Abstract
A taxonomic description of all castes of Colobopsis explodens Laciny & Zettel, sp. n. from Borneo, Thailand, and Malaysia is provided, which serves as a model species for biological studies on “exploding ants” in Southeast Asia. The new species is a member of the Colobopsis cylindrica (COCY) group and falls into a species complex that has been repeatedly summarized under the name Colobopsis saundersi (Emery, 1889) (formerly Camponotus saundersi). The COCY species group is known under its vernacular name “exploding ants” for a unique behaviour: during territorial combat, workers of some species sacrifice themselves by rupturing their gaster and releasing sticky and irritant contents of their hypertrophied mandibular gland reservoirs to kill or repel rivals. This study includes first illustrations and morphometric characterizations of males of the COCY group: Colobopsis explodens Laciny & Zettel, sp. n. and Colobopsis badia (Smith, 1857). Characters of male genitalia and external morphology are compared with other selected taxa of Camponotini. Preliminary notes on the biology of C. explodens Laciny & Zettel, sp. n. are provided. To fix the species identity of the closely related C. badia, a lectotype from Singapore is designated. The following taxonomic changes within the C. saundersi complex are proposed: Colobopsis solenobia (Menozzi, 1926), syn. n. and Colobopsis trieterica (Menozzi, 1926), syn. n. are synonymized with Colobopsis corallina Roger, 1863, a common endemic species of the Philippines. Colobopsis saginata Stitz, 1925, stat. n., hitherto a subspecies of C. badia, is raised to species level.
Highlights
The Colobopsis cylindrica (COCY) group likely represents a monophyletic clade containing Southeast Asian ant species with distinctive hypertrophied mandibular gland reservoirs
The comparison of COI sequences with several hundred COCY sequences available in our local database and 13 sequences deposited in NCBI (Nov. 2017) suggests that this marker can be used for the reliable molecular identification (DNA barcoding) of C. explodens sp. n., as COI sequences of the nearest COCY taxa share only 91% similarity (C. badia), and the similarity to the selected non-COCY species C. aruensis is 83%
The DNA extraction from the gastral parts of the mandibular gland reservoirs of C. explodens sp. n. minor workers resulted in drastically low yields indicating no abundant microbial symbionts present there
Summary
The Colobopsis cylindrica (COCY) group likely represents a monophyletic clade containing Southeast Asian ant species with distinctive hypertrophied mandibular gland reservoirs. Minor workers use the sticky and irritant contents of their enlarged mandibular gland reservoirs to kill or repel rival arthropods In species where this defensive behaviour is more advanced, this happens via the characteristic suicidal “exploding” by voluntary rupture of the gastral integument (autothysis) (Cook 2008). Previously referred to as “yellow goo” (Davidson et al 2007) or “YG” (Davidson et al 2016) for the bright yellow colour of its mandibular gland secretion, was found to have a large colony just at the KBFSC As this abundant species frequently exhibits characteristic autothysis behaviour and can be observed in situ and in vitro, it became the main object of behavioural and chemical experiments, and a model species for biological studies on “exploding ants”. Druzhinina et al in prep.), the aim of this paper is to provide a Colobopsis explodens sp. n., model species for studies on “exploding ants”
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