economic Importance 115 
Life Cycles 116 
Morphology 117 
Definition of the Tribe Allomyrmococcini 119 
List of genera and species of the tribe Allomyrmococcini 119 
Depositories 120 
Key to the genera of the tribe Allomyrmococcini (adult females) 120 

Allomyrmococcus TAKAHASHI 120 
Archeomyrmococcus WILLIAMS gen. n 121 
Bolbococcus WILLIAMS gen. n 124 
Borneococcus WILLIAMS gen. n 129 
Dicranococcus WILLIAMS gen. n 135 
Doryphorococcus WILLIAMS gen. n 141 
Hippeococcus REYNE 143 
Malaicoccus TAKAHASHI 146 
Paramyrmococcus TAKAHASHI 168 
Promyrmococcus WILLIAMS gen. n 170 
Thaimyrmococcus WILLIAMS gen. n 178 

V Biology of the migrating herdsmen symbioses 183 

1 Introduction 183 
2 Localities and general methods 183 
3 Special methods and results 188 
3.1 Colony size, colony structure and queen number 188 
3.2 Nesting behaviour 189 
3.3 Trail systems 190 
3.4 Activity patterns 191 
3.5 Trophobiotic partner species of herdsmen Dolichoderus 193 
3.6 Species-specificity of herdman mutualism and mutual interdependence 
of the herdsmen partners 194 
3.7 Food plants of the Allomyrmococcini 200 
3.8 Distribution of the trophobionts within the Dolichoderus colony 201 
3.9 Behaviour of the trophobiotic partners at the trophobiosis sites 202 
3.10 Transport of the trophobiotic partners 206 
3.11 Colony relocation 218 
3.12 Non-trophobiotic nutrition of herdsmen Dolichoderus 220 

4 Discussion 225 
4.1 Nutrition of herdsmen 225 
4.2 Transport of trophobiosis partners 231 
4.3 Trophobiosis partners in the migrating herdsman's nest 242 
4.4 Nesting mode and nest relocation behaviour 245 
4.5 Colony foundation, colony structure, passing on of the symbiosis, 
and ergatoidy of the queens 248 
4.6 Species specificity of the migrating herdsmen symbiosis and mutual, 
obligate dependence of the partners 251 
4.7 Common traits in the biology of migrating herdsmen species: The 
"Migrating Herdsmen syndrome" 254 
4.8 Differences in the biology of migrating herdsmen species: Indication 
of possible niche differentiation ? 255 
4.9 Evolutionary aspects 261 
4.10 Retrospect and future perspectives 264 

VI A paradox: herdsmen without herdsman's partners - preliminary stage 
to herdsmen lifestyle or secondary loss of the specific partners? 341 

1 Introduction 341 
2 Discovery of colonies of herdsmen Dolichoderus without 
Allomyrmococcini partners 341 
3 Taxonomic status of herdsmen Dolichoderus without Allomyrmococcini 342 
4 Investigations of behaviour and lifestyle of herdsmen Dolichoderus 
without Allomyrmococcini 343 
4.1 General methods 343 
4.2 Colony size and monogyny 343 
4.3 Nesting behaviour 344 
4.4 Trail system, activity patterns, trophobiosis, and non-trophobiotic 
nutrition 344 
4.5 Species-specificity of trophobiotic partners 345 
4.6 Transport of trophobiotic partners 345 
4.7 Occurrence of trophobionts in the nests of Dolichoderus 347 

5 Experimental offering of Allomyrmococcini 348 

6 General discussion 350 

VII Bibliography 355 

Acknowledgments 373

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