An experimental study of microbial nest associates of borneo's exploding ants (Camponotus [Colobopsis] species)

Cavity nesting ants in the Camponotus (Colobopsis) cylindricus (COCY) complex possess hugely hypertrophied mandibular gland (MG) reservoirs containing weakly acidic phenolic acetogenins and/or diterpenes unique for insects. Many taxa ("exploding ants") use these products in suicidal defense of territory, but major workers of all species, and all workers of some species, possess hypertrophied reservoirs and clade-typical products not used in suicidal fights. An additional role of MG products in nest hygiene was suspected. We sampled microbial associates of nest cavity fiber and carton shelving in artificial wooden nests occupied by substantial colony fragments of COCY species and compared them with two controls: microbes in unoccupied nests and nests occupied by other cavity-nesting ant species. Several natural nests in fallen wood were also sampled. Bacteria and fungi cultured on malt extract agar were identified from gene sequences amplified by universal bacterial and fungal primers. Results were related to an expanded data base on MG chemistry. Twentyfour of 55 nests were colonized by ants, mostly by COCY species, nesting naturally or not in dead wood. In colony-level analyses, mycoparasitic Trichoderma fungi were significantly over-represented in nest fiber of COCY species. Their detection was restricted to taxa naturally inhabiting fallen wood; the maj'ority of these taxa produced /w-cresol as the major component of MG volatiles. Burkholderia bacteria were significantly more common in COCY species' nests than in unoccupied nests but only when replicate nests per colony were allowed. Trichoderma and Burkholderia tended to co-occur in nest fiber, perhaps due to traits influencing arrival and survival. Both Trichoderma and Burkholderia may contribute to nest hygiene, and their joint occurrence could potentially affect longevity of nests in dead wood. Both genera also occur as endophytes, and interactions between ants and endophytes merit further study. Documented over-representation in live hosts of genera Antidesma and Cleistanthus [Phyllanthaceae]) could be related to the microbial environment provided by these hosts.