Pheromones in Free-Living and Parasitic Nematodes

Abstract

Nematodes are among the most diverse phyla of animals, occupying almost every ecological niche available. Their ubiquity has led to a number of problems for civilization, including the loss of crops and the spread of neglected tropical diseases. Because they are responsible for a broad range of agricultural and human diseases, many pheromone-mediated nematode behaviors have been described but very few pheromones have been identified. We report, via high-performance liquid chromatography electrospray ionization mass spectrometry, the discovery that many free-living and parasitic nematodes secrete small-molecule pheromones called ascarosides. These pheromones, called ascarosides, were first found to play a role in sex attraction and induction into a stress-resistant diapausal life stage in the free-living organism, Caenorhabditis elegans. We have performed a double-blind purification of the female sex pheromone in the sour paste nematode Panagrellus redivivus and report that the female sex pheromone is composed of at least two ascarosides. We have also found that both free-living and parasitic nematodes respond to different concentrations of ascarosides through attraction or repulsion, demonstrating cross-species communication. These results suggest that ascarosides could be a universal nematode cue, similar to the role of N-Acyl homoserine lactones in bacteria quorum sensing. Because ascarosides are nonvolatile, they can only mediate close-range communication. Nematodes have a well-characterized capacity for long-range chemoattraction to a range of volatile cues. However, no studies have been done towards characterizing natural volatile cues derived from nematodes. Here I describe the discovery of volatile cues are produced by male-female species in the genus Caenorhabditis, but are lacking in the hermaphroditic species C. elegans, C. briggsae, and C. sp11. These volatile cues attract males (and sometimes females) from other Caenorhabditis species, demonstrating a cross-species gonochoristic cue.