ASIAN
MYRMECOLOGY

DOI: 10.20362/am.009015
Asian Myrmecology 9: e009015 (1-15)
article first published online 12/October/2017

Striking polymorphism among infertile helpers in the arboreal ant Gesomyrmex

CHRISTIAN PEETERS^1*, FUMINORI ITO², DECHA WIWATWITAYA³, ROBERTO A. KELLER⁴, ROSLI HASHIM⁵ & MATHIEU MOLET¹

Abstract:

Gesomyrmex (subfamily Formicinae) is a poorly known arboreal ant from the Oriental tropics. We sampled colonies in three localities (NE Thailand, peninsular Malaysia, and Sabah) and examined inhabitants of ten nests inside living branches. None of the nests had a reproductive dealate queen, indicating colonies are polydomous. We distinguished three sterile castes using discrete morphological traits, morphometry and total body size. Observations of behaviour are challenging in tree canopies, and we use functional morphology to predict the specialised functions of different castes. Disproportionately large eyes and piercing mandibles are consistent with workers being agile hunters. Soldiers and supersoldiers share robust mandibles, but the latter have a rectangular head and substantially larger body size, like the queens. This suggests both supersoldiers and queens have the muscular power necessary to chew entrance tunnels in healthy wood. Queens and supersoldiers also share frontal lobes (protection for antennal bases), suggesting that they block nest entrances with their heads. When founding a nest, newly mated queens need to chew an entrance tunnel that reaches the innermost soft pith. Supersoldiers are mostly restricted inside nests where they store nutrients in their gaster, but they may also chew the entrance tunnels of additional nests as the colony expands.

Keywords:

functional morphology, soldiers, supersoldiers, repletes, phragmotic, ovaries, mandibles, mosaics

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¹Institute of Ecology and Environmental Sciences, UMR CNRS 7618, Sorbonne Universités UPMC, Paris 75005, France

²Faculty of Agriculture, Kagawa University, Miki, 761-0795, Japan

³Department of Forest Biology, Kasetsart University, 10900 Bangkok, Thailand

⁴Museu Nacional de História Natural e da Ciência, Lisbon, Portugal

⁵Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia

*Corresponding author: christian.peeters@upmc.fr