Paralyzing Action from a Distance in an Arboreal African Ant Species

Due to their prowess in interspecific competition and ability to catch a wide range of arthropod prey (mostly termites with which they are engaged in an evolutionary arms race), ants are recognized as a good model for studying the chemicals involved in defensive and predatory behaviors. Ants' wide diversity of nesting habits and relationships with plants and prey types implies that these chemicals are also very diverse. Using the African myrmicine ant Crematogaster striatula as our focal species, we adopted a three-pronged research approach. We studied the aggressive and predatory behaviors of the ant workers, conducted bioassays on the effect of their Dufour gland contents on termites, and analyzed these contents. (1) The workers defend themselves or eliminate termites by orienting their abdominal tip toward the opponent, stinger protruded. The chemicals emitted, apparently volatile, trigger the recruitment of nestmates situated in the vicinity and act without the stinger having to come into direct contact with the opponent. Whereas alien ants competing with C. striatula for sugary food sources are repelled by this behavior and retreat further and further away, termites defend their nest whatever the danger. They face down C. striatula workers and end up by rolling onto their backs, their legs batting the air. (2) The bioassays showed that the toxicity of the Dufour gland contents acts in a time-dependent manner, leading to the irreversible paralysis, and, ultimately, death of the termites. (3) Gas chromatography-mass spectrometry analyses showed that the Dufour gland contains a mixture of mono- or polyunsaturated long-chain derivatives, bearing functional groups like oxo-alcohols or oxo-acetates. Electrospray ionization-mass spectrometry showed the presence of a molecule of 1584 Da that might be a large, acetylated alkaloid capable of splitting into smaller molecules that could be responsible for the final degree of venom toxicity

Mass of the peaks from Fig. 2 and the corresponding identification according to Daloze et al. 1987, 1991 [33], [34].

<p>Note that several components have similar masses and fragmentations.</p

Comparison of the effect of time and doses of the <i>Crematogaster striatula</i> Dufour gland extracts applied topically on termite workers.

<p>The doses correspond to the equivalent of one, three or six Dufour gland extracts (N: normal state of the termites that are active; P = paralysis; D: Death). Statistical comparison. Friedman χ² = 20.8; df = 3; P = 0.00011; <i>Post-hoc</i> tests; control <i>vs</i>. 1 gland: NS; control <i>vs</i>. 3 glands: P = 0.0011; control <i>vs</i>. 6 glands: P = 0.0002.</p

Mass spectra collected as total ion current (TIC) from the direct infusion analysis of Dufour gland extracts from <i>Crematogaster striatula</i> (positive mode ESI-MS).

<p>We can see two major peaks at m/z 1584 and 803. (a) MS-MS of m/z 1584: the total fragmentation results only in the ion m/z 803, showing that this ion is a part of ion 1584. (b) MS-MS of the ion m/z 803: partial fragmentation with only the loss of 60 u (the loss of an acetyl radical) resulting in the ion m/z 743.</p

<i>Crematogaster striatula</i> ants capturing a termite worker.

<p>Workers firstly surrounded the termite at a distance of 5–10 mm, their abdominal tip pointed toward the prey. <b>A.</b> After ca. 10 minutes the termite fell down and rolled onto its back, its legs batting the air. One ant approached it very slowly. <b>B.</b> When there were fewer movements of its legs, all of the ants approached the termite. <b>C.</b> Later the ants prepared to seize the termite by an appendage to retrieve it to their nest. <b>D.</b> Interspecific competition. A <i>Crematogaster striatula</i> worker that had discovered several <i>Camponotus brutus</i> imbibing honey on its territory caused them to retreat by very slowly approaching in a backward movement, with its abdominal tip pointed toward the aliens. No contact between the antagonists was noted.</p