Pavement ant extract is a chemotaxis repellent for C. elegans

Abstract

Ant behavior relies on a collection of natural products, from following trail pheromones during foraging to warding off potential predators. How nervous systems sense these compounds to initiate a behavioral response remains unclear. Here, we used Caenorhabditis elegans chemotaxis assays to investigate how ant compounds are detected by heterospecific nervous systems. We found that C. elegans avoid extracts of the pavement ant ( Tetramorium immigrans ) and either osm-9 or tax-4 ion channels are required for this response. These experiments were conducted in an undergraduate laboratory course, demonstrating that new insights into interspecies interactions can be generated through genuine research experiences in a classroom setting.

Figure 1. Pavement ant ( Tetramorium immigrans ) extract induces an osm-9 or tax-4 dependent repulsive chemotaxis response in C. elegans .

(A) Students constructed simple aspirators to collect ants. Photo from Alfonso et al., 2023. (B) Chemotaxis assays were performed on circular plates divided into quadrants. Worms were placed in the center and exposed to ant extracts (E) and solvent (X). (C) The chemotaxis response of wild-type worms (PD1074) was tested in response to Argentine ant ( Linepithemma humile, orange), Western harvester ant ( Pogonomyrmex occidentalis, purple), or pavement ant ( T. immigrans, green) extracts. Wild-type PD1074 worms were attracted to harvester ant extracts and repulsed by pavement ant extract compared to solvent (white). (D) Detection of trail pheromone methyl 2-methoxy-6-methylbenzoate (MMMB) at 22.5 min. Base peak chromatograms from fragments m/z 148-149 were extracted and representative ions m/z 91, 148, 149 and 180 were detailed in the corresponding mass spectrum (insert). (E) The chemotaxis response of wild type worms (PD1074, white), osm-9(ky10) knockout worms (blue), tax-4(p678) knockout worms (yellow), and tax-4(p678);osm-9(ky10) double mutants (green) were tested in response to Western harvester and pavement ant extracts. While worm strains did not respond to Western harvester extract or solvent, the repulsive effect of pavement ant extract was diminished in the tax-4(p678);osm-9(ky10) double mutants. Asterisks indicate significant differences; n.s. (not significant) indicates comparisons with a p-value above 0.05.